US-12627479-B2 - Reception apparatus, transmission apparatus, quantum key distribution system, and peak position detection method

Abstract

The present disclosure includes a reception apparatus performing homodyne detection of a first beam transmitted from a transmission apparatus by using a second beam transmitted from the transmission apparatus and having an optical intensity higher than the first beam, and detecting a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection.

Inventors

• Shinya HIRASHITA

Assignees

• NEC CORPORATION

Dates

Publication Date

20260512

Application Date

20240126

Priority Date

20230201

Claims (7)

1. 1 . A reception apparatus comprising: at least one memory configured to store instructions; and at least one processor configured to execute the instructions to: cause the reception apparatus to receive a first beam and a second beam transmitted from a transmission apparatus, wherein the first beam is not modulated, and the first beam and the second beam are 90 degrees orthogonal to each other; perform homodyne detection of the first beam transmitted from the transmission apparatus by using the second beam transmitted from the transmission apparatus and having an optical intensity higher than the first beam; and detect a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection; and synchronize the transmission apparatus and the reception apparatus.
2. 2 . The reception apparatus according to claim 1 , wherein the at least one processor is further configured to execute the instructions to: take an absolute value of the amplitude of the signal obtained by the homodyne detection; and detect, as the peak position, a timing at which there is a local maximum in the amplitude of the signal that is the absolute value of the amplitude of the signal obtained by the homodyne detection.
3. 3 . The reception apparatus according to claim 1 , wherein the at least one processor is further configured to execute the instructions to: determine whether or not a magnitude of the amplitude at the detected peak position is greater than a predetermined threshold value; and store the peak position when it is determined that the magnitude of the amplitude at the peak position is greater than the predetermined threshold value; wherein, when it is determined that the magnitude of the amplitude at the peak position is equal to or lower than the predetermined threshold value, homodyne detection of the first beam, detection of the peak position, and determination of whether or not the magnitude of the amplitude at the peak position is greater than the predetermined threshold value are repeated.
4. 4 . The reception apparatus according to claim 2 , wherein the at least one processor is further configured to execute the instructions to: determine whether or not a magnitude of the amplitude at the detected peak position is greater than a predetermined threshold value; and store the peak position when it is determined that the magnitude of the amplitude at the peak position is greater than the predetermined threshold value; wherein, when it is determined that the magnitude of the amplitude at the peak position is equal to or lower than the predetermined threshold value, homodyne detection of the first beam, detection of the peak position, and determination of whether or not the magnitude of the amplitude at the peak position is greater than the predetermined threshold value are repeated.
5. 5 . A transmission apparatus comprising: a half-wave plate configured to polarize a first beam including light pulses for synchronizing the transmission apparatus with a reception apparatus, in a direction oriented at 90 degrees with respect to a second beam for homodyne detection of the first beam by the reception apparatus; and a polarizing beam splitter configured to combine, on the same optical axis, the first beam and the second beam, which are polarized in directions oriented at 90 degrees with respect to each other; wherein the transmission apparatus is configured to transmit light combining the first beam and the second beam on the same optical axis to the reception apparatus to synchronize the transmission apparatus and the reception apparatus, and wherein the first beam is not modulated.
6. 6 . A quantum key distribution system comprising the transmission apparatus and the reception apparatus according to claim 1 , wherein: the transmission apparatus is configured to transmit the first beam for synchronizing the transmission apparatus with the reception apparatus, and the second beam having an optical intensity higher than the first beam.
7. 7 . A peak position detection method comprising: receiving a first beam and a second beam transmitted from a transmission apparatus, wherein the first beam is not modulated, and the first beam and the second beam are 90 degrees orthogonal to each other; performing homodyne detection of the first beam transmitted from the transmission apparatus by using the second beam transmitted from the transmission apparatus and having an optical intensity higher than the first beam; and detecting a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection; and synchronizing the transmission apparatus and a reception apparatus.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is based upon and claims the benefit of priority from Japanese patent application No. 2023-013927, filed on Feb. 1, 2023, the disclosure of which is incorporated herein in its entirety by reference. TECHNICAL FIELD The present disclosure relates to a reception apparatus, a transmission apparatus, a quantum key distribution system, and a peak position detection method. BACKGROUND ART As one method for distributing encryption keys, continuous variable quantum key distribution is known (see, for example, Japanese Unexamined Patent Application Publication No. 2000-101570). When synchronizing a transmission apparatus with a reception apparatus in order to perform continuous variable quantum key distribution, it is preferable to be able to transmit and receive light for the purpose of synchronization by using a configuration for quantum key distribution without the need to provide a separate configuration for transmitting and receiving light, even in the case in which a sufficiently large amplitude for synchronizing the reception apparatus cannot be obtained with the light used for transmission of a signal beam by the transmission apparatus. SUMMARY An example of an object of the present disclosure is to provide a reception apparatus, a transmission apparatus, a quantum key distribution system, and a peak position detection method that can solve the problem mentioned above. According to a first example aspect of the present disclosure, a reception apparatus includes signal acquiring means for performing homodyne detection of a first beam transmitted from a transmission apparatus by using a second beam transmitted from the transmission apparatus and having an optical intensity higher than the first beam; and peak position detecting means for detecting a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection. According to a second example aspect of the present disclosure, a transmission apparatus includes a half-wave plate that polarizes a first beam, composed of light pulses for synchronizing the transmission apparatus with a reception apparatus, in a direction oriented at 90 degrees with respect to a second beam for homodyne detection of the first beam by the reception apparatus; and a polarizing beam splitter that combines, on the same optical axis, the first beam and the second beam, which are polarized in directions oriented at 90 degrees with respect to each other; wherein the transmission apparatus transmits light combining the first beam and the second beam on the same optical axis to the reception apparatus. According to a third example aspect of the present disclosure, a quantum key distribution system includes a transmission apparatus and a reception apparatus, wherein the transmission apparatus transmits a first beam for synchronizing the transmission apparatus with the reception apparatus, and a second beam having an optical intensity higher than the first beam, and the reception apparatus includes signal acquiring means for performing homodyne detection of the first beam by using the second beam, and peak position detecting means for detecting a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection. According to a fourth example aspect of the present disclosure, a peak position detection method includes steps of a reception apparatus performing homodyne detection of a first beam transmitted from a transmission apparatus by using a second beam transmitted from the transmission apparatus and having an optical intensity higher than the first beam; and detecting a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection. According to a fifth example aspect of the present disclosure, a program makes a computer that controls a reception apparatus execute a step of detecting a peak position, which is a timing at which there is a local maximum or a local minimum in an amplitude of a signal obtained by the homodyne detection of a first beam transmitted from a transmission apparatus by using a second beam transmitted from the transmission apparatus and having an optical intensity higher than the first beam. According to the present disclosure, when synchronizing a transmission apparatus with a reception apparatus in order to perform continuous variable quantum key distribution, light for the purpose of synchronization can be transmitted and received by using a configuration for quantum key distribution without the need to provide a separate configuration for transmitting and receiving light, even in the case in which a sufficiently large amplitude for synchronizing the reception apparatus cannot be obtained with the light used for transmission of a signal beam by the transmission