14,948 research outputs found
Gradient Echo Quantum Memory for Light using Two-level Atoms
We propose a quantum memory for light that is analogous to the NMR gradient
echo. Our proposal is ideally perfectly efficient and provides simplifications
to current 3-level quantum memory schemes based on controlled inhomogeneous
broadening. Our scheme does not require auxiliary light fields. Instead the
input optical pulse interacts only with two-level atoms that have linearly
increasing Stark shifts. By simply reversing the sign of the atomic Stark
shifts, the pulse is retrieved in the forward direction. We present analytical,
numerical and experimental results of this scheme. We report experimental
efficiencies of up to 15% and suggest simple realizable improvements to
significantly increase the efficiency.Comment: 4 pages, 4 figure
Cluster Production in Quark-Hadron Phase Transition
The problem of cluster formation and growth in first-order quark-hadron phase
transition in heavy-ion collisions is considered. Behaving as Brownian
particles, the clusters carry out random walks and can encounter one another,
leading to coalescence and breakup. A simulation of the process in cellular
automaton suggests the possibility of a scaling distribution in the cluster
sizes. The experimental determination of the cluster-size distribution is urged
as a means to find a clear signature of phase transition.Comment: 12 pages + 1 figure. Report # OITS-517. To be published in Phys. Rev.
Lett. 71, xxx (1994
Pulsed squeezed light: simultaneous squeezing of multiple modes
We analyze the spectral properties of squeezed light produced by means of
pulsed, single-pass degenerate parametric down-conversion. The multimode output
of this process can be decomposed into characteristic modes undergoing
independent squeezing evolution akin to the Schmidt decomposition of the
biphoton spectrum. The main features of this decomposition can be understood
using a simple analytical model developed in the perturbative regime. In the
strong pumping regime, for which the perturbative approach is not valid, we
present a numerical analysis, specializing to the case of one-dimensional
propagation in a beta-barium borate waveguide. Characterization of the
squeezing modes provides us with an insight necessary for optimizing homodyne
detection of squeezing. For a weak parametric process, efficient squeezing is
found in a broad range of local oscillator modes, whereas the intense
generation regime places much more stringent conditions on the local
oscillator. We point out that without meeting these conditions, the detected
squeezing can actually diminish with the increasing pumping strength, and we
expose physical reasons behind this inefficiency
Children's Use of Electronic Games: Choices of Game Mode and Challenge Levels
Introduction. Interactive electronic games are popular and are believed to contribute to physical activity accrual. The purpose of this study was to examine children's electronic game use during conditions in which they had free access to selecting interactive and seated screen-based versions of electronic games and during the interactive versions had free choice in making adjustments to the activity intensity. Methods. We systematically observed 60 Hong Kong primary school children during two 60-minute game sessions while simultaneously recording their game mode choices and physical activity levels using SOFIT (System for Observing Fitness Instruction Time). Results. When given free choice, children spent more than half of their available time participating in interactive versions of games. These versions of games provided significantly more moderate-to-vigorous physical activity and greater energy expenditure than the computer screen versions. Children with the opportunity to modify intensity levels spent more time playing the interactive versions and accrued more physical activity. Conclusions. The tenets of behavioral choice theory were supported. Access to new-generation interactive games, particularly those with modifiable intensity levels, may facilitate children's participation in physical activity
Quantum Noise Locking
Quantum optical states which have no coherent amplitude, such as squeezed
vacuum states, can not rely on standard readout techniques to generate error
signals for control of the quadrature phase. Here we investigate the use of
asymmetry in the quadrature variances to obtain a phase-sensitive readout and
to lock the phase of a squeezed vacuum state, a technique which we call noise
locking (NL). We carry out a theoretical derivation of the NL error signal and
the associated stability of the squeezed and anti-squeezed lock points.
Experimental data for the NL technique both in the presence and absence of
coherent fields are shown, including a comparison with coherent locking
techniques. Finally, we use NL to enable a stable readout of the squeezed
vacuum state on a homodyne detector.Comment: Accepted for publication in Journal of Optics:B special issue on
Quantum Contro
Self-aligned nanoscale SQUID on a tip
A nanometer-sized superconducting quantum interference device (nanoSQUID) is
fabricated on the apex of a sharp quartz tip and integrated into a scanning
SQUID microscope. A simple self-aligned fabrication method results in
nanoSQUIDs with diameters down to 100 nm with no lithographic processing. An
aluminum nanoSQUID with an effective area of 0.034 m displays flux
sensitivity of 1.8 \mu_B/\mathrm{Hz}^{1/2}$ and high bandwidth, the SQUID on a tip is a highly
promising probe for nanoscale magnetic imaging and spectroscopy.Comment: 14 manuscript pages, 5 figure
Quantum study of information delay in electromagetically induced transparency
Using electromagnetically induced transparency (EIT), it is possible to delay
and store light in atomic ensembles. Theoretical modelling and recent
experiments have suggested that the EIT storage mechanism can be used as a
memory for quantum information. We present experiments that quantify the noise
performance of an EIT system for conjugate amplitude and phase quadratures. It
is shown that our EIT system adds excess noise to the delayed light that has
not hitherto been predicted by published theoretical modelling. In analogy with
other continuous-variable quantum information systems, the performance of our
EIT system is characterised in terms of conditional variance and signal
transfer.Comment: 4 pages, 4 figure
Anxiety and depression with neurogenesis defects in exchange protein directly activated by cAMP 2-deficient mice are ameliorated by a selective serotonin reuptake inhibitor, Prozac
Intracellular cAMP and serotonin are important modulators of anxiety and depression. Fluoxetine, a selective serotonin reuptake inhibitor (SSRI) also known as Prozac, is widely used against depression, potentially by activating cAMP response element-binding protein (CREB) and increasing brain-derived neurotrophic factor (BDNF) through protein kinase A (PKA). However, the role of Epac1 and Epac2 (Rap guanine nucleotide exchange factors, RAPGEF3 and RAPGEF4, respectively) as potential downstream targets of SSRI/cAMP in mood regulations is not yet clear. Here, we investigated the phenotypes of Epac1 (Epac1â / â) or Epac2 (Epac2â / â) knockout mice by comparing them with their wild-type counterparts. Surprisingly, Epac2â / â mice exhibited a wide range of mood disorders, including anxiety and depression with learning and memory deficits in contextual and cued fear-conditioning tests without affecting Epac1 expression or PKA activity. Interestingly, rs17746510, one of the three single-nucleotide polymorphisms (SNPs) in RAPGEF4 associated with cognitive decline in Chinese Alzheimerâs disease (AD) patients, was significantly correlated with apathy and mood disturbance, whereas no significant association was observed between RAPGEF3 SNPs and the risk of AD or neuropsychiatric inventory scores. To further determine the detailed role of Epac2 in SSRI/serotonin/cAMP-involved mood disorders, we treated Epac2â / â mice with a SSRI, Prozac. The alteration in open field behavior and impaired hippocampal cell proliferation in Epac2â / â mice were alleviated by Prozac. Taken together, Epac2 gene polymorphism is a putative risk factor for mood disorders in AD patients in part by affecting the hippocampal neurogenesis.published_or_final_versio
Erratum : Squeezing and entanglement delay using slow light
An inconsistency was found in the equations used to calculate the variance of
the quadrature fluctuations of a field propagating through a medium
demonstrating electromagnetically induced transparency (EIT). The decoherence
term used in our original paper introduces inconsistency under weak probe
approximation. In this erratum we give the Bloch equations with the correct
dephasing terms. The conclusions of the original paper remain the same. Both
entanglement and squeezing can be delayed and preserved using EIT without
adding noise when the decoherence rate is small.Comment: 1 page, no figur
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