```
Atomic physics Condensed Matter - Disordered Systems and Neural Networks Condensed Matter - Mesoscale and Nanoscale Physics Condensed Matter - Quantum Gases Condensed Matter - Statistical Mechanics Condensed Matter - Strongly Correlated Electrons Conformal field theory Integrable models Long-range systems Open quantum systems Quantum entanglement Quantum phase transitions Quantum Physics Quantum simulation Renormalization group Topological phases of matter Trapped ions Unconventional pairing mechanisms
```
### 2019

Jaromir Panas, Mathieu Barbier, Andreas Geißler, Walter Hofstetter

Supersolid Phases of Rydberg-Excited Bosons on a Triangular Lattice Journal Article

arXiv:1903.01912 [cond-mat], 2019.

Abstract | BibTeX | Tags: Condensed Matter - Quantum Gases

@article{Panas2019,

title = {Supersolid Phases of Rydberg-Excited Bosons on a Triangular Lattice},

author = {Jaromir Panas and Mathieu Barbier and Andreas Geißler and Walter Hofstetter},

year = {2019},

date = {2019-01-01},

journal = {arXiv:1903.01912 [cond-mat]},

abstract = {Recent experiments with ultracold Rydberg-excited atoms have shown that long-range interactions can give rise to spatially ordered structures. Observation of crystalline phases in a system with Rydberg atoms loaded into an optical lattice seems also within reach. Here we investigate a bosonic model on a triangular lattice suitable for description of such experiments. Numerical simulations based on bosonic dynamical mean-field theory reveal a rich phase diagram with different supersolid phases. Comparison with the results obtained for a square lattice geometry shows qualitatively similar results in a wide range of parameters, however, on a triangular lattice we do not observe the checkerboard supersolid. Moreover, unlike on a square lattice we did not find a phase transition from uniform superfluid to supersolid induced by increase of the hopping amplitude on a triangular lattice. Based on our results we propose an intuitive interpretation of the nature of different supersolid phases. We also propose parameters for the experimental realization.},

keywords = {Condensed Matter - Quantum Gases},

pubstate = {published},

tppubtype = {article}

}

Recent experiments with ultracold Rydberg-excited atoms have shown that long-range interactions can give rise to spatially ordered structures. Observation of crystalline phases in a system with Rydberg atoms loaded into an optical lattice seems also within reach. Here we investigate a bosonic model on a triangular lattice suitable for description of such experiments. Numerical simulations based on bosonic dynamical mean-field theory reveal a rich phase diagram with different supersolid phases. Comparison with the results obtained for a square lattice geometry shows qualitatively similar results in a wide range of parameters, however, on a triangular lattice we do not observe the checkerboard supersolid. Moreover, unlike on a square lattice we did not find a phase transition from uniform superfluid to supersolid induced by increase of the hopping amplitude on a triangular lattice. Based on our results we propose an intuitive interpretation of the nature of different supersolid phases. We also propose parameters for the experimental realization.David Hagenmüller, Johannes Schachenmayer, Cyriaque Genet, Thomas W Ebbesen, Guido Pupillo

Enhancement of the Electron–Phonon Scattering Induced by Intrinsic Surface Plasmon–Phonon Polaritons Journal Article

ACS Photonics, 2019.

Abstract | Links | BibTeX | Tags: Condensed Matter - Mesoscale and Nanoscale Physics

@article{Hagenmuller2019,

title = {Enhancement of the Electron–Phonon Scattering Induced by Intrinsic Surface Plasmon–Phonon Polaritons},

author = {David Hagenmüller and Johannes Schachenmayer and Cyriaque Genet and Thomas W Ebbesen and Guido Pupillo},

doi = {10.1021/acsphotonics.9b00268},

year = {2019},

date = {2019-01-01},

journal = {ACS Photonics},

abstract = {We investigate light–matter coupling in metallic crystals where plasmons coexist with phonons exhibiting large oscillator strength. We demonstrate theoretically that this coexistence can lead to strong light–matter interactions without external resonators. When the frequencies of plasmons and phonons are comparable, hybridization of these collective matter modes occurs in the crystal. We show that the coupling of these modes to photonic degrees of freedom gives rise to intrinsic surface plasmon–phonon polaritons, which offer the unique possibility to control the phonon properties by tuning the electron density and the crystal thickness. In particular, dressed phonons with reduced frequency and large wave vectors arise in the case of quasi-2D crystals, which could lead to large enhancements of the electron–phonon scattering in the vibrational ultrastrong coupling regime. This suggests that photons can play a key role in determining the quantum properties of certain materials. A nonperturbative self-consistent Hamiltonian method is presented that is valid for arbitrarily large coupling strengths.},

keywords = {Condensed Matter - Mesoscale and Nanoscale Physics},

pubstate = {published},

tppubtype = {article}

}

We investigate light–matter coupling in metallic crystals where plasmons coexist with phonons exhibiting large oscillator strength. We demonstrate theoretically that this coexistence can lead to strong light–matter interactions without external resonators. When the frequencies of plasmons and phonons are comparable, hybridization of these collective matter modes occurs in the crystal. We show that the coupling of these modes to photonic degrees of freedom gives rise to intrinsic surface plasmon–phonon polaritons, which offer the unique possibility to control the phonon properties by tuning the electron density and the crystal thickness. In particular, dressed phonons with reduced frequency and large wave vectors arise in the case of quasi-2D crystals, which could lead to large enhancements of the electron–phonon scattering in the vibrational ultrastrong coupling regime. This suggests that photons can play a key role in determining the quantum properties of certain materials. A nonperturbative self-consistent Hamiltonian method is presented that is valid for arbitrarily large coupling strengths.
### 2018

David Hagenmüller, Johannes Schachenmayer, Cyriaque Genet, Thomas W Ebbesen, Guido Pupillo

Enhancement of the Electron-Phonon Scattering Induced by Intrinsic Surface Plasmon-Phonon Polaritons Journal Article

arXiv:1810.10190 [cond-mat], 2018.

Abstract | BibTeX | Tags: Condensed Matter - Mesoscale and Nanoscale Physics

@article{Hagenmuller2018,

title = {Enhancement of the Electron-Phonon Scattering Induced by Intrinsic Surface Plasmon-Phonon Polaritons},

author = {David Hagenmüller and Johannes Schachenmayer and Cyriaque Genet and Thomas W Ebbesen and Guido Pupillo},

year = {2018},

date = {2018-10-01},

journal = {arXiv:1810.10190 [cond-mat]},

abstract = {We investigate light-matter coupling in metallic crystals where plasmons coexist with phonons exhibiting large oscillator strength. We demonstrate theoretically that this coexistence can lead to strong light-matter interactions without external resonators. When the frequencies of plasmons and phonons are comparable, hybridization of these collective matter modes occurs in the crystal. We show that the coupling of these modes to photonic degrees of freedom gives rise to intrinsic surface plasmon-phonon polaritons, which offer the unique possibility to control the phonon properties by tuning the electron density and the crystal thickness. In particular, dressed phonons with reduced frequency and large wave vectors arise in the case of quasi-2D crystals, which leads to large enhancements of the electron-phonon scattering in the vibrational ultrastrong coupling regime. This suggests that photons can play a key role in determining the quantum properties of certain materials. A non-perturbative self-consistent Hamiltonian method is presented that is valid for arbitrarily large coupling strengths.},

keywords = {Condensed Matter - Mesoscale and Nanoscale Physics},

pubstate = {published},

tppubtype = {article}

}

We investigate light-matter coupling in metallic crystals where plasmons coexist with phonons exhibiting large oscillator strength. We demonstrate theoretically that this coexistence can lead to strong light-matter interactions without external resonators. When the frequencies of plasmons and phonons are comparable, hybridization of these collective matter modes occurs in the crystal. We show that the coupling of these modes to photonic degrees of freedom gives rise to intrinsic surface plasmon-phonon polaritons, which offer the unique possibility to control the phonon properties by tuning the electron density and the crystal thickness. In particular, dressed phonons with reduced frequency and large wave vectors arise in the case of quasi-2D crystals, which leads to large enhancements of the electron-phonon scattering in the vibrational ultrastrong coupling regime. This suggests that photons can play a key role in determining the quantum properties of certain materials. A non-perturbative self-consistent Hamiltonian method is presented that is valid for arbitrarily large coupling strengths.Thomas Botzung, Davide Vodola, Piero Naldesi, Markus Müller, Elisa Ercolessi, Guido Pupillo

Algebraic Localization from Power-Law Interactions in Disordered Quantum Wires Journal Article

arXiv:1810.09779 [cond-mat, physics:quant-ph], 2018.

Abstract | BibTeX | Tags: Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Strongly Correlated Electrons, Quantum Physics

@article{Botzung2018,

title = {Algebraic Localization from Power-Law Interactions in Disordered Quantum Wires},

author = {Thomas Botzung and Davide Vodola and Piero Naldesi and Markus Müller and Elisa Ercolessi and Guido Pupillo},

year = {2018},

date = {2018-10-01},

journal = {arXiv:1810.09779 [cond-mat, physics:quant-ph]},

abstract = {We analyze the effects of disorder on the correlation functions of one-dimensional quantum models of fermions and spins with long-range interactions that decay with distance $$backslash$ell$ as a power-law $1/$backslash$ell^$backslash$alpha$. Using a combination of analytical and numerical results, we demonstrate that power-law interactions imply a long-distance algebraic decay of correlations within disordered-localized phases, for all exponents $$backslash$alpha$. The exponent of algebraic decay depends only on $$backslash$alpha$, and not, e.g., on the strength of disorder. We find a similar algebraic localization for wave-functions. These results are in contrast to expectations from short-range models and are of direct relevance for a variety of quantum mechanical systems in atomic, molecular and solid-state physics.},

keywords = {Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Strongly Correlated Electrons, Quantum Physics},

pubstate = {published},

tppubtype = {article}

}

We analyze the effects of disorder on the correlation functions of one-dimensional quantum models of fermions and spins with long-range interactions that decay with distance $$backslash$ell$ as a power-law $1/$backslash$ell^$backslash$alpha$. Using a combination of analytical and numerical results, we demonstrate that power-law interactions imply a long-distance algebraic decay of correlations within disordered-localized phases, for all exponents $$backslash$alpha$. The exponent of algebraic decay depends only on $$backslash$alpha$, and not, e.g., on the strength of disorder. We find a similar algebraic localization for wave-functions. These results are in contrast to expectations from short-range models and are of direct relevance for a variety of quantum mechanical systems in atomic, molecular and solid-state physics.Rogelio Díaz-Méndez, Guido Pupillo, Fabio Mezzacapo, Mats Wallin, Jack Lidmar, Egor Babaev

Phase-Change Switching in 2D via Soft Interactions Journal Article

arXiv:1808.07918 [cond-mat], 2018.

Abstract | BibTeX | Tags: Condensed Matter - Statistical Mechanics

@article{Diaz-Mendez2018,

title = {Phase-Change Switching in 2D via Soft Interactions},

author = {Rogelio {Díaz-Méndez} and Guido Pupillo and Fabio Mezzacapo and Mats Wallin and Jack Lidmar and Egor Babaev},

year = {2018},

date = {2018-01-01},

journal = {arXiv:1808.07918 [cond-mat]},

abstract = {We present a new type of phase-change behavior relevant for information storage applications, that can be observed in 2D systems with cluster-forming ability. The temperature-based control of the ordering in 2D particle systems depends on the existence of a crystal-to-glass transition. We perform molecular dynamics simulations of models with soft interactions, demonstrating that the crystalline and amorphous structures can be easily tuned by heat pulses. The physical mechanism responsible for this behavior is a self-assembled polydispersity, that depends on the cluster-forming ability of the interactions. Therefore, the range of real materials that can perform such a transition is very wide in nature, reading from colloidal suspensions to vortex matter. The state of the art in soft matter experimental setups, controlling interactions, polydispersity and dimensionality, makes it a very fertile ground for practical applications.},

keywords = {Condensed Matter - Statistical Mechanics},

pubstate = {published},

tppubtype = {article}

}

We present a new type of phase-change behavior relevant for information storage applications, that can be observed in 2D systems with cluster-forming ability. The temperature-based control of the ordering in 2D particle systems depends on the existence of a crystal-to-glass transition. We perform molecular dynamics simulations of models with soft interactions, demonstrating that the crystalline and amorphous structures can be easily tuned by heat pulses. The physical mechanism responsible for this behavior is a self-assembled polydispersity, that depends on the cluster-forming ability of the interactions. Therefore, the range of real materials that can perform such a transition is very wide in nature, reading from colloidal suspensions to vortex matter. The state of the art in soft matter experimental setups, controlling interactions, polydispersity and dimensionality, makes it a very fertile ground for practical applications.David Hagenmüller, Stefan Schütz, Johannes Schachenmayer, Claudiu Genes, Guido Pupillo

Cavity-Assisted Mesoscopic Transport of Fermions: Coherent and Dissipative Dynamics Journal Article

Physical Review B, 97 (20), pp. 205303, 2018.

Abstract | Links | BibTeX | Tags:

@article{Hagenmuller2018a,

title = {Cavity-Assisted Mesoscopic Transport of Fermions: Coherent and Dissipative Dynamics},

author = {David Hagenmüller and Stefan Schütz and Johannes Schachenmayer and Claudiu Genes and Guido Pupillo},

doi = {10.1103/PhysRevB.97.205303},

year = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {97},

number = {20},

pages = {205303},

abstract = {We study the interplay between charge transport and light-matter interactions in a confined geometry by considering an open, mesoscopic chain of two-orbital systems resonantly coupled to a single bosonic mode close to its vacuum state. We introduce and benchmark different methods based on self-consistent solutions of nonequilibrium Green's functions and numerical simulations of the quantum master equation, and derive both analytical and numerical results. It is shown that in the dissipative regime where the cavity photon decay rate is the largest parameter, the light-matter coupling is responsible for a steady-state current enhancement scaling with the cooperativity parameter. We further identify different regimes of interest depending on the ratio between the cavity decay rate and the electronic bandwidth. Considering the situation where the lower band has a vanishing bandwidth, we show that for a high-finesse cavity, the properties of the resonant Bloch state in the upper band are transferred to the lower one, giving rise to a delocalized state along the chain. Conversely, in the dissipative regime with low-cavity quality factors, we find that the current enhancement is due to a collective decay of populations from the upper to the lower band.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study the interplay between charge transport and light-matter interactions in a confined geometry by considering an open, mesoscopic chain of two-orbital systems resonantly coupled to a single bosonic mode close to its vacuum state. We introduce and benchmark different methods based on self-consistent solutions of nonequilibrium Green's functions and numerical simulations of the quantum master equation, and derive both analytical and numerical results. It is shown that in the dissipative regime where the cavity photon decay rate is the largest parameter, the light-matter coupling is responsible for a steady-state current enhancement scaling with the cooperativity parameter. We further identify different regimes of interest depending on the ratio between the cavity decay rate and the electronic bandwidth. Considering the situation where the lower band has a vanishing bandwidth, we show that for a high-finesse cavity, the properties of the resonant Bloch state in the upper band are transferred to the lower one, giving rise to a delocalized state along the chain. Conversely, in the dissipative regime with low-cavity quality factors, we find that the current enhancement is due to a collective decay of populations from the upper to the lower band.S. Lepoutre, J. Schachenmayer, L. Gabardos, B. Zhu, B. Naylor, E. Marechal, O. Gorceix, A. M. Rey, L Vernac, B Laburthe-Tolra

Exploring out-of-equilibrium quantum magnetism and thermalization in a spin-3 many-body dipolar lattice system Journal Article Forthcoming

(to appear in Nat. Comm.), pp. arXiv:1803.02628, Forthcoming.

BibTeX | Tags: Condensed Matter - Quantum Gases

@article{2018arXiv180302628L,

title = {Exploring out-of-equilibrium quantum magnetism and thermalization in a spin-3 many-body dipolar lattice system},

author = {S. {Lepoutre} and J. {Schachenmayer} and L. {Gabardos} and B. {Zhu} and B. {Naylor} and E. {Marechal} and O. {Gorceix} and A. M. {Rey} and L {Vernac} and B {Laburthe-Tolra}},

year = {2018},

date = {2018-01-01},

journal = {(to appear in Nat. Comm.)},

pages = {arXiv:1803.02628},

keywords = {Condensed Matter - Quantum Gases},

pubstate = {forthcoming},

tppubtype = {article}

}

### 2017

David Hagenmüller, Johannes Schachenmayer, Stefan Schütz, Claudiu Genes, Guido Pupillo

Cavity-Enhanced Transport of Charge Journal Article

Physical Review Letters, 119 (22), pp. 223601, 2017.

Abstract | Links | BibTeX | Tags:

@article{Hagenmuller2017,

title = {Cavity-Enhanced Transport of Charge},

author = {David Hagenmüller and Johannes Schachenmayer and Stefan Schütz and Claudiu Genes and Guido Pupillo},

doi = {10.1103/PhysRevLett.119.223601},

year = {2017},

date = {2017-11-01},

journal = {Physical Review Letters},

volume = {119},

number = {22},

pages = {223601},

abstract = {We theoretically investigate charge transport through electronic bands of a mesoscopic one-dimensional system, where interband transitions are coupled to a confined cavity mode, initially prepared close to its vacuum. This coupling leads to light-matter hybridization where the dressed fermionic bands interact via absorption and emission of dressed cavity photons. Using a self-consistent nonequilibrium Green's function method, we compute electronic transmissions and cavity photon spectra and demonstrate how light-matter coupling can lead to an enhancement of charge conductivity in the steady state. We find that depending on cavity loss rate, electronic bandwidth, and coupling strength, the dynamics involves either an individual or a collective response of Bloch states, and we explain how this affects the current enhancement. We show that the charge conductivity enhancement can reach orders of magnitudes under experimentally relevant conditions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We theoretically investigate charge transport through electronic bands of a mesoscopic one-dimensional system, where interband transitions are coupled to a confined cavity mode, initially prepared close to its vacuum. This coupling leads to light-matter hybridization where the dressed fermionic bands interact via absorption and emission of dressed cavity photons. Using a self-consistent nonequilibrium Green's function method, we compute electronic transmissions and cavity photon spectra and demonstrate how light-matter coupling can lead to an enhancement of charge conductivity in the steady state. We find that depending on cavity loss rate, electronic bandwidth, and coupling strength, the dynamics involves either an individual or a collective response of Bloch states, and we explain how this affects the current enhancement. We show that the charge conductivity enhancement can reach orders of magnitudes under experimentally relevant conditions.Nóra Sándor, Rosario González-Férez, Paul S Julienne, Guido Pupillo

Rydberg Optical Feshbach Resonances in Cold Gases Journal Article

Physical Review A, 96 (3), pp. 032719, 2017.

Abstract | Links | BibTeX | Tags:

@article{Sandor2017,

title = {Rydberg Optical Feshbach Resonances in Cold Gases},

author = {Nóra Sándor and Rosario {González-Férez} and Paul S Julienne and Guido Pupillo},

doi = {10.1103/PhysRevA.96.032719},

year = {2017},

date = {2017-09-01},

journal = {Physical Review A},

volume = {96},

number = {3},

pages = {032719},

abstract = {We propose a scheme to efficiently tune the scattering length of two colliding ground-state atoms by off-resonantly coupling the scattering state to an excited Rydberg molecular state using laser light. For the s-wave scattering of two colliding 87Rb atoms, we demonstrate that the effective optical length and pole strength of this Rydberg optical Feshbach resonance can be tuned over several orders of magnitude, while incoherent processes and losses are minimized. Given the ubiquity of Rydberg molecular states, this technique should be generally applicable to homonuclear atomic pairs as well as to atomic mixtures with s-wave (or even p-wave) scattering.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We propose a scheme to efficiently tune the scattering length of two colliding ground-state atoms by off-resonantly coupling the scattering state to an excited Rydberg molecular state using laser light. For the s-wave scattering of two colliding 87Rb atoms, we demonstrate that the effective optical length and pole strength of this Rydberg optical Feshbach resonance can be tuned over several orders of magnitude, while incoherent processes and losses are minimized. Given the ubiquity of Rydberg molecular states, this technique should be generally applicable to homonuclear atomic pairs as well as to atomic mixtures with s-wave (or even p-wave) scattering.O. L. Acevedo, A. Safavi-Naini, J. Schachenmayer, M. L. Wall, R. Nandkishore, A. M. Rey

Exploring many-body localization and thermalization using semiclassical methods Journal Article

Phys. Rev. A, 96 , pp. 033604, 2017.

@article{PhysRevA.96.033604,

title = {Exploring many-body localization and thermalization using semiclassical methods},

author = {O. L. Acevedo and A. Safavi-Naini and J. Schachenmayer and M. L. Wall and R. Nandkishore and A. M. Rey},

url = {https://link.aps.org/doi/10.1103/PhysRevA.96.033604},

doi = {10.1103/PhysRevA.96.033604},

year = {2017},

date = {2017-09-01},

journal = {Phys. Rev. A},

volume = {96},

pages = {033604},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

Rogelio Díaz-Méndez, Fabio Mezzacapo, Wolfgang Lechner, Fabio Cinti, Egor Babaev, Guido Pupillo

Glass Transitions in Monodisperse Cluster-Forming Ensembles: Vortex Matter in Type-1.5 Superconductors Journal Article

Physical Review Letters, 118 (6), pp. 067001, 2017.

Abstract | Links | BibTeX | Tags:

@article{Diaz-Mendez2017,

title = {Glass Transitions in Monodisperse Cluster-Forming Ensembles: Vortex Matter in Type-1.5 Superconductors},

author = {Rogelio {Díaz-Méndez} and Fabio Mezzacapo and Wolfgang Lechner and Fabio Cinti and Egor Babaev and Guido Pupillo},

doi = {10.1103/PhysRevLett.118.067001},

year = {2017},

date = {2017-02-01},

journal = {Physical Review Letters},

volume = {118},

number = {6},

pages = {067001},

abstract = {At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster crystal. In the present Letter, we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multiscale intervortex forces. We find that, for small temperatures following a quench, the suppression of the thermally activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in terms of an ``effective polydispersity'' induced by multiscale interactions. This demonstrates that a vortex glass can form in clean systems of thin films of ``type-1.5'' superconductors. An additional setup to study this physics can be layered superconducting systems, where the shape of the effective vortex-vortex interactions can be engineered.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

At low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster crystal. In the present Letter, we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multiscale intervortex forces. We find that, for small temperatures following a quench, the suppression of the thermally activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in terms of an ``effective polydispersity'' induced by multiscale interactions. This demonstrates that a vortex glass can form in clean systems of thin films of ``type-1.5'' superconductors. An additional setup to study this physics can be layered superconducting systems, where the shape of the effective vortex-vortex interactions can be engineered.
### 2016

L Lepori, D Vodola, G Pupillo, G Gori, A Trombettoni

Effective Theory and Breakdown of Conformal Symmetry in a Long-Range Quantum Chain Journal Article

Annals of Physics, 374 , pp. 35-66, 2016, ISSN: 0003-4916.

Abstract | Links | BibTeX | Tags: Conformal field theory, Integrable models, Long-range systems, Quantum entanglement, Quantum phase transitions, Renormalization group

@article{Lepori2016,

title = {Effective Theory and Breakdown of Conformal Symmetry in a Long-Range Quantum Chain},

author = {L Lepori and D Vodola and G Pupillo and G Gori and A Trombettoni},

doi = {10.1016/j.aop.2016.07.026},

issn = {0003-4916},

year = {2016},

date = {2016-11-01},

journal = {Annals of Physics},

volume = {374},

pages = {35-66},

abstract = {We deal with the problem of studying the symmetries and the effective theories of long-range models around their critical points. A prominent issue is to determine whether they possess (or not) conformal symmetry (CS) at criticality and how the presence of CS depends on the range of the interactions. To have a model, both simple to treat and interesting, where to investigate these questions, we focus on the Kitaev chain with long-range pairings decaying with distance as power-law with exponent $alpha$. This is a quadratic solvable model, yet displaying non-trivial quantum phase transitions. Two critical lines are found, occurring respectively at a positive and a negative chemical potential. Focusing first on the critical line at positive chemical potential, by means of a renormalization group approach we derive its effective theory close to criticality. Our main result is that the effective action is the sum of two terms: a Dirac action SD, found in the short-range Ising universality class, and an ``anomalous'' CS breaking term SAN. While SD originates from low-energy excitations in the spectrum, SAN originates from the higher energy modes where singularities develop, due to the long-range nature of the model. At criticality SAN flows to zero for $alpha>$2, while for $alpha<$2 it dominates and determines the breakdown of the CS. Out of criticality SAN breaks, in the considered approximation, the effective Lorentz invariance (ELI) for every finite $alpha$. As $alpha$ increases such ELI breakdown becomes less and less pronounced and in the short-range limit $alpharightarrowinfty$ the ELI is restored. In order to test the validity of the determined effective theory, we compared the two-fermion static correlation functions and the von Neumann entropy obtained from them with the ones calculated on the lattice, finding agreement. These results explain two observed features characteristic of long-range models, the hybrid decay of static correlation functions within gapped phases and the area-law violation for the von Neumann entropy. The proposed scenario is expected to hold in other long-range models displaying quasiparticle excitations in ballistic regime. From the effective theory one can also see that new phases emerge for $alpha<$1. Finally we show that at every finite $alpha$ the critical exponents, defined as for the short-range ($alpharightarrowinfty$) model, are not altered. This also shows that the long-range paired Kitaev chain provides an example of a long-range model in which the value of $alpha$ where the CS is broken does not coincide with the value at which the critical exponents start to differ from the ones of the corresponding short-range model. At variance, for the second critical line, having negative chemical potential, only SAN (SD) is present for 1$$2). Close to this line, where the minimum of the spectrum coincides with the momentum where singularities develop, the critical exponents change where CS is broken.},

keywords = {Conformal field theory, Integrable models, Long-range systems, Quantum entanglement, Quantum phase transitions, Renormalization group},

pubstate = {published},

tppubtype = {article}

}

We deal with the problem of studying the symmetries and the effective theories of long-range models around their critical points. A prominent issue is to determine whether they possess (or not) conformal symmetry (CS) at criticality and how the presence of CS depends on the range of the interactions. To have a model, both simple to treat and interesting, where to investigate these questions, we focus on the Kitaev chain with long-range pairings decaying with distance as power-law with exponent $alpha$. This is a quadratic solvable model, yet displaying non-trivial quantum phase transitions. Two critical lines are found, occurring respectively at a positive and a negative chemical potential. Focusing first on the critical line at positive chemical potential, by means of a renormalization group approach we derive its effective theory close to criticality. Our main result is that the effective action is the sum of two terms: a Dirac action SD, found in the short-range Ising universality class, and an ``anomalous'' CS breaking term SAN. While SD originates from low-energy excitations in the spectrum, SAN originates from the higher energy modes where singularities develop, due to the long-range nature of the model. At criticality SAN flows to zero for $alpha>$2, while for $alpha<$2 it dominates and determines the breakdown of the CS. Out of criticality SAN breaks, in the considered approximation, the effective Lorentz invariance (ELI) for every finite $alpha$. As $alpha$ increases such ELI breakdown becomes less and less pronounced and in the short-range limit $alpharightarrowinfty$ the ELI is restored. In order to test the validity of the determined effective theory, we compared the two-fermion static correlation functions and the von Neumann entropy obtained from them with the ones calculated on the lattice, finding agreement. These results explain two observed features characteristic of long-range models, the hybrid decay of static correlation functions within gapped phases and the area-law violation for the von Neumann entropy. The proposed scenario is expected to hold in other long-range models displaying quasiparticle excitations in ballistic regime. From the effective theory one can also see that new phases emerge for $alpha<$1. Finally we show that at every finite $alpha$ the critical exponents, defined as for the short-range ($alpharightarrowinfty$) model, are not altered. This also shows that the long-range paired Kitaev chain provides an example of a long-range model in which the value of $alpha$ where the CS is broken does not coincide with the value at which the critical exponents start to differ from the ones of the corresponding short-range model. At variance, for the second critical line, having negative chemical potential, only SAN (SD) is present for 1$<alpha<$2 (for $alpha>$2). Close to this line, where the minimum of the spectrum coincides with the momentum where singularities develop, the critical exponents change where CS is broken.Marina Litinskaya, Edoardo Tignone, Guido Pupillo

Cavity Polaritons with Rydberg Blockade and Long-Range Interactions Journal Article

Journal of Physics B: Atomic, Molecular and Optical Physics, 49 (16), pp. 164006, 2016, ISSN: 0953-4075.

Abstract | Links | BibTeX | Tags:

@article{Litinskaya2016,

title = {Cavity Polaritons with Rydberg Blockade and Long-Range Interactions},

author = {Marina Litinskaya and Edoardo Tignone and Guido Pupillo},

doi = {10.1088/0953-4075/49/16/164006},

issn = {0953-4075},

year = {2016},

date = {2016-08-01},

journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},

volume = {49},

number = {16},

pages = {164006},

abstract = {We study interactions between polaritons, arising when photons strongly couple to collective excitations in an array of two-level atoms trapped in an optical lattice inside a cavity. We consider two types of interactions between atoms: dipolar forces and atomic saturability, which range from hard-core repulsion to Rydberg blockade. We show that, in spite of the underlying repulsion in the subsystem of atomic excitations, saturability induces a broadband bunching of photons for two-polariton scattering states. We interpret this bunching as a result of interference, and trace it back to the mismatch of the quantization volumes for atomic excitations and photons. We also examine bound bipolaritonic states: these include states created by dipolar forces, as well as a gap bipolariton, which forms solely due to saturability effects in the atomic transition. Both types of bound states exhibit strong bunching in the photonic component. We discuss the dependence of bunching on experimentally relevant parameters.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study interactions between polaritons, arising when photons strongly couple to collective excitations in an array of two-level atoms trapped in an optical lattice inside a cavity. We consider two types of interactions between atoms: dipolar forces and atomic saturability, which range from hard-core repulsion to Rydberg blockade. We show that, in spite of the underlying repulsion in the subsystem of atomic excitations, saturability induces a broadband bunching of photons for two-polariton scattering states. We interpret this bunching as a result of interference, and trace it back to the mismatch of the quantization volumes for atomic excitations and photons. We also examine bound bipolaritonic states: these include states created by dipolar forces, as well as a gap bipolariton, which forms solely due to saturability effects in the atomic transition. Both types of bound states exhibit strong bunching in the photonic component. We discuss the dependence of bunching on experimentally relevant parameters.Alejandro Mendoza-Coto, Rogelio Díaz-Méndez, Guido Pupillo

Event-Driven Monte Carlo: Exact Dynamics at All Time Scales for Discrete-Variable Models Journal Article

EPL (Europhysics Letters), 114 (5), pp. 50003, 2016, ISSN: 0295-5075.

Abstract | Links | BibTeX | Tags:

@article{Mendoza-Coto2016,

title = {Event-Driven Monte Carlo: Exact Dynamics at All Time Scales for Discrete-Variable Models},

author = {Alejandro {Mendoza-Coto} and Rogelio {Díaz-Méndez} and Guido Pupillo},

doi = {10.1209/0295-5075/114/50003},

issn = {0295-5075},

year = {2016},

date = {2016-06-01},

journal = {EPL (Europhysics Letters)},

volume = {114},

number = {5},

pages = {50003},

abstract = {We present an algorithm for the simulation of the exact real-time dynamics of classical many-body systems with discrete energy levels. In the same spirit of kinetic Monte Carlo methods, a stochastic solution of the master equation is found, with no need to define any other phase-space construction. However, unlike existing methods, the present algorithm does not assume any particular statistical distribution to perform moves or to advance the time, and thus is a unique tool for the numerical exploration of fast and ultra-fast dynamical regimes. By decomposing the problem in a set of two-level subsystems, we find a natural variable step size, that is well defined from the normalization condition of the transition probabilities between the levels. We successfully test the algorithm with known exact solutions for non-equilibrium dynamics and equilibrium thermodynamical properties of Ising-spin models in one and two dimensions, and compare to standard implementations of kinetic Monte Carlo methods. The present algorithm is directly applicable to the study of the real-time dynamics of a large class of classical Markovian chains, and particularly to short-time situations where the exact evolution is relevant.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We present an algorithm for the simulation of the exact real-time dynamics of classical many-body systems with discrete energy levels. In the same spirit of kinetic Monte Carlo methods, a stochastic solution of the master equation is found, with no need to define any other phase-space construction. However, unlike existing methods, the present algorithm does not assume any particular statistical distribution to perform moves or to advance the time, and thus is a unique tool for the numerical exploration of fast and ultra-fast dynamical regimes. By decomposing the problem in a set of two-level subsystems, we find a natural variable step size, that is well defined from the normalization condition of the transition probabilities between the levels. We successfully test the algorithm with known exact solutions for non-equilibrium dynamics and equilibrium thermodynamical properties of Ising-spin models in one and two dimensions, and compare to standard implementations of kinetic Monte Carlo methods. The present algorithm is directly applicable to the study of the real-time dynamics of a large class of classical Markovian chains, and particularly to short-time situations where the exact evolution is relevant.Marina Litinskaya, Edoardo Tignone, Guido Pupillo

Broadband Photon-Photon Interactions Mediated by Cold Atoms in a Photonic Crystal Fiber Journal Article

Scientific Reports, 6 , pp. 25630, 2016, ISSN: 2045-2322.

Abstract | Links | BibTeX | Tags:

@article{Litinskaya2016a,

title = {Broadband Photon-Photon Interactions Mediated by Cold Atoms in a Photonic Crystal Fiber},

author = {Marina Litinskaya and Edoardo Tignone and Guido Pupillo},

doi = {10.1038/srep25630},

issn = {2045-2322},

year = {2016},

date = {2016-05-01},

journal = {Scientific Reports},

volume = {6},

pages = {25630},

abstract = {We demonstrate theoretically that photon-photon attraction can be engineered in the continuum of scattering states for pairs of photons propagating in a hollow-core photonic crystal fiber filled with cold atoms. The atoms are regularly spaced in an optical lattice configuration and the photons are resonantly tuned to an internal atomic transition. We show that the hard-core repulsion resulting from saturation of the atomic transitions induces bunching in the photonic component of the collective atom-photon modes (polaritons). Bunching is obtained in a frequency range as large as tens of GHz, and can be controlled by the inter-atomic separation. We provide a fully analytical explanation for this phenomenon by proving that correlations result from a mismatch of the quantization volumes for atomic excitations and photons in the continuum. Even stronger correlations can be observed for in-gap two-polariton bound states. Our theoretical results use parameters relevant for current experiments and suggest a simple and feasible way to induce interactions between photons.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We demonstrate theoretically that photon-photon attraction can be engineered in the continuum of scattering states for pairs of photons propagating in a hollow-core photonic crystal fiber filled with cold atoms. The atoms are regularly spaced in an optical lattice configuration and the photons are resonantly tuned to an internal atomic transition. We show that the hard-core repulsion resulting from saturation of the atomic transitions induces bunching in the photonic component of the collective atom-photon modes (polaritons). Bunching is obtained in a frequency range as large as tens of GHz, and can be controlled by the inter-atomic separation. We provide a fully analytical explanation for this phenomenon by proving that correlations result from a mismatch of the quantization volumes for atomic excitations and photons in the continuum. Even stronger correlations can be observed for in-gap two-polariton bound states. Our theoretical results use parameters relevant for current experiments and suggest a simple and feasible way to induce interactions between photons.Fabio Mezzacapo, Adriano Angelone, Guido Pupillo

Two Holes in a Two-Dimensional Quantum Antiferromagnet: A Variational Study Based on Entangled-Plaquette States Journal Article

Physical Review B, 94 (15), pp. 155120, 2016.

Abstract | Links | BibTeX | Tags:

@article{Mezzacapo2016,

title = {Two Holes in a Two-Dimensional Quantum Antiferromagnet: A Variational Study Based on Entangled-Plaquette States},

author = {Fabio Mezzacapo and Adriano Angelone and Guido Pupillo},

doi = {10.1103/PhysRevB.94.155120},

year = {2016},

date = {2016-01-01},

journal = {Physical Review B},

volume = {94},

number = {15},

pages = {155120},

abstract = {We show that the entangled-plaquette variational Ansatz can be adapted to study the two-dimensional t-J model in the presence of two mobile holes. Specifically, we focus on a square lattice comprising up to N=256 sites in the parameter range 0.4$łeq$J/t$łeq$2.0. Ground state energies are obtained via the optimization of a wave function in which the weight of a given configuration is expressed in terms of variational coefficients associated with square and linear entangled plaquettes. Our estimates are in excellent agreement with exact results available for the N=16 lattice. By extending our study to considerably larger systems we find, based on the analysis of the long-distance tail of the probability of finding two holes at spatial separation r, and on our computed two-hole binding energies, the existence of a two-hole bound state for all the values of J/t explored here. It is estimated that d-wave binding of the two holes does not occur for J/t},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We show that the entangled-plaquette variational Ansatz can be adapted to study the two-dimensional t-J model in the presence of two mobile holes. Specifically, we focus on a square lattice comprising up to N=256 sites in the parameter range 0.4$łeq$J/t$łeq$2.0. Ground state energies are obtained via the optimization of a wave function in which the weight of a given configuration is expressed in terms of variational coefficients associated with square and linear entangled plaquettes. Our estimates are in excellent agreement with exact results available for the N=16 lattice. By extending our study to considerably larger systems we find, based on the analysis of the long-distance tail of the probability of finding two holes at spatial separation r, and on our computed two-hole binding energies, the existence of a two-hole bound state for all the values of J/t explored here. It is estimated that d-wave binding of the two holes does not occur for J/tTao Ying, Marcello Dalmonte, Adriano Angelone, Fabio Mezzacapo, Peter Zoller, Guido Pupillo

Cluster Bose Metals Journal Article

arXiv:1606.04267 [cond-mat], 2016.

Abstract | BibTeX | Tags: Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons

@article{Ying2016,

title = {Cluster Bose Metals},

author = {Tao Ying and Marcello Dalmonte and Adriano Angelone and Fabio Mezzacapo and Peter Zoller and Guido Pupillo},

year = {2016},

date = {2016-01-01},

journal = {arXiv:1606.04267 [cond-mat]},

abstract = {Quantum phases of matter are usually characterised by broken symmetries. Identifying physical mechanisms and microscopic Hamiltonians that elude this paradigm is one of the key present challenges in many-body physics. Here, we use quantum Monte-Carlo simulations to show that a Bose metal phase, breaking no symmetries, is realized in simple Hubbard models for bosonic particles on a square lattice complemented by soft-shoulder interactions. The Bose metal appears at strong coupling and is separated from a supersolid phase and a superfluid at weaker couplings. The enabling mechanism is provided by cluster formation in the corresponding classical tiling problem. The identification of the cluster mechanism paves the way to the realization of exotic quantum liquids in both natural and synthetic quantum matter that harbors cluster formation.},

keywords = {Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons},

pubstate = {published},

tppubtype = {article}

}

Quantum phases of matter are usually characterised by broken symmetries. Identifying physical mechanisms and microscopic Hamiltonians that elude this paradigm is one of the key present challenges in many-body physics. Here, we use quantum Monte-Carlo simulations to show that a Bose metal phase, breaking no symmetries, is realized in simple Hubbard models for bosonic particles on a square lattice complemented by soft-shoulder interactions. The Bose metal appears at strong coupling and is separated from a supersolid phase and a superfluid at weaker couplings. The enabling mechanism is provided by cluster formation in the corresponding classical tiling problem. The identification of the cluster mechanism paves the way to the realization of exotic quantum liquids in both natural and synthetic quantum matter that harbors cluster formation.Adriano Angelone, Fabio Mezzacapo, Guido Pupillo

Superglass Phase of Interaction-Blockaded Gases on a Triangular Lattice Journal Article

Physical Review Letters, 116 (13), pp. 135303, 2016.

Abstract | Links | BibTeX | Tags:

@article{Angelone2016,

title = {Superglass Phase of Interaction-Blockaded Gases on a Triangular Lattice},

author = {Adriano Angelone and Fabio Mezzacapo and Guido Pupillo},

doi = {10.1103/PhysRevLett.116.135303},

year = {2016},

date = {2016-01-01},

journal = {Physical Review Letters},

volume = {116},

number = {13},

pages = {135303},

abstract = {We investigate the quantum phases of monodispersed bosonic gases confined to a triangular lattice and interacting via a class of soft-shoulder potentials. The latter correspond to soft-core potentials with an additional hard-core onsite interaction. Using exact quantum Monte Carlo simulations, we show that the low temperature phases for weak and strong interactions following a temperature quench are a homogeneous superfluid and a glass, respectively. The latter is an insulating phase characterized by inhomogeneity in the density distribution and structural disorder. Remarkably, we find that for intermediate interaction strengths a superglass occurs in an extended region of the phase diagram, where glassy behavior coexists with a sizable finite superfluid fraction. This glass phase is obtained in the absence of geometrical frustration or external disorder and is a result of the competition of quantum fluctuations and cluster formation in the corresponding classical ground state. For high enough temperature, the glass and superglass turn into a floating stripe solid and a supersolid, respectively. Given the simplicity and generality of the model, these phases should be directly relevant for state-of-the-art experiments with Rydberg-dressed atoms in optical lattices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We investigate the quantum phases of monodispersed bosonic gases confined to a triangular lattice and interacting via a class of soft-shoulder potentials. The latter correspond to soft-core potentials with an additional hard-core onsite interaction. Using exact quantum Monte Carlo simulations, we show that the low temperature phases for weak and strong interactions following a temperature quench are a homogeneous superfluid and a glass, respectively. The latter is an insulating phase characterized by inhomogeneity in the density distribution and structural disorder. Remarkably, we find that for intermediate interaction strengths a superglass occurs in an extended region of the phase diagram, where glassy behavior coexists with a sizable finite superfluid fraction. This glass phase is obtained in the absence of geometrical frustration or external disorder and is a result of the competition of quantum fluctuations and cluster formation in the corresponding classical ground state. For high enough temperature, the glass and superglass turn into a floating stripe solid and a supersolid, respectively. Given the simplicity and generality of the model, these phases should be directly relevant for state-of-the-art experiments with Rydberg-dressed atoms in optical lattices.Nobuyuki Takei, Christian Sommer, Claudiu Genes, Guido Pupillo, Haruka Goto, Kuniaki Koyasu, Hisashi Chiba, Matthias Weidemüller, Kenji Ohmori

Direct Observation of Ultrafast Many-Body Electron Dynamics in an Ultracold Rydberg Gas Journal Article

Nature Communications, 7 , pp. 13449, 2016, ISSN: 2041-1723.

Abstract | Links | BibTeX | Tags:

@article{Takei2016,

title = {Direct Observation of Ultrafast Many-Body Electron Dynamics in an Ultracold Rydberg Gas},

author = {Nobuyuki Takei and Christian Sommer and Claudiu Genes and Guido Pupillo and Haruka Goto and Kuniaki Koyasu and Hisashi Chiba and Matthias Weidemüller and Kenji Ohmori},

doi = {10.1038/ncomms13449},

issn = {2041-1723},

year = {2016},

date = {2016-01-01},

journal = {Nature Communications},

volume = {7},

pages = {13449},

abstract = {Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale.Davide Vodola, Luca Lepori, Elisa Ercolessi, Guido Pupillo

Long-Range Ising and Kitaev Models: Phases, Correlations and Edge Modes Journal Article

New Journal of Physics, 18 (1), pp. 015001, 2016, ISSN: 1367-2630.

Abstract | Links | BibTeX | Tags:

@article{Vodola2016,

title = {Long-Range Ising and Kitaev Models: Phases, Correlations and Edge Modes},

author = {Davide Vodola and Luca Lepori and Elisa Ercolessi and Guido Pupillo},

doi = {10.1088/1367-2630/18/1/015001},

issn = {1367-2630},

year = {2016},

date = {2016-01-01},

journal = {New Journal of Physics},

volume = {18},

number = {1},

pages = {015001},

abstract = {We analyze the quantum phases, correlation functions and edge modes for a class of spin-1/2 and fermionic models related to the one-dimensional Ising chain in the presence of a transverse field. These models are the Ising chain with anti-ferromagnetic long-range interactions that decay with distance r as ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn1.gif] $1/r^$backslash$alpha $ , as well as a related class of fermionic Hamiltonians that generalize the Kitaev chain, where both the hopping and pairing terms are long-range and their relative strength can be varied. For these models, we provide the phase diagram for all exponents $alpha$ , based on an analysis of the entanglement entropy, the decay of correlation functions, and the edge modes in the case of open chains. We demonstrate that violations of the area law can occur for ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn2.gif] $$backslash$alpha $backslash$lesssim 1$ , while connected correlation functions can decay with a hybrid exponential and power-law behavior, with a power that is $alpha$ -dependent. Interestingly, for the fermionic models we provide an exact analytical derivation for the decay of the correlation functions at every $alpha$ . Along the critical lines, for all models breaking of conformal symmetry is argued at low enough $alpha$ . For the fermionic models we show that the edge modes, massless for ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn3.gif] $$backslash$alpha $backslash$gtrsim 1$ , can acquire a mass for ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn4.gif] $$backslash$alpha $backslash$lt 1$ . The mass of these modes can be tuned by varying the relative strength of the kinetic and pairing terms in the Hamiltonian. Interestingly, for the Ising chain a similar edge localization appears for the first and second excited states on the paramagnetic side of the phase diagram, where edge modes are not expected. We argue that, at least for the fermionic chains, these massive states correspond to the appearance of new phases, notably approached via quantum phase transitions without mass gap closure. Finally, we discuss the possibility to detect some of these effects in experiments with cold trapped ions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We analyze the quantum phases, correlation functions and edge modes for a class of spin-1/2 and fermionic models related to the one-dimensional Ising chain in the presence of a transverse field. These models are the Ising chain with anti-ferromagnetic long-range interactions that decay with distance r as ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn1.gif] $1/r^$backslash$alpha $ , as well as a related class of fermionic Hamiltonians that generalize the Kitaev chain, where both the hopping and pairing terms are long-range and their relative strength can be varied. For these models, we provide the phase diagram for all exponents $alpha$ , based on an analysis of the entanglement entropy, the decay of correlation functions, and the edge modes in the case of open chains. We demonstrate that violations of the area law can occur for ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn2.gif] $$backslash$alpha $backslash$lesssim 1$ , while connected correlation functions can decay with a hybrid exponential and power-law behavior, with a power that is $alpha$ -dependent. Interestingly, for the fermionic models we provide an exact analytical derivation for the decay of the correlation functions at every $alpha$ . Along the critical lines, for all models breaking of conformal symmetry is argued at low enough $alpha$ . For the fermionic models we show that the edge modes, massless for ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn3.gif] $$backslash$alpha $backslash$gtrsim 1$ , can acquire a mass for ##IMG## [http://ej.iop.org/images/1367-2630/18/1/015001/njpaa0ba8ieqn4.gif] $$backslash$alpha $backslash$lt 1$ . The mass of these modes can be tuned by varying the relative strength of the kinetic and pairing terms in the Hamiltonian. Interestingly, for the Ising chain a similar edge localization appears for the first and second excited states on the paramagnetic side of the phase diagram, where edge modes are not expected. We argue that, at least for the fermionic chains, these massive states correspond to the appearance of new phases, notably approached via quantum phase transitions without mass gap closure. Finally, we discuss the possibility to detect some of these effects in experiments with cold trapped ions.
### 2015

Rogelio Díaz-Méndez, Fabio Mezzacapo, Fabio Cinti, Wolfgang Lechner, Guido Pupillo

Monodisperse Cluster Crystals: Classical and Quantum Dynamics Journal Article

Physical Review E, 92 (5), pp. 052307, 2015.

Abstract | Links | BibTeX | Tags:

@article{Diaz-Mendez2015,

title = {Monodisperse Cluster Crystals: Classical and Quantum Dynamics},

author = {Rogelio {Díaz-Méndez} and Fabio Mezzacapo and Fabio Cinti and Wolfgang Lechner and Guido Pupillo},

doi = {10.1103/PhysRevE.92.052307},

year = {2015},

date = {2015-11-01},

journal = {Physical Review E},

volume = {92},

number = {5},

pages = {052307},

abstract = {We study the phases and dynamics of a gas of monodisperse particles interacting via soft-core potentials in two spatial dimensions, which is of interest for soft-matter colloidal systems and quantum atomic gases. Using exact theoretical methods, we demonstrate that the equilibrium low-temperature classical phase simultaneously breaks continuous translational symmetry and dynamic space-time homogeneity, whose absence is usually associated with out-of-equilibrium glassy phenomena. This results in an exotic self-assembled cluster crystal with coexisting liquidlike long-time dynamical properties, which corresponds to a classical analog of supersolid behavior. We demonstrate that the effects of quantum fluctuations and bosonic statistics on cluster-glassy crystals are separate and competing: Zero-point motion tends to destabilize crystalline order, which can be restored by bosonic statistics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study the phases and dynamics of a gas of monodisperse particles interacting via soft-core potentials in two spatial dimensions, which is of interest for soft-matter colloidal systems and quantum atomic gases. Using exact theoretical methods, we demonstrate that the equilibrium low-temperature classical phase simultaneously breaks continuous translational symmetry and dynamic space-time homogeneity, whose absence is usually associated with out-of-equilibrium glassy phenomena. This results in an exotic self-assembled cluster crystal with coexisting liquidlike long-time dynamical properties, which corresponds to a classical analog of supersolid behavior. We demonstrate that the effects of quantum fluctuations and bosonic statistics on cluster-glassy crystals are separate and competing: Zero-point motion tends to destabilize crystalline order, which can be restored by bosonic statistics.Wolfgang Lechner, Fabio Cinti, Guido Pupillo

Tunable Defect Interactions and Supersolidity in Dipolar Quantum Gases on a Lattice Potential Journal Article

Physical Review A, 92 (5), pp. 053625, 2015.

Abstract | Links | BibTeX | Tags:

@article{Lechner2015,

title = {Tunable Defect Interactions and Supersolidity in Dipolar Quantum Gases on a Lattice Potential},

author = {Wolfgang Lechner and Fabio Cinti and Guido Pupillo},

doi = {10.1103/PhysRevA.92.053625},

year = {2015},

date = {2015-11-01},

journal = {Physical Review A},

volume = {92},

number = {5},

pages = {053625},

abstract = {Point defects in self-assembled crystals, such as vacancies and interstitials, attract each other and form stable clusters. This leads to a phase separation between perfect crystalline structures and defect conglomerates at low temperatures. We propose a method that allows one to tune the effective interactions between point defects from attractive to repulsive by means of external periodic fields. In the quantum regime, this allows one to engineer strongly correlated many-body phases. We exemplify the microscopic mechanism by considering dipolar quantum gases of ground-state polar molecules and weakly bound molecules of strongly magnetic atoms trapped in a weak optical lattice in a two-dimensional configuration. By tuning the lattice depth, defect interactions turn repulsive, which allows us to deterministically design a novel supersolid phase in the continuum limit.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

Point defects in self-assembled crystals, such as vacancies and interstitials, attract each other and form stable clusters. This leads to a phase separation between perfect crystalline structures and defect conglomerates at low temperatures. We propose a method that allows one to tune the effective interactions between point defects from attractive to repulsive by means of external periodic fields. In the quantum regime, this allows one to engineer strongly correlated many-body phases. We exemplify the microscopic mechanism by considering dipolar quantum gases of ground-state polar molecules and weakly bound molecules of strongly magnetic atoms trapped in a weak optical lattice in a two-dimensional configuration. By tuning the lattice depth, defect interactions turn repulsive, which allows us to deterministically design a novel supersolid phase in the continuum limit.Johannes Schachenmayer, Claudiu Genes, Edoardo Tignone, Guido Pupillo

Cavity-Enhanced Transport of Excitons Journal Article

Physical Review Letters, 114 (19), pp. 196403, 2015.

Abstract | Links | BibTeX | Tags:

@article{Schachenmayer2015,

title = {Cavity-Enhanced Transport of Excitons},

author = {Johannes Schachenmayer and Claudiu Genes and Edoardo Tignone and Guido Pupillo},

doi = {10.1103/PhysRevLett.114.196403},

year = {2015},

date = {2015-05-01},

journal = {Physical Review Letters},

volume = {114},

number = {19},

pages = {196403},

abstract = {We show that exciton-type transport in certain materials can be dramatically modified by their inclusion in an optical cavity: the modification of the electromagnetic vacuum mode structure introduced by the cavity leads to transport via delocalized polariton modes rather than through tunneling processes in the material itself. This can help overcome exponential suppression of transmission properties as a function of the system size in the case of disorder and other imperfections. We exemplify massive improvement of transmission for excitonic wave packets through a cavity, as well as enhancement of steady-state exciton currents under incoherent pumping. These results may have implications for experiments of exciton transport in disordered organic materials. We propose that the basic phenomena can be observed in quantum simulators made of Rydberg atoms, cold molecules in optical lattices, as well as in experiments with trapped ions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We show that exciton-type transport in certain materials can be dramatically modified by their inclusion in an optical cavity: the modification of the electromagnetic vacuum mode structure introduced by the cavity leads to transport via delocalized polariton modes rather than through tunneling processes in the material itself. This can help overcome exponential suppression of transmission properties as a function of the system size in the case of disorder and other imperfections. We exemplify massive improvement of transmission for excitonic wave packets through a cavity, as well as enhancement of steady-state exciton currents under incoherent pumping. These results may have implications for experiments of exciton transport in disordered organic materials. We propose that the basic phenomena can be observed in quantum simulators made of Rydberg atoms, cold molecules in optical lattices, as well as in experiments with trapped ions.M Dalmonte, W Lechner, Zi Cai, M Mattioli, A M Läuchli, G Pupillo

Cluster Luttinger Liquids and Emergent Supersymmetric Conformal Critical Points in the One-Dimensional Soft-Shoulder Hubbard Model Journal Article

Physical Review B, 92 (4), pp. 045106, 2015.

Abstract | Links | BibTeX | Tags:

@article{Dalmonte2015,

title = {Cluster Luttinger Liquids and Emergent Supersymmetric Conformal Critical Points in the One-Dimensional Soft-Shoulder Hubbard Model},

author = {M Dalmonte and W Lechner and Zi Cai and M Mattioli and A M Läuchli and G Pupillo},

doi = {10.1103/PhysRevB.92.045106},

year = {2015},

date = {2015-01-01},

journal = {Physical Review B},

volume = {92},

number = {4},

pages = {045106},

abstract = {We investigate the quantum phases of hard-core bosonic atoms in an extended Hubbard model where particles interact via soft-shoulder potentials in one dimension. Using a combination of field-theoretical methods and strong-coupling perturbation theory, we demonstrate that the low-energy phase can be a conformal cluster Luttinger liquid (CLL) phase with central charge c=1, where the microscopic degrees of freedom correspond to mesoscopic ensembles of particles. Using numerical density-matrix renormalization-group methods, we demonstrate that the CLL phase [first predicted in M. Mattioli et al., Phys. Rev. Lett. 111, 165302 (2013)] is separated from a conventional Tomonaga-Luttinger liquid by an exotic critical point with central charge c=32. The latter is expression of an emergent conformal supersymmetry, which is not present in the original Hamiltonian. We discuss the observability of the CLL phase in realistic experimental settings with weakly dressed Rydberg atoms confined to optical lattices. Using quantum Monte Carlo simulations, we show that the typical features of CLLs are stable up to comparatively high temperatures. Using exact diagonalizations and quantum trajectory methods, we provide a protocol for adiabatic state preparation as well as quantitative estimates on the effects of particle losses.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We investigate the quantum phases of hard-core bosonic atoms in an extended Hubbard model where particles interact via soft-shoulder potentials in one dimension. Using a combination of field-theoretical methods and strong-coupling perturbation theory, we demonstrate that the low-energy phase can be a conformal cluster Luttinger liquid (CLL) phase with central charge c=1, where the microscopic degrees of freedom correspond to mesoscopic ensembles of particles. Using numerical density-matrix renormalization-group methods, we demonstrate that the CLL phase [first predicted in M. Mattioli et al., Phys. Rev. Lett. 111, 165302 (2013)] is separated from a conventional Tomonaga-Luttinger liquid by an exotic critical point with central charge c=32. The latter is expression of an emergent conformal supersymmetry, which is not present in the original Hamiltonian. We discuss the observability of the CLL phase in realistic experimental settings with weakly dressed Rydberg atoms confined to optical lattices. Using quantum Monte Carlo simulations, we show that the typical features of CLLs are stable up to comparatively high temperatures. Using exact diagonalizations and quantum trajectory methods, we provide a protocol for adiabatic state preparation as well as quantitative estimates on the effects of particle losses.A Shalabney, J George, J Hutchison, G Pupillo, C Genet, T W Ebbesen

Coherent Coupling of Molecular Resonators with a Microcavity Mode Journal Article

Nature Communications, 6 , pp. 5981, 2015, ISSN: 2041-1723.

Abstract | Links | BibTeX | Tags:

@article{Shalabney2015,

title = {Coherent Coupling of Molecular Resonators with a Microcavity Mode},

author = {A Shalabney and J George and J Hutchison and G Pupillo and C Genet and T W Ebbesen},

doi = {10.1038/ncomms6981},

issn = {2041-1723},

year = {2015},

date = {2015-01-01},

journal = {Nature Communications},

volume = {6},

pages = {5981},

abstract = {The optical hybridization of the electronic states in strongly coupled molecule–cavity systems have revealed unique properties, such as lasing, room temperature polariton condensation and the modification of excited electronic landscapes involved in molecular isomerization. Here we show that molecular vibrational modes of the electronic ground state can also be coherently coupled with a microcavity mode at room temperature, given the low vibrational thermal occupation factors associated with molecular vibrations, and the collective coupling of a large ensemble of molecules immersed within the cavity-mode volume. This enables the enhancement of the collective Rabi-exchange rate with respect to the single-oscillator coupling strength. The possibility of inducing large shifts in the vibrational frequency of selected molecular bonds should have immediate consequences for chemistry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

The optical hybridization of the electronic states in strongly coupled molecule–cavity systems have revealed unique properties, such as lasing, room temperature polariton condensation and the modification of excited electronic landscapes involved in molecular isomerization. Here we show that molecular vibrational modes of the electronic ground state can also be coherently coupled with a microcavity mode at room temperature, given the low vibrational thermal occupation factors associated with molecular vibrations, and the collective coupling of a large ensemble of molecules immersed within the cavity-mode volume. This enables the enhancement of the collective Rabi-exchange rate with respect to the single-oscillator coupling strength. The possibility of inducing large shifts in the vibrational frequency of selected molecular bonds should have immediate consequences for chemistry.
### 2014

Edoardo Tignone, Guido Pupillo, Claudiu Genes

Transmissive Optomechanical Platforms with Engineered Spatial Defects Journal Article

Physical Review A, 90 (5), pp. 053831, 2014.

Abstract | Links | BibTeX | Tags:

@article{Tignone2014,

title = {Transmissive Optomechanical Platforms with Engineered Spatial Defects},

author = {Edoardo Tignone and Guido Pupillo and Claudiu Genes},

doi = {10.1103/PhysRevA.90.053831},

year = {2014},

date = {2014-11-01},

journal = {Physical Review A},

volume = {90},

number = {5},

pages = {053831},

abstract = {Linear optomechanical photon-phonon couplings in the membrane-in-the-middle setup can be enhanced by taking a multielement approach as it was recently shown [A. Xuereb, C. Genes, and A. Dantan, Phys. Rev. Lett. 109, 223601 (2012)]. The particular example considered consists of a periodic array of membranes embedded in a high-finesse optical cavity and operating in the transmissive regime, i.e., around resonances of the compound cavity-membrane system. Here we propose further improvements in such a setup by breaking the translational invariance of the array, i.e., by considering quasiperiodic arrays with engineered quadratic spatial defects in the membrane positions. The localization of light modes induced by the defect combined with the access of the aforementioned transmissive regime window can lead to additional enhancement of the strength of both linear and quadratic optomechanical couplings.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

Linear optomechanical photon-phonon couplings in the membrane-in-the-middle setup can be enhanced by taking a multielement approach as it was recently shown [A. Xuereb, C. Genes, and A. Dantan, Phys. Rev. Lett. 109, 223601 (2012)]. The particular example considered consists of a periodic array of membranes embedded in a high-finesse optical cavity and operating in the transmissive regime, i.e., around resonances of the compound cavity-membrane system. Here we propose further improvements in such a setup by breaking the translational invariance of the array, i.e., by considering quasiperiodic arrays with engineered quadratic spatial defects in the membrane positions. The localization of light modes induced by the defect combined with the access of the aforementioned transmissive regime window can lead to additional enhancement of the strength of both linear and quadratic optomechanical couplings.Davide Vodola, Luca Lepori, Elisa Ercolessi, Alexey V Gorshkov, Guido Pupillo

Kitaev Chains with Long-Range Pairing Journal Article

Physical Review Letters, 113 (15), pp. 156402, 2014.

Abstract | Links | BibTeX | Tags:

@article{Vodola2014,

title = {Kitaev Chains with Long-Range Pairing},

author = {Davide Vodola and Luca Lepori and Elisa Ercolessi and Alexey V Gorshkov and Guido Pupillo},

doi = {10.1103/PhysRevLett.113.156402},

year = {2014},

date = {2014-10-01},

journal = {Physical Review Letters},

volume = {113},

number = {15},

pages = {156402},

abstract = {We propose and analyze a generalization of the Kitaev chain for fermions with long-range p-wave pairing, which decays with distance as a power law with exponent $alpha$. Using the integrability of the model, we demonstrate the existence of two types of gapped regimes, where correlation functions decay exponentially at short range and algebraically at long range ($alpha>$1) or purely algebraically ($alpha<$1). Most interestingly, along the critical lines, long-range pairing is found to break conformal symmetry for sufficiently small $alpha$. This is accompanied by a violation of the area law for the entanglement entropy in large parts of the phase diagram in the presence of a gap and can be detected via the dynamics of entanglement following a quench. Some of these features may be relevant for current experiments with cold atomic ions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We propose and analyze a generalization of the Kitaev chain for fermions with long-range p-wave pairing, which decays with distance as a power law with exponent $alpha$. Using the integrability of the model, we demonstrate the existence of two types of gapped regimes, where correlation functions decay exponentially at short range and algebraically at long range ($alpha>$1) or purely algebraically ($alpha<$1). Most interestingly, along the critical lines, long-range pairing is found to break conformal symmetry for sufficiently small $alpha$. This is accompanied by a violation of the area law for the entanglement entropy in large parts of the phase diagram in the presence of a gap and can be detected via the dynamics of entanglement following a quench. Some of these features may be relevant for current experiments with cold atomic ions.Aurélien Dantan, Bhagya Nair, Guido Pupillo, Claudiu Genes

Hybrid Cavity Mechanics with Doped Systems Journal Article

Physical Review A, 90 (3), pp. 033820, 2014.

Abstract | Links | BibTeX | Tags:

@article{Dantan2014,

title = {Hybrid Cavity Mechanics with Doped Systems},

author = {Aurélien Dantan and Bhagya Nair and Guido Pupillo and Claudiu Genes},

doi = {10.1103/PhysRevA.90.033820},

year = {2014},

date = {2014-09-01},

journal = {Physical Review A},

volume = {90},

number = {3},

pages = {033820},

abstract = {We investigate the dynamics of a mechanical resonator in which is embedded an ensemble of two-level systems interacting with an optical cavity field. We show that this hybrid approach to optomechanics allows for enhanced effective interactions between the mechanics and the cavity field, leading, for instance, to ground-state cooling of the mechanics, even in regimes, like the unresolved sideband regime, in which standard radiation pressure cooling would be inefficient.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We investigate the dynamics of a mechanical resonator in which is embedded an ensemble of two-level systems interacting with an optical cavity field. We show that this hybrid approach to optomechanics allows for enhanced effective interactions between the mechanics and the cavity field, leading, for instance, to ground-state cooling of the mechanics, even in regimes, like the unresolved sideband regime, in which standard radiation pressure cooling would be inefficient.André Xuereb, Claudiu Genes, Guido Pupillo, Mauro Paternostro, Aurélien Dantan

Reconfigurable Long-Range Phonon Dynamics in Optomechanical Arrays Journal Article

Physical Review Letters, 112 (13), pp. 133604, 2014.

Abstract | Links | BibTeX | Tags:

@article{Xuereb2014,

title = {Reconfigurable Long-Range Phonon Dynamics in Optomechanical Arrays},

author = {André Xuereb and Claudiu Genes and Guido Pupillo and Mauro Paternostro and Aurélien Dantan},

doi = {10.1103/PhysRevLett.112.133604},

year = {2014},

date = {2014-04-01},

journal = {Physical Review Letters},

volume = {112},

number = {13},

pages = {133604},

abstract = {We investigate periodic optomechanical arrays as reconfigurable platforms for engineering the coupling between multiple mechanical and electromagnetic modes and for exploring many-body phonon dynamics. Exploiting structural resonances in the coupling between light fields and collective motional modes of the array, we show that tunable effective long-range interactions between mechanical modes can be achieved. This paves the way towards the implementation of controlled phononic walks and heat transfer on densely connected graphs as well as the coherent transfer of excitations between distant elements of optomechanical arrays.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We investigate periodic optomechanical arrays as reconfigurable platforms for engineering the coupling between multiple mechanical and electromagnetic modes and for exploring many-body phonon dynamics. Exploiting structural resonances in the coupling between light fields and collective motional modes of the array, we show that tunable effective long-range interactions between mechanical modes can be achieved. This paves the way towards the implementation of controlled phononic walks and heat transfer on densely connected graphs as well as the coherent transfer of excitations between distant elements of optomechanical arrays.F Cinti, T Macr`i, W Lechner, G Pupillo, T Pohl

Defect-Induced Supersolidity with Soft-Core Bosons Journal Article

Nature Communications, 5 , pp. 3235, 2014, ISSN: 2041-1723.

Abstract | Links | BibTeX | Tags:

@article{Cinti2014,

title = {Defect-Induced Supersolidity with Soft-Core Bosons},

author = {F Cinti and T Macr`i and W Lechner and G Pupillo and T Pohl},

doi = {10.1038/ncomms4235},

issn = {2041-1723},

year = {2014},

date = {2014-02-01},

journal = {Nature Communications},

volume = {5},

pages = {3235},

abstract = {More than 40 years ago, Andreev, Lifshitz and Chester suggested the possible existence of a peculiar solid phase of matter, the microscopic constituents of which can flow superfluidly without resistance due to the formation of zero-point defects in the ground state of self-assembled crystals. Yet, a physical system where this mechanism is unambiguously established remains to be found, both experimentally and theoretically. Here we investigate the zero-temperature phase diagram of two-dimensional bosons with finite-range soft-core interactions. For low particle densities, the system is shown to feature a solid phase in which zero-point vacancies emerge spontaneously and give rise to superfluid flow of particles through the crystal. This provides the first example of defect-induced, continuous-space supersolidity consistent with the Andreev–Lifshitz–Chester scenario.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

More than 40 years ago, Andreev, Lifshitz and Chester suggested the possible existence of a peculiar solid phase of matter, the microscopic constituents of which can flow superfluidly without resistance due to the formation of zero-point defects in the ground state of self-assembled crystals. Yet, a physical system where this mechanism is unambiguously established remains to be found, both experimentally and theoretically. Here we investigate the zero-temperature phase diagram of two-dimensional bosons with finite-range soft-core interactions. For low particle densities, the system is shown to feature a solid phase in which zero-point vacancies emerge spontaneously and give rise to superfluid flow of particles through the crystal. This provides the first example of defect-induced, continuous-space supersolidity consistent with the Andreev–Lifshitz–Chester scenario.
### 2013

Marco Mattioli, Marcello Dalmonte, Wolfgang Lechner, Guido Pupillo

Cluster Luttinger Liquids of Rydberg-Dressed Atoms in Optical Lattices Journal Article

Physical Review Letters, 111 (16), pp. 165302, 2013.

Abstract | Links | BibTeX | Tags:

@article{Mattioli2013,

title = {Cluster Luttinger Liquids of Rydberg-Dressed Atoms in Optical Lattices},

author = {Marco Mattioli and Marcello Dalmonte and Wolfgang Lechner and Guido Pupillo},

doi = {10.1103/PhysRevLett.111.165302},

year = {2013},

date = {2013-10-01},

journal = {Physical Review Letters},

volume = {111},

number = {16},

pages = {165302},

abstract = {We investigate the zero-temperature phases of bosonic and fermionic gases confined to one dimension and interacting via a class of finite-range soft-shoulder potentials (i.e., soft-core potentials with an additional hard-core onsite interaction). Using a combination of analytical and numerical methods, we demonstrate the stabilization of critical quantum liquids with qualitatively new features with respect to the Tomonaga-Luttinger liquid paradigm. These features result from frustration and cluster formation in the corresponding classical ground state. Characteristic signatures of these liquids are accessible in state-of-the-art experimental setups with Rydberg-dressed ground-state atoms trapped in optical lattices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We investigate the zero-temperature phases of bosonic and fermionic gases confined to one dimension and interacting via a class of finite-range soft-shoulder potentials (i.e., soft-core potentials with an additional hard-core onsite interaction). Using a combination of analytical and numerical methods, we demonstrate the stabilization of critical quantum liquids with qualitatively new features with respect to the Tomonaga-Luttinger liquid paradigm. These features result from frustration and cluster formation in the corresponding classical ground state. Characteristic signatures of these liquids are accessible in state-of-the-art experimental setups with Rydberg-dressed ground-state atoms trapped in optical lattices.Claudiu Genes, André Xuereb, Guido Pupillo, Aurélien Dantan

Enhanced Optomechanical Readout Using Optical Coalescence Journal Article

Physical Review A, 88 (3), pp. 033855, 2013.

Abstract | Links | BibTeX | Tags:

@article{Genes2013,

title = {Enhanced Optomechanical Readout Using Optical Coalescence},

author = {Claudiu Genes and André Xuereb and Guido Pupillo and Aurélien Dantan},

doi = {10.1103/PhysRevA.88.033855},

year = {2013},

date = {2013-09-01},

journal = {Physical Review A},

volume = {88},

number = {3},

pages = {033855},

abstract = {We present a scheme to strongly enhance the readout sensitivity of the squared displacement of a mobile scatterer placed in a Fabry-Pérot cavity. We investigate the largely unexplored regime of cavity electrodynamics in which a highly reflective element positioned between the end mirrors of a symmetric Fabry-Pérot resonator strongly modifies the cavity response function, such that two longitudinal modes with different spatial parity are brought close to frequency degeneracy and interfere in the cavity output field. In the case of a movable middle reflector we show that the interference in this generic ``optical coalescence'' phenomenon gives rise to an enhanced frequency shift of the peaks of the cavity transmission that can be exploited in optomechanics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We present a scheme to strongly enhance the readout sensitivity of the squared displacement of a mobile scatterer placed in a Fabry-Pérot cavity. We investigate the largely unexplored regime of cavity electrodynamics in which a highly reflective element positioned between the end mirrors of a symmetric Fabry-Pérot resonator strongly modifies the cavity response function, such that two longitudinal modes with different spatial parity are brought close to frequency degeneracy and interfere in the cavity output field. In the case of a movable middle reflector we show that the interference in this generic ``optical coalescence'' phenomenon gives rise to an enhanced frequency shift of the peaks of the cavity transmission that can be exploited in optomechanics.Ehsan Khatami, Guido Pupillo, Mark Srednicki, Marcos Rigol

Fluctuation-Dissipation Theorem in an Isolated System of Quantum Dipolar Bosons after a Quench Journal Article

Physical Review Letters, 111 (5), pp. 050403, 2013.

Abstract | Links | BibTeX | Tags:

@article{Khatami2013,

title = {Fluctuation-Dissipation Theorem in an Isolated System of Quantum Dipolar Bosons after a Quench},

author = {Ehsan Khatami and Guido Pupillo and Mark Srednicki and Marcos Rigol},

doi = {10.1103/PhysRevLett.111.050403},

year = {2013},

date = {2013-07-01},

journal = {Physical Review Letters},

volume = {111},

number = {5},

pages = {050403},

abstract = {We examine the validity of fluctuation-dissipation relations in isolated quantum systems taken out of equilibrium by a sudden quench. We focus on the dynamics of trapped hard-core bosons in one-dimensional lattices with dipolar interactions whose strength is changed during the quench. We find indications that fluctuation-dissipation relations hold if the system is nonintegrable after the quench, as well as if it is integrable after the quench if the initial state is an equilibrium state of a nonintegrable Hamiltonian. On the other hand, we find indications that they fail if the system is integrable both before and after quenching.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We examine the validity of fluctuation-dissipation relations in isolated quantum systems taken out of equilibrium by a sudden quench. We focus on the dynamics of trapped hard-core bosons in one-dimensional lattices with dipolar interactions whose strength is changed during the quench. We find indications that fluctuation-dissipation relations hold if the system is nonintegrable after the quench, as well as if it is integrable after the quench if the initial state is an equilibrium state of a nonintegrable Hamiltonian. On the other hand, we find indications that they fail if the system is integrable both before and after quenching.A Safavi-Naini, c S G Söyler, G Pupillo, H R Sadeghpour, B Capogrosso-Sansone

Quantum Phases of Dipolar Bosons in Bilayer Geometry Journal Article

New Journal of Physics, 15 (1), pp. 013036, 2013, ISSN: 1367-2630.

Abstract | Links | BibTeX | Tags:

@article{Safavi-Naini2013,

title = {Quantum Phases of Dipolar Bosons in Bilayer Geometry},

author = {A {Safavi-Naini} and {c S} G Söyler and G Pupillo and H R Sadeghpour and B {Capogrosso-Sansone}},

doi = {10.1088/1367-2630/15/1/013036},

issn = {1367-2630},

year = {2013},

date = {2013-01-01},

journal = {New Journal of Physics},

volume = {15},

number = {1},

pages = {013036},

abstract = {We investigate the quantum phases of hard-core dipolar bosons confined to a square lattice in a bilayer geometry. Using exact theoretical techniques, we discuss the many-body effects resulting from the pairing of particles across layers at finite density, including a novel pair supersolid, superfluid and solid phases. These results are of direct relevance to experiments with polar molecules and atoms with large magnetic dipole moments trapped in optical lattices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We investigate the quantum phases of hard-core dipolar bosons confined to a square lattice in a bilayer geometry. Using exact theoretical techniques, we discuss the many-body effects resulting from the pairing of particles across layers at finite density, including a novel pair supersolid, superfluid and solid phases. These results are of direct relevance to experiments with polar molecules and atoms with large magnetic dipole moments trapped in optical lattices.
### 2012

A W Glaetzle, R Nath, B Zhao, G Pupillo, P Zoller

Driven-Dissipative Dynamics of a Strongly Interacting Rydberg Gas Journal Article

Physical Review A, 86 (4), pp. 043403, 2012.

Abstract | Links | BibTeX | Tags:

@article{Glaetzle2012,

title = {Driven-Dissipative Dynamics of a Strongly Interacting Rydberg Gas},

author = {A W Glaetzle and R Nath and B Zhao and G Pupillo and P Zoller},

doi = {10.1103/PhysRevA.86.043403},

year = {2012},

date = {2012-10-01},

journal = {Physical Review A},

volume = {86},

number = {4},

pages = {043403},

abstract = {We study the nonequilibrium many-body dynamics of a cold gas of ground-state alkali-metal atoms weakly admixed by Rydberg states with laser light. On a time scale shorter than the lifetime of the dressed states, effective dipole-dipole or van der Waals interactions between atoms can lead to the formation of strongly correlated phases, such as atomic crystals. Using a semiclassical approach, we study the long-time dynamics where decoherence and dissipative processes due to spontaneous emission and blackbody radiation dominate, leading to heating and melting of atomic crystals as well as particle losses. These effects can be substantially mitigated by performing active laser cooling in the presence of atomic dressing.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study the nonequilibrium many-body dynamics of a cold gas of ground-state alkali-metal atoms weakly admixed by Rydberg states with laser light. On a time scale shorter than the lifetime of the dressed states, effective dipole-dipole or van der Waals interactions between atoms can lead to the formation of strongly correlated phases, such as atomic crystals. Using a semiclassical approach, we study the long-time dynamics where decoherence and dissipative processes due to spontaneous emission and blackbody radiation dominate, leading to heating and melting of atomic crystals as well as particle losses. These effects can be substantially mitigated by performing active laser cooling in the presence of atomic dressing.M A Baranov, M Dalmonte, G Pupillo, P Zoller

Condensed Matter Theory of Dipolar Quantum Gases Journal Article

Chemical Reviews, 112 (9), pp. 5012-5061, 2012, ISSN: 0009-2665.

Links | BibTeX | Tags: Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons

@article{Baranov2012,

title = {Condensed Matter Theory of Dipolar Quantum Gases},

author = {M A Baranov and M Dalmonte and G Pupillo and P Zoller},

doi = {10.1021/cr2003568},

issn = {0009-2665},

year = {2012},

date = {2012-09-01},

journal = {Chemical Reviews},

volume = {112},

number = {9},

pages = {5012-5061},

keywords = {Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons},

pubstate = {published},

tppubtype = {article}

}

Markus Müller, Sebastian Diehl, Guido Pupillo, Peter Zoller

Engineered Open Systems and Quantum Simulations with Atoms and Ions Incollection

Berman, Paul; Arimondo, Ennio; Lin, Chun (Ed.): Advances In Atomic, Molecular, and Optical Physics, 61 , pp. 1-80, Academic Press, 2012.

Abstract | Links | BibTeX | Tags: Atomic physics, Open quantum systems, Quantum phase transitions, Quantum simulation, Topological phases of matter, Trapped ions, Unconventional pairing mechanisms

@incollection{Muller2012,

title = {Engineered Open Systems and Quantum Simulations with Atoms and Ions},

author = {Markus Müller and Sebastian Diehl and Guido Pupillo and Peter Zoller},

editor = {Paul Berman and Ennio Arimondo and Chun Lin},

doi = {10.1016/B978-0-12-396482-3.00001-6},

year = {2012},

date = {2012-07-01},

booktitle = {Advances In Atomic, Molecular, and Optical Physics},

volume = {61},

pages = {1-80},

publisher = {Academic Press},

series = {Advances in Atomic, Molecular, and Optical Physics},

abstract = {The enormous experimental progress in atomic, molecular, and optical (AMO) physics during the last decades allows us nowadays to isolate single, a few or even many-body ensembles of microscopic particles, and to manipulate their quantum properties at a level of precision, which still seemed unthinkable some years ago. This versatile set of tools has enabled the development of the well-established concept of engineering of many-body Hamiltonians in various physical platforms. These available tools, however, can also be harnessed to extend the scenario of Hamiltonian engineering to a more general Liouvillian setting, which in addition to coherent dynamics also includes controlled dissipation in many-body quantum systems. Here, we review recent theoretical and experimental progress in different directions along these lines, with a particular focus on physical realizations with systems of atoms and ions. This comprises digital quantum simulations in a general open system setting, as well as engineering and understanding new classes of systems far away from thermodynamic equilibrium. In the context of digital quantum simulation, we first outline the basic concepts and illustrate them on the basis of a recent experiment with trapped ions. We also discuss theoretical work proposing an intrinsically scalable simulation architecture for spin models with high-order interactions such as Kitaev's toric code, based on Rydberg atoms stored in optical lattices. We then turn to the digital simulation of dissipative many-body dynamics, pointing out a route for the general quantum state preparation in complex spin models, and discuss a recent experiment demonstrating the basic building blocks of a full-fledged open-system quantum simulator. In view of creating novel classes of out-of-equilibrium systems, we focus on ultracold atoms. We point out how quantum mechanical long-range order can be established via engineered dissipation, and present genuine many-body aspects of this setting: in the context of bosons, we discuss dynamical phase transitions resulting from competing Hamiltonian and dissipative dynamics. In the context of fermions, we present a purely dissipative pairing mechanism, and show how this could pave the way for the quantum simulation of the Fermi–Hubbard model. We also propose and analyze the key properties of dissipatively targeted topological phases of matter.},

keywords = {Atomic physics, Open quantum systems, Quantum phase transitions, Quantum simulation, Topological phases of matter, Trapped ions, Unconventional pairing mechanisms},

pubstate = {published},

tppubtype = {incollection}

}

The enormous experimental progress in atomic, molecular, and optical (AMO) physics during the last decades allows us nowadays to isolate single, a few or even many-body ensembles of microscopic particles, and to manipulate their quantum properties at a level of precision, which still seemed unthinkable some years ago. This versatile set of tools has enabled the development of the well-established concept of engineering of many-body Hamiltonians in various physical platforms. These available tools, however, can also be harnessed to extend the scenario of Hamiltonian engineering to a more general Liouvillian setting, which in addition to coherent dynamics also includes controlled dissipation in many-body quantum systems. Here, we review recent theoretical and experimental progress in different directions along these lines, with a particular focus on physical realizations with systems of atoms and ions. This comprises digital quantum simulations in a general open system setting, as well as engineering and understanding new classes of systems far away from thermodynamic equilibrium. In the context of digital quantum simulation, we first outline the basic concepts and illustrate them on the basis of a recent experiment with trapped ions. We also discuss theoretical work proposing an intrinsically scalable simulation architecture for spin models with high-order interactions such as Kitaev's toric code, based on Rydberg atoms stored in optical lattices. We then turn to the digital simulation of dissipative many-body dynamics, pointing out a route for the general quantum state preparation in complex spin models, and discuss a recent experiment demonstrating the basic building blocks of a full-fledged open-system quantum simulator. In view of creating novel classes of out-of-equilibrium systems, we focus on ultracold atoms. We point out how quantum mechanical long-range order can be established via engineered dissipation, and present genuine many-body aspects of this setting: in the context of bosons, we discuss dynamical phase transitions resulting from competing Hamiltonian and dissipative dynamics. In the context of fermions, we present a purely dissipative pairing mechanism, and show how this could pave the way for the quantum simulation of the Fermi–Hubbard model. We also propose and analyze the key properties of dissipatively targeted topological phases of matter.N Henkel, F Cinti, P Jain, G Pupillo, T Pohl

Supersolid Vortex Crystals in Rydberg-Dressed Bose-Einstein Condensates Journal Article

Physical Review Letters, 108 (26), pp. 265301, 2012.

Abstract | Links | BibTeX | Tags:

@article{Henkel2012,

title = {Supersolid Vortex Crystals in Rydberg-Dressed Bose-Einstein Condensates},

author = {N Henkel and F Cinti and P Jain and G Pupillo and T Pohl},

doi = {10.1103/PhysRevLett.108.265301},

year = {2012},

date = {2012-06-01},

journal = {Physical Review Letters},

volume = {108},

number = {26},

pages = {265301},

abstract = {We study rotating quasi-two-dimensional Bose–Einstein condensates, in which atoms are dressed to a highly excited Rydberg state. This leads to weak effective interactions that induce a transition to a mesoscopic supersolid state. Considering slow rotation, we determine its superfluidity using quantum Monte Carlo simulations as well as mean field calculations. For rapid rotation, the latter reveal an interesting competition between the supersolid crystal structure and the rotation-induced vortex lattice that gives rise to new phases, including arrays of mesoscopic vortex crystals.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study rotating quasi-two-dimensional Bose–Einstein condensates, in which atoms are dressed to a highly excited Rydberg state. This leads to weak effective interactions that induce a transition to a mesoscopic supersolid state. Considering slow rotation, we determine its superfluidity using quantum Monte Carlo simulations as well as mean field calculations. For rapid rotation, the latter reveal an interesting competition between the supersolid crystal structure and the rotation-induced vortex lattice that gives rise to new phases, including arrays of mesoscopic vortex crystals.B Zhao, A W Glaetzle, G Pupillo, P Zoller

Atomic Rydberg Reservoirs for Polar Molecules Journal Article

Physical Review Letters, 108 (19), pp. 193007, 2012.

Abstract | Links | BibTeX | Tags:

@article{Zhao2012,

title = {Atomic Rydberg Reservoirs for Polar Molecules},

author = {B Zhao and A W Glaetzle and G Pupillo and P Zoller},

doi = {10.1103/PhysRevLett.108.193007},

year = {2012},

date = {2012-05-01},

journal = {Physical Review Letters},

volume = {108},

number = {19},

pages = {193007},

abstract = {We discuss laser-dressed dipolar and van der Waals interactions between atoms and polar molecules, so that a cold atomic gas with laser admixed Rydberg levels acts as a designed reservoir for both elastic and inelastic collisional processes. The elastic scattering channel is characterized by large elastic scattering cross sections and repulsive shields to protect from close encounter collisions. In addition, we discuss a dissipative (inelastic) collision where a spontaneously emitted photon carries away (kinetic) energy of the collision partners, thus providing a significant energy loss in a single collision. This leads to the scenario of rapid thermalization and cooling of a molecule in the mK down to the $mu$K regime by cold atoms.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We discuss laser-dressed dipolar and van der Waals interactions between atoms and polar molecules, so that a cold atomic gas with laser admixed Rydberg levels acts as a designed reservoir for both elastic and inelastic collisional processes. The elastic scattering channel is characterized by large elastic scattering cross sections and repulsive shields to protect from close encounter collisions. In addition, we discuss a dissipative (inelastic) collision where a spontaneously emitted photon carries away (kinetic) energy of the collision partners, thus providing a significant energy loss in a single collision. This leads to the scenario of rapid thermalization and cooling of a molecule in the mK down to the $mu$K regime by cold atoms.
### 2010

F Cinti, P Jain, M Boninsegni, A Micheli, P Zoller, G Pupillo

Supersolid Droplet Crystal in a Dipole-Blockaded Gas Journal Article

Physical Review Letters, 105 (13), pp. 135301, 2010.

Abstract | Links | BibTeX | Tags:

@article{Cinti2010,

title = {Supersolid Droplet Crystal in a Dipole-Blockaded Gas},

author = {F Cinti and P Jain and M Boninsegni and A Micheli and P Zoller and G Pupillo},

doi = {10.1103/PhysRevLett.105.135301},

year = {2010},

date = {2010-09-01},

journal = {Physical Review Letters},

volume = {105},

number = {13},

pages = {135301},

abstract = {A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the dipole-blockade regime, interacting via a repulsive dipolar potential softened at short distances. Using exact numerical techniques, we study the low-temperature phase diagram of this system, and observe an intriguing phase consisting of a crystal of mesoscopic superfluid droplets. At low temperature, phase coherence throughout the whole system, and the ensuing bulk superfluidity, are established through tunnelling of identical particles between neighboring droplets.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the dipole-blockade regime, interacting via a repulsive dipolar potential softened at short distances. Using exact numerical techniques, we study the low-temperature phase diagram of this system, and observe an intriguing phase consisting of a crystal of mesoscopic superfluid droplets. At low temperature, phase coherence throughout the whole system, and the ensuing bulk superfluidity, are established through tunnelling of identical particles between neighboring droplets.G Pupillo, A Micheli, M Boninsegni, I Lesanovsky, P Zoller

Strongly Correlated Gases of Rydberg-Dressed Atoms: Quantum and Classical Dynamics Journal Article

Physical Review Letters, 104 (22), pp. 223002, 2010.

Abstract | Links | BibTeX | Tags:

@article{Pupillo2010,

title = {Strongly Correlated Gases of Rydberg-Dressed Atoms: Quantum and Classical Dynamics},

author = {G Pupillo and A Micheli and M Boninsegni and I Lesanovsky and P Zoller},

doi = {10.1103/PhysRevLett.104.223002},

year = {2010},

date = {2010-06-01},

journal = {Physical Review Letters},

volume = {104},

number = {22},

pages = {223002},

abstract = {We discuss techniques to generate long-range interactions in a gas of ground state alkali atoms, by weakly admixing excited Rydberg states with laser light. This provides a tool to engineer strongly correlated phases with reduced decoherence from inelastic collisions and spontaneous emission. As an illustration, we discuss the quantum phases of dressed atoms with dipole-dipole interactions confined in a harmonic potential, as relevant to experiments. We show that residual spontaneous emission from the Rydberg state acts as a heating mechanism, leading to a quantum-classical crossover.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We discuss techniques to generate long-range interactions in a gas of ground state alkali atoms, by weakly admixing excited Rydberg states with laser light. This provides a tool to engineer strongly correlated phases with reduced decoherence from inelastic collisions and spontaneous emission. As an illustration, we discuss the quantum phases of dressed atoms with dipole-dipole interactions confined in a harmonic potential, as relevant to experiments. We show that residual spontaneous emission from the Rydberg state acts as a heating mechanism, leading to a quantum-classical crossover.M Dalmonte, G Pupillo, P Zoller

One-Dimensional Quantum Liquids with Power-Law Interactions: The Luttinger Staircase Journal Article

Physical Review Letters, 105 (14), pp. 140401, 2010.

Abstract | Links | BibTeX | Tags:

@article{Dalmonte2010,

title = {One-Dimensional Quantum Liquids with Power-Law Interactions: The Luttinger Staircase},

author = {M Dalmonte and G Pupillo and P Zoller},

doi = {10.1103/PhysRevLett.105.140401},

year = {2010},

date = {2010-01-01},

journal = {Physical Review Letters},

volume = {105},

number = {14},

pages = {140401},

abstract = {We study one-dimensional fermionic and bosonic gases with repulsive power-law interactions 1/|x|$beta$, with $beta>$1, in the framework of Tomonaga-Luttinger liquid (TLL) theory. We obtain an accurate analytical expression linking the TLL parameter to the microscopic Hamiltonian, for arbitrary $beta$ and strength of the interactions. In the presence of a small periodic potential, power-law interactions make the TLL unstable towards the formation of a cascade of lattice solids with fractional filling, a ``Luttinger staircase.'' Several of these quantum phases and phase transitions are realized with ground state polar molecules and weakly bound magnetic Feshbach molecules.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study one-dimensional fermionic and bosonic gases with repulsive power-law interactions 1/|x|$beta$, with $beta>$1, in the framework of Tomonaga-Luttinger liquid (TLL) theory. We obtain an accurate analytical expression linking the TLL parameter to the microscopic Hamiltonian, for arbitrary $beta$ and strength of the interactions. In the presence of a small periodic potential, power-law interactions make the TLL unstable towards the formation of a cascade of lattice solids with fractional filling, a ``Luttinger staircase.'' Several of these quantum phases and phase transitions are realized with ground state polar molecules and weakly bound magnetic Feshbach molecules.B Capogrosso-Sansone, C Trefzger, M Lewenstein, P Zoller, G Pupillo

Quantum Phases of Cold Polar Molecules in 2D Optical Lattices Journal Article

Physical Review Letters, 104 (12), pp. 125301, 2010.

Abstract | Links | BibTeX | Tags:

@article{Capogrosso-Sansone2010,

title = {Quantum Phases of Cold Polar Molecules in 2D Optical Lattices},

author = {B {Capogrosso-Sansone} and C Trefzger and M Lewenstein and P Zoller and G Pupillo},

doi = {10.1103/PhysRevLett.104.125301},

year = {2010},

date = {2010-01-01},

journal = {Physical Review Letters},

volume = {104},

number = {12},

pages = {125301},

abstract = {We study the quantum phases of hard-core bosonic polar molecules on a two-dimensional square lattice interacting via repulsive dipole-dipole interactions. In the limit of small tunneling, we find evidence for a devil's staircase, where Mott solids appear at rational fillings of the lattice. For finite tunneling, we establish the existence of extended regions of parameters where the ground state is a supersolid, obtained by doping the solids either with particles or vacancies. We discuss the effects of finite temperature and finite-size confining potentials as relevant to experiments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We study the quantum phases of hard-core bosonic polar molecules on a two-dimensional square lattice interacting via repulsive dipole-dipole interactions. In the limit of small tunneling, we find evidence for a devil's staircase, where Mott solids appear at rational fillings of the lattice. For finite tunneling, we establish the existence of extended regions of parameters where the ground state is a supersolid, obtained by doping the solids either with particles or vacancies. We discuss the effects of finite temperature and finite-size confining potentials as relevant to experiments.
### 2009

G Pupillo, A Micheli, M Boninsegni, I Lesanovsky, P Zoller

Mesoscopic Phases of Dipolar Ensembles with Polar Molecules and Rydberg Atoms Journal Article

arXiv:0904.2735 [cond-mat], 2009.

Abstract | BibTeX | Tags: Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics

@article{Pupillo2009,

title = {Mesoscopic Phases of Dipolar Ensembles with Polar Molecules and Rydberg Atoms},

author = {G Pupillo and A Micheli and M Boninsegni and I Lesanovsky and P Zoller},

year = {2009},

date = {2009-04-01},

journal = {arXiv:0904.2735 [cond-mat]},

abstract = {We discuss the realization of mesoscopic phases of dipolar gases relevant to current experiments with cold polar molecules and Rydberg atoms confined to two dimensions. We predict the existence of superfluid clusters, mesoscopic supersolids, and crystals for a small number of trapped particles, with no counterpart in the homogeneous situation. For certain strengths of the dipole-dipole interactions, the stabilization of purely $backslash$it non-classical crystals by quantum fluctuations is possible. We propose a magnification scheme to detect the spatial structure of these crystalline phases.},

keywords = {Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics},

pubstate = {published},

tppubtype = {article}

}

We discuss the realization of mesoscopic phases of dipolar gases relevant to current experiments with cold polar molecules and Rydberg atoms confined to two dimensions. We predict the existence of superfluid clusters, mesoscopic supersolids, and crystals for a small number of trapped particles, with no counterpart in the homogeneous situation. For certain strengths of the dipole-dipole interactions, the stabilization of purely $backslash$it non-classical crystals by quantum fluctuations is possible. We propose a magnification scheme to detect the spatial structure of these crystalline phases.
### 2007

H P Büchler, E Demler, M Lukin, A Micheli, N Prokof'ev, G Pupillo, P Zoller

Strongly Correlated 2D Quantum Phases with Cold Polar Molecules: Controlling the Shape of the Interaction Potential Journal Article

Physical Review Letters, 98 (6), pp. 060404, 2007.

Abstract | Links | BibTeX | Tags:

@article{Buchler2007,

title = {Strongly Correlated 2D Quantum Phases with Cold Polar Molecules: Controlling the Shape of the Interaction Potential},

author = {H P Büchler and E Demler and M Lukin and A Micheli and N Prokof'ev and G Pupillo and P Zoller},

doi = {10.1103/PhysRevLett.98.060404},

year = {2007},

date = {2007-01-01},

journal = {Physical Review Letters},

volume = {98},

number = {6},

pages = {060404},

abstract = {We discuss techniques to tune and shape the long-range part of the interaction potentials in quantum gases of bosonic polar molecules by dressing rotational excitations with static and microwave fields. This provides a novel tool towards engineering strongly correlated quantum phases in combination with low-dimensional trapping geometries. As an illustration, we discuss the 2D superfluid-crystal quantum phase transition for polar molecules interacting via an electric-field-induced dipole-dipole potential.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

We discuss techniques to tune and shape the long-range part of the interaction potentials in quantum gases of bosonic polar molecules by dressing rotational excitations with static and microwave fields. This provides a novel tool towards engineering strongly correlated quantum phases in combination with low-dimensional trapping geometries. As an illustration, we discuss the 2D superfluid-crystal quantum phase transition for polar molecules interacting via an electric-field-induced dipole-dipole potential.

# Publications

```
Atomic physics Condensed Matter - Disordered Systems and Neural Networks Condensed Matter - Mesoscale and Nanoscale Physics Condensed Matter - Quantum Gases Condensed Matter - Statistical Mechanics Condensed Matter - Strongly Correlated Electrons Conformal field theory Integrable models Long-range systems Open quantum systems Quantum entanglement Quantum phase transitions Quantum Physics Quantum simulation Renormalization group Topological phases of matter Trapped ions Unconventional pairing mechanisms
```
### 2019

Supersolid Phases of Rydberg-Excited Bosons on a Triangular Lattice Journal Article

arXiv:1903.01912 [cond-mat], 2019.

Enhancement of the Electron–Phonon Scattering Induced by Intrinsic Surface Plasmon–Phonon Polaritons Journal Article

ACS Photonics, 2019.

### 2018

Enhancement of the Electron-Phonon Scattering Induced by Intrinsic Surface Plasmon-Phonon Polaritons Journal Article

arXiv:1810.10190 [cond-mat], 2018.

Algebraic Localization from Power-Law Interactions in Disordered Quantum Wires Journal Article

arXiv:1810.09779 [cond-mat, physics:quant-ph], 2018.

Phase-Change Switching in 2D via Soft Interactions Journal Article

arXiv:1808.07918 [cond-mat], 2018.

Cavity-Assisted Mesoscopic Transport of Fermions: Coherent and Dissipative Dynamics Journal Article

Physical Review B, 97 (20), pp. 205303, 2018.

Exploring out-of-equilibrium quantum magnetism and thermalization in a spin-3 many-body dipolar lattice system Journal Article Forthcoming

(to appear in Nat. Comm.), pp. arXiv:1803.02628, Forthcoming.

### 2017

Cavity-Enhanced Transport of Charge Journal Article

Physical Review Letters, 119 (22), pp. 223601, 2017.

Rydberg Optical Feshbach Resonances in Cold Gases Journal Article

Physical Review A, 96 (3), pp. 032719, 2017.

Exploring many-body localization and thermalization using semiclassical methods Journal Article

Phys. Rev. A, 96 , pp. 033604, 2017.

Glass Transitions in Monodisperse Cluster-Forming Ensembles: Vortex Matter in Type-1.5 Superconductors Journal Article

Physical Review Letters, 118 (6), pp. 067001, 2017.

### 2016

Effective Theory and Breakdown of Conformal Symmetry in a Long-Range Quantum Chain Journal Article

Annals of Physics, 374 , pp. 35-66, 2016, ISSN: 0003-4916.

Cavity Polaritons with Rydberg Blockade and Long-Range Interactions Journal Article

Journal of Physics B: Atomic, Molecular and Optical Physics, 49 (16), pp. 164006, 2016, ISSN: 0953-4075.

Event-Driven Monte Carlo: Exact Dynamics at All Time Scales for Discrete-Variable Models Journal Article

EPL (Europhysics Letters), 114 (5), pp. 50003, 2016, ISSN: 0295-5075.

Broadband Photon-Photon Interactions Mediated by Cold Atoms in a Photonic Crystal Fiber Journal Article

Scientific Reports, 6 , pp. 25630, 2016, ISSN: 2045-2322.

Two Holes in a Two-Dimensional Quantum Antiferromagnet: A Variational Study Based on Entangled-Plaquette States Journal Article

Physical Review B, 94 (15), pp. 155120, 2016.

Cluster Bose Metals Journal Article

arXiv:1606.04267 [cond-mat], 2016.

Superglass Phase of Interaction-Blockaded Gases on a Triangular Lattice Journal Article

Physical Review Letters, 116 (13), pp. 135303, 2016.

Direct Observation of Ultrafast Many-Body Electron Dynamics in an Ultracold Rydberg Gas Journal Article

Nature Communications, 7 , pp. 13449, 2016, ISSN: 2041-1723.

Long-Range Ising and Kitaev Models: Phases, Correlations and Edge Modes Journal Article

New Journal of Physics, 18 (1), pp. 015001, 2016, ISSN: 1367-2630.

### 2015

Monodisperse Cluster Crystals: Classical and Quantum Dynamics Journal Article

Physical Review E, 92 (5), pp. 052307, 2015.

Tunable Defect Interactions and Supersolidity in Dipolar Quantum Gases on a Lattice Potential Journal Article

Physical Review A, 92 (5), pp. 053625, 2015.

Cavity-Enhanced Transport of Excitons Journal Article

Physical Review Letters, 114 (19), pp. 196403, 2015.

Cluster Luttinger Liquids and Emergent Supersymmetric Conformal Critical Points in the One-Dimensional Soft-Shoulder Hubbard Model Journal Article

Physical Review B, 92 (4), pp. 045106, 2015.

Coherent Coupling of Molecular Resonators with a Microcavity Mode Journal Article

Nature Communications, 6 , pp. 5981, 2015, ISSN: 2041-1723.

### 2014

Transmissive Optomechanical Platforms with Engineered Spatial Defects Journal Article

Physical Review A, 90 (5), pp. 053831, 2014.

Kitaev Chains with Long-Range Pairing Journal Article

Physical Review Letters, 113 (15), pp. 156402, 2014.

Hybrid Cavity Mechanics with Doped Systems Journal Article

Physical Review A, 90 (3), pp. 033820, 2014.

Reconfigurable Long-Range Phonon Dynamics in Optomechanical Arrays Journal Article

Physical Review Letters, 112 (13), pp. 133604, 2014.

Defect-Induced Supersolidity with Soft-Core Bosons Journal Article

Nature Communications, 5 , pp. 3235, 2014, ISSN: 2041-1723.

### 2013

Cluster Luttinger Liquids of Rydberg-Dressed Atoms in Optical Lattices Journal Article

Physical Review Letters, 111 (16), pp. 165302, 2013.

Enhanced Optomechanical Readout Using Optical Coalescence Journal Article

Physical Review A, 88 (3), pp. 033855, 2013.

Fluctuation-Dissipation Theorem in an Isolated System of Quantum Dipolar Bosons after a Quench Journal Article

Physical Review Letters, 111 (5), pp. 050403, 2013.

Quantum Phases of Dipolar Bosons in Bilayer Geometry Journal Article

New Journal of Physics, 15 (1), pp. 013036, 2013, ISSN: 1367-2630.

### 2012

Driven-Dissipative Dynamics of a Strongly Interacting Rydberg Gas Journal Article

Physical Review A, 86 (4), pp. 043403, 2012.

Condensed Matter Theory of Dipolar Quantum Gases Journal Article

Chemical Reviews, 112 (9), pp. 5012-5061, 2012, ISSN: 0009-2665.

Engineered Open Systems and Quantum Simulations with Atoms and Ions Incollection

Berman, Paul; Arimondo, Ennio; Lin, Chun (Ed.): Advances In Atomic, Molecular, and Optical Physics, 61 , pp. 1-80, Academic Press, 2012.

Supersolid Vortex Crystals in Rydberg-Dressed Bose-Einstein Condensates Journal Article

Physical Review Letters, 108 (26), pp. 265301, 2012.

Atomic Rydberg Reservoirs for Polar Molecules Journal Article

Physical Review Letters, 108 (19), pp. 193007, 2012.

### 2010

Supersolid Droplet Crystal in a Dipole-Blockaded Gas Journal Article

Physical Review Letters, 105 (13), pp. 135301, 2010.

Strongly Correlated Gases of Rydberg-Dressed Atoms: Quantum and Classical Dynamics Journal Article

Physical Review Letters, 104 (22), pp. 223002, 2010.

One-Dimensional Quantum Liquids with Power-Law Interactions: The Luttinger Staircase Journal Article

Physical Review Letters, 105 (14), pp. 140401, 2010.

Quantum Phases of Cold Polar Molecules in 2D Optical Lattices Journal Article

Physical Review Letters, 104 (12), pp. 125301, 2010.

### 2009

Mesoscopic Phases of Dipolar Ensembles with Polar Molecules and Rydberg Atoms Journal Article

arXiv:0904.2735 [cond-mat], 2009.

### 2007

Strongly Correlated 2D Quantum Phases with Cold Polar Molecules: Controlling the Shape of the Interaction Potential Journal Article

Physical Review Letters, 98 (6), pp. 060404, 2007.