3,650 research outputs found
Quantum tunneling through vacuum-multiparticle induced potentials
The vacuum cavity mode induces a potential barrier and a well when an
ultra-slow excited atom enters the interaction region so that it can be
reflected or transmitted with a certain probability. We demonstrate here that a
slow-velocity excited particle tunnels freely through a vacuum electromagnetic
field mode filled with ground state atoms. The reason for this is the
trapping of the moving atom into its upper state due to multiparticle
influences and the corresponding decoupling from the interaction with the
environment such that the emitter does not {\it see} the induced potentials.Comment: Multiparticle samples, quantum tunneling, vacuum induced potential
Raman Adiabatic Transfer of Optical States
We analyze electromagnetically induced transparency and light storage in an
ensemble of atoms with multiple excited levels (multi-Lambda configuration)
which are coupled to one of the ground states by quantized signal fields and to
the other one via classical control fields. We present a basis transformation
of atomic and optical states which reduces the analysis of the system to that
of EIT in a regular 3-level configuration. We demonstrate the existence of dark
state polaritons and propose a protocol to transfer quantum information from
one optical mode to another by an adiabatic control of the control fields
Optimal quantum control of Bose Einstein condensates in magnetic microtraps
Transport of Bose-Einstein condensates in magnetic microtraps, controllable
by external parameters such as wire currents or radio-frequency fields, is
studied within the framework of optimal control theory (OCT). We derive from
the Gross-Pitaevskii equation the optimality system for the OCT fields that
allow to efficiently channel the condensate between given initial and desired
states. For a variety of magnetic confinement potentials we study transport and
wavefunction splitting of the condensate, and demonstrate that OCT allows to
drastically outperfrom more simple schemes for the time variation of the
microtrap control parameters.Comment: 11 pages, 7 figure
Using a qubit to measure photon number statistics of a driven, thermal oscillator
We demonstrate theoretically how photon number statistics of a driven, damped
oscillator at finite temperature can be extracted by measuring the dephasing
spectrum of a two-level system dispersively coupled to the oscillator; we thus
extend the work of Dykman (1987) and Gambetta et al. (2006). We carefully
consider the fidelity of this scheme-- to what extent does the measurement
reflect the initial number statistics of the mode? We also derive analytic
results for the dephasing of a qubit by a driven, thermal mode, and compare
results obtained at different levels of approximation. Our results have
relevance both to experiments in circuit cavity QED, as well as to
nano-electromechanical systems.Comment: 11 pages; 2 figures adde
Entanglement and State Preparation
When a subset of particles in an entangled state is measured, the state of
the subset of unmeasured particles is determined by the outcome of the
measurement. This first measurement may be thought of as a state preparation
for the remaining particles. In this paper, we examine how the duration of the
first measurement effects the state of the unmeasured subsystem. The state of
the unmeasured subsytem will be a pure or mixed state depending on the nature
of the measurement.
In the case of quantum teleportation we show that there is an eigenvalue
equation which must be satisfied for accurate teleportation. This equation
provides a limitation to the states that can be accurately teleported.Comment: 24 pages, 3 figures, submitted to Phys. Rev.
The second law, Maxwell's daemon and work derivable from quantum heat engines
With a class of quantum heat engines which consists of two-energy-eigenstate
systems undergoing, respectively, quantum adiabatic processes and energy
exchanges with heat baths at different stages of a cycle, we are able to
clarify some important aspects of the second law of thermodynamics. The quantum
heat engines also offer a practical way, as an alternative to Szilard's engine,
to physically realise Maxwell's daemon. While respecting the second law on the
average, they are also capable of extracting more work from the heat baths than
is otherwise possible in thermal equilibrium
A Bayesian Estimate of the Primordial Helium Abundance
We introduce a new statistical method to estimate the primordial helium
abundance, Y_p from observed abundances in a sample of galaxies which have
experienced stellar helium enrichment. Rather than using linear regression on
metal abundance we construct a likelihood function using a Bayesian prior,
where the key assumption is that the true helium abundance must always exceed
the primordial value. Using a sample of measurements compiled from the
literature we find estimates of Y_p between 0.221 and 0.236, depending on the
specific subsample and prior adopted, consistent with previous estimates either
from a linear extrapolation of the helium abundance with respect to
metallicity, or from the helium abundance of the lowest metallicity HII region,
I Zw 18. We also find an upper limit which is insensitive to the specific
subsample or prior, and estimate a model-independent bound Y_p < 0.243 at 95%
confidence, favoring a low cosmic baryon density and a high primordial
deuterium abundance. The main uncertainty is not the model of stellar
enrichment but possible common systematic biases in the estimate of Y in each
individual HII region.Comment: 14 pages, latex, 3 ps figure
Refractive Index Enhancement with Vanishing Absorption in an Atomic Vapor
We report a proof-of-principle experiment where the refractive index of an
atomic vapor is enhanced while maintaining vanishing absorption of the beam.
The key idea is to drive alkali atoms in a vapor with appropriate control
lasers and induce a gain resonance and an absorption resonance for a probe beam
in a two-photon Raman configuration. The strength and the position of these two
resonances can be manipulated by changing the parameters of the control lasers.
By using the interference between these two resonances, we obtain an enhanced
refractive index without an increase in the absorption.Comment: 11 pages, 4 figure
Dynamic optical bistability in resonantly enhanced Raman generation
We report observations of novel dynamic behavior in resonantly-enhanced
stimulated Raman scattering in Rb vapor. In particular, we demonstrate a
dynamic hysteresis of the Raman scattered optical field in response to changes
of the drive laser field intensity and/or frequency. This effect may be
described as a dynamic form of optical bistability resulting from the formation
and decay of atomic coherence. We have applied this phenomenon to the
realization of an all-optical switch.Comment: 4 pages, 5 figure
Platelet biology in regenerative medicine of skeletal muscle
Plateletâbased applications such as plateletârich plasma (PRP) and platelet releasate have gained unprecedented attention in regenerative medicine across a variety of tissues as of late. The rationale behind utilizing PRP originates in the delivery of key cytokines and growth factors from αâgranules to the targeted area, which in turn act as cell cycle regulators and promote the healing process across a variety of tissues. The aim of the present review is to assimilate current experimental evidence on the role of platelets as biomaterials in tissue regeneration, particularly in skeletal muscle, by integrating findings from human, animal and cell studies. This review is composed of 3 parts: firstly, we review key aspects of platelet biology that precede the preparation and use of plateletârelated applications for tissue regeneration. Secondly, we critically discuss relevant evidence on plateletâmediated regeneration in skeletal muscle focusing on findings from (i) clinical trials, (ii) experimental animal studies and (iii) cell culture studies; and thirdly, we discuss the application of platelets in the regeneration of several other tissues including tendon, bone, liver, vessels and nerve. Finally, we review key technical variations in platelet preparation that may account for the large discrepancy in outcomes from different studies. This review provides an upâtoâdate reference tool for biomedical and clinical scientists involved in plateletâmediated tissue regenerative applications
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