655 research outputs found
Absence of a Direct Superfluid to Mott Insulator Transition in Disordered Bose Systems
We prove the absence of a direct quantum phase transition between a
superfluid and a Mott insulator in a bosonic system with generic, bounded
disorder. We also prove compressibility of the system on the
superfluid--insulator critical line and in its neighborhood. These conclusions
follow from a general {\it theorem of inclusions} which states that for any
transition in a disordered system one can always find rare regions of the
competing phase on either side of the transition line. Quantum Monte Carlo
simulations for the disordered Bose-Hubbard model show an even stronger result,
important for the nature of the Mott insulator to Bose glass phase transition:
The critical disorder bound, , corresponding to the onset of
disorder-induced superfluidity, satisfies the relation , with the half-width of the Mott gap in the pure system.Comment: 4 pages, 3 figures; replaced with resubmitted versio
Criticality in Trapped Atomic Systems
We discuss generic limits posed by the trap in atomic systems on the accurate
determination of critical parameters for second-order phase transitions, from
which we deduce optimal protocols to extract them. We show that under current
experimental conditions the in-situ density profiles are barely suitable for an
accurate study of critical points in the strongly correlated regime. Contrary
to recent claims, the proper analysis of time-of-fight images yields critical
parameters accurately.Comment: 4 pages, 3 figures; added reference
Comment on "Direct Mapping of the Finite Temperature Phase Diagram of Strongly Correlated Quantum Models" by Q. Zhou, Y. Kato, N. Kawashima, and N. Trivedi, Phys. Rev. Lett. 103, 085701 (2009)
In their Letter, Zhou, Kato, Kawashima, and Trivedi claim that
finite-temperature critical points of strongly correlated quantum models
emulated by optical lattice experiments can generically be deduced from kinks
in the derivative of the density profile of atoms in the trap with respect to
the external potential, . In this comment we demonstrate
that the authors failed to achieve their goal: to show that under realistic
experimental conditions critical densities can be extracted from
density profiles with controllable accuracy.Comment: 1 page, 1 figur
The Higgs mode in a two-dimensional superfluid
We present solid evidence for the existence of a well-defined Higgs amplitude
mode in two-dimensional relativistic field theories based on analytically
continued results from quantum Monte Carlo simulations of the Bose-Hubbard
model in the vicinity of the superfluid-Mott insulator quantum critical point,
featuring emergent particle-hole symmetry and Lorentz-invariance. The Higgs
boson, seen as a well-defined low-frequency resonance in the spectral density,
is quickly pushed to high energies in the superfluid phase and disappears by
merging with the broad secondary peak at the characteristic interaction scale.
Simulations of a trapped system of ultra-cold Rb atoms demonstrate that
the low-frequency resonance feature is lost for typical experimental
parameters, while the characteristic frequency for the onset of strong response
is preserved.Comment: 9 pages, 13 figures; replaced with published versio
Superfluid-insulator transition in strongly disordered one-dimensional systems
We present an asymptotically exact renormalization-group theory of the superfluid-insulator transition in one-dimensional (1D) disordered systems, with emphasis on an accurate description of the interplay between the Giamarchi-Schulz (instanton-anti-instanton) and weak-link (scratched-XY) criticalities. Combining the theory with extensive quantum Monte Carlo simulations allows us to shed new light on the ground-state phase diagram of the 1D disordered Bose-Hubbard model at unit filling
Quantum Monte Carlo simulation in the canonical ensemble at finite temperature
A quantum Monte Carlo method with non-local update scheme is presented. The
method is based on a path-integral decomposition and a worm operator which is
local in imaginary time. It generates states with a fixed number of particles
and respects other exact symmetries. Observables like the equal-time Green's
function can be evaluated in an efficient way. To demonstrate the versatility
of the method, results for the one-dimensional Bose-Hubbard model and a nuclear
pairing model are presented. Within the context of the Bose-Hubbard model the
efficiency of the algorithm is discussed.Comment: 11 pages, 8 figure
Comment on "Absence of Off-Diagonal Long- Range Order in hcp He Dislocation Cores"
We contend that the arguments provided in Phys. Rev. Lett. 130, 016001
(2023), purporting to show the absence of off-diagonal long-range order in hcp
He dislocation cores are misleading and incorrect. In particular, the
one-body density matrix averaged over the whole crystalline sample provides no
useful information on the possible superfluid behavior inside the
quasi-one-dimensional core of a dislocation in the crystal
Finite-temperature effects on the superfluid Bose-Einstein condensation of confined ultracold atoms in three-dimensional optical lattices
We discuss the finite-temperature phase diagram in the three-dimensional
Bose-Hubbard (BH) model in the strong correlation regime, relevant for
Bose-Einstein condensates in optical lattices, by employing a quantum rotor
approach. In systems with strong on site repulsive interactions, the rotor U(1)
phase variable dual to the local boson density emerges as an important
collective field. After establishing the connection between the rotor
construction and the the on--site interaction in the BH model the robust
effective action formalism is developed which allows us to study the superfluid
phase transition in various temperature--interaction regimes
Phase diagram of the disordered Bose-Hubbard model
We establish the phase diagram of the disordered three-dimensional
Bose-Hubbard model at unity filling, which has been controversial for many
years. The theorem of inclusions, proven in Ref. [1], states that the Bose
glass phase always intervenes between the Mott insulating and superfluid
phases. Here, we note that assumptions on which the theorem is based exclude
phase transitions between gapped (Mott insulator) and gapless phases (Bose
glass). The apparent paradox is resolved through a unique mechanism: such
transitions have to be of the Griffiths type when the vanishing of the gap at
the critical point is due to a zero concentration of rare regions where extreme
fluctuations of disorder mimic a {\it regular} gapless system. An exactly
solvable random transverse field Ising model in one dimension is used to
illustrate the point. A highly non-trivial overall shape of the phase diagram
is revealed with the worm algorithm. The phase diagram features a long
superfluid finger at strong disorder and on-site interaction. Moreover, bosonic
superfluidity is extremely robust against disorder in a broad range of
interaction parameters; it persists in random potentials nearly 50 (!) times
larger than the particle half-bandwidth. Finally, we comment on the feasibility
of obtaining this phase diagram in cold-atom experiments, which work with
trapped systems at finite temperature.Comment: 9 pages, 5 figure
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