24 research outputs found
Stationary inversion of a two level system coupled to an off-resonant cavity with strong dissipation
We present an off-resonant excitation scheme that realizes pronounced
stationary inversion in a two level system. The created inversion exploits a
cavity-assisted two photon resonance to enhance the multi-photon regime of
nonlinear cavity QED and survives even in a semiconductor environment, where
the cavity decay rate is comparable to the cavity-dot coupling rate. Exciton
populations of greater than 0.75 are obtained in the presence of realistic
decay and pure dephasing. Quantum trajectory simulations and quantum master
equation calculations help elucidate the underlying physics and delineate the
limitations of a simplified rate equation model. Experimental signatures of
inversion and multi-photon cavity QED are predicted in the fluorescence
intensity and second-order correlation function measured as a function of drive
power.Comment: 4 page lette
Finite Size Effects in Thermal Field Theory
We consider a neutral self-interacting massive scalar field defined in a
d-dimensional Euclidean space. Assuming thermal equilibrium, we discuss the
one-loop perturbative renormalization of this theory in the presence of rigid
boundary surfaces (two parallel hyperplanes), which break translational
symmetry. In order to identify the singular parts of the one-loop two-point and
four-point Schwinger functions, we use a combination of dimensional and
zeta-function analytic regularization procedures. The infinities which occur in
both the regularized one-loop two-point and four-point Schwinger functions fall
into two distinct classes: local divergences that could be renormalized with
the introduction of the usual bulk counterterms, and surface divergences that
demand countertems concentrated on the boundaries. We present the detailed form
of the surface divergences and discuss different strategies that one can assume
to solve the problem of the surface divergences. We also briefly mention how to
overcome the difficulties generated by infrared divergences in the case of
Neumann-Neumann boundary conditions.Comment: 31 pages, latex, to appear in J. Math. Phy
Casimir forces in a T operator approach
We explore the scattering approach to Casimir forces. Our main tool is the
description of Casimir energy in terms of transition operators, as presented in
Kenneth and Klich, Phys. Rev. Lett. 97, 160401 (2006). We study the convergence
properties of the formula and how to utilize it, together with scattering data
to compute the force. We illustrate the approach by describing the force
between scatterers in 1d and 3d,, and in particular show how it may be applied
in order to study the interaction between two spherical bodies at all
distances
Quantum Radiation of a Uniformly Accelerated Refractive Body
We study quantum radiation generated by an accelerated motion of a small body
with a refractive index n which differes slightly from 1. To simplify
calculations we consider a model with a scalar massless field. We use the
perturbation expansion in a small parameter n-1 to obtain a correction to the
vacuum Hadamard function for a uniformly accelerated motion of the body. We
obtain the vacuum expectation for the energy density flux in the wave zone and
discuss its properties.Comment: 16 pages, 1 figur
Quantum Effects in the Presence of Expanding Semi-Transparent Spherical Mirrors
We study quantum effects in the presence of a spherical semi-transparent
mirror or a system of two concentric mirrors which expand with a constant
acceleration in a flat D-dimensional spacetime. Using the Euclidean approach,
we obtain expressions for fluctuations and the renormalized value of
stress-energy tensor for a scalar non-minimally coupled massless field.
Explicit expressions are obtained for the energy fluxes at the null infinity
generated by such mirrors in the physical spacetime and their properties are
discussed.Comment: 28 pages, Paper is slightly reorganized, additional references are
adde
Perturbations of Noise: The origins of Isothermal Flows
We make a detailed analysis of both phenomenological and analytic background
for the "Brownian recoil principle" hypothesis (Phys. Rev. A 46, (1992), 4634).
A corresponding theory of the isothermal Brownian motion of particle ensembles
(Smoluchowski diffusion process approximation), gives account of the
environmental recoil effects due to locally induced tiny heat flows. By means
of local expectation values we elevate the individually negligible phenomena to
a non-negligible (accumulated) recoil effect on the ensemble average. The main
technical input is a consequent exploitation of the Hamilton-Jacobi equation as
a natural substitute for the local momentum conservation law. Together with the
continuity equation (alternatively, Fokker-Planck), it forms a closed system of
partial differential equations which uniquely determines an associated
Markovian diffusion process. The third Newton law in the mean is utilised to
generate diffusion-type processes which are either anomalous (enhanced), or
generically non-dispersive.Comment: Latex fil