In some semiconductor devices, such as light-emitting diodes, an applied voltage can dislodge electrons from some atoms, leaving behind a hole which behaves in some situations as if it were a positively charged particle in its own right.
A "current" of holes can move through the material and the holes can recombine later with electrons to produce light. In very loose analogy, James Franson (Johns Hopkins, 443-778-6226, james.franson@jhuapl.edu) suggests that photonic holes might be created; a photon hole, to give one example, would be a place in an otherwise intense laser-beam wavefront where a photon had been removed, for example by passing the laser beam through vapor.
Not only can there be photon holes, Franson suggests, but the holes can be entangled, meaning that their quantum properties would be correlated, even if far apart from each other. Such entangled photon-holes would be able to propagate through optical fibers just as well as entangled photons, but might be even more robust against the decoherence -- the undoing of the quantum correlations -- that plagues present efforts to establish quantum information schemes.
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