1,126 research outputs found
Quantum Communication and Computing With Atomic Ensembles Using Light-Shift Imbalance Induced Blockade
Recently, we have shown that for conditions under which the so-called
light-shift imbalance induced blockade (LSIIB) occurs, the collective
excitation of an ensemble of a multi-level atom can be treated as a closed two
level system. In this paper, we describe how such a system can be used as a
quantum bit (qubit) for quantum communication and quantum computing.
Specifically, we show how to realize a C-NOT gate using the collective qubit
and an easily accessible ring cavity, via an extension of the so-called
Pellizzari scheme. We also describe how multiple, small-scale quantum computers
realized using these qubits can be linked effectively for implementing a
quantum internet. We describe the details of the energy levels and transitions
in 87Rb atom that could be used for implementing these schemes.Comment: 16 pages, 9 figures. Accepted in Phys. Rev.
Determination of the phase of an electromagnetic field via incoherent detection of fluorescence
We show that the phase of a field can be determined by incoherent detection
of the population of one state of a two-level system if the Rabi frequency is
comparable to the Bohr frequency so that the rotating wave approximation is
inappropriate. This implies that a process employing the measurement of
population is not a square-law detector in this limit. We discuss how the
sensitivity of the degree of excitation to the phase of the field may pose
severe constraints on precise rotations of quantum bits involving low-frequency
transitions. We present a scheme for observing this effect in an atomic beam,
despite the spread in the interaction time.Comment: 4 pages, 2 fig
Fast-Light in a Photorefractive Crystal for Gravitational Wave Detection
We demonstrate superluminal light propagation using two frequency multiplexed
pump beams to produce a gain doublet in a photorefractive crystal of Ce:BaTiO3.
The two gain lines are obtained by two-wave mixing between a probe field and
two individual pump fields. The angular frequencies of the pumps are
symmetrically tuned from the frequency of the probe. The frequency difference
between the pumps corresponds to the separation of the two gain lines; as it
increases, the crystal gradually converts from normal dispersion without
detuning to an anomalously dispersive medium. The time advance is measured as
0.28 sec for a pulse propagating through a medium with a 2Hz gain separation,
compared to the same pulse propagating through empty space. We also demonstrate
directly anomalous dispersion profile using a modfied experimental
configuration. Finally, we discuss how anomalous dispersion produced this way
in a faster photorefractive crystal (such as SPS: Sn2P2S6) could be employed to
enhance the sensitivity-bandwidth product of a LIGO type gravitational wave
detector augmented by a White Light Cavity.Comment: 14 pages, 5 figure
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