869 research outputs found
Asymptotical photon distributions in the dissipative Dynamical Casimir Effect
Asymptotical formulas for the photon distribution function of a quantum
oscillator with time-dependent frequency and damping coefficients, interacting
with a thermal reservoir, are derived in the case of a large mean number of
quanta. Different regimes of excitation of an initial thermal state with an
arbitrary temperature are considered. New formulas are used to predict the
statistical properties of the electromagnetic field created in the experiments
on the Dynamical Casimir Effect which are now under preparation.Comment: 11 pages, accepted contribution to CEWQO 2009 proceedings (to appear
in Physica Scripta
Photon creation from vacuum and interactions engineering in nonstationary circuit QED
We study theoretically the nonstationary circuit QED system in which the
artificial atom transition frequency, or the atom-cavity coupling, have a small
periodic time modulation, prescribed externally. The system formed by the atom
coupled to a single cavity mode is described by the Rabi Hamiltonian. We show
that, in the dispersive regime, when the modulation periodicity is tuned to the
`resonances', the system dynamics presents the dynamical Casimir effect,
resonant Jaynes-Cummings or resonant Anti-Jaynes-Cummings behaviors, and it can
be described by the corresponding effective Hamiltonians. In the resonant
atom-cavity regime and under the resonant modulation, the dynamics is similar
to the one occurring for a stationary two-level atom in a vibrating cavity, and
an entangled state with two photons can be created from vacuum. Moreover, we
consider the situation in which the atom-cavity coupling, the atomic frequency,
or both have a small nonperiodic time modulation, and show that photons can be
created from vacuum in the dispersive regime. Therefore, an analog of the
dynamical Casimir effect can be simulated in circuit QED, and several photons,
as well as entangled states, can be generated from vacuum due to the
anti-rotating term in the Rabi Hamiltonian.Comment: 14 pages, 6 figures. Talk presented at the International Workshop "60
Years of Casimir Effect", 23 - 27 June, 2008, Brasili
Decoherence and thermalization dynamics of a quantum oscillator
We introduce the quantitative measures characterizing the rates of
decoherence and thermalization of quantum systems. We study the time evolution
of these measures in the case of a quantum harmonic oscillator whose relaxation
is described in the framework of the standard master equation, for various
initial states (coherent, `cat', squeezed and number). We establish the
conditions under which the true decoherence measure can be approximated by the
linear entropy . We show that at low temperatures and for
highly excited initial states the decoherence process consists of three
distinct stages with quite different time scales. In particular, the `cat'
states preserve 50% of the initial coherence for a long time interval which
increases logarithmically with increase of the initial energy.Comment: 24 pages, LaTex, 8 ps figures, accepted for publication in J. Opt.
Time dependent nonclassical properties of even and odd nonlinear coherent states
We construct even and odd nonlinear coherent states of a parametric
oscillator and examine their nonclassical properties.It has been shown that
these superpositions exhibit squeezing and photon antibunching which change
with time.Comment: 3 eps figure
Quantum Hall Droplets on Disc and Effective Wess-Zumino-Witten Action for Edge States
We algebraically analysis the quantum Hall effect of a system of particles
living on the disc in the presence of an uniform magnetic field
. For this, we identify the non-compact disc with the coset space
. This allows us to use the geometric quantization in order to
get the wavefunctions as the Wigner -functions satisfying a suitable
constraint. We show that the corresponding Hamiltonian coincides with the Maass
Laplacian. Restricting to the lowest Landau level, we introduce the
noncommutative geometry through the star product. Also we discuss the state
density behavior as well as the excitation potential of the quantum Hall
droplet. We show that the edge excitations are described by an effective
Wess-Zumino-Witten action for a strong magnetic field and discuss their nature.
We finally show that
LLL wavefunctions are intelligent states.Comment: 18 pages, clarifications and misprints corrected, version published
in IJGMM
Field quantization and squeezed states generation in resonators with time-dependent parameters
The problem of electromagnetic field quantization is usually considered in textbooks under the assumption that the field occupies some empty box. The case when a nonuniform time-dependent dielectric medium is confined in some space region with time-dependent boundaries is studied. The basis of the subsequent consideration is the system of Maxwell's equations in linear passive time-dependent dielectric and magnetic medium without sources
Speeding up antidynamical Casimir effect with nonstationary qutrits
The antidynamical Casimir effect (ADCE) is a term coined to designate the
coherent annihilation of excitations due to resonant external perturbation of
system parameters, allowing for extraction of quantum work from nonvacuum
states of some field. Originally proposed for a two-level atom (qubit) coupled
to a single cavity mode in the context of nonstationary quantum Rabi model, it
suffered from very low transition rate and correspondingly narrow resonance
linewidth. In this paper we show analytically and numerically that the ADCE
rate can be increased by at least one order of magnitude by replacing the qubit
by an artificial three-level atom (qutrit) in a properly chosen configuration.
For the cavity thermal state we demonstrate that the dynamics of the average
photon number and atomic excitation is completely different from the qubit's
case, while the behavior of the total number of excitations is qualitatively
similar yet significantly faster.Comment: 9 pages, 4 figure
Dynamical Casimir Effect in a Leaky Cavity at Finite Temperature
The phenomenon of particle creation within an almost resonantly vibrating
cavity with losses is investigated for the example of a massless scalar field
at finite temperature. A leaky cavity is designed via the insertion of a
dispersive mirror into a larger ideal cavity (the reservoir). In the case of
parametric resonance the rotating wave approximation allows for the
construction of an effective Hamiltonian. The number of produced particles is
then calculated using response theory as well as a non-perturbative approach.
In addition we study the associated master equation and briefly discuss the
effects of detuning. The exponential growth of the particle numbers and the
strong enhancement at finite temperatures found earlier for ideal cavities turn
out to be essentially preserved. The relevance of the results for experimental
tests of quantum radiation via the dynamical Casimir effect is addressed.
Furthermore the generalization to the electromagnetic field is outlined.Comment: 48 pages, 8 figures typos corrected & references added and update
Quantum master equations from classical Lagrangians with two stochastic forces
We show how a large family of master equations, describing quantum Brownian
motion of a harmonic oscillator with translationally invariant damping, can be
derived within a phenomenological approach, based on the assumption that an
environment can be simulated by two classical stochastic forces. This family is
determined by three time-dependent correlation functions (besides the frequency
and damping coefficients), and it includes as special cases the known master
equations, whose dissipative part is bilinear with respect to the operators of
coordinate and momentum.Comment: 10 pages, no figure
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