27,990 research outputs found
Quantum Ratchet Accelerator without a Bichromatic Lattice Potential
In a quantum ratchet accelerator system, a linearly increasing directed
current can be dynamically generated without using a biased field. Generic
quantum ratchet acceleration with full classical chaos [Gong and Brumer, Phys.
Rev. Lett. 97, 240602 (2006)] constitutes a new element of quantum chaos and an
interesting violation of a sum rule of classical ratchet transport. Here we
propose a simple quantum ratchet accelerator model that can also generate
linearly increasing quantum current with full classical chaos. This new model
does not require a bichromatic lattice potential. It is based on a variant of
an on-resonance kicked-rotor system, periodically kicked by two optical lattice
potentials of the same lattice constant, but with unequal amplitudes and a
fixed phase shift between them. The dependence of the ratchet current
acceleration rate on the system parameters is studied in detail. The cold-atom
version of our new quantum ratchet accelerator model should be realizable by
introducing slight modifications to current cold-atom experiments.Comment: 9 pages, 6 figures, submitted to Phys. Rev.
Controlled Quantum State Transfer in a Spin Chain
Control of the transfer of quantum information encoded in quantum wavepackets
moving along a spin chain is demonstrated. Specifically, based on a
relationship with control in a paradigm of quantum chaos, it is shown that
wavepackets with slow dispersion can automatically emerge from a class of
initial superposition states involving only a few spins, and that arbitrary
unspecified travelling wavepackets can be nondestructively stopped and later
relaunched with perfection. The results establish an interesting application of
quantum chaos studies in quantum information science.Comment: 6 pages, 3 figures, to appear in Physical Review
Extended Holographic dark energy
The idea of relating the infrared and ultraviolet cutoffs is applied to
Brans-Dicke theory of gravitation. We find that extended holographic dark
energy from the Hubble scale or the particle horizon as the infrared cutoff
will not give accelerating expansion. The dynamical cosmological constant with
the event horizon as the infrared cutoff is a viable dark energy model.Comment: one reference is corrected, 3 pages, no figure,V3: minor correction
Diffusion Models for Double-ended Queues with Renewal Arrival Processes
We study a double-ended queue where buyers and sellers arrive to conduct
trades. When there is a pair of buyer and seller in the system, they
immediately transact a trade and leave. Thus there cannot be non-zero number of
buyers and sellers simultaneously in the system. We assume that sellers and
buyers arrive at the system according to independent renewal processes, and
they would leave the system after independent exponential patience times. We
establish fluid and diffusion approximations for the queue length process under
a suitable asymptotic regime. The fluid limit is the solution of an ordinary
differential equation, and the diffusion limit is a time-inhomogeneous
asymmetric Ornstein-Uhlenbeck process (O-U process). A heavy traffic analysis
is also developed, and the diffusion limit in the stronger heavy traffic regime
is a time-homogeneous asymmetric O-U process. The limiting distributions of
both diffusion limits are obtained. We also show the interchange of the heavy
traffic and steady state limits
Improved cosmological constraints on the curvature and equation of state of dark energy
We apply the Constitution compilation of 397 supernova Ia, the baryon
acoustic oscillation measurements including the parameter, the distance
ratio and the radial data, the five-year Wilkinson microwave anisotropy probe
and the Hubble parameter data to study the geometry of the universe and the
property of dark energy by using the popular Chevallier-Polarski-Linder and
Jassal-Bagla-Padmanabhan parameterizations. We compare the simple
method of joined contour estimation and the Monte Carlo Markov chain method,
and find that it is necessary to make the marginalized analysis on the error
estimation. The probabilities of and in the
Chevallier-Polarski-Linder model are skew distributions, and the marginalized
errors are ,
, , and
. For the Jassal-Bagla-Padmanabhan model, the
marginalized errors are ,
, , and
. The equation of state parameter of dark energy
is negative in the redshift range at more than level.
The flat CDM model is consistent with the current observational data
at the level.Comment: 10 figures, 12 pages, Classical and Quantum Gravity in press; v2 to
match the pulished versio
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