Quantum key distribution system and method
Method and system for transmitting optical clock signals and quantum key signals on a single optical channel. A multi-photon optical clock signal is received at an electro-optic switch at a first clock rate. The electro-optic switch may be configured for an interval defined by a second clock rate for generating a single photon quantum key signal. The multi-photon optical clock signal and the single photon quantum key signal are combined such that the single optical channel transmits the single photon quantum key signal at a first interval and the multi-photon optical clock signal at a second interval. The quantum key signal is transmitted from a transmitter at a first timing, and detected by a detector at a receiver. An output signal of the detector is sampled at a second timing that is delayed relative to the first timing for reducing quantum bit error rate.
1. A method for transmitting optical clock signals and quantum key signals on a single optical channel in a quantum key distribution system, the method comprising:
receiving a multi-photon optical clock signal at an electro-optic switch at a first clock rate;
configuring the electro-optic switch for an interval defined by a second clock rate for generating a single photon quantum key signal;
combining the multi-photon optical clock signal and the single photon quantum key signal to form a combined multi-photon optical clock signal and single photon quantum key signal; and
transmitting the combined multi-photon optical clock signal and single photon quantum key signal on the single optical channel, wherein the single optical channel transmits the single photon quantum key signal at a first time interval and transmits the multi-photon optical clock signal at a second time interval.
2. The method according to claim 1 , wherein the receiving, configuring and combining are performed at a transmitter, and wherein the transmitting comprises transmitting the combined multi-photon optical clock signal and single photon quantum key signal from the transmitter to a receiver on the single optical channel, wherein the transmitter and receiver are synchronized using the single optical channel.
3. The method according to claim 2 , wherein transmitting the combined multi-photon optical clock signal and single photon quantum key signal from the transmitter to a receiver on the single optical channel, comprises:
transmitting the combined multi-photon optical clock signal and single photon quantum key signal from the transmitter to the receiver on the single optical channel across free space.
4. The method according to claim 2 , and further comprising:
separating the combined multi-photon optical clock signal and single photon quantum key signal at the receiver;
sending the separated multi-photon optical clock signal to a clock recovery unit; and
sending the separated single photon quantum key signal to a single photon detector.
5. The method according to claim 4 , and further comprising:
synchronizing the transmitter and receiver using a correlation between a bit error rate of the single photon detector and a relative difference of addresses between the transmitter and the receiver.
6. The method according to claim 1 , and further comprising:
transmitting the second clock rate to the receiver via a wireless communications link to synchronize the transmitter and receiver.
7. The method according to claim 6 , and further comprising:
transmitting address information via the wireless communications link.
8. The method according to claim 1 , wherein the first clock rate is a GHz clock rate and the second clock rate is a MHz clock rate.
9. A quantum key distribution system, comprising:
a transmitter;
a receiver; and
a single optical channel for transmitting an optical clock signal and a quantum key signal from the transmitter to the receiver,
the transmitter comprising:
an optical source for generating an optical clock signal; and
a first electro-optic switch on the transmitter for receiving the optical clock signal at a first clock rate and configurable for generating a single photon quantum key signal from the optical clock signal for transmission on the single optical channel at a first time interval and configurable for transmitting the optical clock signal on the single optical channel at a second time interval; and
the receiver comprising:
a second electro-optic switch on the receiver for receiving the single photon quantum key signal and the optical clock signal, the second electro-optic switch configurable for directing the single photon quantum key signal to a single photon detector at the first time interval and configurable for directing the optical clock signal to a clock recovery unit at the second time interval.
10. The quantum key distribution system according to claim 9 , and further comprising:
a clock on the transmitter for transmitting frame frequency signals at a second clock rate to the first electro-optic switch on the transmitter and to the second electro-optic switch on the receiver, wherein the frame frequency signals are transmitted to the second electro-optic switch via a wireless communications link between the transmitter and the receiver.
11. The quantum key distribution system according to claim 10 , wherein the first clock rate is a GHz clock rate and the second clock rate is a MHz clock rate.
12. The quantum key distribution system according to claim 9 , wherein the single optical channel is across free space.
13. The quantum key distribution system according to claim 9 , wherein the optical clock signal comprises a multi-photon optical clock signal.
14. The quantum key distribution system according to claim 13 , wherein the second electro-optical switch is configured for separating the single photon quantum key signal and the multi-photon optical clock signal for directing the single photon quantum key signal to the single photon detector at the first time interval and for directing the multi-photon optical clock signal to the clock recovery unit at the second time interval.
15. A method for transmitting optical clock signals and quantum key signals on a single optical channel between a transmitter and a receiver in a quantum key distribution system, the method comprising:
combining a multi-photon optical clock signal and a single photon quantum key signal at the transmitter to provide a combined optical signal;
transmitting the combined optical signal from the transmitter to the receiver on the single optical channel, wherein the single photon quantum key signal is transmitted to the receiver at a first time interval and the multi-photon optical clock signal is transmitted to the receiver at a second time interval;
receiving the combined optical signal at the receiver;
separating the combined optical signal at the receiver to provide the multi-photon optical clock signal and the single photon quantum key signal at the receiver;
directing the single photon quantum key signal at the receiver to a single photon detector at the first time interval; and
directing the multi-photon optical clock signal at the receiver to a clock recovery unit at the second time interval.
16. The method according to claim 15 , wherein transmitting the combined optical signal from the transmitter to the receiver on the single optical channel, comprises:
transmitting the combined optical signal from the transmitter to the receiver on the single optical channel across free space.
17. The method according to claim 15 , wherein combining a multi-photon optical clock signal and a single photon quantum key signal at the transmitter to provide a combined optical signal, comprises:
receiving the multi-photon optical clock signal at an electro-optic switch at the transmitter at a first clock rate; and
configuring the electro-optic switch at the transmitter for an interval defined by a second clock rate for generating the single photon quantum key signal to provide the combined optical signal.
18. The method according to claim 17 , wherein separating the combined signal at the receiver to provide the multi-photon optical clock signal and the single photon quantum key signal at the receiver, comprises:
separating the combined signal at an electro-optic switch at the receiver.
19. The method according to claim 17 , and further comprising:
transmitting the second clock rate to the receiver via a wireless communications link to synchronize the transmitter and receiver.
20. The method according to claim 19 , and further comprising:
synchronizing the transmitter and receiver by use of a correlation between a bit error rate of the single photon detector and a relative difference of addresses between the transmitter and the receiver.
21. A method for reducing quantum bit error rate in a quantum key distribution system, the method comprising:
transmitting a quantum key signal from a transmitter to a receiver at a first timing;
detecting the transmitted quantum key signal by a detector at the receiver; and
sampling an output signal of the detector at a second timing that is delayed relative to the first timing, the second timing being delayed relative to the first timing such that a rise time of the output signal at a sampling time is contained inside a boundary defined by a preceding sampling time and a subsequent sampling time.
22. The method according to claim 21 , wherein transmitting a quantum key signal from a transmitter to a receiver at a first timing comprises:
transmitting the quantum key signal from the transmitter to the receiver across free space.
23. The method according to claim 21 , wherein the quantum key signal comprises a laser pulse train.
24. The method according to claim 23 , and further comprising:
generating the laser pulse train by a single mode Vertical Cavity Surface Emitting Laser driven by a data generator.
25. The method according to claim 21 , wherein detecting the transmitted quantum key signal by a detector at the receiver, comprises:
detecting the transmitted quantum key signal by a single photon detector at the receiver.
26. The method according to claim 21 , and further comprising:
analyzing the sampled output signal.
27. A quantum key distribution system, comprising:
a transmitter for transmitting a quantum key signal at a first timing, the transmitter comprising a photon source for generating the quantum key signal;
a receiver including a detector for detecting the transmitted quantum key signal; and
a sampling time delay mechanism for sampling an output signal of the detector at a second timing that is delayed relative to the first timing, wherein the sampling time delay mechanism delays the second timing relative to the first timing such that a rise time of the output signal at a sampling time is contained inside a boundary defined by a preceding sampling time and a subsequent sampling time.
28. The quantum key distribution system according to claim 27 , wherein the photon source comprises a laser driven by a data generator.
29. The quantum key distribution system according to claim 28 , wherein the laser comprises a single mode Vertical Cavity Surface Emitting Laser.
30. The quantum key distribution system according to claim 27 , wherein the sampling time delay mechanism comprises one of a hardware sampling time delay mechanism and a software sampling time delay mechanism.
31. The quantum key distribution system according to claim 30 , wherein the hardware sampling time delay mechanism comprises one of an electrical circuit and a physical delay line.
32. The quantum key distribution system according to claim 27 , wherein the transmitter transmits the quantum key signal to the receiver across free space.
33. The quantum key distribution system according to claim 27 , and further comprising:
an analyzer for analyzing the sampled output signal.
34. A method for reducing quantum bit error rate in a free space quantum key distribution system, the method comprising:
transmitting a quantum key signal from a transmitter across free space to a receiver at a first timing;
detecting the transmitted quantum key signal by a single photon detector at the receiver; and
sampling an output signal of the single photon detector at a second timing that is delayed relative to the first timing, wherein the second timing is delayed relative to the first timing such that a rise time of the output signal at a sampling time is contained inside a boundary defined by a preceding sampling time and a subsequent sampling time.
35. The method according to claim 34 , wherein the quantum key signal comprises a laser pulse train generated by a single mode Vertical Cavity Surface Emitting Laser driven by a data generator.
36. The method according to claim 34 , and further comprising:
analyzing the sampled output signal.