Abstract: Differential phase shift (DPS) quantum key distribution (QKD) is provided, where the average number of photons per transmitted pulse is predetermined such that the secure key generation rate is maximal or nearly maximal, given other system parameters. These parameters include detector quantum efficiency, channel transmittance and pulse spacing (or clock rate). Additional system parameters that can optionally be included in the optimization include baseline error rate, sifted key error rate, detector dead time, detector dark count rate, and error correction algorithm performance factor. The security analysis leading to these results is based on consideration of a hybrid beam splitter and intercept-resend attack.

Abstract: Differential phase shift (DPS) quantum key distribution (QKD) is provided, where the average number of photons per transmitted pulse is predetermined such that the secure key generation rate is maximal or nearly maximal, given other system parameters. These parameters include detector quantum efficiency, channel transmittance and pulse spacing (or clock rate). Additional system parameters that can optionally be included in the optimization include baseline error rate, sifted key error rate, detector dead time, detector dark count rate, and error correction algorithm performance factor. The security analysis leading to these results is based on consideration of a hybrid beam splitter and intercept-resend attack.

Abstract: A system and method for quantum key distribution uses a regulated single-photon source to sequentially generate a first photon and a second photon separated by a time interval ?t. The two photons are directed through a beam splitter that directs each photon to one of two transmission lines, which lead to two respective receivers. When one of the photons arrives at a receiver, it passes through an interferometer. One arm of the interferometer has a path length longer than the other arm by an amount equivalent to a photon time delay of ?t. The photon is then detected in one of three time slots by one of two single-photon detectors associated with each of the two interferometer outputs. Due to quantum-mechanical entanglement in phase and time between the two photons, the receivers can determine a secret quantum key bit value from their measurements of the time slots in which the photons arrived, or of the detectors where the photons arrived.

Abstract: A system and method for quantum key distribution uses a regulated single-photon source to sequentially generate a first photon and a second photon separated by a time interval ?t. The two photons are directed through a beam splitter that directs each photon to one of two transmission lines, which lead to two respective receivers. When one of the photons arrives at a receiver, it passes through an interferometer. One arm of the interferometer has a path length longer than the other arm by an amount equivalent to a photon time delay of ?t. The photon is then detected in one of three time slots by one of two single-photon detectors associated with each of the two interferometer outputs. Due to quantum-mechanical entanglement in phase and time between the two photons, the receivers can determine a secret quantum key bit value from their measurements of the time slots in which the photons arrived, or of the detectors where the photons arrived.

Abstract: An optical device is presented which is useful for optical signal transmission and switching systems by multiplexing and demultiplexing optical signals in looped optical paths, consisting of a plurality of individual loop-back optical paths. The device is essentially a multi/demultiplexer having an arrayed waveguide grating disposed between a plurality of input sections and output sections which are joined by the plurality of individual loop-back optical paths. Because the modulated signals are looped back into the same optical paths using the same devices, problems of mismatching performance introduced by using different optical devices are avoided. The device processes individual optical signals of different wavelengths, minimizes splitting losses, and reduces noise components by producing narrow bandpass signals of high signal to noise ratio. Optical signal splitting and insertion, delay line memory and delay equalization circuits can all be handled by the same circuit configuration.