3,137 research outputs found
Radiative coupling and weak lasing of exciton-polariton condensates
In spite of having finite life-time exciton-polaritons in microcavities are
known to condense at strong enough pumping of the reservoir. We present an
analytical theory of such Bose-condensates on a set of localized one-particle
states: condensation centers. To understand physics of these arrays one has to
supplement the Josephson coupling by the radiative coupling caused by the
interference of the light emitted by different centers. Combination of these
couplings with the one-site interaction between the bosons leads to a rich
nonlinear dynamics. In particular, a new regime of radiation appears. We call
it weak lasing: the centers have macroscopic occupations and radiate
coherently, but the coupling alone is sufficient for stabilization. The system
can have several stable states and switch between them. Moreover, the time
reversal symmetry in this regime is, as a rule, broken. A number of existing
experimental puzzles find natural interpretation in the framework of this
theory.Comment: 5 pages, 2 figure
Gaussian-State Theory of Two-Photon Imaging
Biphoton states of signal and idler fields--obtained from spontaneous
parametric downconversion (SPDC) in the low-brightness, low-flux regime--have
been utilized in several quantum imaging configurations to exceed the
resolution performance of conventional imagers that employ coherent-state or
thermal light. Recent work--using the full Gaussian-state description of
SPDC--has shown that the same resolution performance seen in quantum optical
coherence tomography and the same imaging characteristics found in quantum
ghost imaging can be realized by classical-state imagers that make use of
phase-sensitive cross correlations. This paper extends the Gaussian-state
analysis to two additional biphoton-state quantum imaging scenarios: far field
diffraction-pattern imaging; and broadband thin-lens imaging. It is shown that
the spatial resolution behavior in both cases is controlled by the nonzero
phase-sensitive cross correlation between the signal and idler fields. Thus,
the same resolution can be achieved in these two configurations with
classical-state signal and idler fields possessing a nonzero phase-sensitive
cross correlation.Comment: 14 pages, 5 figure
Experimental Quantum Imaging exploiting multi-mode spatial correlation of twin beams
Properties of quantum states have disclosed new and revolutionary
technologies, ranging from quantum information to quantum imaging. This last
field is addressed to overcome limits of classical imaging by exploiting
specific properties of quantum states of light. One of the most interesting
proposed scheme exploits spatial quantum correlations between twin beams for
realizing sub-shot-noise imaging of the weak absorbing objects, leading ideally
to a noise-free imaging. Here we discuss in detail the experimental realization
of this scheme, showing its capability to reach a larger signal to noise ratio
with respect to classical imaging methods and, therefore, its interest for
future practical applications
Duality Between Spatial and Angular Shift in Optical Reflection
We report a unified representation of the spatial and angular Goos-Hanchen
and Imbert-Fedorov shifts that occur when a light beam reflects from a plane
interface. We thus reveal the dual nature of spatial and angular shifts in
optical beam reflection. In the Goos-Hanchen case we show theoretically and
experimentally that this unification naturally arises in the context of
reflection from a lossy surface (e.g., a metal).Comment: 4 pages, 3 figure
Signal-to-noise ratio of Gaussian-state ghost imaging
The signal-to-noise ratios (SNRs) of three Gaussian-state ghost imaging
configurations--distinguished by the nature of their light sources--are
derived. Two use classical-state light, specifically a joint signal-reference
field state that has either the maximum phase-insensitive or the maximum
phase-sensitive cross correlation consistent with having a proper
representation. The third uses nonclassical light, in particular an entangled
signal-reference field state with the maximum phase-sensitive cross correlation
permitted by quantum mechanics. Analytic SNR expressions are developed for the
near-field and far-field regimes, within which simple asymptotic approximations
are presented for low-brightness and high-brightness sources. A high-brightness
thermal-state (classical phase-insensitive state) source will typically achieve
a higher SNR than a biphoton-state (low-brightness, low-flux limit of the
entangled-state) source, when all other system parameters are equal for the two
systems. With high efficiency photon-number resolving detectors, a
low-brightness, high-flux entangled-state source may achieve a higher SNR than
that obtained with a high-brightness thermal-state source.Comment: 12 pages, 4 figures. This version incorporates additional references
and a new analysis of the nonclassical case that, for the first time,
includes the complete transition to the classical signal-to-noise ratio
asymptote at high source brightnes
Decoherence-free preparation of Dicke states of trapped ions by collective stimulated Raman adiabatic passage
We propose a simple technique for the generation of arbitrary-sized Dicke
states in a chain of trapped ions. The method uses global addressing of the
entire chain by two pairs of delayed but partially overlapping laser pulses to
engineer a collective adiabatic passage along a multi-ion dark state. Our
technique, which is a many-particle generalization of stimulated Raman
adiabatic passage (STIRAP), is decoherence-free with respect to spontaneous
emission and robust against moderate fluctuations in the experimental
parameters. Furthermore, because the process is very rapid, the effects of
heating are almost negligible under realistic experimental conditions. We
predict that the overall fidelity of synthesis of a Dicke state involving ten
ions sharing two excitations should approach 98% with currently achievable
experimental parameters.Comment: 14 pages, 8 figure
Feelings of dual-insecurity among European workers: A multi-level analysis
This article analyses European Social Survey data for 22 countries. We assess the relationship between feelings of employment and income insecurity (dual-insecurity) among workers and national flexicurity policies in the areas of lifelong learning, active labour market policy, modern social security systems and flexible and reliable contractual arrangements. We find that dual-insecurity feelings are lower in countries that score better on most flexicurity polices, but these effects are in all cases outweighed by levels of GDP per capita. Thus feelings of insecurity are reduced more by the affluence of a country than by its social policies. However, affluence is strongly correlated with the policy efforts designed to reduce insecurity, especially active labour market policies and life-long learning, two policy areas that are threatened with cuts as a result of austerity
Robust creation of arbitrary-sized Dicke states using a single laser pulse
We propose a novel technique for the creation of maximally entangled
symmetric Dicke states in an ion trap using adiabatic passage, which requires
only a pair of chirped pulses from a single laser and is applicable to any
number of ions and excitations. By utilising a particular factorisation of the
Hilbert space for multi-level ladders we show that the problem can be reduced
to `bow-tie' configuration energy-level crossings. This technique is naturally
robust against fluctuations in the laser intensity and the chirp rate. Even
when realistic heating rates are considered, we estimate that the overall
fidelity should remain high (e.g. 98% for a ten-ion Dicke state), which
represents a significant improvement over traditional approaches.Comment: 5 pages, 4 figures. Minor changes. Journal Ref Adde
Photon-added coherent states as nonlinear coherent states
The states , defined as up to a
normalization constant and is a nonnegative integer, are shown to be the
eigenstates of where is a nonlinear
function of the number operator . The explicit form of
is constructed. The eigenstates of this operator for negative values of are
introduced. The properties of these states are discussed and compared with
those of the state .Comment: Rev Tex file with two figures as postscript files attached. Email:
[email protected]
Quantum Monte Carlo study of ring-shaped polariton parametric luminescence in a semiconductor microcavity
We present a quantum Monte Carlo study of the quantum correlations in the
parametric luminescence from semiconductor microcavities in the strong
exciton-photon coupling regime. As already demonstrated in recent experiments,
a ring-shaped emission is obtained by applying two identical pump beams with
opposite in-plane wavevectors, providing symmetrical signal and idler beams
with opposite in-plane wavevectors on the ring. We study the squeezing of the
signal-idler difference noise across the parametric instability threshold,
accounting for the radiative and non-radiative losses, multiple scattering and
static disorder. We compare the results of the complete multimode Monte Carlo
simulations with a simplified linearized quantum Langevin analytical model
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