Abstract: A quantum approach to the economically significant n-player public goods or similar n-player game requires only two-particle entanglement and is thus much easier to implement than games requiring n-particle entanglements. Two-particle entanglements are sufficient to give near optimal expected payoff when players use a simple mixed strategy for which no player can benefit by making different choices. This mechanism can also address some heterogeneous preferences among the players. Quantum games in accordance with the invention can be simulated on classical computers without requiring impractical amounts of processing power for large numbers of players.

Abstract: Various embodiments of the present invention are directed to methods and systems for circumventing, and altering transmission-channel users of, transmission-channel disruptions. In one embodiment of the present invention, a source encodes information in a first signal and transmits the first signal in a source channel to a multiplexer. The multiplexer distributes the first signal over N transmission channels. A demultiplexer combines the signals distributed over the N transmission channels into a second signal encoding of the information. The distribution system also includes a detector that receives the second signal output from the demultiplexer, and one or more detectors that receive one or more additional signals output from the demultiplexer. The additional signals are produced by the demultiplexer when a disruption occurs in one or more of the transmission channels and are used to alert transmission-channel users of the disruption.

Abstract: Nonlinear electromagnetic elements can efficiently implement quantum information processing tasks such as controlled phase shifts, non-demolition state detection, quantum subspace projections, non-demolition Bell state analysis, heralded state preparation, quantum non-demolition encoding, and fundamental quantum gate operations. Direct use of electromagnetic non-linearity can amplify small phase shifts and use feed forward systems in a near deterministic manner with high operating efficiency. Measurements using homodyne detectors can cause near deterministic projection of input states on a Hilbert subspace identified by the measurement results. Feed forward operation can then alter the projected state if desired to achieve a desired output state with near 100% efficiency.

Abstract: A method of verifying the position of a tagging device is described.

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: 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: 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: 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.