273 research outputs found
Quantum-state extraction from high-Q cavities
The problem of extraction of a single-mode quantum state from a high-Q cavity
is studied for the case in which the time of preparation of the quantum state
of the cavity mode is short compared with its decay time. The temporal
evolution of the quantum state of the field escaping from the cavity is
calculated in terms of phase-space functions. A general condition is derived
under which the quantum state of the pulse built up outside the cavity is a
nearly perfect copy of the quantum state the cavity field was initially
prepared in. The results show that unwanted losses prevent the realization of a
nearly perfect extraction of nonclassical quantum states from high-Q optical
microcavities with presently available technology.Comment: RevTeX4, 9 pages with 6 figures; extended version as submitted to
Phys. Rev.
Canonical quantization of electromagnetic field in an anisotropic polarizable and magnetizable medium with spatial-temporal dispersion
Modeling an anisotropic spatially and temporarily dispersive
magnetodielectric medium by two independent collections of three dimensional
vector fields, we demonstrate a fully canonical quantization of electromagnetic
field in the presence of such a medium. Two tensor fields which couple the
electromagnetic field with the medium and have an important role in this
quantization method are introduced. The electric and magnetic polarization
fields of the medium naturally are concluded in terms of the coupling tensors
and the dynamical variables modeling the magnetodielectric medium. In
Heisenberg picture, the constitutive equations of the medium together with the
Maxwell laws are obtained as the equations of motion of the total system and
the susceptibility tensors of the medium are calculated in terms of the
coupling tensors. Following a perturbation method the Green function related to
the total system is found and the time dependence of electromagnetic field
operators is derived.Comment: 19 pages, No figur
Theoretical framework of entangled-photon generation from biexcitons in nano-to-bulk crossover regime with planar geometry
We have constructed a theoretical framework of the biexciton-resonant
hyperparametric scattering for the pursuit of high-power and high-quality
generation of entangled photon pairs. Our framework is applicable to
nano-to-bulk crossover regime where the center-of-mass motion of excitons and
biexcitons is confined. Material surroundings and the polarization correlation
of generated photons can be considered. We have analyzed the entangled-photon
generation from CuCl film, by which ultraviolet entangled-photon pairs are
generated, and from dielectric microcavity embedding a CuCl layer. We have
revealed that in the nano-to-bulk crossover regime we generally get a high
performance from the viewpoint of statistical accuracy, and the generation
efficiency can be enhanced by the optical cavity with maintaining the high
performance. The nano-to-bulk crossover regime has a variety of degrees of
freedom to tune the entangled-photon generation, and the scattering spectra
explicitly reflect quantized exciton-photon coupled modes in the finite
structure.Comment: 18 pages, 10 figure
Resonant Energy Exchange between Atoms in Dispersing and Absorbing Surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, a master equation describing both the resonant dipole-dipole interaction
(RDDI) and the resonant atom-field interaction (RAFI) in the presence of
dispersing and absorbing macroscopic bodies is derived, with the relevant
couplings being expressed in terms of the surroundings-assisted Green tensor.
It is shown that under certain conditions the RDDI can be regarded as being
governed by an effective Hamiltonian. The theory, which applies to both weak
and strong atom-field coupling, is used to study the resonant energy exchange
between two (two-level) atoms sharing initially a single excitation. In
particular, it is shown that in the regime of weak atom-field coupling there is
a time window, where the energy transfer follows a transfer-rate law of the
type obtained by ordinary second-order perturbation theory. Finally, the
spectrum of the light emitted during the energy transfer is studied and the
line splittings are discussed.Comment: 9 pages, 5 figs, Proceedings of ICQO'2002, Raubichi, to appear in
Optics and Spectroscop
Casimir Forces and Graphene Sheets
The Casimir force between two infinitely thin parallel sheets in a setting of
such sheets is found. The finite two-dimensional conductivities, which
describe the dispersive and absorptive properties of each sheet, are taken into
account, whereupon the theory is applied to interacting graphenes. By exploring
similarities with in-plane optical spectra for graphite, the conductivity of
graphene is modeled as a combination of Lorentz type oscillators. We find that
the graphene transparency and the existence of a universal constant
conductivity result in graphene/graphene Casimir interaction at
large separations to have the same distance dependence as the one for perfect
conductors but with much smaller magnitude
Green functions and propagation of waves in strongly inhomogeneous media
We show that Green functions of second-order differential operators with
singular or unbounded coefficients can have an anomalous behaviour in
comparison to the well-known properties of Green functions of operators with
bounded coefficients. We discuss some consequences of such an anomalous short
or long distance behaviour for a diffusion and wave propagation in an
inhomogeneous medium
Entanglement degradation of a two-mode squeezed vacuum in absorbing and amplifying optical fibers
Applying the recently developed formalism of quantum-state transformation at
absorbing dielectric four-port devices [L.~Kn\"oll, S.~Scheel, E.~Schmidt,
D.-G.~Welsch, and A.V.~Chizhov, Phys. Rev. A {\bf 59}, 4716 (1999)], we
calculate the quantum state of the outgoing modes of a two-mode squeezed vacuum
transmitted through optical fibers of given extinction coefficients. Using the
Peres--Horodecki separability criterion for continuous variable systems
[R.~Simon, Phys. Rev. Lett. {\bf 84}, 2726 (2000)], we compute the maximal
length of transmission of a two-mode squeezed vacuum through an absorbing
system for which the transmitted state is still inseparable. Further, we
calculate the maximal gain for which inseparability can be observed in an
amplifying setup. Finally, we estimate an upper bound of the entanglement
preserved after transmission through an absorbing system. The results show that
the characteristic length of entanglement degradation drastically decreases
with increasing strength of squeezing.Comment: Paper presented at the International Conference on Quantum Optics and
VIII Seminar on Quantum Optics, Raubichi, Belarus, May 28-31, 2000, 11 pages,
LaTeX2e, 4 eps figure
Casimir-Polder forces: A non-perturbative approach
Within the frame of macroscopic QED in linear, causal media, we study the
radiation force of Casimir-Polder type acting on an atom which is positioned
near dispersing and absorbing magnetodielectric bodies and initially prepared
in an arbitrary electronic state. It is shown that minimal and multipolar
coupling lead to essentially the same lowest-order perturbative result for the
force acting on an atom in an energy eigenstate. To go beyond perturbation
theory, the calculations are based on the exact center-of-mass equation of
motion. For a nondriven atom in the weak-coupling regime, the force as a
function of time is a superposition of force components that are related to the
electronic density-matrix elements at a chosen time. Even the force component
associated with the ground state is not derivable from a potential in the
ususal way, because of the position dependence of the atomic polarizability.
Further, when the atom is initially prepared in a coherent superposition of
energy eigenstates, then temporally oscillating force components are observed,
which are due to the interaction of the atom with both electric and magnetic
fields.Comment: 23 pages, 3 figures, additional misprints correcte
Surface-induced heating of cold polar molecules
We study the rotational and vibrational heating of diatomic molecules placed
near a surface at finite temperature on the basis of macroscopic quantum
electrodynamics. The internal molecular evolution is governed by transition
rates that depend on both temperature and position. Analytical and numerical
methods are used to investigate the heating of several relevant molecules near
various surfaces. We determine the critical distances at which the surface
itself becomes the dominant source of heating and we investigate the transition
between the long-range and short-range behaviour of the heating rates. A simple
formula is presented that can be used to estimate the surface-induced heating
rates of other molecules of interest. We also consider how the heating depends
on the thickness and composition of the surface.Comment: 17 pages, 7 figure
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