645 research outputs found
Violations of a new inequality for classical fields
Two entangled photons incident upon two distant interferometers can give a coincidence counting rate that depends nonlocally on the sum of the phases of the two interferometers. It has recently been shown that experiments of this kind may violate a simple inequality that must be satisfied by any classical or semi-classical field theory. The inequality provides a graphic illustration of the lack of objective realism of the electric field. The results of a recent experiment which violates this inequality and in which the optical path length between the two interferometers was greater than 100 m are briefly described
Nonclassical Nature of Dispersion Cancellation and Nonlocal Interferometry
Several recent papers have shown that some forms of dispersion cancellation
have classical analogs and that some aspects of nonlocal two-photon
interferometry are consistent with local realistic models. It is noted here
that the classical analogs only apply to local dispersion cancellation
experiments [A.M. Steinberg et al., Phys. Rev. Lett. 68, 2421 (1992)] and that
nonlocal dispersion cancellation [J.D. Franson, Phys. Rev. A 45, 3126 (1992)]
is inconsistent with any classical field theory and has no classical analog.
The local models that have been suggested for two-photon interferometry are
shown to be local but not realistic if the spatial extent of the
interferometers is taken into account. It is the inability of classical models
to describe all of the relevant aspects of these experiments that distinguishes
between quantum and classical physics, which is also the case in Bell's
inequality.Comment: 10 pages, 8 figures; minor revisions, to appear in Phys. Rev.
Cyclical Quantum Memory for Photonic Qubits
We have performed a proof-of-principle experiment in which qubits encoded in
the polarization states of single-photons from a parametric down-conversion
source were coherently stored and read-out from a quantum memory device. The
memory device utilized a simple free-space storage loop, providing a cyclical
read-out that could be synchronized with the cycle time of a quantum computer.
The coherence of the photonic qubits was maintained during switching operations
by using a high-speed polarizing Sagnac interferometer switch.Comment: 4 pages, 5 figure
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