1,653 research outputs found
Quantum local-field corrections and spontaneous decay
A recently developed scheme [S. Scheel, L. Knoll, and D.-G. Welsch, Phys.
Rev. A 58, 700 (1998)] for quantizing the macroscopic electromagnetic field in
linear dispersive and absorbing dielectrics satisfying the Kramers-Kronig
relations is used to derive the quantum local-field correction for the standard
virtual-sphere-cavity model. The electric and magnetic local-field operators
are shown to be consistent with QED only if the polarization noise is fully
taken into account. It is shown that the polarization fluctuations in the local
field can dramatically change the spontaneous decay rate, compared with the
familiar result obtained from the classical local-field correction. In
particular, the spontaneous emission rate strongly depends on the radius of the
local-field virtual cavity.Comment: 7 pages, using RevTeX, 4 figure
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
Numerical simulations of neutron star-black hole binaries in the near-equal-mass regime
Simulations of neutron star-black hole (NSBH) binaries generally consider
black holes with masses in the range , where we expect to find
most stellar mass black holes. The existence of lower mass black holes,
however, cannot be theoretically ruled out. Low-mass black holes in binary
systems with a neutron star companion could mimic neutron star-neutron (NSNS)
binaries, as they power similar gravitational wave (GW) and electromagnetic
(EM) signals. To understand the differences and similarities between NSNS
mergers and low-mass NSBH mergers, numerical simulations are required. Here, we
perform a set of simulations of low-mass NSBH mergers, including systems
compatible with GW170817. Our simulations use a composition and temperature
dependent equation of state (DD2) and approximate neutrino transport, but no
magnetic fields. We find that low-mass NSBH mergers produce remnant disks
significantly less massive than previously expected, and consistent with the
post-merger outflow mass inferred from GW170817 for moderately asymmetric mass
ratio. The dynamical ejecta produced by systems compatible with GW170817 is
negligible except if the mass ratio and black hole spin are at the edge of the
allowed parameter space. That dynamical ejecta is cold, neutron-rich, and
surprisingly slow for ejecta produced during the tidal disruption of a neutron
star : . We also find that the final mass of the remnant
black hole is consistent with existing analytical predictions, while the final
spin of that black hole is noticeably larger than expected -- up to for our equal mass case
Casimir forces from a loop integral formulation
We reformulate the Casimir force in the presence of a non-trivial background.
The force may be written in terms of loop variables, the loop being a curve
around the scattering sites. A natural path ordering of exponentials take place
when a particular representation of the scattering centres is given. The basic
object to be evaluated is a reduced (or abbreviated) classical pseudo-action
that can be operator valued.Comment: references added, text clarified in place
Atomic multipole relaxation rates near surfaces
The spontaneous relaxation rates for an atom in free space and close to an
absorbing surface are calculated to various orders of the electromagnetic
multipole expansion. The spontaneous decay rates for dipole, quadrupole and
octupole transitions are calculated in terms of their respective primitive
electric multipole moments and the magnetic relaxation rate is calculated for
the dipole and quadrupole transitions in terms of their respective primitive
magnetic multipole moments. The theory of electromagnetic field quantization in
magnetoelectric materials is used to derive general expressions for the decay
rates in terms of the dyadic Green function. We focus on the decay rates in
free space and near an infinite half space. For the decay of atoms near to an
absorbing dielectric surface we find a hierarchy of scaling laws depending on
the atom-surface distance z.Comment: Updated to journal version. 16 page
Casimir effect from macroscopic quantum electrodynamics
The canonical quantization of macroscopic electromagnetism was recently
presented in New J. Phys. 12 (2010) 123008. This theory is here used to derive
the Casimir effect, by considering the special case of thermal and zero-point
fields. The stress-energy-momentum tensor of the canonical theory follows from
Noether's theorem, and its electromagnetic part in thermal equilibrium gives
the Casimir energy density and stress tensor. The results hold for arbitrary
inhomogeneous magnetodielectrics and are obtained from a rigorous quantization
of electromagnetism in dispersive, dissipative media. Continuing doubts about
the status of the standard Lifshitz theory as a proper quantum treatment of
Casimir forces do not apply to the derivation given here. Moreover, the correct
expressions for the Casimir energy density and stress tensor inside media
follow automatically from the simple restriction to thermal equilibrium,
without the need for complicated thermodynamical or mechanical arguments.Comment: Minor corrections. 21 pages. To appear in New J. Phy
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