25 research outputs found
Time-of-Flight Measurements as a Possible Method to Observe Anyonic Statistics
We propose a standard time-of-flight experiment as a method for observing the
anyonic statistics of quasiholes in a fractional quantum Hall state of
ultracold atoms. The quasihole states can be stably prepared by pinning the
quasiholes with localized potentials and a measurement of the mean square
radius of the freely expanding cloud, which is related to the average total
angular momentum of the initial state, offers direct signatures of the
statistical phase. Our proposed method is validated by Monte Carlo calculations
for and fractional quantum Hall liquids containing a realistic
number of particles. Extensions to quantum Hall liquids of light and to
non-Abelian anyons are briefly discussed.Comment: Title change, enhanced Supplemental Material, almost published
version (to appear in Phys. Rev. Lett.
Two-dimensional repulsive Fermi polarons with short and long-range interactions
We study the repulsive polaron problem in a two-component two-dimensional
system of fermionic atoms. We use two different interaction models: a
short-range (hard-disk) potential and a dipolar potential. In our approach, all
the atoms have the same mass and we consider the system to be composed of a
uniform bath of a single species and a single atomic impurity. We use the
diffusion Monte Carlo method to evaluate polaron properties such as its
chemical potential and pair distribution functions, together with a discussion
on the deficit of volume induced by the impurity. We also evaluate observables
that allow us to determine the validity of the quasi-particle picture: the
quasi-particle residue and the effective mass of the polaron. Employing two
different potentials allows us to identify the universality regime, where the
properties depend only on the gas parameter fixed by the bath density
and the two-dimensional scattering length
Fusion channels of non-Abelian anyons from angular-momentum and density-profile measurements
We present a method to characterize non-Abelian anyons that is based only on
static measurements and that does not rely on any form of interference. For
geometries where the anyonic statistics can be revealed by rigid rotations of
the anyons, we link this property to the angular momentum of the initial state.
We test our method on the paradigmatic example of the Moore-Read state, that is
known to support excitations with non-Abelian statistics of Ising type. As an
example, we reveal the presence of different fusion channels for two such
excitations, a defining feature of non-Abelian anyons. This is obtained by
measuring density-profile properties, like the mean square radius of the system
or the depletion generated by the anyons. Our study paves the way to novel
methods for characterizing non-Abelian anyons, both in the experimental and
theoretical domains.Comment: 6+10 pages, 2+3 figures -- revised text and Supp. Mat. -- to be
published in Phys. Rev. Let
Liquid-solid transitions in the three-body hard-core model
We determine the phase diagram for a generalisation of two-and
three-dimensional hard spheres: a classical system with three-body interactions
realised as a hard cut-off on the mean-square distance for each triplet of
particles. Quantum versions of this model are important in the context of the
unitary Bose gas, which is currently under close theoretical and experimental
scrutiny. In two dimensions, the three-body hard-core model possesses a
conventional atomic liquid phase and a peculiar solid phase formed by dimers.
These dimers interact effectively as hard disks. In three dimensions, the solid
phase consists of isolated atoms that arrange in a simple-hexagonal lattice.Comment: 6 pages, 8 figures; reorganized introduction, expanded 3D sectio
Two-dimensional Mixture of Dipolar Fermions: Equation of State and Magnetic Phases
We study a two-component mixture of fermionic dipoles in two dimensions at
zero temperature, interacting via a purely repulsive potential. This
model can be realized with ultracold atoms or molecules, when their dipole
moments are aligned in the confinement direction orthogonal to the plane. We
characterize the unpolarized mixture by means of the Diffusion Monte Carlo
technique. Computing the equation of state, we identify the regime of validity
for a mean-field theory based on a low-density expansion and compare our
results with the hard-disk model of repulsive fermions. At high density, we
address the possibility of itinerant ferromagnetism, namely whether the ground
state can be fully polarized in the fluid phase. Within the fixed-node
approximation, we show that the accuracy of Jastrow-Slater trial wave
functions, even with the typical two-body backflow correction, is not
sufficient to resolve the relevant energy differences. By making use of the
iterative-backflow improved trial wave functions, we observe no signature of a
fully-polarized ground state up to the freezing density.Comment: 12 pages, 6 figure
Two-dimensional Mixture of Dipolar Fermions: Equation of State and Magnetic Phases
We study a two-component mixture of fermionic dipoles in two dimensions at
zero temperature, interacting via a purely repulsive potential. This
model can be realized with ultracold atoms or molecules, when their dipole
moments are aligned in the confinement direction orthogonal to the plane. We
characterize the unpolarized mixture by means of the Diffusion Monte Carlo
technique. Computing the equation of state, we identify the regime of validity
for a mean-field theory based on a low-density expansion and compare our
results with the hard-disk model of repulsive fermions. At high density, we
address the possibility of itinerant ferromagnetism, namely whether the ground
state can be fully polarized in the fluid phase. Within the fixed-node
approximation, we show that the accuracy of Jastrow-Slater trial wave
functions, even with the typical two-body backflow correction, is not
sufficient to resolve the relevant energy differences. By making use of the
iterative-backflow improved trial wave functions, we observe no signature of a
fully-polarized ground state up to the freezing density.Comment: 12 pages, 6 figure
Scalable spin squeezing in a dipolar Rydberg atom array
The standard quantum limit bounds the precision of measurements that can be
achieved by ensembles of uncorrelated particles. Fundamentally, this limit
arises from the non-commuting nature of quantum mechanics, leading to the
presence of fluctuations often referred to as quantum projection noise. Quantum
metrology relies on the use of non-classical states of many-body systems in
order to enhance the precision of measurements beyond the standard quantum
limit. To do so, one can reshape the quantum projection noise -- a strategy
known as squeezing. In the context of many-body spin systems, one typically
utilizes all-to-all interactions (e.g. the one-axis twisting model) between the
constituents to generate the structured entanglement characteristic of spin
squeezing. Motivated by recent theoretical work, here we explore the prediction
that short-range interactions -- and in particular, the two-dimensional dipolar
XY model -- can also enable the realization of scalable spin squeezing. Working
with a dipolar Rydberg quantum simulator of up to 100 atoms, we demonstrate
that quench dynamics from a polarized initial state lead to spin squeezing that
improves with increasing system size up to a maximum of -3.5 dB (prior to
correcting for detection errors, or approximately -5 dB after correction).
Finally, we present two independent refinements: first, using a multistep
spin-squeezing protocol allows us to further enhance the squeezing by
approximately 1 dB, and second, leveraging Floquet engineering to realize
Heisenberg interactions, we demonstrate the ability to extend the lifetime of
the squeezed state by freezing its dynamics.Comment: 12 pages, 10 figure
De la physique atomique à peu de corps à la physique statistique à N-corps : le gaz de Bose unitaire et le modèle de cœur dur à trois corps
Ultracold atomic gases offer unprecedented possibilities to realize and manipulate quantum systems. The control on interparticle interactions allows to reach the strongly-interacting regime, with both fermionic and bosonic atomic species. In the unitary limit, where the interaction strength is at its maximum, universal properties emerge. For bosonic atoms, these include the Efimov effect, the surprising existence of an infinite sequence of three-body bound states. In this thesis, we have studied a system of unitary bosons. Starting from the two- and three-body cases, we have shown that the chosen model correctly captures the universal features of the Efimov effect. For the corresponding many-body problem, we have developed a quantum Monte Carlo algorithm capable of realizing the different thermodynamic phases in which the system may exist: The high-temperature normal gas, Bose-Einstein condensate, and Efimov liquid. A single ingredient of our model would remain relevant in the infinite-temperature limit, namely the three-body hard-core repulsion, which constitutes a generalization of the classical hard-sphere potential. For this model, we have proposed a solution to the two- and three-dimensional packing problem, based on an analytical ansatz and on the simulated-annealing technique. Extending these results to finite pressure showed that the system has a discontinuous melting transition, which we identified through the Monte Carlo method.Les gaz d'atomes ultrafroids offrent des possibilités sans précédent pour la réalisation et la manipulation des systèmes quantiques. Le contrôle exercé sur les interactions entre particules permet d'atteindre le régime de fortes interactions, pour des espèces d'atomes à la fois fermioniques et bosoniques. Dans la limite unitaire, où la force d'interaction est à son maximum, des propriétés universelles émergent. Pour les atomes bosoniques, celles-ci comprennent l'effet Efimov, l'existance surprenante d'une séquence infinie d'états liés à trois corps. Dans cette thèse, nous avons étudiés un système de bosons unitaires. Partant des cas à deux et à trois corps, nous avons montrés que le modèle choisi capturait correctement les caractéristiques universelles de l'effet Efimov. Pour le modèle à N-corps, nous avons développé un algorithme de Monte Carlo quantique capable de réaliser les différentes phases thermodynamiques du système : gaz normal à haute-température, condensat de Bose-Einstein, et liquide d'Efimov. Un unique composant de notre modèle resterait pertinent à la limite de température infinie, à savoir la répulsion corps dur à trois corps, qui constitue une généralisation du potentiel classique entre sphères dures. Pour ce modèle, nous avons proposé une solution au problème d'empilement compact en deux et trois dimensions, fondée sur une Ansatz analytique et sur la technique de recuit simulé. En étendant ces résultats à une situation de pression finie, nous avons montré que le système présente une transition de fusion discontinue, que nous avons identifié à travers la méthode de Monte Carlo
anneal: Release 1.0
<p>Anneal is a python implementation of a general-purpose simulated-annealing algorithm for optimization. The optimization procedure is decoupled from the optimization problem, so that it can be used in a large set of different cases.</p