6,012 research outputs found
Environment-induced uncertainties on moving mirrors in quantum critical theories via holography
Environment effects on a -dimensional mirror from the strongly coupled
d-dimensional quantum critical fields with a dynamic exponent in weakly
squeezed states are studied by the holographic approach. The dual description
is a -dimensional probe brane moving in the -dimensional asymptotic
Lifshitz geometry with gravitational wave perturbations. Using the holographic
influence functional method, we find that the large coupling constant of the
fields reduces the position uncertainty of the mirror, but enhances the
momentum uncertainty. As such, the product of the position and momentum
uncertainties is independent of the coupling constant. The proper choices of
the phase of the squeezing parameter might reduce the uncertainties,
nevertheless large values of its amplitude always lead to the larger
uncertainties due to the fact that more quanta are excited as compared with the
corresponding normal vacuum and thermal states. In the squeezed vacuum state,
the position and momentum of the mirror gain maximum uncertainties from the
field at the dynamic exponent when the same squeezed mode is
considered. As for the squeezed thermal state, the contributions of thermal
fluctuations to the uncertainties decrease as the temperature increases in the
case the contributions increase as the
temperature increases. These results are in sharp contrast with those in the
environments of the relativistic free field. Some possible observable effects
are discussed.Comment: This is the version (v2) published in the Annals of Physic
Time evolution of entanglement entropy of moving mirrors influenced by strongly coupled quantum critical fields
The evolution of the Von Neumann entanglement entropy of a -dimensional
mirror influenced by the strongly coupled -dimensional quantum critical
fields with a dynamic exponent is studied by the holographic approach. The
dual description is a -dimensional probe brane moving in the
-dimensional asymptotic Lifshitz geometry ended at , which plays a
role as the UV energy cutoff. Using the holographic influence functional
method, we find that in the linear response region, by introducing a harmonic
trap for the mirror, which serves as a IR energy cutoff, the Von Neumann
entropy at late times will saturate by a power-law in time for generic values
of and . The saturated value and the relaxation rate depend on the
parameter , which is restricted to but
. We find that the saturated values of the entropy are
qualitatively different for the theories with and .
Additionally, the power law relaxation follows the rate . This probe brane approach provides an alternative way to study
the time evolution of the entanglement entropy in the linear response region
that shows the similar power-law relaxation behavior as in the studies of
entanglement entropies based on Ryu-Takayanagi conjecture. We also compare our
results with quantum Brownian motion in a bath of relativistic free fields.Comment: The published versio
Subvacuum effects in Quantum Critical Theories from Holographic Approach
Subvacuum phenomena on a massive particle induced by a squeezed vacuum state
of strongly coupled critical fields with a dynamical scaling are studied by
employing the holographic approach. The corresponding dual description is the
string moving in the 4+1-dimensional Lifshitz geometry. The squeezed vacuum
state is constructed from the Bogoliubov transformations of the creation and
annihilation operators of the pure vacuum state as a result from the perturbed
geometry. Then the influence on particle's velocity dispersion from the
squeezed vacuum is studied. With appropriate choices of squeezing parameters,
the velocity dispersion is found smaller than the value caused by the normal
vacuum fluctuations. This leads to a subvacuum effect. We find that the
reduction in the velocity dispersion is suppressed by a large coupling constant
of quantum critical fields, but is in principle observable. We then investigate
the effect of the squeezed vacuum to the decoherence dynamics of a quantum
particle. It is found possible for this decoherence to be below the level from
the pure vacuum, rendering another subvacuum phenomenon of recoherence. We make
some estimates of the degree of recoherence, and show that, in contrary to the
velocity dispersion, the recoherence effect is proportional to the large
coupling constant, and can potentially be observed. Finally we make a
comparison with the effect on the particle influenced by a relativistic free
field with the dynamical scaling .Comment: This is the version (v2) published in PR
A Holographic Description of Negative Energy States
Using the AdS/CFT duality, we study the expectation value of stress tensor in
-dimensional quantum critical theories with a general dynamical scaling
, and explore various constrains on negative energy density for strongly
coupled field theories. The holographic dual theory is the theory of gravity in
3+1-dimensional Lifshitz backgrounds. We adopt a consistent approach to obtain
the boundary stress tensor from bulk construction, which satisfies the trace
Ward identity associated with Lifshitz scaling symmetry. In particular, the
boundary stress tensor, constructed from the gravitational wave deformed
Lifshitz geometry, is found up to second order in gravitational wave
perturbations. {The result} is compared to its counterpart in free {scalar}
field theory at the same order in an expansion of small squeezing parameters.
This allows us to relate the boundary values of gravitational waves to the
squeezing parameters of squeezed vacuum states. We find that, in both cases
with , the stress tensor satisfies the averaged null energy condition, and
is consistent with the quantum interest conjecture. Moreover, the negative
lower bound on null-contracted stress tensor, which is averaged over time-like
trajectories along nearly null directions, is obtained. We find a weaker
constraint on the magnitude and duration of negative null energy density in
strongly coupled field theory as compared with the constraint in free
relativistic field theory. The implications are discussed.Comment: This is the version(v2) published in JHE
Nonequilibrium Damping of Collective Motion of Homogeneous Cold Fermi Condensates with Feshbach Resonances
Collisionless damping of a condensate of cold Fermi atoms, whose scattering
is controlled by a Feshbach resonance, is explored throughout the BCS and BEC
regimes when small perturbations on its phase and amplitude modes are turned on
to drive the system slightly out of equilibrium. Using a one-loop effective
action, we first recreate the known result that for a broad resonance the
amplitude of the condensate decays as at late times in the BCS
regime whereas it decays as in the BEC regime. We then examine the
case of an idealized narrow resonance, and find that this collective mode
decays as throughout both the BCS and BEC regimes. Although this
seems to contradict earlier results that damping is identical for both broad
and narrow resonances, the breakdown of the narrow resonance limit restores
this universal behaviour. More measureably, the phase perturbation may give a
shift on the saturated value to which the collective amplitude mode decays,
which vanishes only in the deep BCS regime when the phase and amplitude modes
are decoupled.Comment: 9 pages, 1 figur
Derivation of hydrodynamics for the gapless mode in the BEC-BCS crossover from the exact one-loop effective action
We show that many hydrodynamical properties of the BEC/BCS crossover in the
presence of a Feshbach resonance at T=0 can be derived easily from the
derivative expansion of the (exact) fully renormalized one-loop effective
action. In particular, we calculate the velocity of sound throughout the BCS
and BEC regimes and derive the generalized superfluid continuity equations for
the composite two-fluid system.Comment: Four pages, 1 figure. Whereas v.2 contained additional references,
but was otherwise unchanged, this new version contains new material
concerning our ability to provide a hydrodynamical description of the BEC/BSC
system. This explains the change of title. Our old results are unaffecte
Analogue stochastic gravity phenomena in two-component Bose-Einstein condensates: Sound cone fluctuations
We investigate the properties of the condensates of cold atoms at zero
temperature in the tunable binary Bose-Einstein condensate system with a Rabi
transition between atomic hyperfine states. We use this system to examine the
effect of quantum fluctuations in a tunable quantum gas on phonon propagation.
We show that the system can be represented by a coupled two-field model of a
gapless phonon and a gapped mode, which are analogous to the Goldstone and
Higgs particles in particle physics. We then further trace out the gapped modes
to give an effective purely phononic theory using closed-time-path formalism.
In particular, we are interested in the sound cone fluctuations due to the
variation of the speed-of-sound acoustic metric, induced by quantum
fluctuations of the gapped modes. These fluctuations can be interpreted as
inducing a stochastic space-time, and thus are regarded as analogue phenomena
of light cone fluctuations presumably arising from quantum gravity effects. The
effects of fluctuations can be displayed in the variation in the travel time of
sound waves. We suggest the relevant experiments to discuss the possibility of
experimental observations.Comment: 19 pages, 7 figures. Revised version as published in Physical Review
Geodesic Motion of Neutral Particles around a Kerr-Newman Black Hole
We examine the dynamics of a neutral particle around a Kerr-Newman black
hole, and in particular focus on the effects of the charge of the spinning
black hole on the motion of the particle. We first consider the innermost
stable circular orbits (ISCO) on the equatorial plane. It is found that the
presence of the charge of the black hole leads to the effective potential of
the particle with stronger repulsive effects as compared with the Kerr black
hole. As a result, the radius of ISCO decreases as charge of the black hole
increases for a fixed value of black hole's angular momentum . We then
consider a kick on the particle from its initial orbit out of the equatorial
motion. The perturbed motion of the particle will eventually be bounded, or
unbounded so that it escapes to spatial infinity. Even more, the particle will
likely be captured by the black hole. Thus we analytically and numerically
determine the parameter regions of the corresponding motions, in terms of the
initial radius of the orbital motion and the strength of the kick. The
comparison will be made with the motion of a neutral particle in the Kerr black
hole.Comment: Published version; 18 pages, 7 figure
The Non-universal behaviour of Cold Fermi Condensates with Narrow Feshbach Resonances
In this paper we construct an effective field theory for a condensate of cold
Fermi atoms whose scattering is controlled by a narrow Feshbach resonance. We
show how, from first principles, it permits a hydrodynamic description of the
BEC-BCS crossover from which the equation of state, intimately related to the
speed of sound, can be derived. Specifically, we stress the non-universal
behaviour of the equation of state at the unitary limit of infinite scattering
length that arises when either, or both, of the range of the inter-atomic force
and the scale of the molecular field become large.Comment: 7 pages, there is no differences in results between this (v2) and the
older version (v1), but v2 makes the nature of the non-canonical behavior of
the EOS cleare
Large phonon time-of-flight fluctuations in expanding flat condensates of cold fermi gases
We reexamine how quantum density fluctuations in condensates of ultra-cold
fermi gases lead to fluctuations in phonon times-of-flight, an effect that
increases as density is reduced. We suggest that these effects should be
measurable in pancake-like (two-dimensional) condensates on their release from
their confining optical traps, providing their initial (width/thickness) aspect
ratio is suitably large.Comment: In this version v4 (9 pages, 1 figures), we have modified slightly
the introduction, the results are unchange
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