6,726 research outputs found
Atom laser dynamics in a tight-waveguide
We study the transient dynamics that arise during the formation of an atom
laser beam in a tight waveguide. During the time evolution the density profile
develops a series of wiggles which are related to the diffraction in time
phenomenon. The apodization of matter waves, which relies on the use of smooth
aperture functions, allows to suppress such oscillations in a time interval,
after which there is a revival of the diffraction in time. The revival time
scale is directly related to the inverse of the harmonic trap frequency for the
atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th
WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ",
organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007
Scaling-up quantum heat engines efficiently via shortcuts to adiabaticity
The finite-time operation of a quantum heat engine that uses a single
particle as a working medium generally increases the output power at the
expense of inducing friction that lowers the cycle efficiency. We propose to
scale up a quantum heat engine utilizing a many-particle working medium in
combination with the use of shortcuts to adiabaticity to boost the nonadiabatic
performance by eliminating quantum friction and reducing the cycle time. To
this end, we first analyze the finite-time thermodynamics of a quantum Otto
cycle implemented with a quantum fluid confined in a time-dependent harmonic
trap. We show that nonadiabatic effects can be controlled and tailored to match
the adiabatic performance using a variety of shortcuts to adiabaticity. As a
result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat
engine exhibits no friction and the cycle can be run at maximum efficiency with
a tunable output power. We demonstrate our results with a working medium
consisting of particles with inverse-square pairwise interactions, that
includes noninteracting and hard-core bosons as limiting cases.Comment: 15 pages, 3 figures; typo in Eq. (51) fixed. Feature paper in the
Special Issue "Quantum Thermodynamics" edited by Prof. Dr. Ronnie Koslof
Dynamics of a Tonks-Girardeau gas released from a hard-wall trap
We study the expansion dynamics of a Tonks-Girardeau gas released from a hard
wall trap. Using the Fermi-Bose map, the density profile is found analytically
and shown to differ from that one of a classical gas in the microcanonical
ensemble even at macroscopic level, for any observation time larger than a
critical time. The relevant time scale arises as a consequence of
fermionization.Comment: 4 pages, 6 figure
Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism
The non-equilibrium dynamics of an ion chain in a highly anisotropic trap is
studied when the transverse trap frequency is quenched across the value at
which the chain undergoes a continuous phase transition from a linear to a
zigzag structure. Within Landau theory, an equation for the order parameter,
corresponding to the transverse size of the zigzag structure, is determined
when the vibrational motion is damped via laser cooling. The number of
structural defects produced during a linear quench of the transverse trapping
frequency is predicted and verified numerically. It is shown to obey the
scaling predicted by the Kibble-Zurek mechanism, when extended to take into
account the spatial inhomogeneities of the ion chain in a linear Paul trap.Comment: 5 pages, 3 figure
Tachyon warm inflationary universe model in the weak dissipative regime
Warm inflationary universe model in a tachyon field theory is studied in the
weak dissipative regime. We develop our model for an exponential potential and
the dissipation parameter =constant. We describe scalar and
tensor perturbations for this scenario.Comment: 9 pages, accepted by European Physical Journal
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