591 research outputs found
Remote Macroscopic Entanglement on a Photonic Crystal Architecture
The outstanding progress in nanostructure fabrication and cooling
technologies allows what was unthinkable a few decades ago: bringing
single-mode mechanical vibrations to the quantum regime. The coupling between
photon and phonon excitations is a natural source of nonclassical states of
light and mechanical vibrations, and its study within the field of cavity
optomechanics is developing lightning-fast. Photonic crystal cavities are
highly integrable architectures that have demonstrated the strongest
optomechanical coupling to date, and should therefore play a central role for
such hybrid quantum state engineering. In this context, we propose a realistic
heralding protocol for the on-chip preparation of remotely entangled mechanical
states, relying on the state-of-the-art optomechanical parameters of a
silicon-based nanobeam structure. Pulsed sideband excitation of a Stokes
process, combined with single photon detection, allows writing a delocalised
mechanical Bell state in the system, signatures of which can then be read out
in the optical field. A measure of entanglement in this protocol is provided by
the visibility of a characteristic quantum interference pattern in the emitted
light.Comment: 8 pages, 5 Figure
The threshold criteria for the 75g oral glucose tolerance test in pregnancy and short-term adverse pregnancy outcomes
The significant threshold values for the 75g oGTT during pregnancy have yet to be conclusively determined. The study aims to identify the risk significance of a borderline oGTT result. Women undergoing a 75g OGTT during the third trimester of pregnancy were classified into two groups - borderline tolerance (2-h post-load glucose 8.0-8.5 mmol/l: n=75), and GDM (2:8.6 mmol/l: n=236). Outcome indicators of these two groups of women were compared to the parameters of the women with a presumed normal carbohydrate metabolism (n = 12185). GDM women showed themselves to be at a significantly increased risk of developing hypertensive disorders during pregnancy and to require obstetric intervention in the form of induction of labour and caesarean section. Their infants were more likely to be macrosomic or preterm and having a low Apgar score at birth. Shoulder dystocia was similarly more likely in infants born to GDM mothers. Women with borderline glucose tolerance did not in any way show any statistically significant increased predisposition to these complications. It would appear the significant threshold for the 75g oGTT during pregnancy should be of the order proposed by the American Diabetes Association criteria where the 2-hour post-load glucose value is 2: 8.6 mmol/l.peer-reviewe
Quantum complementarity of microcavity polaritons
We present an experiment that probes polariton quantum correlations by
exploiting quantum complementarity. Specifically, we find that polaritons in
two distinct idler-modes interfere if and only if they share the same
signal-mode so that "which-way" information cannot be gathered. The
experimental results prove the existence of polariton pair correlations that
store the "which-way" information. This interpretation is confirmed by a
theoretical analysis of the measured interference visibility in terms of
quantum Langevin equations
Thermodynamics and Excitations of Condensed Polaritons in Disordered Microcavities
We study the thermodynamic condensation of microcavity polaritons using a
realistic model of disorder in semiconductor quantum wells. This approach
correctly describes the polariton inhomogeneous broadening in the low density
limit, and treats scattering by disorder to all orders in the condensed regime.
While the weak disorder changes the thermodynamic properties of the transition
little, the effects of disorder in the condensed state are prominent in the
excitations and can be seen in resonant Rayleigh scattering.Comment: 5 pages, 3 eps figures (published version
Energy Relaxation in a 1-D Polariton Condensate
We study the kinetics of polariton condensation accounting for the
condensation process as well as the energy relaxation of condensed polaritons
due to their scattering with phonons and excitons. By assuming a Boltzmann
kinetic description of the scattering process, we show that intra-condensate
relaxation can be accounted for by an additional time-dependent term in the
Gross-Pitaevskii equation. As an example, we apply the formalism to the
experimental results recently obtained in polariton microwires [E. Wertz, et
al., Nature Phys. 6, 860 (2010)]. In the presence of a local non-resonant
optical pump, a dynamic balance between spatially dependent relaxation and
particle loss develops and excites a series of modes, roughly equally spaced in
energy. Upon comparison, excellent agreement is found with the experimental
data.Comment: 6 pages, 4 figure
Report on the radiometric analysis of the Ghar Dalam fossil specimens prepared for the Ghar Dalam Museum
Uranium is a radioactive element
emitting mainly alpha rays, but its daughter
elements Th and Ra are gamma ray
emitters. A high resolution gamma ray
spectrometry system can be used to determine
gamma-emitting radionuclides with energies
ranging from 1 keV to 10 MeV depending on
the type of detector in a large variety of sample
matrices. The simultaneous detection of
several gamma radionuclide emitters in the
sample material was carried out with a coaxial
germanium detector of high resolution
connected to a multichannel analyser.
Automatic processing of the collected spectral
data was controlled by a computer system with
selected software. Sources of error in the
technique may be caused by improper spectral
identities, changes in background, errors in
calibration and/or geometry, and lack of
homogeneity in samples. Since the samples
tested were not in a standardised geometry,
some variation in the readings could be
expected due to the difference in sample
homogeneity. The results obtained for the
various samples were standardised as a ratio
of 40K, on the assumption that the high
solubility of potassium salts would result in a
steady equilibrium in all samples.
Several fossil specimens kept in the Ghar
Dalam Museum were borrowed by courtesy of
Dr. G. Zammit Maempel. The specimens had
unfortunately no information as to the level
they were excavated from, and their
providence could not be reliably confirmed.peer-reviewe
Emergence of entanglement from a noisy environment: The case of polaritons
We show theoretically that polariton pairs with a high degree of polarization
entanglement can be produced through parametric scattering. We demonstrate that
it can emerge in coincidence experiments, even at low excitation densities
where the dynamics is dominated by incoherent photoluminesce. Our analysis is
based on a microscopic quantum statistical approach that treats coherent and
incoherent processes on an equal footing, thus allowing for a quantitative
assessment of the amount of entanglement under realistic experimental
conditions. This result puts forward the robustness of pair correlations in
solid-state devices, even when noise dominates one-body correlations.Comment: revised version. new figure
The new physics of non-equilibrium condensates: insights from classical dynamics
We discuss the dynamics of classical Dicke-type models, aiming to clarify the
mechanisms by which coherent states could develop in potentially
non-equilibrium systems such as semiconductor microcavities. We present
simulations of an undamped model which show spontaneous coherent states with
persistent oscillations in the magnitude of the order parameter. These states
are generalisations of superradiant ringing to the case of inhomogeneous
broadening. They correspond to the persistent gap oscillations proposed in
fermionic atomic condensates, and arise from a variety of initial conditions.
We show that introducing randomness into the couplings can suppress the
oscillations, leading to a limiting dynamics with a time-independent order
parameter. This demonstrates that non-equilibrium generalisations of polariton
condensates can be created even without dissipation. We explain the dynamical
origins of the coherence in terms of instabilities of the normal state, and
consider how it can additionally develop through scattering and dissipation.Comment: 10 pages, 4 figures, submitted for a special issue of J. Phys.:
Condensed Matter on "Optical coherence and collective phenomena in
nanostructures". v2: added discussion of links to exact solution
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