Circuit and method for controlling quality of random numbers

A system for receiving by a receiver of a quantum key distribution system in which a sender and the receiver are connected to each other through a transmission line, wherein the receiver comprises:

• a photodetector which receives optical pulses to detect a random-number signal from a first communication device through the transmission line to output a plurality of values of received random numbers, wherein the photodetector comprises a plurality of photodetectors each corresponding to the plurality of values, wherein the photodetector varies in reception efficiency depending on applied bias voltage, wherein the detected random numbers are used for the generation of a quantum key;
• a random-number quality monitor which monitors the quality of the received random numbers;
• and
• a controller which changes a reception efficiency of the photodetector based on the monitored quality of the received random numbers, wherein the controller controls the reception efficiency by independently adjusting respective bias voltages applied to the plurality of photodetectors.

A receiver of a quantum key distribution system for receiving a random-number signal, the receiver comprising:

• a photodetecting section which receives optical pulses to detect the random-number signal to output received random numbers, wherein the photodetecting section comprises a plurality of photodetectors each corresponding to a plurality of values included in the received random numbers, wherein the photodetecting section varies in reception efficiency depending on applied bias voltage, wherein the detected random numbers are used for the generation of a quantum key;
• a random-number quality monitor which monitors quality of the received random numbers;
• and
• a controller which changes a reception efficiency of the photodetecting section based on the monitored quality of the received random numbers, wherein the controller controls the reception efficiency by independently adjusting respective bias voltages applied to the plurality of photodetectors.

A method for receiving in a quantum key distribution system in which a sender and a receiver are connected to each other through a transmission line, the method comprising:

• receiving, by one of two communication devices, optical pulses to detect random numbers to separately output a plurality of values of the random numbers according to independent reception efficiencies for respective ones of the plurality of values, wherein the one of the two communication devices varies in reception efficiency depending on applied bias voltage, wherein the detected random numbers are used for the generation of a quantum key, wherein the one of the two communication devices comprises a plurality of photodetectors corresponding to the plurality of values;
• storing, by a memory device, a predetermined amount of received random numbers;
• generating, by the one of the two communication devices, a proportion of count of each of the plurality of values in the predetermined amount of received random numbers;
• and
• independently changing the independent reception efficiencies, by the one of the two communication devices, so as to bring the proportion closer to a desired value, wherein the one of the two communication devices controls the reception efficiency by independently adjusting respective bias voltages applied to the plurality of photodetectors.

A method for receiving in a quantum key distribution system in which a sender and a receiver are connected to each other through a transmission line, the method comprising:

• transmitting, by a first communication device, a random-number signal to a second communication device;
• sharing random numbers between the first communication device and the second communication device based on the random-number signal;
• receiving, by the second communication device, which includes a photodetecting section comprising a plurality of photodetectors each corresponding to the plurality of values, optical pulses to detect the random-number signal to output received random numbers, wherein the photodetecting section varies in reception efficiency depending on applied bias voltage, wherein the detected random numbers are used for the generation of a quantum key, wherein the photodetecting comprises a plurality of photodetectors corresponding to the plurality of values;
• monitoring, by a random number quality monitor, the quality of the received random numbers;
• and
• changing, by a reception efficiency changing device, a reception efficiency of the photodetecting section based on the monitored quality of the received random numbers, wherein the reception efficiency is changed by independently adjusting respective bias voltages applied to the plurality of photodetectors.

A method for receiving in a quantum key distribution system in which a sender and the receiver are connected through a transmission line, the method comprising:

• receiving, at a photodetecting section, optical pulses to detect the random-number signal to output received random numbers, the photodetecting section comprising a plurality of photodetectors each corresponding to a plurality of values included in the received random numbers, wherein a reception efficiency varies depending on applied bias voltage, wherein the detected random numbers are used for the generation of a quantum key;
• monitoring, by a random number quality monitor, quality of the received random numbers obtained from the detected random-number signal;
• and
• changing, by a reception efficiency changing device, the reception efficiency of the photodetecting section based on the monitored quality of the received random numbers, wherein the reception efficiency is changed by independently adjusting respective bias voltages applied to the plurality of photodetectors.

A non-transitory computer-readable storage medium storing a program containing instructions for instructing a computer to execute operations to receive in a quantum key distribution system, the operations comprising:

• receiving, at a photodetecting section, optical pulses to detect random numbers to separately output a plurality of values according to independent reception efficiencies for respective ones of the plurality of values, wherein the reception efficiencies vary depending on applied bias voltage, wherein detected random numbers are used for the generation of a quantum key, wherein the photodetecting section comprises a plurality of photodetectors corresponding to the plurality of values;
• storing a predetermined amount of received random numbers in a memory;
• generating a proportion of count of each of the plurality of values in the predetermined amount of received random numbers;
• and
• independently changing the independent reception efficiencies so as to bring the proportion closer to a desired value, wherein the reception efficiency is changed by independently adjusting respective bias voltages applied to the plurality of photodetectors.

A non-transitory computer-readable storage medium storing a program containing instructions for instructing a computer to execute operations to receiving in a quantum key distribution system through a transmission line, the operations comprising:

• receiving optical pulses to detect a random-number signal to output received random numbers at a photodetecting section which comprises a plurality of photodetectors each corresponding to a plurality of values included in the received random numbers, wherein reception efficiencies vary depending on applied bias voltage, wherein the received random numbers are used for the generation of a quantum key;
• monitoring quality of the received random numbers obtained from the detected random-number signal;
• and
• changing a reception efficiency of the photodetecting section based on the monitored quality of the received random numbers, wherein the reception efficiency is changed by independently adjusting respective bias voltages applied to the plurality of photodetectors.