Receiver, cryptographic key distribution system, method for controlling receiver, and control program

A method for controlling a receiver, the method comprising:

• modulating a phase of a reference light by using a reception base randomly assigned so as to correspond to a transmission base that is randomly assigned to each of a plurality of weak lights transmitted from a transmitter and received through a quantum communication path;
• causing the plurality of weak lights to be interfered with by the reference light the phase of which has been modulated, to thereby detect a plurality of pieces of bit information from each of the plurality of weak lights interfered with by the reference light in which a base value of the reception base matches that of the transmission base;
• extracting a plurality of pieces of bit information each having an amplitude component equal to or greater than a threshold from among the plurality of pieces of detected bit information;
• acquiring information about a weather forecast in an area where, among the quantum communication paths, a quantum communication path installed on the ground is present;
• predicting a load status of the receiver based on the information about a weather forecast;
• and
• adjusting the threshold in accordance with the predicted load status of the receiver.

A cryptographic key distribution system comprising:

• a transmitter;
• a receiver;
• and
• a quantum communication path provided between the transmitter and the receiver, wherein
• the transmitter comprises:
• at least one transmitting-side memory;
• and
• at least one transmitting-side processor coupled to the at least one transmitting-side memory,
• the at least one transmitting-side processor is configured to:
• generate a plurality of weak lights;
• and
• modulate phases of the plurality of weak lights one by one using bit information and a transmission base randomly selected in the transmitter, and transmit the plurality of weak lights the phases of which have been modulated to the receiver through the quantum communication path,
• the receiver comprises:
• at least one receiving-side memory;
• and
• at least one receiving-side processor coupled to the at least one receiving-side memory, and
• the at least one receiving-side processor is configured to:
• modulate a phase of a reference light by using a reception base randomly assigned in the receiver so as to correspond to a transmission base that is randomly assigned to each of the plurality of weak lights transmitted from the transmitter and received through the quantum communication path;
• cause the plurality of weak lights to be interfered with by the reference light the phase of which has been modulated, to thereby detect a plurality of pieces of bit information from each of the plurality of weak lights interfered with by the reference light in which a base value of the reception base matches that of the transmission base;
• extract a plurality of pieces of bit information each having an amplitude component equal to or greater than a threshold from among the plurality of pieces of detected bit information;
• acquire information about a weather forecast in an area where, among the quantum communication paths, a quantum communication path installed on the ground is present;
• predict a load status of the receiver based on the information about a weather forecast;
• and
• adjust the threshold in accordance with the predicted load status of the receiver.