1,025 research outputs found
On quantum logic operations based on photon-exchange interactions in an ensemble of non-interacting atoms
The recently proposed idea to generate entanglement between photon states via
exchange interactions in an ensemble of atoms (J.D. Franson and T.B. Pitman,
Phys. Rev. A 60, 917 (1999) and J.D. Franson et al., (quant-ph/9912121)) is
discussed using an S-matix approach. It is shown that if the nonlinear response
of the atoms is negligible and no additional atom-atom interactions are
present, exchange interactions cannot produce entanglement between photons
states in a process that returns the atoms to their initial state. Entanglement
generation requires the presence of a nonlinear atomic response or atom-atom
interactions.Comment: 6 pages, no figure
Mirrorless oscillation based on resonantly enhanced 4-wave mixing: All-order analytic solutions
The phase transition to mirrorless oscillation in resonantly enhanced
four-wave mixing in double- systems are studied analytically for the
ideal case of infinite lifetimes of ground-state coherences. The stationary
susceptibilities are obtained in all orders of the generated fields and
analytic solutions of the coupled nonlinear differential equations for the
field amplitudes are derived and discussed.Comment: proceedings ICLPQO'99 (Shanghai 99), 10 pages, 4 figure
The one-dimensional Bose-Fermi-Hubbard model in the heavy-fermion limit
We study the phase diagram of the zero-temperature, one-dimensional
Bose-Fermi-Hubbard model for fixed fermion density in the limit of small
fermionic hopping. This model can be regarded as an instance of a disordered
Bose-Hubbard model with dichotomic values of the stochastic variables. Phase
boundaries between compressible, incompressible (Mott-insulating) and partially
compressible phases are derived analytically within a generalized
strong-coupling expansion and numerically using density matrix renormalization
group (DMRG) methods. We show that first-order correlations in the partially
compressible phases decay exponentially, indicating a glass-type behaviour.
Fluctuations within the respective incompressible phases are determined using
perturbation theory and are compared to DMRG results.Comment: 11 pages, 15 figures, 2nd, revised versio
Storing and releasing light in a gas of moving atoms
We propose a scheme of storing and releasing pulses or cw beams of light in a
moving atomic medium illuminated by two stationary and spatially separated
control lasers. The method is based on electromagnetically induced transparency
(EIT) but in contrast to previous schemes, storage and retrieval of the probe
pulse can be achieved at different locations and without switching off the
control laser.Comment: 4 pages, 3 figures, revised versio
Quantum limit of optical magnetometry in the presence of ac-Stark shifts
We analyze systematic (classical) and fundamental (quantum) limitations of
the sensitivity of optical magnetometers resulting from ac-Stark shifts. We
show that in contrast to absorption-based techniques, the signal reduction
associated with classical broadening can be compensated in magnetometers based
on phase measurements using electromagnetically induced transparency (EIT).
However due to ac-Stark associated quantum noise the signal-to-noise ratio of
EIT-based magnetometers attains a maximum value at a certain laser intensity.
This value is independent on the quantum statistics of the light and defines a
standard quantum limit of sensitivity. We demonstrate that an EIT-based optical
magnetometer in Faraday configuration is the best candidate to achieve the
highest sensitivity of magnetic field detection and give a detailed analysis of
such a device.Comment: 11 pages, 4 figure
Coherent Control of Stationary Light Pulses
We present a detailed analysis of the recently demonstrated technique to
generate quasi-stationary pulses of light [M. Bajcsy {\it et al.}, Nature
(London) \textbf{426}, 638 (2003)] based on electromagnetically induced
transparency. We show that the use of counter-propagating control fields to
retrieve a light pulse, previously stored in a collective atomic Raman
excitation, leads to quasi-stationary light field that undergoes a slow
diffusive spread. The underlying physics of this process is identified as pulse
matching of probe and control fields. We then show that spatially modulated
control-field amplitudes allow us to coherently manipulate and compress the
spatial shape of the stationary light pulse. These techniques can provide
valuable tools for quantum nonlinear optics and quantum information processing.Comment: 27 pages, 10 figure
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