Nec Corporation

National Institute of Information and Communications Technology, Incorporated

Hokkaido University

The University of Tokyo

Ken-ichiro Yoshino

Akio Tajima

Takao Ochi

Akihisa Tomita

Mikio Fujiwara

Masahide Sasaki

Yoshihiro Nambu

Morio Toyoshima

Masato Koashi

Masahiro Takeoka

An object is to prevent eavesdropping in quantum key distribution. A photon detector outputs an output current indicating a result of detecting a quantum signal. A current-voltage conversion unit converts the output current into an output voltage signal. An analog-to-digital converter outputs an output voltage signal obtained by analog-digital conversion of the output voltage signal. A signal processing unit performs predetermined signal processing on the output voltage signal, and outputs a photon detection signal indicating a result of detecting the quantum signal. When a time difference between a timing at which the quantum signal is incident into the photon detector and a reference timing determined based on a clock signal is not within a determination range, the photon detection signal is not output from the signal processing unit.

Photon detection device, reception device, quantum key distribution system, and method for detecting quantum signal

A first device transmits a first random number to a second device through a first quantum channel, and receives a second random number from the second device through a second quantum channel. The first device generates a first encryption key based on the first random number and the second random number. The second device transmits the second random number to the first device through the second quantum channel, and receives the first random number from the first device through the first quantum channel. The second device generates a second encryption key based on the first random number and the second random number.

Encryption key generation

A random number supply device that generates three states required for operation of a signal processing unit from two-bit random number, includes a decision section decides whether a first random number generated by a first random number generator matches a predetermined value, and a control section supplies the signal processing unit with two-bit random number including the first random number by not using a second random number generated by a second random number generator when the first random number matches the predetermined value, and by using the second random number when the first random number does not match the predetermined value.

Random number supply method and device

A synthetic judgment section performs synthetic judgment of randomness test for shared random numbers by combining a result of a first randomness test and a result of a second randomness test, the first randomness test being performed on the shared random numbers by a first communication device and the second randomness test being performed on the shared random numbers by a second communication device wherein a result of the synthetic judgment is safely notified to at least one of the first communication device and the second communication device, wherein the first randomness test and the second randomness test are different with respect to at least one of randomness test to be used and random number portion to be tested.

Random number quality management method and apparatus

An optical sender is disclosed, which alone makes it possible to reliably decide whether modulation timing is correct or incorrect and to adjust the modulation timing. The optical sender includes: a first modulator that outputs a first optical pulse train subjected to intensity modulation; an asymmetric interferometer that outputs a second optical pulse train of double pulses; a second modulator () that outputs a third optical pulse train subjected to send-data modulation for each pulse pair; nd an optical intensity measuring device that measures an optical intensity of the third optical pulse train, a controller, when changing either of a first optical pulse train according to intensity modulation pattern and a second optical pulse train according to send-data modulation pattern, decides whether the modulation timing is correct or incorrect, based on optical intensity of the third optical pulse train.

Optical sender and method for deciding modulation timing correctness

An optical modulation method and device capable of stably generating an optical signal including a zero-intensity state among four states required for phase-time coding scheme by a nested modulator, is provided. A controller controls the phase difference generated by the phase shifter and an intensity and a magnitude of phase modulation provided by each of the first modulator and the second modulator to change an output lightwave of the nested modulator between four constellation points (S1-S4) on IQ plane. A first constellation point (S4) of the four constellation points has an intensity of 0, a second constellation point (S1) has a relative intensity of 1, each of a third constellation point (S2) and a fourth constellation point (S3) has a relative intensity ranging from 0 to 1, and the third and the fourth constellation points has a phase difference of 90 degrees.

Optical modulation method and device using nested optical modulator

A quantum key distribution device is provided with an encoding unit which encodes an optical pulse train; an intensity modulating unit which subjects the encoded optical pulse train to N (where N is an integer at least equal to 3) types of intensity modulation having mutually different intensities, with different timings; and a first key distillation processing unit which generates an encryption key on the basis of a data sequence obtained by removing data obtained from an optical pulse having a specific modulation pattern from a data sequence used by the encoding unit and the intensity modulating unit.

Transmitting device, receiving device, quantum key distribution method, and quantum key distribution program for quantum key distribution system

[Problem] A method, a device, a system and a program that can adjust the drive timing of a photon detector with high speed and high reliability is provided. [Solution] A timing adjustment device for adjusting timing for driving a photon detector () of a receiver (), includes: an asymmetric interferometer () that inputs an optical pulse sequence from a sender () and outputs an interference output optical pulse to the photon detector (), wherein the optical pulse sequence includes two consecutive pulses, the sender subjecting the two consecutive pulses to phase-modulation according to send data fixed to a predetermined bit value, wherein the interference output optical pulse is generated by the two consecutive pulses interfering with each other depending on a phase difference, and wherein the interference output optical pulse is output to the photon detector corresponding to the phase difference; and a controller () configured to: record photon counts of photons detected by the photon detector while shifting gate application timing for the photon detector over a predetermined range; and set gate application timing for the photon detector with reference to a timing indicating a peak value of the photon counts.

Drive-timing adjustment method and device for a photon detector, and optical communication system

In order to achieve the dispersion of a processing load between communication devices that perform information transmission, an information communication system according to an exemplary aspect of the present invention includes a first transmission system configured to transmit information in a direction from a first communication device to a second communication device; and a second transmission system configured to transmit information in a direction opposite to the direction of the first transmission system, wherein part of transmission information is received as received information in each of the first transmission system and the second transmission system.

Information communication system, information communication method and device

(Object) To provide an optical receiver and a control method thereof that enable equalization of both the quantum efficiencies and the dark count probabilities of multiple photon detectors. (Solving Means) An optical receiver includes multiple photon detectors, a first equalizing means that equalizes either dark count probabilities or quantum efficiencies of the multiple photon detectors, and a second equalizing means that equalizes the other ones without affecting the equalization by the first equalizing means.

Optical receiver and control method thereof

[Problem] It is to provide an optical receiving device, a control method and device of a photon detector, and a dark count evaluation method of the photon detector that make it possible to perform a dark count evaluation with the photon detector performing a receiving operation. [Solution] It is to include a Z pulse information detection unitand a control unitselectively extracting outputs of photon detectors PDand PDto a transmission light pulse with light intensity substantially equal to zero included in a transmission light pulse train and a dark count evaluation unitevaluating dark counts of the photon detectors based on photon detection counts indicated by the extracted outputs.

Optical receiving device in optical communication system, control method and device of photon detector, and dark count evaluation method of photon detector

It is an object of the present invention to provide a network system for quantum key distribution (QKD) for free space and fiber networks. The system of the present invention generates a couple of photons which have different wavelength and inputs each of the photons into the asymmetric Mach-Zehnder interferometer to obtain time-bin entangled state. It provides polarization information with one part of the photons. Then it can obtain hybrid quantum entanglement. The system of the present invention may be used hybrid quantum key distribution system applied for both free space and fibers.

Growing community of inventors

Tokyo, Japan

Ken-ichiro Yoshino