17,591 research outputs found
Tunneling Times and Superluminality: a Tutorial
Experiments have shown that individual photons penetrate an optical tunnel
barrier with an effective group velocity considerably greater than the vacuum
speed of light. The experiments were conducted with a two-photon parametric
down-conversion light source, which produced correlated, but random, emissions
of photon pairs. The two photons of a given pair were emitted in slightly
different directions so that one photon passed through the tunnel barrier,
while the other photon passed through the vacuum. The time delay for the
tunneling photon relative to its twin was measured by adjusting the path length
difference between the two photons in a Hong-Ou-Mandel interferometer, in order
to achieve coincidence detection. We found that the photon transit time through
the barrier was smaller than the twin photon's transit time through an equal
distance in vacuum, indicating that the process of tunneling in quantum
mechanics is superluminal. Various conflicting theories of tunneling times are
compared with experiment.Comment: 13 pages, Latex, 4 Figure
Proposed observations of gravity waves from the early Universe via "Millikan oil drops"
Pairs of Planck-mass drops of superfluid helium coated by electrons (i.e.,
``Millikan oil drops''), when levitated in a superconducting magnetic trap, can
be efficient quantum transducers between electromagnetic (EM) and gravitational
(GR) radiation. This leads to the possibility of a Hertz-like experiment, in
which EM waves are converted at the source into GR waves, and then
back-converted at the receiver from GR waves back into EM waves. Detection of
the gravity-wave analog of the cosmic microwave background using these drops
can discriminate between various theories of the early Universe.Comment: 10 pages, 2 figures, NASA "Quantum-to-Cosmos" conference proceedings
to be published in IJMP
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