11 research outputs found
Nonequilibrium scenarios in cluster-forming quantum lattice models
We investigate the out-of-equilibrium physics of monodisperse bosonic
ensembles on a square lattice. The effective Hamiltonian description of these
systems is given in terms of an extended Hubbard model with cluster-forming
interactions relevant to experimental realizations with cold Rydberg-dressed
atoms. The ground state of the model, recently investigated in Phys. Rev. Lett.
123, 045301 (2019), features, aside from a superfluid and a stripe crystalline
phase occurring at small and large interaction strength , respectively, a
rare first-order transition between an isotropic and an anisotropic stripe
supersolid at intermediate . By means of quantum Monte Carlo calculations we
show that the equilibrium crystal may be turned into a glass by simulated
temperature quenches and that out-of-equilibrium isotropic (super)solid states
may emerge also when their equilibrium counterparts are anisotropic. These
out-of-equilibrium states are of experimental interest, their excess energy
with respect to the ground state being within the energy window typically
accessed in cold atom experiments. We find, after quenching, no evidence of
coexistence between superfluid and glassy behavior. Such an absence of
superglassiness is qualitatively explained.Comment: 8 pages, 6 figure
Many-body physics of strongly interacting Rydberg atoms
The understanding of the strongly correlated dynamics of many-body quantum systems out of equilibrium is one of the most challenging tasks in modern physics. Rydberg atoms, which are atoms excited to states with high principal quantum number, have proved to be a very successful platform for the study of these systems. The detailed understanding of the excitation dynamics will be helpful for the implementation of various quantum simulation and quantum computation protocols.
In the present thesis the emergent properties of a many-body system are studied in conditions where the dynamics of the internal and external degrees of freedom can be partially decoupled. The study is done by means of Monte Carlo simulations upon a simple toy model.
Internally the system is modelled as an Ising-like spin system coupled to an external field and with long range interactions among the spins. Dissipation is also included in the model, and a master equation approach is used to derive the time evolution of the system. Different Kinetic Monte Carlo methods are discussed in order to solve that master equation.
We used the model and the methods developed to study emergent phenomena in the excitation dynamics of a cold gas of Rydberg atoms. In the resonant regime we observed the effects of the blockade where the presence of an excited atom inhibits the excitation of his neighbors. In the off resonant regime we observed facilitated excitation, whereby an excitation in the system shifts a ground state atom at a well-defined distance into resonance. We also performed simulations of the excitation process with quenches of the detuning finding interesting and unexpected results in the dynamics approaching the equilibrium.
The dynamics of the external (translational) degrees of freedom is modelled as as that of classical particles which interact by means of a potential C_α/r^α. The features of different algorithms to solve the classical equations of motion are discussed focusing on the requirement that the Hamiltonian must be conserved while integrating the Hamilton equations for such systems.
We performed simulations on the external dynamics of a cluster of Rydberg atoms replicating the features of an experiment performed in the laboratory. Our experiment aims to measure directly the effect of van der Waals forces between atoms of Rubidium excited to Rydberg states. We used the simulations to analyze the outcome to the experiment and found good agreement between the experimental data and the simulation
Scale-invariant phase transition of disordered bosons in one dimension
The disorder-induced quantum phase transition between superfluid and
non-superfluid states of bosonic particles in one dimension is generally
expected to be of the Berezinskii-Kosterlitz-Thouless (BKT) type. Here, we show
that hard-core lattice bosons with integrable power-law hopping decaying with
distance as - corresponding in spin language to a model with
power-law couplings - undergo a non-BKT continuous phase transition instead. We
use exact quantum Monte-Carlo methods to determine the phase diagram for
different values of the exponent , focusing on the regime .
We find that the scaling of the superfluid stiffness with the system size is
scale-invariant at the transition point for any - a behavior
incompatible with the BKT scenario and typical of continuous phase transitions
in higher dimension. By scaling analysis near the transition point, we find
that our data are consistent with a correlation length exponent satisfying the
Harris bound and demonstrate a new universal behavior of
disordered bosons in one dimension. For our data are consistent with
a BKT scenario where the liquid is pinned by infinitesimal disorder
Seeded excitation avalanches in off-resonantly driven Rydberg gases
We report an experimental investigation of the facilitated excitation
dynamics in off-resonantly driven Rydberg gases by separating the initial
off-resonant excitation phase from the facilitation phase, in which successive
facilitation events lead to excitation avalanches. We achieve this by creating
a controlled number of initial seed excitations. Greater insight into the
avalanche mechanism is obtained from an analysis of the full counting
distributions. We also present simple mathematical models and numerical
simulations of the excitation avalanches that agree well with our experimental
results.Comment: 13 pages, 6 figure
Phénomènes quantiques exotiques dans les gaz atomiques froids : approches numériques
The central aim of this thesis is the study of the low-energy and low-temperature properties of strongly correlated systems of bosonic particles interacting via finite- and long-range potentials, and relevant to experimental realization with cold atomic gases. This study is carried out with a combination of state-of-the-art numerical techniques such as Path Integral Monte Carlo and analytical techniques. The main result of my work is the demonstration of the existence of a stripe supersolid phase and of a rare transition between isotropic and anisotropic supersolids in a finite-range interacting model of hard-bosons on a square lattice. I also investigate the out-of-equilibrium scenarios of such models via simulated temperature quenches. Finally, I investigate how restoring energy extensivity in long-range interacting systems can have a profound incidence on the low-energy properties in the thermodynamic limit.L'objectif principal de cette thèse est l'étude des propriétés à basse énergie et température de systèmes fortement corrélés de bosons interagissant via des potentiels à portée longue et étendue, et pertinentes pour la réalisation expérimentale avec des gaz atomiques froids. Cette étude est réalisée à l'aide d'une combinaison de techniques numériques, comme le Path Integral Montecarlo et de techniques analytiques. Le principal résultat de mon travail est la démonstration de l’existence d’une phase supersolide à bandes et d’une rare transition entre différents supersolides dans un modèle à interaction finie de bosons de coer dur sur un réseau carré. J'étudie également les scénarios hors d'équilibre de tels modèles via des quenches de température simulées. Enfin, j'étudie comment la restauration de l'extensibilité énergétique dans des systèmes en interaction à longue portée peut avoir une incidence profonde sur les propriétés de basse énergie dans la limite thermodynamique
Anti-Drude Metal of Bosons
In the absence of frustration, interacting bosons in the ground state exist
either in the superfluid or insulating phases. Superfluidity corresponds to
frictionless flow of the matter field, and in optical conductivity is revealed
through a distinct -functional peak at zero frequency with the
amplitude known as the Drude weight. This characteristic low-frequency feature
is instead absent in insulating phases, defined by zero static optical
conductivity. Here we demonstrate that bosonic particles in disordered one
dimensional, , systems can also exist in a conducting, non-superfluid,
phase when their hopping is of the dipolar type, often viewed as short-ranged
in . This phase is characterized by finite static optical conductivity,
followed by a broad anti-Drude peak at finite frequencies. Off-diagonal
correlations are also unconventional: they feature an integrable algebraic
decay for arbitrarily large values of disorder. These results do not fit the
description of any known quantum phase and strongly suggest the existence of a
novel conducting state of bosonic matter in the ground state.Comment: 8 pages, 6 figure
Supersolid Stripe Crystal from Finite-Range Interactions on a Lattice
6+3 pages, 5+4 figuresInternational audienceStrong, long-range interactions present a unique challenge for the theoretical investigation of quantum many-body lattice models, due to the generation of large numbers of competing states at low energy. Here, we investigate a class of extended bosonic Hubbard models with off-site terms interpolating between short and infinite range, thus allowing for an exact numerical solution for all interaction strengths. We predict a novel type of stripe crystal at strong coupling. Most interestingly, for intermediate interaction strengths we demonstrate that the stripes can turn superfluid, thus leading to a self-assembled array of quasi-one-dimensional superfluids. These bosonic superstripes turn into an isotropic supersolid with decreasing the interaction strength. The mechanism for stripe formation is based on cluster self-assembling in the corresponding classical ground state, reminiscent of classical soft-matter models of polymers, different from recently proposed mechanisms for cold gases of alkali or dipolar magnetic atoms