Quantum dense coding system

• US 7,330,653 B1
• Filed: 11/15/2004
• Issued: 02/12/2008
• Est. Priority Date: 11/15/2004
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Roberts, Mark W., Lasher, Markham E.
• Primary Examiner(s): Vanderpuye; Kenneth
• Assistant Examiner(s): Liu; Li
• Application Number:
  US10/989,139
• Time in Patent Office: 1,184 Days
• Field of Search: 398/39, 398/40, 398/152, 398/158, 398/183, 398/184, 398/192, 398/202, 398/208, 398/140, 380/44, 380/256, 380/260, 380277-283, 380/255, 359/108, 359/330, 372/21, 372/102, 356/450
• US Class Current: 398/40
• CPC Class Codes: H04B 10/70 Photonic quantum communication

Abstract

A Quantum Dense Coding System. The system includes a source, a transmitter and a receiver. The source is capable of down-converting a pump photon into a signal photon and an idler photon and outputting probability amplitudes, the signal photon and the idler photon, wherein the signal photon and the idler photon have an equal probability of outputting to a transmission channel and a reception channel. The transmitter is capable of receiving probability amplitudes, signal photons and idler photons from the transmission channel; and selectively changing vertical and horizontal phases of probability amplitudes of signal photons and idler photons; and outputting probability amplitudes, signal photons and idler photons. The receiver is capable of receiving probability amplitudes, signal photons and idler photons from the reception channel and the transmitter; and identifying vertical and horizontal phase changes created by the transmitter. A method for the system is also described.

Claims

1. A Quantum Dense Coding System, comprising:

a) a source, capable of down-converting a pump photon into a signal photon and an idler photon that have a common frequency, capable of time separating said signal photon and said idler photon so that said signal photon and said idler photon do not overlap in said QDCS, and capable of outputting probability amplitudes, said signal photon and said idler photon, wherein said signal photon and said idler photon have an equal probability of outputting to a transmission channel and a reception channel;

b) a transmitter, operatively coupled to said source, capable of receiving probability amplitudes, signal photons and idler photons from said transmission channel, capable of selectively changing vertical and horizontal phases of probability amplitudes, signal photons and idler photons, and capable of outputting probability amplitudes, signal photons and idler photons;

c) a receiver, operatively coupled to said transmitter and said source, capable of receiving probability amplitudes, signal photons and idler photons from said reception channel and said transmitter, and capable of identifying vertical and horizontal phase changes created by said transmitter.

2. The system of claim 1, wherein said source and said receiver are collocated, and wherein said source and said transmitter are not collocated.

3. The system of claim 1, wherein said transmitter is capable of transmitting two bits of information corresponding to four messages, wherein a first message comprises +H+V, a second message comprises −

H+V, a third message comprises +H−

V and a fourth message comprises −

H−

V.

4. The system of claim 1, wherein said transmitter is capable of selectively changing vertical and horizontal phases of probability amplitudes of signal photons and idler photons by zero degrees and 180 degrees.

5. The system of claim 1, wherein said source comprises:

i) a continuous wave laser, capable of outputting pump photons;

ii) a nonlinear crystal, operatively coupled to said continuous wave laser, capable of receiving and down-converting said pump photon into said signal photon and said idler photon;

iii) a first 50/50 amplitude beam splitter, operatively coupled to said nonlinear crystal, capable of receiving said signal photon and said idler photon, capable of outputting probability amplitudes, said signal photon and said idler photon to said transmission channel and said reception channel, wherein said signal photon and said idler photon have an equal probability of outputting to said transmission channel and said reception channel.

6. The system of claim 5, wherein said source further comprises a wavelength selective mirror, operatively coupled to said nonlinear crystal and said first 50/50 amplitude beam splitter, capable of receiving said signal photon and said idler photon from said nonlinear crystal, capable of reflecting said pump photon into a beamstop, and capable of transmitting said signal photon and said idler photon to said first 50/50 amplitude beam splitter.

7. The system of claim 5, wherein said nonlinear crystal comprises a configuration capable of down-converting via non-collinear, type I or type II phase matching.

8. The system of claim 5, wherein said nonlinear crystal comprises a configuration capable of down-converting via collinear, degenerate, type II phase matching.

9. The system of claim 1, wherein said transmitter comprises:

i) a first transmitter polarizing beam splitter, operatively coupled to said transmission channel, capable of receiving said probability amplitudes, said signal photon and said idler photon via said transmission channel, capable of transmitting said idler photon and said probability amplitudes having horizontal polarization, and capable of reflecting said signal photon and said probability amplitudes having vertical polarization;

ii) a horizontal phase controller, operatively coupled to said first transmitter polarizing beam splitter, capable of receiving said idler photon and said probability amplitudes having horizontal polarization, capable of selectively changing a phase of said idler photon and said probability amplitudes having horizontal polarization, and capable of outputting said idler photon and said probability amplitudes having horizontal polarization;

iii) a vertical phase controller, operatively coupled to said first transmitter polarizing beam splitter, capable of receiving said signal photon and said probability amplitudes having vertical polarization, capable of selectively changing a phase of said signal photon and said probability amplitudes having vertical polarization, and capable of outputting said signal photon and said probability amplitudes having vertical polarization;

iv) a second transmitter polarizing beam splitter, operatively coupled to said horizontal phase controller and said vertical phase controller, capable of receiving said probability amplitudes, said signal photon and said idler photon, and capable of outputting said probability amplitudes, said signal photon and said idler photon to said receiver.

10. The system of claim 9, wherein said transmitter further comprises mirrors, operatively coupled to said vertical phase controller, said horizontal phase controller and said second transmitter polarizing beam splitter, capable of receiving and reflecting said probability amplitudes, said signal photon and said idler photon from said vertical phase controller and said horizontal phase controller to said second transmitter polarizing beam splitter.

11. The system of claim 9, wherein said horizontal phase controller selectively changes said phase of said idler photons and said probability amplitudes having horizontal polarization by setting a fast axis of said horizontal phase controller horizontally or setting a slow axis of said horizontal phase controller horizontally.

12. The system of claim 9, wherein said vertical phase controller selectively changes said phase of said signal photons and said probability amplitudes having vertical polarization by setting a fast axis of said vertical phase controller vertically or setting a slow axis of said vertical phase controller vertically.

13. The system of claim 1, wherein said receiver comprises:

i) a second amplitude beam splitter, operatively coupled to said reception channel and said transmitter, capable of receiving said probability amplitudes, said signal photon and said idler photon via said reception channel and said transmitter, capable of recombining V phase amplitudes and H phase amplitudes of signal and idler photons, capable of transmitting signal and idler photons having recombined V phase amplitudes and H phase amplitudes in phase to a plus channel, and capable of reflecting signal and idler photons having recombined V phase amplitudes and H phase amplitudes out of phase to a minus channel;

ii) a first receiver polarizing beam splitter, operatively coupled to said second amplitude beam splitter, capable of receiving said idler photon and said signal photon via said plus channel, capable of transmitting horizontally polarized photons to a first detector, and capable of reflecting vertically polarized photons to a second detector;

iii) a second receiver polarizing beam splitter, operatively coupled to said second amplitude beam splitter, capable of receiving said idler photon and said signal photon via said minus channel, capable of transmitting horizontally polarized photons to a third detector, and capable of reflecting vertically polarized photons to a fourth detector.

14. The system of claim 13, wherein said receiver is capable of identifying two bits of information corresponding to four messages by determining when said first detector, said second detector, said third detector and said fourth detector receive photons.

15. A method for a Quantum Dense Coding System, the method comprising the steps of:

a) down-converting a pump photon into a signal photon and an idler photon having a common frequency;

b) time-separating said signal photon and said idler photon so said signal photon and said idler photon do not overlap in said quantum dense coding system;

c) outputting probability amplitudes, said signal photon and said idler photon to a transmission channel and a reception channel, wherein said signal photon and said idler photon have an equal probability of outputting to said transmission channel and said reception channel;

d) changing selectively vertical and horizontal phases of probability amplitudes of said signal photon and said idler photon received by a transmitter in said transmission channel;

e) identifying vertical and horizontal phase changes created by said transmitter from probability amplitudes of said signal photon and said idler photon received in a receiver via said reception channel and said transmitter.

16. The method of claim 15, wherein said changing selectively STEP (d) uses a horizontal phase controller and a vertical phase controller.

17. The method of claim 15, wherein said method is capable of transmitting two bits of information corresponding to four messages, wherein a first message comprises +H+V, a second message comprises −

H+V, a third message comprises +H−

V and a fourth message comprises −

H−

V.

18. A Quantum Dense Coding System, comprising:

a) means for down-converting a pump photon into a signal photon and an idler photon having a common frequency;

b) means for time-separating said signal photon and said idler photon so said signal photon and said idler photon do not overlap in said quantum dense coding system;

c) means, operatively coupled to said means for down-converting a pump photon, for outputting probability amplitudes, said signal photon and said idler photon to a transmission channel and a reception channel, wherein said signal photon and said idler photon have an equal probability of outputting to said transmission channel and said reception channel;

d) means, operatively coupled to said means for outputting probability amplitudes, said signal photon and said idler photon to a transmission channel and a reception channel, for selectively changing vertical and horizontal phases of probability amplitudes of said signal photon and said idler photon received by a transmitter in said transmission channel;

e) means, operatively coupled to said means for outputting probability amplitudes, said signal photon and said idler photon to a transmission channel and a reception channel and said means for selectively changing vertical and horizontal phases of probability amplitudes of said signal photon and said idler photon, for identifying vertical and horizontal phase changes created by said transmitter from probability amplitudes of said signal photon and said idler photon received in a receiver via said reception channel and said transmitter.

19. The Quantum Dense Coding System of claim 18, wherein said means for selectively changing horizontal and vertical phases uses a horizontal phase controller and a vertical phase controller.

20. The Quantum Dense Coding System of claim 18, wherein said quantum dense coding system is capable of transmitting two bits of information corresponding to four messages, wherein a first message comprises +H+V, a second message comprises −

H+V, a third message comprises +H−

V and a fourth message comprises −

H−

V.