93 research outputs found
Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder
Ultracold gases offer an unprecedented opportunity to engineer disorder and
interactions in a controlled manner. In an effort to understand the interplay
between disorder, dipolar interaction and quantum degeneracy, we study
two-dimensional hard-core dipolar lattice bosons in the presence of on-site
bound disorder. Our results are based on large-scale path-integral quantum
Monte Carlo simulations by the Worm algorithm. We study the ground state phase
diagram at fixed half-integer filling factor for which the clean system is
either a superfluid at lower dipolar interaction strength or a checkerboard
solid at larger dipolar interaction strength. We find that, even for weak
dipolar interaction, superfluidity is destroyed in favor of a Bose glass at
relatively low disorder strength. Interestingly, in the presence of disorder,
superfluidity persists for values of dipolar interaction strength for which the
clean system is a checkerboard solid. At fixed disorder strength, as the
dipolar interaction is increased, superfluidity is destroyed in favor of a Bose
glass. As the interaction is further increased, the system eventually develops
extended checkerboard patterns in the density distribution. Due to the presence
of disorder, though, grain boundaries and defects, responsible for a finite
residual compressibility, are present in the density distribution. Finally, we
study the robustness of the superfluid phase against thermal fluctuations
Nonequilibrium dynamics of spin-boson models from phase space methods
An accurate description of the nonequilibrium dynamics of systems with
coupled spin and bosonic degrees of freedom remains theoretically challenging,
especially for large system sizes and in higher than one dimension. Phase space
methods such as the Truncated Wigner Approximation (TWA) have the advantage of
being easily scalable and applicable to arbitrary dimensions. In this work we
adapt the TWA to generic spin-boson models by making use of recently developed
algorithms for discrete phase spaces [Schachenmayer, PRX 5, 011022 (2015)].
Furthermore we go beyond the standard TWA approximation by applying a scheme
based on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of equations
[Pucci, PRB 93, 174302 (2016)] to our coupled spin-boson model. This allows in
principle to study how systematically adding higher order corrections improves
the convergence of the method. To test various levels of approximation we study
an exactly solvable spin-boson model which is particularly relevant for
trapped-ion arrays. Using TWA and its BBGKY extension we accurately reproduce
the time evolution of a number of one- and two-point correlation functions in
several dimensions and for arbitrary number of bosonic modes.Comment: 10+5 pages, 5 figure
Equilibrium Phases of Tilted Dipolar Lattice Bosons
The recent advances in creating nearly degenerate quantum dipolar gases in
optical lattices are opening the doors for the exploration of equilibrium
physics of quantum systems with anisotropic and long-range dipolar
interactions. In this paper we study the zero- and finite-temperature phase
diagrams of a system of hard-core dipolar bosons at half-filling, trapped in a
two-dimensional optical lattice. The dipoles are aligned parallel to one
another and tilted out of the optical lattice plane by means of an external
electric field. At zero-temperature, the system is a superfluid at all tilt
angles provided that the strength of dipolar interaction is below a
critical value . Upon increasing the interaction strength while
keeping fixed, the superfluid phase is destabilized in favor of a
checkerboard or a stripe solid depending on the tilt angle. We explore the
nature of the phase transition between the two solid phases and find evidence
of a micro-emulsion phase, following the Spivak-Kivelson scenario, separating
these two solid phases. Additionally, we study the stability of these quantum
phases against thermal fluctuations and find that the stripe solid is the most
robust, making it the best candidate for experimental observation.Comment: 7 pages, 6 figure
Quantum phases of hard-core dipolar bosons in coupled one-dimensional optical lattices
Hard-core dipolar bosons trapped in a parallel stack of N ≥ 2 one-dimensional optical lattices (tubes) can develop several phases made of composites of particles from different tubes: superfluids, supercounterfluids, and insulators as well as mixtures of those. Bosonization analysis shows that these phases are thresholdless with respect to the dipolar interaction, with the key “control knob” being filling factors in each tube, provided the intertube tunneling is suppressed. The effective ab initio quantum Monte Carlo algorithm capturing these phases is introduced and some results are presented.National Science Foundation (U.S.) (Grant CNS-0855217)National Science Foundation (U.S.) (Grant CNS-0958379)National Science Foundation (U.S.) (Grant ACI-1126113
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