2,988 research outputs found
Strong and weak thermalization of infinite non-integrable quantum systems
When a non-integrable system evolves out of equilibrium for a long time,
local observables are expected to attain stationary expectation values,
independent of the details of the initial state. However, intriguing
experimental results with ultracold gases have shown no thermalization in
non-integrable settings, triggering an intense theoretical effort to decide the
question. Here we show that the phenomenology of thermalization in a quantum
system is much richer than its classical counterpart. Using a new numerical
technique, we identify two distinct thermalization regimes, strong and weak,
occurring for different initial states. Strong thermalization, intrinsically
quantum, happens when instantaneous local expectation values converge to the
thermal ones. Weak thermalization, well-known in classical systems, happens
when local expectation values converge to the thermal ones only after time
averaging. Remarkably, we find a third group of states showing no
thermalization, neither strong nor weak, to the time scales one can reliably
simulate.Comment: 12 pages, 21 figures, including additional materia
Multiscaling at Point J: Jamming is a Critical Phenomenon
We analyze the jamming transition that occurs as a function of increasing
packing density in a disordered two-dimensional assembly of disks at zero
temperature for ``Point J'' of the recently proposed jamming phase diagram. We
measure the total number of moving disks and the transverse length of the
moving region, and find a power law divergence as the packing density increases
toward a critical jamming density. This provides evidence that the T = 0
jamming transition as a function of packing density is a {\it second order}
phase transition. Additionally we find evidence for multiscaling, indicating
the importance of long tails in the velocity fluctuations.Comment: 4 pages, 5 figures; extensive new numerical data; final version in
press at PR
Bose Glass in Large N Commensurate Dirty Boson Model
The large N commensurate dirty boson model, in both the weakly and strongly
commensurate cases, is considered via a perturbative renormalization group
treatment. In the weakly commensurate case, there exists a fixed line under RG
flow, with varying amounts of disorder along the line. Including 1/N
corrections causes the system to flow to strong disorder, indicating that the
model does not have a phase transition perturbatively connected to the Mott
Insulator-Superfluid (MI-SF) transition. I discuss the qualitative effects of
instantons on the low energy density of excitations. In the strongly
commensurate case, a fixed point found previously is considered and results are
obtained for higher moments of the correlation functions. To lowest order,
correlation functions have a log-normal distribution. Finally, I prove two
interesting theorems for large N vector models with disorder, relevant to the
problem of replica symmetry breaking and frustration in such systems.Comment: 16 pages, 7 figure
An area law for entanglement from exponential decay of correlations
Area laws for entanglement in quantum many-body systems give useful
information about their low-temperature behaviour and are tightly connected to
the possibility of good numerical simulations. An intuition from quantum
many-body physics suggests that an area law should hold whenever there is
exponential decay of correlations in the system, a property found, for
instance, in non-critical phases of matter. However, the existence of quantum
data-hiding state--that is, states having very small correlations, yet a volume
scaling of entanglement--was believed to be a serious obstruction to such an
implication. Here we prove that notwithstanding the phenomenon of data hiding,
one-dimensional quantum many-body states satisfying exponential decay of
correlations always fulfil an area law. To obtain this result we combine
several recent advances in quantum information theory, thus showing the
usefulness of the field for addressing problems in other areas of physics.Comment: 8 pages, 3 figures. Short version of arXiv:1206.2947 Nature Physics
(2013
Algebraic vortex liquid theory of a quantum antiferromagnet on the kagome lattice
There is growing evidence from both experiment and numerical studies that low
half-odd integer quantum spins on a kagome lattice with predominant
antiferromagnetic near neighbor interactions do not order magnetically or break
lattice symmetries even at temperatures much lower than the exchange
interaction strength. Moreover, there appear to be a plethora of low energy
excitations, predominantly singlets but also spin carrying, which suggest that
the putative underlying quantum spin liquid is a gapless ``critical spin
liquid'' rather than a gapped spin liquid with topological order. Here, we
develop an effective field theory approach for the spin-1/2 Heisenberg model
with easy-plane anisotropy on the kagome lattice. By employing a vortex duality
transformation, followed by a fermionization and flux-smearing, we obtain
access to a gapless yet stable critical spin liquid phase, which is described
by (2+1)-dimensional quantum electrodynamics (QED) with an emergent
flavor symmetry. The specific heat, thermal conductivity, and
dynamical structure factor are extracted from the effective field theory, and
contrasted with other theoretical approaches to the kagome antiferromagnet.Comment: 14 pages, 8 figure
Evolution of the far-infrared luminosity functions in the Spitzer Wide-area Infrared Extragalactic Legacy Survey
We present new observational determination of the evolution of the rest-frame
70 and 160 micron and total infrared (TIR) galaxy luminosity functions (LFs)
using 70 micron data from the Spitzer Wide-area Infrared Extragalactic Legacy
Survey (SWIRE). The LFs were constructed for sources with spectroscopic
redshifts only in the XMM-LSS and Lockman Hole fields from the SWIRE
photometric redshift catalogue. The 70 micron and TIR LFs were constructed in
the redshift range 0<z<1.2 and the 160 micron LF was constructed in the
redshift range 0<z<0.5 using a parametric Bayesian and the vmax methods. We
assume in our models, that the faint-end power-law index of the LF does not
evolve with redshifts. We find the the double power-law model is a better
representation of the IR LF than the more commonly used power-law and Gaussian
model. We model the evolution of the FIR LFs as a function of redshift where
where the characteristic luminosity, evolve as
\propto(1+z)^{\alpha_\textsc{l}}. The rest-frame 70 micron LF shows a strong
luminosity evolution out to z=1.2 with alpha_l=3.41^{+0.18}_{-0.25}. The
rest-frame 160 micron LF also showed rapid luminosity evolution with
alpha_l=5.53^{+0.28}_{-0.23} out to z=0.5. The rate of evolution in luminosity
is consistent with values estimated from previous studies using data from IRAS,
ISO and Spitzer. The TIR LF evolves in luminosity with
alpha_l=3.82^{+0.28}_{-0.16} which is in agreement with previous results from
Spitzer 24 micron which find strong luminosity evolution. By integrating the LF
we calculated the co-moving IR luminosity density out to z=1.2, which confirm
the rapid evolution in number density of LIRGs and ULIRGs which contribute
~68^{+10}_{-07} % to the co-moving star formation rate density at z=1.2. Our
results based on 70 micron data confirms that the bulk of the star formation at
z=1 takes place in dust obscured objects.Comment: 17 pages, 14 figure
Random Unitaries Give Quantum Expanders
We show that randomly choosing the matrices in a completely positive map from
the unitary group gives a quantum expander. We consider Hermitian and
non-Hermitian cases, and we provide asymptotically tight bounds in the
Hermitian case on the typical value of the second largest eigenvalue. The key
idea is the use of Schwinger-Dyson equations from lattice gauge theory to
efficiently compute averages over the unitary group.Comment: 14 pages, 1 figur
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