Quantum cryptography key distribution system and method
AssigneeNEC Corporation
InventorsYoshihiro Nambu, Toshiyuki Kambe
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Abstract
In a quantum cryptography key distribution system for sharing a secret key between a transmitter and a receiver site, an unbalanced interferometer system in the transmitter site has a Mach-Zehnder interferometer switch with a phase modulator while the receiver site records photon arrival time slots. The system utilizes a whole of arrival photons in the receiver site and dispenses with any phase modulator in the receiver site. This system serves to improve a photon utilization efficiency.
Claims32
A quantum cryptography key distribution system for use in sharing a secret key between a transmitter site and a receiver site on the basis of a quantum cryptography key distribution protocol of four non-orthogonal states that are represented by superposition of quantum wave packet states each consisting of a single photon with different time and space characteristics, the transmitter site comprising:
- an unbalanced interferometer system having two different optical paths, a light splitting portion, and a light coupling portion;
- and
- a Mach-Zehnder interferometer switch which is located at either one of the light splitting portion and the light coupling portion and which includes a phase modulator;
- the receiving comprising:
- photon detectors;
- and
- a recording device for recording photon detection times at which the photon is received by each of the photon detectors.
A transmitter site for use in a quantum cryptography key distribution system to transmit a quantum signal to a receiver site by using four non-orthogonal states of single photons, the transmitter site comprising:
- an unbalanced interferometer system having two different optical paths, a light splitting portion, and a light coupling portion;
- and
- a Mach-Zehnder interferometer switch which is located at either one of the light splitting portion and the light coupling portion and which includes a phase modulator;
- and
- an output device for outputting, as the quantum signal, each single photon that is subjected to phase modulation by the phase modulator and that is specified by single photon packet states different in time and space from one another and determined by the phase modulation.
A method of transmitting a quantum signal in the form of a single photon from a transmitter site to a receiver site, the single photon being specified by single photon packet states that are non-orthogonal to one another, comprising the steps of:
- phase modulating a light pulse by phase modulation values by a phase modulator included in the transmitter site to produce two light output signals subjected to the phase modulation and different in amplitude from each other;
- allowing the two light output signal to pass through a long arm and a short arm of an unbalanced interferometer system to obtain the single photon that is determined by the phase modulation values and the long and the short arms and that are different in time and space from one another;
- and
- producing each of the signal photons as the quantum signal.
A method of transmitting a quantum signal in the form of a single photon from a transmitter site to a receiver site, the single photon being specified by single photon packet states that are non-orthogonal to one another, comprising the steps of:
- allowing a light pulse to pass through a long arm and a short arm of an unbalanced interferometer system to obtain light output pulses different in time from each other;
- phase modulating the light output pulses by phase modulation values by a phase modulator included in the transmitter site to produce the single photon that is determined by the phase modulation values and the long and the short arms and that is specified by the single photon packet states.
Dependencies are inferred from the claim text.