Abstract: A device capable of efficiently detecting a single-photon signal includes a matter system, sources of a first beam and a second beam, and a measurement system. The matter system has a first energy level and a second energy level such that a signal photon couples to a transition between the first energy level and the second energy level. The first beam contains photons that couple to a transition between the second energy level and a third energy level of the matter system, and the second beam contains photons that couple to a transition between the third energy level and a fourth energy level of the matter system. The measurement system measures a change in the first or second beam to detect the absence, the presence, or the number of the photons in the signal.

Abstract: Photon resolving detectors with near unit detection efficiency distinguish between a target state including n photons and a target state including n+1 photons by measuring a phase shift that a probe photon state receives in a quantum gate. The detection does not destroy the photons from the target state, so that photons can be used after detection. A system using a non-destructive detector in conjunction with one or more single photon storage systems can store a determined number of photons and release one or more stored photons when required to produce a photon state including a determined number of photons.

Abstract: A device capable of efficiently detecting a single-photon signal includes a matter system, sources of a first beam and a second beam, and a measurement system. The matter system has a first energy level and a second energy level such that a signal photon couples to a transition between the first energy level and the second energy level. The first beam contains photons that couple to a transition between the second energy level and a third energy level of the matter system, and the second beam contains photons that couple to a transition between the third energy level and a fourth energy level of the matter system. The measurement system measures a change in the first or second beam to detect the absence, the presence, or the number of the photons in the signal.

Abstract: Photon resolving detectors with near unit detection efficiency distinguish between a target state including n photons and a target state including n+1 photons by measuring a phase shift that a probe photon state receives in a quantum gate. The detection does not destroy the photons from the target state, so that photons can be used after detection. A system using a non-destructive detector in conjunction with one or more single photon storage systems can store a determined number of photons and release one or more stored photons when required to produce a photon state including a determined number of photons.

Abstract: A device capable of efficiently detecting a single-photon signal preserves a photon characteristic such as polarization or angular momentum. The device can include a beam splitter that splits an input photon state into modes that are distinguished by states of a characteristic of signal photons in the input photon state, a non-destructive measurement system capable of measuring a total number of photons in the modes without identifying a photon number for any individual one of the modes; and a beam combiner positioned to combine the modes after output from the non-destructive detection system.

Abstract: Quantum information processing structures and methods use photons and four-level matter systems in electromagnetically induced transparency (EIT) arrangements for one and two-qubit quantum gates, two-photon phase shifters, and Bell state measurement devices. For efficient coupling of the matter systems to the photons while decoupling the matter systems from the phonon bath, molecular cages or molecular tethers maintain the atoms within the electromagnetic field of the photon, e.g., in the evanescent field surrounding the core of an optical fiber carrying the photons. To reduce decoherence caused by spontaneous emissions, the matter systems can be embedded in photonic bandgap crystals or the matter systems can be selected to include metastable energy levels.