All-Optical Switching Using the Quantum Zeno Effect and Two-Photon Absorption

We have previously shown that the quantum Zeno effect can be used to implement quantum logic gates for quantum computing applications, where the Zeno effect was produced using a strong two-photon absorbing medium. Here we show that the Zeno effect can also be used to implement classical logic gates whose inputs and outputs are high-intensity fields (coherent states). The operation of the devices can be understood using a quasi-static analysis, and their switching times are calculated using a dynamic approach. The two-photon absorption coefficient of rubidium vapor is shown to allow operation of these devices at relatively low power levels.Comment: 21 pages, 11 figures. Submitted to Phys. Rev.

Sensitivity of entangled photon holes to loss and amplification

Energy-time entangled photon holes are shown to be relatively insensitive to photon loss due to absorption by atoms whose coherence times are longer than the time delays typically employed in nonlocal interferometry (a fraction of a nanosecond). Roughly speaking, the excited atoms do not retain any significant "which-path" information regarding the time at which a photon was absorbed. High-intensity entangled photon holes can also be amplified under similar conditions. Decoherence does occur from losses at beam splitters, and these results show that photon loss cannot always be adequately modeled using a sequence of beam splitters. These properties of entangled photon holes may be useful in quantum communications systems where the range of the system is limited by photon loss.Comment: 10 pages, 6 figure

Investigation of a single-photon source based on quantum interference

We report on an experimental investigation of a single-photon source based on a quantum interference effect first demonstrated by Koashi, Matsuoka, and Hirano [Phys. Rev. A 53, 3621 (1996)]. For certain types of measurement-based quantum information processing applications this technique may be useful as a high rate, but random, source of single photons.Comment: Submitted to the New J. Phys. Focus Issue on "Measurement-based quantum information processing

Time-bin entangled photon holes

The general concept of entangled photon holes is based on a correlated absence of photon pairs in an otherwise constant optical background. Here we consider the specialized case when this background is confined to two well-defined time bins, which allows the formation of time-bin entangled photon holes. We show that when the typical coherent state background is replaced by a true single-photon (Fock state) background, the basic time-bin entangled photon-hole state becomes equivalent to one of the time-bin entangled photon-pair states. We experimentally demonstrate these ideas using a parametric down-conversion photon-pair source, linear optics, and post-selection to violate a Bell inequality with time-bin entangled photon holes.Comment: 6 pages, 5 figure