1,772 research outputs found
Observational Signatures of Quantum Gravity in Interferometers
We consider the uncertainty in the arm length of an interferometer due to
metric fluctuations from the quantum nature of gravity, proposing a concrete
microscopic model of energy fluctuations in holographic degrees of freedom on
the surface bounding a causally connected region of spacetime. In our model,
fluctuations longitudinal to the beam direction accumulate in the infrared and
feature strong long distance correlation in the transverse direction. This
leads to a signal that could be observed in a gravitational wave
interferometer. We connect the positional uncertainty principle arising from
our calculations to the 't Hooft gravitational S-matrix.Comment: 6 pages, 1 figur
What is "system": some decoherence-theory arguments
We discuss the possibility of making the {\it initial} definitions of
mutually different (possibly interacting, or even entangled) systems in the
context of decoherence theory. We point out relativity of the concept of
elementary physical system as well as point out complementarity of the
different possible divisions of a composite system into "subsystems", thus
eventually sharpening the issue of 'what is system'.Comment: 9 pages, no figure
Unconditional Pointer States from Conditional Master Equations
When part of the environment responsible for decoherence is used to extract
information about the decohering system, the preferred {\it pointer states}
remain unchanged. This conclusion -- reached for a specific class of models --
is investigated in a general setting of conditional master equations using
suitable generalizations of predictability sieve. We also find indications that
the einselected states are easiest to infer from the measurements carried out
on the environment.Comment: 4 pages, 3 .eps figures; final version to appear in Phys.Rev.Let
Highly sensitive multichannel spectrometer for subpicosecond spectroscopy in the midinfrared
A spectrometer system is presented for time-resolved probing in the midinfrared between 5 and 11 /tLmw ith a
temporal resolution of better than 400 fs. Multichannel detection with HgCdTe detector arrays consisting of
ten elements in combination with a high repetition rate permits one to record weak absorbance changes with an
accuracy of 0.1 mOD
Gaussian Decoherence and Gaussian Echo from Spin Environments
We examine an exactly solvable model of decoherence -- a spin-system
interacting with a collection of environment spins. We show that in this simple
model (introduced some time ago to illustrate environment--induced
superselection) generic assumptions about the coupling strengths lead to a
universal (Gaussian) suppression of coherence between pointer states. We
explore the regime of validity of this result and discuss its relation to
spectral features of the environment. We also consider its relevance to the
experiments on the so-called Loschmidt echo (which measures, in effect, the
fidelity between the initial and time-reversed or "echo" signal). In
particular, we show that for partial reversals (e.g., when of only a part of
the total Hamiltonian changes sign) fidelity will exhibit a Gaussian dependence
on the time of reversal. In such cases echo may become independent of the
details of the reversal procedure or the specifics of the coupling to the
environment. This puzzling behavior was observed in several NMR experiments.
Natural candidates for such two environments (one of which is easily reversed,
while the other is ``irreversible'') are suggested for the experiment involving
ferrocene.Comment: Improved text and figures, to appear in the special issue of Acta
Physica Polonica B celebrating the 100th anniversary of Smoluchowski's
equation and his paper explaining Brownian motion (in
http://th-www.if.uj.edu.pl/acta/vol38/pdf/v38p1685.pdf
Quantum Chaotic Environments, The Butterfly Effect, And Decoherence
We investigate the sensitivity of quantum systems that are chaotic in a
classical limit, to small perturbations of their equations of motion. This
sensitivity, originally studied in the context of defining quantum chaos, is
relevant to decoherence in situations when the environment has a chaotic
classical counterpart.Comment: 4 pages, 3 figure
The Trispectrum in the Effective Field Theory of Large Scale Structure
We compute the connected four point correlation function (the trispectrum in
Fourier space) of cosmological density perturbations at one-loop order in
Standard Perturbation Theory (SPT) and the Effective Field Theory of Large
Scale Structure (EFT of LSS). This paper is a companion to our earlier work on
the non-Gaussian covariance of the matter power spectrum, which corresponds to
a particular wavenumber configuration of the trispectrum. In the present
calculation, we highlight and clarify some of the subtle aspects of the EFT
framework that arise at third order in perturbation theory for general
wavenumber configurations of the trispectrum. We consistently incorporate
vorticity and non-locality in time into the EFT counterterms and lay out a
complete basis of building blocks for the stress tensor. We show predictions
for the one-loop SPT trispectrum and the EFT contributions, focusing on
configurations which have particular relevance for using LSS to constrain
primordial non-Gaussianity.Comment: 25+3 pages, 7 figure
Decoherence and the Loschmidt echo
Environment--induced decoherence causes entropy increase. It can be
quantified using, e.g., the purity . When the
Hamiltonian of a quantum system is perturbed, its sensitivity to such
perturbation can be measured by the Loschmidt echo . It is given by
the average squared overlap between the perturbed and unperturbed state. We
describe the relation between the temporal behavior of and . In this way we show that the decay of the Loschmidt echo can be analyzed
using tools developed in the study of decoherence. In particular, for systems
with a classically chaotic Hamiltonian the decay of and
has a regime where it is dominated by the classical Lyapunov exponent
Decoherence, Chaos, and the Second Law
We investigate implications of decoherence for quantum systems which are
classically chaotic. We show that, in open systems, the rate of von Neumann
entropy production quickly reaches an asymptotic value which is: (i)
independent of the system-environment coupling, (ii) dictated by the dynamics
of the system, and (iii) dominated by the largest Lyapunov exponent. These
results shed a new light on the correspondence between quantum and classical
dynamics as well as on the origins of the ``arrow of time.''Comment: 13 Pages, 2 Figures available upon request, Preprint LA-UR-93-, The
new version contains the text, the previous one had only the Macros: sorry
Decoherence and the rate of entropy production in chaotic quantum systems
We show that for an open quantum system which is classically chaotic (a
quartic double well with harmonic driving coupled to a sea of harmonic
oscillators) the rate of entropy production has, as a function of time, two
relevant regimes: For short times it is proportional to the diffusion
coefficient (fixed by the system--environment coupling strength). For longer
times (but before equilibration) there is a regime where the entropy production
rate is fixed by the Lyapunov exponent. The nature of the transition time
between both regimes is investigated.Comment: Revtex, 4 pages, 3 figures include
- …