2,727 research outputs found
Ultra-bright omni-directional collective emission of correlated photon pairs from atomic vapors
Spontaneous four-wave mixing can generate highly correlated photon pairs from
atomic vapors. We show that multi-photon pumping of dipole-forbidden
transitions in a recoil-free geometry can result in ultra-bright pair-emission
in the full 4\pi solid angle, while strongly suppresses background Rayleigh
scattering and associated atomic heating, Such a system can produce photon
pairs at rates of ~ 10 ^12 per second, given only moderate optical depths of 10
~ 100, or alternatively, the system can generate paired photons with
sub-natural bandwidths at lower production rates. We derive a rate-equation
based theory of the collective atomic population and coherence dynamics, and
present numerical simulations for a toy model, as well as realistic model
systems based on 133 Cs and 171 Yb level structures. Lastly, we demonstrate
that dark-state adiabatic following (EIT) and/or timescale hierarchy protects
the paired photons from reabsorption as they propagate through an optically
thick sample
Condensation of N interacting bosons: Hybrid approach to condensate fluctuations
We present a new method of calculating the distribution function and
fluctuations for a Bose-Einstein condensate (BEC) of N interacting atoms. The
present formulation combines our previous master equation and canonical
ensemble quasiparticle techniques. It is applicable both for ideal and
interacting Bogoliubov BEC and yields remarkable accuracy at all temperatures.
For the interacting gas of 200 bosons in a box we plot the temperature
dependence of the first four central moments of the condensate particle number
and compare the results with the ideal gas. For the interacting mesoscopic BEC,
as with the ideal gas, we find a smooth transition for the condensate particle
number as we pass through the critical temperature.Comment: 6 pages, 4 figures, to appear in Phys. Rev. Let
Early Stage of Superradiance from Bose-Einstein Condensates
We investigate the dynamics of matter and optical waves at the early stage of
superradiant Rayleigh scattering from Bose-Einstein Condensates. Our analysis
is within a spatially dependent quantum model which is capable of providing
analytic solutions for the operators of interest. The predictions of the
present model are compared to the predictions of a closely related mean field
model, and we provide a procedure that allows one to calculate quantum
expectation values by averaging over semiclassical solutions. The coherence
properties of the outgoing scattered light are also analyzed, and it is shown
that the corresponding correlation functions may provide detailed information
about the internal dynamics of the system.Comment: 27 pages, 8 figure
Decoherence in a system of many two--level atoms
I show that the decoherence in a system of degenerate two--level atoms
interacting with a bosonic heat bath is for any number of atoms governed by
a generalized Hamming distance (called ``decoherence metric'') between the
superposed quantum states, with a time--dependent metric tensor that is
specific for the heat bath.The decoherence metric allows for the complete
characterization of the decoherence of all possible superpositions of
many-particle states, and can be applied to minimize the over-all decoherence
in a quantum memory. For qubits which are far apart, the decoherence is given
by a function describing single-qubit decoherence times the standard Hamming
distance. I apply the theory to cold atoms in an optical lattice interacting
with black body radiation.Comment: replaced with published versio
Analytical solution to position dependent mass Schr\"odinger equation
Using a recently developed technique to solve Schr\"odinger equation for
constant mass, we studied the regime in which mass varies with position i.e
position dependent mass Schr\"odinger equation(PDMSE). We obtained an
analytical solution for the PDMSE and applied our approach to study a position
dependent mass particle scattered by a potential . We
also studied the structural analogy between PDMSE and two-level atomic system
interacting with a classical field.Comment: 5 pages, 4 figure
Improved qubit bifurcation readout in the straddling regime of circuit QED
We study bifurcation measurement of a multi-level superconducting qubit using
a nonlinear resonator biased in the straddling regime, where the resonator
frequency sits between two qubit transition frequencies. We find that
high-fidelity bifurcation measurements are possible because of the enhanced
qubit-state-dependent pull of the resonator frequency, the behavior of
qubit-induced nonlinearities and the reduced Purcell decay rate of the qubit
that can be realized in this regime. Numerical simulations find up to a
threefold improvement in qubit readout fidelity when operating in, rather than
outside of, the straddling regime. High-fidelity measurements can be obtained
at much smaller qubit-resonator couplings than current typical experimental
realizations, reducing spectral crowding and potentially simplifying the
implementation of multi-qubit devices.Comment: 9 pages, 6 figure
Momentum transfer for momentum transfer-free which-path experiments
We analyze the origin of interference disappearance in which-path double
aperture experiments. We show that we can unambiguously define an observable
momentum transfer between the quantum particle and the path detector and we
prove in particular that the so called ``momentum transfer free'' experiments
can be in fact logically interpreted in term of momentum transfer.Comment: to appear in Phys. Rev . A (2006). (7 pages, 2 figures
Teleportation of entangled states without Bell-state measurement
In a recent paper [Phys. Rev. A 70, 025803 (2004)] we presented a scheme to
teleport an entanglement of zero- and one-photon states from a bimodal cavity
to another one, with 100% success probability. Here, inspired on recent results
in the literature, we have modified our previous proposal to teleport the same
entangled state without using Bell-state measurements. For comparison, the time
spent, the fidelity, and the success probability for this teleportation are
considered.Comment: 4 pages, 1 figure, published in Phys. Rev. A 72, 045802 (2005
Accuracy of a teleported trapped field state inside a single bimodal cavity
We propose a simplified scheme to teleport a superposition of coherent states
from one mode to another of the same bimodal lossy cavity. Based on current
experimental capabilities, we present a calculation of the fidelity that can be
achieved, demonstrating accurate teleportation if the mean photon number of
each mode is at most 1.5. Our scheme applies as well for teleportation of
coherent states from one mode of a cavity to another mode of a second cavity,
both cavities embedded in a common reservoir.Comment: 4 pages, 2 figures, in appreciation for publication in Physical
Review
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