345 research outputs found
Local versus global equilibration near the bosonic Mott-superfluid transition
We study the response of trapped two dimensional cold bosons to time
dependent lattices. We find that in lattice ramps from 11 (superfluid,
ms, ms) to 16 recoils (Mott,
ms, ms) the local number
fluctuations remains at their equilibrium values if ramps are slower than 3 ms.
Global transport, however, is much slower (1s), especially in the presence of
Mott shells. This separation of timescales has practical implications for cold
atom experiments and cooling protocols.Comment: 4 pages, 4 figs. 6 subfigure
Universality class of quantum criticality in the two-dimensional Hubbard model at intermediate temperatures ()
We show that the dilute Fermi gas quantum critical universality class
quantitatively describes the Mott/metal crossover of the two-dimensional
Hubbard model for temperatures somewhat less than (roughly half) the tunneling
but much greater than (roughly twice) the superexchange energy. We calculate
the observables expected to be universal near the transition --- density and
compressibility --- with numerically exact determinantal quantum Monte Carlo.
We find they are universal functions of the chemical potential. Despite arising
from the strongly correlated regime of the Hubbard model, these functions are
given by the weakly interacting, dilute Fermi gas model. These observables and
their derivatives are the only expected universal static observables of this
universality class, which we also confirm by verifying there is no scaling
collapse of the kinetic energy, fraction of doubly occupied sites, and nearest
neighbor spin correlations. Our work resolves the universality class of the
intermediate temperature Mott/metal crossover, which had alternatively been
proposed to be described by more exotic theories. However, in the presence of a
Zeeman magnetic field, we find that interplay of spin with itinerant charge can
lead to physics beyond the dilute Fermi gas universality class.Comment: Main text: 4 pages, 2 figures (6 panels). Supplementary info.: 2
pages, 3 figures (7 panels
Exploring out-of-equilibrium quantum magnetism and thermalization in a spin-3 many-body dipolar lattice system
Understanding quantum thermalization through entanglement build-up in
isolated quantum systems addresses fundamental questions on how unitary
dynamics connects to statistical physics. Here, we study the spin dynamics and
approach towards local thermal equilibrium of a macroscopic ensemble of S = 3
spins prepared in a pure coherent spin state, tilted compared to the magnetic
field, under the effect of magnetic dipole-dipole interactions. The experiment
uses a unit filled array of 104 chromium atoms in a three dimensional optical
lattice, realizing the spin-3 XXZ Heisenberg model. The buildup of quantum
correlation during the dynamics, especially as the angle approaches pi/2, is
supported by comparison with an improved numerical quantum phase-space method
and further confirmed by the observation that our isolated system thermalizes
under its own dynamics, reaching a steady state consistent with the one
extracted from a thermal ensemble with a temperature dictated from the system's
energy. This indicates a scenario of quantum thermalization which is tied to
the growth of entanglement entropy. Although direct experimental measurements
of the Renyi entropy in our macroscopic system are unfeasible, the excellent
agreement with the theory, which can compute this entropy, does indicate
entanglement build-up.Comment: 12 figure
A Novel Dielectric Anomaly in Cuprates and Nickelates: Signature of an Electronic Glassy State
The low-frequency dielectric response of hole-doped insulators
La_{2}Cu_{1-x}Li_{x}O_{4} and La_{2-x}Sr_{x}NiO_{4} shows a large dielectric
constant \epsilon ^{'} at high temperature and a step-like drop by a factor of
100 at a material-dependent low temperature T_{f}. T_{f} increases with
frequency and the dielectric response shows universal scaling in a Cole-Cole
plot, suggesting that a charge glass state is realized both in the cuprates and
in the nickelates.Comment: 5 pages, 4 figure
Exploring quantum criticality based on ultracold atoms in optical lattices
Critical behavior developed near a quantum phase transition, interesting in
its own right, offers exciting opportunities to explore the universality of
strongly-correlated systems near the ground state. Cold atoms in optical
lattices, in particular, represent a paradigmatic system, for which the quantum
phase transition between the superfluid and Mott insulator states can be
externally induced by tuning the microscopic parameters. In this paper, we
describe our approach to study quantum criticality of cesium atoms in a
two-dimensional lattice based on in situ density measurements. Our research
agenda involves testing critical scaling of thermodynamic observables and
extracting transport properties in the quantum critical regime. We present and
discuss experimental progress on both fronts. In particular, the thermodynamic
measurement suggests that the equation of state near the critical point follows
the predicted scaling law at low temperatures.Comment: 15 pages, 6 figure
A Support Group for Inpatient Abused Adolescents
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75359/1/j.1744-6171.1990.tb00438.x.pd
A two-dimensional programmable tweezer array of fermions
We prepare high-filling two-component arrays of up to fifty fermionic atoms
in optical tweezers, with the atoms in the ground motional state of each
tweezer. Using a stroboscopic technique, we configure the arrays in various
two-dimensional geometries with negligible Floquet heating. Full spin- and
density-resolved readout of individual sites allows us to post-select near-zero
entropy initial states for fermionic quantum simulation. We prepare a
correlated state in a two-by-two tunnel-coupled Hubbard plaquette,
demonstrating all the building blocks for realizing a programmable fermionic
quantum simulator
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