3,152 research outputs found
Quantum Coherence and Correlations of optical radiation by atomic ensembles interacting with a two-level atom in microwave cavity
We examine quantum statistics of optical photons emitted from atomic
ensembles which are classically driven and simultaneously coupled to a
two-level atom via microwave photon exchange. Quantum statistics and
correlations are analyzed by calculating second order coherence degree, von
Neumann entropy, spin squeezing for multi-particle entanglement, as well as
genuine two and three-mode entanglement parameters for steady state and
non-equilibrium situations. Coherent transfer of population between the
radiation modes and quantum state mapping between the two-level atom and the
optical modes are discussed. A potential experimental realization of the
theoretical results in a superconducting coplanar waveguide resonator
containing diamond crystals with Nitrogen-Vacancy color centers and a
superconducting artificial two-level atom is discussed.Comment: 15 pages, 17 figures, submitted to Phys. Rev.
Emergent Radiation in an Atom-Field System at Twice-Resonance
A two-level atom interacting with a single mode of quantized electromagnetic
radiation is discussed using a representation in which the atom and the
radiation are unified into a {\em new} canonical radiation. At the {\em
twice-resonance}, when the frequency of the original radiation is twice the
atomic transition frequency (), the {\em emergent} unified
field in the non-interacting atom-field system resembles a free radiation of
frequency . This free emergent radiation is further shown to exist in
the presence of an interaction which looks similar to the atom-field
interaction in the dipole approximation. The one-photon correlation and the
population inversion are discussed as the possible means of observing the
emergent radiation. The entanglement properties of the emergent radiation are
also discussed.Comment: 4+ pages, 2 figures, submitted for publication; included a discussion
on the entanglemen
Multimode quantum limits to the linewidth of an atom laser
The linewidth of an atom laser can be limited by excitation of higher energy
modes in the source Bose-Einstein condensate, energy shifts in that condensate
due to the atomic interactions, or phase diffusion of the lasing mode due to
those interactions. The first two are effects that can be described with a
semiclassical model, and have been studied in detail for both pumped and
unpumped atom lasers. The third is a purely quantum statistical effect, and has
been studied only in zero dimensional models. We examine an unpumped atom laser
in one dimension using a quantum field theory using stochastic methods based on
the truncated Wigner approach. This allows spatial and statistical effects to
be examined simultaneously, and the linewidth limit for unpumped atom lasers is
quantified in various limits.Comment: 8 Figure
Shot noise spectrum of superradiant entangled excitons
The shot noise produced by tunneling of electrons and holes into a double dot
system incorporated inside a p-i-n junction is investigated theoretically. The
enhancement of the shot noise is shown to originate from the entangled
electron-hole pair created by superradiance. The analogy to the superconducting
cooper pair box is pointed out. A series of Zeno-like measurements is shown to
destroy the entanglement, except for the case of maximum entanglement.Comment: 5 pages, 3 figures, to appear in Phys. Rev. B (2004
Quantum optical effective-medium theory for loss-compensated metamaterials
A central aim in metamaterial research is to engineer sub-wavelength unit
cells that give rise to desired effective-medium properties and parameters,
such as a negative refractive index. Ideally one can disregard the details of
the unit cell and employ the effective description instead. A popular strategy
to compensate for the inevitable losses in metallic components of metamaterials
is to add optical gain material. Here we study the quantum optics of such
loss-compensated metamaterials at frequencies for which effective parameters
can be unambiguously determined. We demonstrate that the usual effective
parameters are insufficient to describe the propagation of quantum states of
light. Furthermore, we propose a quantum-optical effective-medium theory
instead and show that it correctly predicts the properties of the light
emerging from loss-compensated metamaterials.Comment: 6 pages, 3 figures. Accepted for Physical Review Letter
Spatial Correlation Functions of one-dimensional Bose gases at Equilibrium
The dependence of the three lowest order spatial correlation functions of a
harmonically confined Bose gas on temperature and interaction strength is
presented at equilibrium. Our analysis is based on a stochastic Langevin
equation for the order parameter of a weakly-interacting gas. Comparison of the
predicted first order correlation functions to those of appropriate mean field
theories demonstrates the potentially crucial role of density fluctuations on
the equilibrium coherence length. Furthermore,the change in both coherence
length and shape of the correlation function, from gaussian to exponential,
with increasing temperature is quantified. Moreover, the presented results for
higher order correlation functions are shown to be in agreeement with existing
predictions. Appropriate consideration of density-density correlations is shown
to facilitate a precise determination of quasi-condensate density profiles,
providing an alternative approach to the bimodal density fits typically used
experimentally
Phase modulation induced by cooperative effects in electromagnetically induced transparency
We analyze the influence of dipole-dipole interactions in an
electromagnetically induced transparency setup at high density. We show both
analytically and numerically that the polarization contribution to the local
field strongly modulates the phase of a weak pulse. We give an intuitive
explanation for this local field induced phase modulation and show that it
distinctively differs from the nonlinear self-phase modulation a strong pulse
experiences in a Kerr medium
Optically-Induced Polarons in Bose-Einstein Condensates: Monitoring Composite Quasiparticle Decay
Nonresonant light-scattering off atomic Bose-Einstein condensates (BECs) is
predicted to give rise to hitherto unexplored composite quasiparticles:
unstable polarons, i.e., local ``impurities'' dressed by virtual phonons.
Optical monitoring of their spontaneous decay can display either Zeno or
anti-Zeno deviations from the Golden Rule, and thereby probe the temporal
correlations of elementary excitations in BECs.Comment: 4 pages, 3 figure
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