5,729 research outputs found
On spontaneous photon emission in collapse models
We reanalyze the problem of spontaneous photon emission in collapse models.
We show that the extra term found by Bassi and Duerr is present for non-white
(colored) noise, but its coefficient is proportional to the zero frequency
Fourier component of the noise. This leads one to suspect that the extra term
is an artifact. When the calculation is repeated with the final electron in a
wave packet and with the noise confined to a bounded region, the extra term
vanishes in the limit of continuum state normalization. The result obtained by
Fu and by Adler and Ramazanoglu from application of the Golden Rule is then
recovered.Comment: 23 pages, LaTex. Minor changes with respect to previous versio
Universal contact and collective excitations of a strongly interacting Fermi gas
We study the relationship between Tan's contact parameter and the macroscopic
dynamic properties of an ultracold trapped gas, such as the frequencies of the
collective oscillations and the propagation of sound in one-dimensional (1D)
configurations. We find that the value of the contact, extracted from the most
recent low-temperature measurements of the equation of state near unitarity,
reproduces with accuracy the experimental values of the collective frequencies
of the radial breathing mode at the lowest temperatures. The available
experiment results for the 1D sound velocities near unitarity are also
investigated.Comment: 5 pages, 3 figure
Algorithmic differentiation and the calculation of forces by quantum Monte Carlo
We describe an efficient algorithm to compute forces in quantum Monte Carlo
using adjoint algorithmic differentiation. This allows us to apply the space
warp coordinate transformation in differential form, and compute all the 3M
force components of a system with M atoms with a computational effort
comparable with the one to obtain the total energy. Few examples illustrating
the method for an electronic system containing several water molecules are
presented. With the present technique, the calculation of finite-temperature
thermodynamic properties of materials with quantum Monte Carlo will be feasible
in the near future.Comment: 32 pages, 4 figure, to appear in The Journal of Chemical Physic
Continuity properties of a factor of Markov chains
Starting from a Markov chain with a finite alphabet, we consider the chain
obtained when all but one symbol are undistinguishable for the practitioner. We
study necessary and sufficient conditions for this chain to have continuous
transition probabilities with respect to the past
Engineering many-body quantum dynamics by disorder
Going beyond the currently investigated regimes in experiments on quantum
transport of ultracold atoms in disordered potentials, we predict a crossover
between regular and quantum-chaotic dynamics when varying the strength of
disorder. Our spectral approach is based on the Bose-Hubbard model describing
interacting atoms in deep random potentials. The predicted crossover from
localized to diffusive dynamics depends on the simultaneous presence of
interactions and disorder, and can be verified in the laboratory by monitoring
the evolution of typical experimental initial states.Comment: 4 pages, 4 figures (improved version), to be published in PR
Fermi Gases in Slowly Rotating Traps: Superfluid vs Collisional Hydrodynamics
The dynamic behavior of a Fermi gas confined in a deformed trap rotating at
low angular velocity is investigated in the framework of hydrodynamic theory.
The differences exhibited by a normal gas in the collisional regime and a
superfluid are discussed. Special emphasis is given to the collective
oscillations excited when the deformation of the rotating trap is suddenly
removed or when the rotation is suddenly stopped. The presence of vorticity in
the normal phase is shown to give rise to precession and beating phenomena
which are absent in the superfluid phase.Comment: 4 pages, 2 figure
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