8,133 research outputs found
Unified Treatment of Quantum Fluctuation Theorem and Jarzynski Equality in Terms of microscopic reversibility
There are two related theorems which hold even in far from equilibrium,
namely fluctuation theorem and Jarzynski equality. Fluctuation theorem states
the existence of symmetry of fluctuation of entropy production, while Jarzynski
equality enables us to estimate the free energy change between two states by
using irreversible processes. On the other hand, relationship between these
theorems was investigated by Crooks for the classical stochastic systems. In
this letter, we derive quantum analogues of fluctuation theorem and Jarzynski
equality microscopic reversibility condition. In other words, the quantum
analogue of the work by Crooks is presented.Comment: 7pages, revised versio
Speculations and inquiries regarding the possibilities for and limitations to practical interstellar travel
The existence of superluminal phenomena have now been independently confirmed by physicists working in several different laboratories, most notably by the team of Alain Aspect in Paris. The two major variants of these experiments are described and their implications for superluminal communication and superluminal travel are discussed. It is noted that while the original suggestion for these experiments is due in part to Albert Einstein (Einstein, Rosen, and Podolsky, 1935), their recent empirical validation presents a significant anomaly within the theoretical framework of the special theory of quantum mechanics. How a newly emerging paradigm broadly encompassing the empirical sciences, and informed by both the social sciences and general systems theory may resolve this theoretical crisis is discussed. With the impasse to further elaboration of these effects for possible superluminal applications removed, the discussion concludes with a research proposal
Simulation of complete many-body quantum dynamics using controlled quantum-semiclassical hybrids
A controlled hybridization between full quantum dynamics and semiclassical
approaches (mean-field and truncated Wigner) is implemented for interacting
many-boson systems. It is then demonstrated how simulating the resulting hybrid
evolution equations allows one to obtain the full quantum dynamics for much
longer times than is possible using an exact treatment directly. A collision of
sodium BECs with 1.x10^5 atoms is simulated, in a regime that is difficult to
describe semiclassically. The uncertainty of physical quantities depends on the
statistics of the full quantum prediction. Cutoffs are minimised to a
discretization of the Hamiltonian. The technique presented is quite general and
extension to other systems is considered.Comment: Published version. Broader background and discussion, slightly
shortened, less figures in epaps. Research part unchanged. Article + epaps
(4+4 pages), 8 figure
Quantum turbulence and correlations in Bose-Einstein condensate collisions
We investigate numerically simulated collisions between experimentally
realistic Bose-Einstein condensate wavepackets, within a regime where highly
populated scattering haloes are formed. The theoretical basis for this work is
the truncated Wigner method, for which we present a detailed derivation, paying
particular attention to its validity regime for colliding condensates. This
paper is an extension of our previous Letter [A. A. Norrie, R. J. Ballagh, and
C. W. Gardiner, Phys. Rev. Lett. 94, 040401 (2005)] and we investigate both
single-trajectory solutions, which reveal the presence of quantum turbulence in
the scattering halo, and ensembles of trajectories, which we use to calculate
quantum-mechanical correlation functions of the field
Quantum Kinetic Theory VI: The Growth of a Bose-Einstein Condensate
A detailed analysis of the growth of a BEC is given, based on quantum kinetic
theory, in which we take account of the evolution of the occupations of lower
trap levels, and of the full Bose-Einstein formula for the occupations of
higher trap levels, as well as the Bose stimulated direct transfer of atoms to
the condensate level introduced by Gardiner et al. We find good agreement with
experiment at higher temperatures, but at lower temperatures the experimentally
observed growth rate is somewhat more rapid. We also confirm the picture of the
``kinetic'' region of evolution, introduced by Kagan et al., for the time up to
the initiation of the condensate. The behavior after initiation essentially
follows our original growth equation, but with a substantially increased rate
coefficient.
Our modelling of growth implicitly gives a model of the spatial shape of the
condensate vapor system as the condensate grows, and thus provides an
alternative to the present phenomenological fitting procedure, based on the sum
of a zero-chemical potential vapor and a Thomas-Fermi shaped condensate. Our
method may give substantially different results for condensate numbers and
temperatures obtained from phenomentological fits, and indicates the need for
more systematic investigation of the growth dynamics of the condensate from a
supersaturated vapor.Comment: TeX source; 29 Pages including 26 PostScript figure
Markovian feedback to control continuous variable entanglement
We present a model to realize quantum feedback control of continuous variable
entanglement. It consists of two interacting bosonic modes subject to amplitude
damping and achieving entangled Gaussian steady state. The possibility to
greatly improve the degree of entanglement by means of Markovian (direct)
feedback is then shown.Comment: 4 pages Revtex, new figures, added comment
Disruption of reflecting Bose-Einstein condensates due to inter-atomic interactions and quantum noise
We perform fully three-dimensional simulations, using the truncated Wigner
method, to investigate the reflection of Bose-Einstein condensates from abrupt
potential barriers. We show that the inter-atomic interactions can disrupt the
internal structure of a cigar-shaped cloud with a high atom density at low
approach velocities, damping the center-of-mass motion and generating vortices.
Furthermore, by incorporating quantum noise we show that scattering halos form
at high approach velocities, causing an associated condensate depletion. We
compare our results to recent experimental observations.Comment: 5 figure
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