4,732 research outputs found
Scalable quantum information processing with atomic ensembles and flying photons
We present a scheme for scalable quantum information processing (QIP) with
atomic ensembles and flying photons. Using the Rydberg blockade, we encode the
qubits in the collective atomic states, which could be manipulated fast and
easily due to the enhanced interaction, in comparison to the single-atom case.
We demonstrate that our proposed gating could be applied to generation of
two-dimensional cluster states for measurement-based quantum computation.
Moreover, the atomic ensembles also function as quantum repeaters useful for
long distance quantum state transfer. We show the possibility of our scheme to
work in bad cavity or in weak coupling regime, which could much relax the
experimental requirement. The efficient coherent operations on the ensemble
qubits enable our scheme to be switchable between quantum computation and
quantum communication using atomic ensembles.Comment: 8 pages, 7 figure
Constraining the Mass of the Photon with Gamma-Ray Bursts
One of the cornerstones of modern physics is Einstein's special relativity,
with its constant speed of light and zero photon mass assumptions. Constraint
on the rest mass m_{\gamma} of photons is a fundamental way to test Einstein's
theory, as well as other essential electromagnetic and particle theories. Since
non-zero photon mass can give rise to frequency-(or energy-) dependent
dispersions, measuring the time delay of photons with different frequencies
emitted from explosive astrophysical events is an important and
model-independent method to put such a constraint. The cosmological gamma-ray
bursts (GRBs), with short time scales, high redshifts as well as broadband
prompt and afterglow emissions, provide an ideal testbed for m_{\gamma}
constraints. In this paper we calculate the upper limits of the photon mass
with GRB early time radio afterglow observations as well as multi-band radio
peaks, thus improve the results of Schaefer (1999) by nearly half an order of
magnitude.Comment: 25 pages, 2 tables, Accepted by Journal of High Energy Astrophysic
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