66 research outputs found
Positioning and clock synchronization through entanglement
A method is proposed to employ entangled and squeezed light for determining
the position of a party and for synchronizing distant clocks. An accuracy gain
over analogous protocols that employ classical resources is demonstrated and a
quantum-cryptographic positioning application is given, which allows only
trusted parties to learn the position of whatever must be localized. The
presence of a lossy channel and imperfect photodetection is considered. The
advantages in using partially entangled states is discussed.Comment: Revised version. 9 pages, 6 figure
Spatial coherence and density correlations of trapped Bose gases
We study first and second order coherence of trapped dilute Bose gases using
appropriate correlation functions. Special attention is given to the discussion
of second order or density correlations. Except for a small region around the
surface of a Bose-Einstein condensate the correlations can be accurately
described as those of a locally homogeneous gas with a spatially varying
chemical potential. The degrees of first and second order coherence are
therefore functions of temperature, chemical potential, and position. The
second order correlation function is governed both by the tendency of bosonic
atoms to cluster and by a strong repulsion at small distances due to atomic
interactions. In present experiments both effects are of comparable magnitude.
Below the critical temperature the range of the bosonic correlation is affected
by the presence of collective quasi-particle excitations. The results of some
recent experiments on second and third order coherence are discussed. It is
shown that the relation between the measured quantities and the correlation
functions is much weaker than previously assumed.Comment: RevTeX, 25 pages with 7 Postscript figure
Macroscopic superpositions of Bose-Einstein condensates
We consider two dilute gas Bose-Einstein condensates with opposite velocities
from which a monochromatic light field detuned far from the resonance of the
optical transition is coherently scattered. In the thermodynamic limit, when
the relative fluctuations of the atom number difference between the two
condensates vanish, the relative phase between the Bose-Einstein condensates
may be established in a superposition state by detections of spontaneously
scattered photons, even though the condensates have initially well-defined atom
numbers. For a finite system, stochastic simulations show that the measurements
of the scattered photons lead to a randomly drifting relative phase and drive
the condensates into entangled superpositions of number states. This is because
according to Bose-Einstein statistics the scattering to an already occupied
state is enhanced.Comment: 18 pages, RevTex, 5 postscript figures, 1 MacBinary eps-figur
Homodyne detection for measuring internal quantum correlations of optical pulses
A new method is described for determining the quantum correlations at
different times in optical pulses by using balanced homodyne detection. The
signal pulse and sequences of ultrashort test pulses are superimposed, where
for chosen distances between the test pulses their relative phases and
intensities are varied from measurement to measurement. The correlation
statistics of the signal pulse is obtained from the time-integrated difference
photocurrents measured.Comment: 7 pages, A4.sty include
Fractional transport equations for Levy stable processes
The influence functional method of Feynman and Vernon is used to obtain a
quantum master equation for a Brownian system subjected to a Levy stable random
force. The corresponding classical transport equations for the Wigner function
are then derived, both in the limit of weak and strong friction. These are
fractional extensions of the Klein-Kramers and the Smoluchowski equations. It
is shown that the fractional character acquired by the position in the
Smoluchowski equation follows from the fractional character of the momentum in
the Klein-Kramers equation. Connections among fractional transport equations
recently proposed are clarified.Comment: 4 page
Floquet-Markov description of the parametrically driven, dissipative harmonic quantum oscillator
Using the parametrically driven harmonic oscillator as a working example, we
study two different Markovian approaches to the quantum dynamics of a
periodically driven system with dissipation. In the simpler approach, the
driving enters the master equation for the reduced density operator only in the
Hamiltonian term. An improved master equation is achieved by treating the
entire driven system within the Floquet formalism and coupling it to the
reservoir as a whole. The different ensuing evolution equations are compared in
various representations, particularly as Fokker-Planck equations for the Wigner
function. On all levels of approximation, these evolution equations retain the
periodicity of the driving, so that their solutions have Floquet form and
represent eigenfunctions of a non-unitary propagator over a single period of
the driving. We discuss asymptotic states in the long-time limit as well as the
conservative and the high-temperature limits. Numerical results obtained within
the different Markov approximations are compared with the exact path-integral
solution. The application of the improved Floquet-Markov scheme becomes
increasingly important when considering stronger driving and lower
temperatures.Comment: 29 pages, 7 figure
Nonclassical Fields and the Nonlinear Interferometer
We demonstrate several new results for the nonlinear interferometer, which
emerge from a formalism which describes in an elegant way the output field of
the nonlinear interferometer as two-mode entangled coherent states. We clarify
the relationship between squeezing and entangled coherent states, since a weak
nonlinear evolution produces a squeezed output, while a strong nonlinear
evolution produces a two-mode, two-state entangled coherent state. In between
these two extremes exist superpositions of two-mode coherent states manifesting
varying degrees of entanglement for arbitrary values of the nonlinearity. The
cardinality of the basis set of the entangled coherent states is finite when
the ratio is rational, where is the nonlinear strength. We
also show that entangled coherent states can be produced from product coherent
states via a nonlinear medium without the need for the interferometric
configuration. This provides an important experimental simplification in the
process of creating entangled coherent states.Comment: 21 pages, 2 figure
Flux to a trap
The flux of particles to a single trap is investigated for two systems: (1) particles in 3D space which jump a fixed step length l (the Rayleigh flight) and are adsorbed by a spherical surface, and (2) particles on a lattice, jumping to nearest neighbor sites, with a single adsorbing site. Initially, the particles are uniformly distributed outside the traps. When the jump length goes to zero, both processes go over to regular diffusion, and the first case yields the diffusive flux to a sphere as solved by Smoluchowski. For nonzero step length, the flux for large times is given by a modified form of Smoluchowski's result, with the effective radius replaced by R-cl , where c =0.29795219 and cl is the Milne extrapolation length for this problem. For the second problem, a similar expression for the flux is found, with the effective trap radius a function of the lattice (sc, bcc, fcc) being considered.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45165/1/10955_2005_Article_BF01049608.pd
Über eine Klasse polynomialer Scharen selbstadjungierter Operatoren im Hilbertraum
HEK293A cells expressing either mouse MOG (mMOG) or rat MOG (rMOG) C terminally tagged with EGFP. (DOCX 2792Â kb
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