Patents by Inventor Akihisa Tomita

Akihisa Tomita has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 11502831
    Abstract: 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.
    Type: Grant
    Filed: August 31, 2017
    Date of Patent: November 15, 2022
    Assignees: NEC CORPORATION, NATIONAL INSTITUTE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY, National University Corporation Hokkaido University
    Inventors: Ken-ichiro Yoshino, Mikio Fujiwara, Masahide Sasaki, Akihisa Tomita
  • Patent number: 11362817
    Abstract: A quantum cryptographic key output apparatus includes a semiconductor laser device that repeatedly generates pulsed laser light, an encoder that encodes the pulsed laser light based on a quantum cryptographic key, an optical branching unit that branches the pulsed laser light, and an attenuator that attenuates a light intensity of first pulsed laser light so that the number of photons of the first pulsed laser light has any one of a plurality of candidate values that are values equal to or smaller than 1. Further, the output apparatus includes a light intensity determination unit that determines whether or not a light intensity of a second pulsed laser light is in a predetermined range, and an information output unit that outputs specifying information for specifying the first pulsed laser light corresponding to second pulsed laser light of which the light intensity is not in the predetermined range to an input apparatus.
    Type: Grant
    Filed: September 4, 2017
    Date of Patent: June 14, 2022
    Assignee: NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
    Inventors: Akihisa Tomita, Kensuke Nakata
  • Patent number: 11057201
    Abstract: A random number sequence generation apparatus includes: a semiconductor laser device repeatedly generating a pulsed laser beam having a disordered phase; an interferometer including a first transmission line and a second transmission line, a first port connected to an input terminal side and to which the pulsed laser beam is input, a second port connected to an output terminal side and outputs the pulsed laser beam, and a third port connected to the input terminal side; a Faraday mirror connected to the second port and reflecting the pulsed laser beam; a photodiode connected to the third port and outputs an electrical signal in accordance with interference light of the pulsed laser beam that is reflected by the Faraday mirror and passes through one of the transmission lines; and an AD converter configured to generate a random number sequence on the basis of the electrical signal and a threshold.
    Type: Grant
    Filed: February 3, 2017
    Date of Patent: July 6, 2021
    Assignee: NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
    Inventors: Akihisa Tomita, Kensuke Nakata
  • Publication number: 20190245685
    Abstract: 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.
    Type: Application
    Filed: August 31, 2017
    Publication date: August 8, 2019
    Applicants: NEC CORPORATION, NATIONAL INSTITUTE OF INFORMATION AND COMMUNICATION UNIVERSITY, NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
    Inventors: Ken-ichiro YOSHINO, Mikio FUJIWARA, Masahide SASAKI, Akihisa TOMITA
  • Publication number: 20190190707
    Abstract: A quantum cryptographic key output apparatus includes a semiconductor laser device that repeatedly generates pulsed laser light, an encoder that encodes the pulsed laser light based on a quantum cryptographic key, an optical branching unit that branches the pulsed laser light, and an attenuator that attenuates a light intensity of first pulsed laser light so that the number of photons of the first pulsed laser light has any one of a plurality of candidate values that are values equal to or smaller than 1. Further, the output apparatus includes a light intensity determination unit that determines whether or not a light intensity of a second pulsed laser light is in a predetermined range, and an information output unit that outputs specifying information for specifying the first pulsed laser light corresponding to second pulsed laser light of which the light intensity is not in the predetermined range to an input apparatus.
    Type: Application
    Filed: September 4, 2017
    Publication date: June 20, 2019
    Applicant: NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
    Inventors: Akihisa TOMITA, Kensuke NAKATA
  • Publication number: 20190044713
    Abstract: A random number sequence generation apparatus includes: a semiconductor laser device repeatedly generating a pulsed laser beam having a disordered phase; an interferometer including a first transmission line and a second transmission line, a first port connected to an input terminal side and to which the pulsed laser beam is input, a second port connected to an output terminal side and outputs the pulsed laser beam, and a third port connected to the input terminal side; a Faraday mirror connected to the second port and reflecting the pulsed laser beam; a photodiode connected to the third port and outputs an electrical signal in accordance with interference light of the pulsed laser beam that is reflected by the Faraday mirror and passes through one of the transmission lines; and an AD converter configured to generate a random number sequence on the basis of the electrical signal and a threshold.
    Type: Application
    Filed: February 3, 2017
    Publication date: February 7, 2019
    Applicant: NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
    Inventors: Akihisa TOMITA, Kensuke NAKATA
  • Patent number: 8509446
    Abstract: 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.
    Type: Grant
    Filed: December 28, 2010
    Date of Patent: August 13, 2013
    Assignees: National Institute of Information and Communications Technology, NEC Corporation
    Inventors: Mikio Fujiwara, Morio Toyoshima, Masahide Sasaki, Akihisa Tomita, Yoshihiro Nambu, Ken-ichiro Yoshino
  • Publication number: 20110170695
    Abstract: 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.
    Type: Application
    Filed: December 28, 2010
    Publication date: July 14, 2011
    Applicants: NATIONAL INSTITUTE OF INFORMATION AND COMMUNICATIONS TECHNOLOGY, NEC CORPORATION
    Inventors: Mikio FUJIWARA, Morio TOYOSHIMA, Masahide SASAKI, Akihisa TOMITA, Yoshihiro NAMBU, Ken-ichiro YOSHINO
  • Patent number: 7974540
    Abstract: A communication system capable of employing polarization-dependent phase modulators with a reversing configuration that preserves security against disturbance of a polarization state at a transmission path but without using Faraday mirrors and a communication method using the same are provided. A quantum cryptography system of the present invention includes a first station 1, a transmission path 2, and a second station 3. The first station 1 has means for emitting time-divided optical pulses into the transmission path 2 and measuring a phase difference between the optical pulses returning from the transmission path 2. The transmission path 2 is a medium of light.
    Type: Grant
    Filed: November 29, 2004
    Date of Patent: July 5, 2011
    Assignees: Japan Science and Technology Agency, NEC Corporation
    Inventors: Akihisa Tomita, Kazuo Nakamura, Akio Tajima, Akihiro Tanaka, Yoshihiro Nanbu, Shuuji Suzuki, Takeshi Takeuchi, Wakako Maeda, Seigo Takahashi
  • Patent number: 7583438
    Abstract: A quantum circuit and a quantum computer are capable of performing multi-bit quantum computation. In the quantum circuit, a quantum bit is represented by polarization directions of light, a sequence of polarized light pulses representing a quantum bit string is sequentially supplied to the quantum circuit, and an amount of polarization rotation and phase difference applied to a certain light pulse are determined on the basis of a result of a polarization measurement of a preceding input light pulse sequence, thus realizing a controlled-unitary transform. In addition, regarding the light pulses representing the quantum bits, the number of photons included in one pulse is larger than 1, resulting in a reduction of the influence of error.
    Type: Grant
    Filed: October 2, 2002
    Date of Patent: September 1, 2009
    Assignees: Japan Science and Technology Agency
    Inventor: Akihisa Tomita
  • Publication number: 20090031137
    Abstract: Signature requestor terminal device (10) codes a plurality of messages to a quantum state and transmits it to signer terminal device (20). Signer terminal device (20) issues a blind signature for the plurality of the messages coded to the quantum state, codes the messages and the signature to a quantum state and sends them back to signature requestor terminal device (10).
    Type: Application
    Filed: January 12, 2007
    Publication date: January 29, 2009
    Applicant: NEC CORORATION
    Inventors: Satoshi Ishizaka, Akihisa Tomita
  • Publication number: 20070110242
    Abstract: A communication system capable of employing polarization-dependent phase modulators with a reversing configuration that preserves security against disturbance of a polarization state at a transmission path but without using Faraday mirrors and a communication method using the same are provided. A quantum cryptography system of the present invention includes a first station 1, a transmission path 2, and a second station 3. The first station 1 has means for emitting time-divided optical pulses into the transmission path 2 and measuring a phase difference between the optical pulses returning from the transmission path 2. The transmission path 2 is a medium of light.
    Type: Application
    Filed: November 29, 2004
    Publication date: May 17, 2007
    Applicant: JAPAN SCIENCE AND TECHNOLOGY AGENCY
    Inventors: Akihisa Tomita, Kazuo Nakamura, Akio Tajima, Akihiro Tanaka, Yoshihiro Nanbu, Shuuji Suzuki, Takeshi Takeuchi, Wakako Maeda, Seigo Takahashi
  • Publication number: 20060208311
    Abstract: The present invention realizes a quantum circuit and a quantum computer capable of performing multi-bit quantum computation. A quantum bit is represented by the polarization directions of light, a sequence of polarized light pulses representing a quantum bit string is sequentially supplied, and the amount of polarization rotation applied to a certain light pulse and the amount of phase difference are determined on the basis of a result of the measurement of polarization of the preceding input light pulse sequence, thus realizing a controlled-unitary transform. In addition, regarding the light pulses representing the quantum bits, the number of photons included in one pulse is larger than 1, resulting in a reduction of the influence of error.
    Type: Application
    Filed: October 2, 2002
    Publication date: September 21, 2006
    Inventor: Akihisa Tomita
  • Patent number: 6895092
    Abstract: A cryptographic key distribution method, in which coherent light being suitable for optical fiber communication network is used and high security is secured, is provided. A sending end encodes random numbers so that symmetry probability distributions can be obtained at a receiving end, and also sets light intensity and a modulation index of signal light radiating from the sending end so that the SNR of an eavesdropper is less than 2 dB even when said eavesdropper uses a most suitable receiving equipment at the sending end, and also so that the SNR of the receiving end is more than ?10 dB, and transmits signals. The receiving end calculates probability distributions of obtained signals and sets a discrimination threshold value after a set of random numbers was transmitted from the sending end. When the probability distributions have some abnormal states, it is judged that the eavesdropper exists, and distributing the cryptographic key is stopped and a fresh cryptographic key is distributed again.
    Type: Grant
    Filed: August 21, 2001
    Date of Patent: May 17, 2005
    Assignee: NEC Corporation
    Inventor: Akihisa Tomita
  • Patent number: 6678379
    Abstract: A method for testing the reliability of a quantum key distribution apparatus is provided. The method includes the steps of: producing a set of quanta by the sender, the set of quanta comprising first, second, and third quantum, the first, second, and third quantum having a quantum correlation; measuring the first and second quantum at a sender using one of two prearranged bases; transmitting the third quantum to the receiver over the quantum channel; measuring the third quantum at a receiver using one of the two prearranged bases; and exchanging information regarding the measured bases between the sender and receiver over a public channel to check for a known behavior of the quantum apparatus based upon the quantum correlation, wherein if the quantum apparatus behaves as is known or within a tolerable limit the reliability of the quantum apparatus is confirmed. A similar method for quantum key distribution is also disclosed.
    Type: Grant
    Filed: June 18, 1999
    Date of Patent: January 13, 2004
    Assignee: NEC Corporation
    Inventors: Dominic Mayers, Yoshie Kohno, Yoshihiro Nambu, Akihisa Tomita
  • Patent number: 6665486
    Abstract: A single photon generating apparatus includes an optical waveguide, an active medium section and a resonator section. In the active medium section, a single electron is excited in response to application of exciting energy, and a single photon is emitted from the electron. The resonator section optically resonates with the active medium section, holds the photon emitted from the electron in the resonator, and transfers the held photon to the optical waveguide in response to a first control signal.
    Type: Grant
    Filed: February 14, 2001
    Date of Patent: December 16, 2003
    Assignee: NEC Corporation
    Inventor: Akihisa Tomita
  • Publication number: 20030002674
    Abstract: A quantum cryptography multi-node communication system includes a quantum communication channel and a plurality of nodes including a transmission node and a reception node and connected with the quantum communication channel. The transmission node transmits a light signal as a time series of photons to the reception node through the quantum communication channel, a quantum state of the photons is modulated, and transmits a quantum state sequence to the reception node. The reception node predetermines a quantum state sequence, receives the light signal transmitted from the transmission node, measures quantum states of the received light signal, and determines presence or absence of interception based on the predetermined quantum state sequence, the transmitted quantum state sequence and the measured quantum states.
    Type: Application
    Filed: June 28, 2002
    Publication date: January 2, 2003
    Applicant: NEC Corporation
    Inventors: Yoshihiro Nambu, Akihisa Tomita
  • Patent number: 6444999
    Abstract: With the object of providing a practical quantum circuit capable of discriminating Bell states in order to realize transmission of quantum states with high fidelity, a quantum circuit comprises: a two-photon absorbing crystal that selectively absorbs, in accordance with known selection rules, a photon pair of a Bell state that is determined depending on crystal symmetry of said two-photon absorbing crystal; a two-photon absorption detector that detects absorption of photon pairs by said two-photon absorbing crystal; and a polarization element that converts the Bell state of a polarized photon pair. The two-photon absorbing crystal makes two-photon absorption of a photon pair of a specific Bell state only. Electrons that have been excited by the two-photon absorption are detected by the detector.
    Type: Grant
    Filed: July 31, 2001
    Date of Patent: September 3, 2002
    Assignee: NEC Corporation
    Inventor: Akihisa Tomita
  • Publication number: 20020030186
    Abstract: With the object of providing a practical quantum circuit capable of discriminating Bell states in order to realize transmission of quantum states with high fidelity, a quantum circuit comprises: a two-photon absorbing crystal that selectively absorbs, in accordance with known selection rules, a photon pair of a Bell state that is determined depending on crystal symmetry of said two-photon absorbing crystal; a two-photon absorption detector that detects absorption of photon pairs by said two-photon absorbing crystal; and a polarization element that converts the Bell state of a polarized photon pair. The two-photon absorbing crystal makes two-photon absorption of a photon pair of a specific Bell state only. Electrons that have been excited by the two-photon absorption are detected by the detector. Use of the polarization element enables one-to-one conversion of one Bell state to another.
    Type: Application
    Filed: July 31, 2001
    Publication date: March 14, 2002
    Applicant: NEC Corporation
    Inventor: Akihisa Tomita
  • Publication number: 20020025041
    Abstract: A cryptographic key distribution method, in which coherent light being suitable for optical fiber communication network is used and high security is secured, is provided. A sending end encodes random numbers so that symmetry probability distributions can be obtained at a receiving end, and also sets light intensity and a modulation index of signal light radiating from the sending end so that the SNR of an eavesdropper is less than 2 dB even when said eavesdropper uses a most suitable receiving equipment at the sending end, and also so that the SNR of the receiving end is more than −10 dB, and transmits signals. The receiving end calculates probability distributions of obtained signals and sets a discrimination threshold value after a set of random numbers was transmitted from the sending end. When the probability distributions have some abnormal states, it is judged that the eavesdropper exists, and distributing the cryptographic key is stopped and a fresh cryptographic key is distributed again.
    Type: Application
    Filed: August 21, 2001
    Publication date: February 28, 2002
    Applicant: NEC CORPORATION
    Inventor: Akihisa Tomita