Free-space quantum cryptography system

• US 6,289,104 B1
• Filed: 08/07/1998
• Issued: 09/11/2001
• Est. Priority Date: 08/07/1998
• Status: Expired due to Fees

• Current Assignee: Illinois Institute of Technology
• Original Assignee: Ilinois Institute of Technology
• Inventors: Patterson, David B., Kubik, James M.
• Primary Examiner(s): Barrón, Jr., Gilberto
• Assistant Examiner(s): SONG, HOSUK
• Application Number:
  US09/131,015
• Time in Patent Office: 1,131 Days
• Field of Search: 380/256, 380/283, 380/270, 380/44, 380/46, 380/31, 359/112, 359/157, 359/158, 359/173
• US Class Current: 380/283
• CPC Class Codes: H04L 9/0858 Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding

Abstract

A system and method for quantum key delivery in a single-photon, free-space cryptography scheme including a transmitter and a receiver. The transmitter includes two pairs of photon sources, each of which represents a specific photon polarization direction. The first pair of photon sources represents a first polarization basis while the remaining pair of photon sources represents a second polarization basis. The first and second polarization basis are rotated with respect to each other so as to produce non-orthogonal polarization eigenstates. A transmitter polarizing beamsplitter corresponding to each of the pairs of the photon sources is provided whereby the polarizations of each of the photon sources of each pair of photon sources are recombined. A transmitter non-polarizing beamsplitter is provided whereby the recombined polarizations are combined for output to the receiver. The receiver includes a set of optics inversely disposed with respect to the optics of the transmitter and two pairs of photon detectors.

Claims

1. A system for quantum key delivery in a single-photon, free-space cryptography scheme comprising:

a transmitter comprising two pairs of photon sources, each said photon source representing a specific photon polarization direction, a first said pair of photon sources representing a first polarization basis and a remaining said pair of photon sources representing a second polarization basis, said first polarization basis and said second polarization basis prepared as conjugate bases by one of being rotated with respect to each other and disposition of at least one retardation plate in a transmitter path of a photon emitted by at least one of said photon sources resulting in non-orthogonal polarization eigenstates, a transmitter polarizing beamsplitter corresponding to each said pair of photon sources whereby the polarizations of each said photon source of each said pair of photon sources are recombined, a transmitter non-polarizing beamsplitter whereby said recombined polarizations are combined for output to a receiver, and a photon output; and

a receiver comprising a photon input, a receiver non-polarizing beamsplitter whereby said output from said transmitter is separated resulting in a random polarization basis selection, two pairs of photon receivers and a receiver polarizing beamsplitter corresponding to each said pair of photon receivers, said photon receivers and said receiver polarizing beamsplitters disposed inversely with respect to said photon sources and said receiver polarizing beamsplitters having been prepared as conjugate bases by one of being rotated with respect to each other and disposition of at least one retardation plate in a receiver path of a photon received by at least one of said photon receivers, said receiver in communication with said transmitter through a free-space channel.

2. A system in accordance with claim 1, wherein a spatial filter is disposed at said photon input of said receiver.

3. A system in accordance with claim 2, wherein said spatial filter comprises at least two optically aligned lenses and an optical barrier disposed between said optically aligned lenses and forming a pinhole aligned with said optically aligned lenses.

4. A system in accordance with claim 1, wherein said photon output comprises at least one optical fiber.

5. A system in accordance with claim 4, wherein said photon receivers are photomultiplier tubes.

6. A system in accordance with claim 4, wherein said photon receivers are avalanche photo diodes in a Geiger mode.

7. A system in accordance with claim 1, wherein said photon sources are selected from the group consisting of lasers and light emitting diodes.

8. A system in accordance with claim 1, wherein said photon receivers are photomultiplier tubes.

9. A system in accordance with claim 1, wherein said photon receivers are avalanche photo diodes in a Geiger mode.

10. A system in accordance with claim 1, wherein said polarization bases are selected from the group consisting of linear, circular, elliptical and combinations thereof.

11. A method for quantum key delivery in a single-photon, free-space system comprising the steps of:

transmitting a photon having a polarization direction corresponding to a bit value from one of two non-orthogonal transmitter polarization basis systems through a transmitter polarizing beamsplitter, from said transmitter polarizing beamsplitter through a transmitter non-polarizing beamsplitter, through a photon output of a transmitter and into a photon input of a receiver; and

passing said photon through a receiver non-polarizing beamsplitter, from said receiver non-polarizing beamsplitter through a receiver polarizing beamsplitter corresponding to one of two non-orthogonal receiver polarization basis systems, and to one of two photon detectors comprising said one of said two non-orthogonal receiver basis systems in said receiver.

12. A method in accordance with claim 11, wherein said photon is passed through a spatial filter disposed in a free-space channel between said transmitter and a receiver at said photon input of said receiver.

13. A method in accordance with claim 12, wherein said spatial filter comprises at least two optically aligned lenses and an optical barrier disposed between said optically aligned lenses and forming a pinhole aligned with said optically aligned lenses.

14. A method in accordance with claim 11, wherein said non-orthogonal bases are linear.

15. A method in accordance with claim 11, wherein said photons are randomly produced by one of two photon sources within a basis system.

16. A method in accordance with claim 11, wherein said photon detectors are photomultiplier tubes.

17. A method in accordance with claim 11, wherein said polarization bases systems are selected from the group consisting of linear, circular, elliptical, and combinations thereof.