2,055 research outputs found
Quantum work statistics, Loschmidt echo and information scrambling
A universal relation is established between the quantum work probability
distribution of an isolated driven quantum system and the Loschmidt echo
dynamics of a two-mode squeezed state. When the initial density matrix is
canonical, the Loschmidt echo of the purified double thermofield state provides
a direct measure of information scrambling and can be related to the analytic
continuation of the partition function. Information scrambling is then
described by the quantum work statistics associated with the time-reversal
operation on a single copy, associated with the sudden negation of the system
Hamiltonian.Comment: 6 pages, 1 figure, published versio
Curvature in causal BD-type inflationary cosmology
We study a closed model of the universe filled with viscous fluid and
quintessence matter components in a Brans-Dicke type cosmological model. The
dynamical equations imply that the universe may look like an accelerated flat
Friedmann-Robertson-Walker universe at low redshift. We consider here
dissipative processes which follow a causal thermodynamics. The theory is
applied to viscous fluid inflation, where accepted values for the total entropy
in the observable universe is obtained.Comment: 11 pages, revtex 4. For a festschrift honoring Alberto Garcia. To be
publishen in Gen. Rel. Gra
Stability of spinor Fermi gases in tight waveguides
The two and three-body correlation functions of the ground state of an
optically trapped ultracold spin-1/2 Fermi gas (SFG) in a tight waveguide (1D
regime) are calculated in the plane of even and odd-wave coupling constants,
assuming a 1D attractive zero-range odd-wave interaction induced by a 3D p-wave
Feshbach resonance, as well as the usual repulsive zero-range even-wave
interaction stemming from 3D s-wave scattering. The calculations are based on
the exact mapping from the SFG to a ``Lieb-Liniger-Heisenberg'' model with
delta-function repulsions depending on isotropic Heisenberg spin-spin
interactions, and indicate that the SFG should be stable against three-body
recombination in a large region of the coupling constant plane encompassing
parts of both the ferromagnetic and antiferromagnetic phases. However, the
limiting case of the fermionic Tonks-Girardeau gas (FTG), a spin-aligned 1D
Fermi gas with infinitely attractive p-wave interactions, is unstable in this
sense. Effects due to the dipolar interaction and a Zeeman term due to a
resonance-generating magnetic field do not lead to shrinkage of the region of
stability of the SFG.Comment: 5 pages, 6 figure
An accelerated closed universe
We study a model in which a closed universe with dust and quintessence matter
components may look like an accelerated flat Friedmann-Robertson-Walker (FRW)
universe at low redshifts. Several quantities relevant to the model are
expressed in terms of observed density parameters, and
, and of the associated density parameter related
to the quintessence scalar field .Comment: 11 pages. For a festschrift honoring Alberto Garcia. To appear in
Gen. Rel. Gra
Quantum dynamics and entanglement of a 1D Fermi gas released from a trap
We investigate the entanglement properties of the nonequilibrium dynamics of
one-dimensional noninteracting Fermi gases released from a trap. The gas of N
particles is initially in the ground state within hard-wall or harmonic traps,
then it expands after dropping the trap. We compute the time dependence of the
von Neumann and Renyi entanglement entropies and the particle fluctuations of
spatial intervals around the original trap, in the limit of a large number N of
particles. The results for these observables apply to one-dimensional gases of
impenetrable bosons as well.
We identify different dynamical regimes at small and large times, depending
also on the initial condition, whether it is that of a hard-wall or harmonic
trap. In particular, we analytically show that the expansion from hard-wall
traps is characterized by the asymptotic small-time behavior of the von Neumann entanglement entropy, and the relation
where V is the particle variance, which are analogous to
the equilibrium behaviors whose leading logarithms are essentially determined
by the corresponding conformal field theory with central charge . The time
dependence of the entanglement entropy of extended regions during the expansion
from harmonic traps shows the remarkable property that it can be expressed as a
global time-dependent rescaling of the space dependence of the initial
equilibrium entanglement entropy.Comment: 19 pages, 18 fig
Disclosing hidden information in the quantum Zeno effect: Pulsed measurement of the quantum time of arrival
Repeated measurements of a quantum particle to check its presence in a region
of space was proposed long ago [G. R. Allcock, Ann. Phys. {\bf 53}, 286 (1969)]
as a natural way to determine the distribution of times of arrival at the
orthogonal subspace, but the method was discarded because of the quantum Zeno
effect: in the limit of very frequent measurements the wave function is
reflected and remains in the original subspace. We show that by normalizing the
small bits of arriving (removed) norm, an ideal time distribution emerges in
correspondence with a classical local-kinetic-energy distribution.Comment: 5 pages, 4 figures, minor change
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