Method and device for producing a choice of either single photons or pairs of photons in an optical channel

• US 6,430,345 B1
• Filed: 09/27/2000
• Issued: 08/06/2002
• Est. Priority Date: 05/28/1998
• Status: Expired due to Term

• Current Assignee: Deutsche Telekom AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Dultz, Wolfgang, Schmitzer, Heidrun, Dultz, Gisela, Becker, Helmar A.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): HASAN, MOHAMMED A
• Application Number:
  US09/463,685
• Time in Patent Office: 678 Days
• Field of Search: 385/122
• US Class Current: 385/122
• CPC Class Codes: G02F 1/21 by interference
• CPC Class Codes: G02F 1/212 Mach-Zehnder type
• CPC Class Codes: G02F 1/39 for parametric generation or amplification of light, infrared or ultraviolet waves
• CPC Class Codes: G02F 3/00 Optical logic elements; Optical bistable devices
• CPC Class Codes: H04L 9/0852 Quantum cryptography transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03

Abstract

A method and device for generating a choice of individual photons or photon pairs in an optical channel. The generation of this choice involves generating a two-photon state corresponding to a photon pair and spatially separating the photon pair while preserving the quantum-mechanical correlation, in the event the photons are emitted in a collinear manner. One photon is coupled into one optical channel each, the one channel containing an interferometer with variable optical path-length difference δ1_F−δ1_S, and the other channel including an optical delay section having the optical length δ1. The channels are spatially reunited through a beam splitter, and an adjustment of the quantities δ1_F, δ1_S, and δ1 occurs in such a way that the probability K for coincidences between the outputs of the beam splitter is a choice of approximately K=0 or approximately K=1, or approximately a predetermined intermediate value, with K=0 corresponding to a photon pair in one of the output channels of the beam splitter, and K=1 corresponding to two individual photons in both output channels of the beam splitter. With this choice generation, an optical separating filter or gate can be implemented for a choice of one-photon or two-photon states, which is usable in quantum cryptography and as a basic element of a quantum-optical computing machine.

Claims

1. A method for generating a choice of one of individual photons and photon pairs in at least one of a first optical channel and a second optical channel, comprising the steps of:

generating a two-photon state corresponding to a photon pair;

spatially separating the photon pair while preserving a quantum-mechanical correlation if photons of the photon pair are emitted in a collinear manner;

coupling one of the photons of the photon pair into one of the first optical channel and the second optical channel and another one of the photons of the photon pair into another one of the first optical channel and the second optical channel, wherein one of the first optical channel and the second optical channel includes an interferometer providing a variable optical path-length difference δ

1_F−

δ

1_S, and the other one of the first optical channel and the second optical channel includes an optical delay section having an optical length δ

1;

spatially reuniting both the first optical channel and the second optical channel through a beam splitter; and

adjusting quantities δ

1_F, δ

1_S, and δ

1 such that a probability K for coincidences between outputs of the beam splitter is a choice corresponding to one of K=0, approximately K=1, and K corresponding approximately to a predetermined intermediate value, wherein K=0 corresponds to the photon pair being present in one of the outputs of the beam splitter, and K=1 corresponds to one of the photons of the photon pair being present in one of the outputs of the beam splitter and another one of the photons of the photon pair being present in another one of the outputs of the beam splitter.

2. The method according to claim 1, wherein:

the two-photon state corresponding to the photon pair is generated by a parametric fluorescence by pumping an optically non-linear crystal with a pumping laser light having a frequency of 2ω

₀.

3. The method according to claim 2, wherein:

the pumping laser light includes a coherence length that is greater than the path-length difference δ

1_F−

δ

1_S in the interferometer.

4. The method according to claim 1, further comprising the step of:

setting the path-length difference δ

1_F−

δ

1_S in the interferometer to approximately an integral multiple of a half average wavelength λ

₀ of the photons of the photon pair to produce a relationship corresponding to |δ

1_F−

δ

1_S|=n/2λ

₀, wherein;

n=0, 1, 2 . . . ,

δ

1 is adjusted to an average path difference ½

(δ

1_F+δ

1_S) of the interferometer to produce a relationship corresponding to δ

1≈

½

(δ

1_F+δ

1_S), and

a transition from n to n±

1 corresponds to a transition from one of K≈

0 to K≈

1 and K≈

1 to K≈

0.

5. The method according to claim 1, further comprising the step of:

determining the probability K as a function of at least one of quantities δ

1_F, δ

1_S, and δ

1, the step of determining the probability K being performed by mounting a plurality of detectors at the outputs of the beam splitter and measuring a coincidence rate according to an experimental technique, wherein settings for δ

1_F, δ

1_S, and δ

1 resulting in at least one of K≈

0, K≈

1, and K corresponding to the predetermined intermediate value are recorded.

6. The method according to claim 5, further comprising the step of:

making a switchover among occurrences of K≈

0, K≈

1, and K corresponding to the predetermined intermediate value by performing a remote-controlled change of at least one of the quantities δ

1_F, δ

1_S, and δ

1.

7. A device, comprising:

a light source for a quantum-optically correlated photon pair;

an arrangement for separating the photon pair if photons of the photon pair are emitted in a collinear manner;

a plurality of beam-component paths arranged such that each one of the photons is coupled into a corresponding one of the plurality of beam-component paths;

a beam splitter;

an arrangement for reuniting the plurality of beam-component paths at the beam splitter to superimpose and transfer the plurality of beam components into a plurality of shared output channels;

an interferometer arranged in one of the plurality of beam-component paths and including a first interferometer arm corresponding to optical path length δ

1_F and a second interferometer arm corresponding to optical path length δ

1_S;

an optical delay section corresponding to optical length δ

1 and arranged in another one of the plurality of beam-component paths; and

an arrangement for changing at least one of optical path lengths δ

1_F, δ

1_S, and δ

1.

8. The device according to claim 7, wherein the device is configured as at least one of a controllable light source for one of a one-photon state and a two-photon state, and as one of a controllable separating filter and a controllable gate for quantum states.

9. The device according to claim 7, wherein:

the light source includes;

an optically non-linear crystal,

a pumping light source producing a pump light, and

an optical filter for suppressing the pump light at an output of the

optically non-linear crystal, and

the photon pair is generated in the optically non-linear crystal by a parametric conversion of one photon of the pump light.

10. The device according to claim 9, wherein:

the pumping light source corresponds to a laser.

11. The device according to claim 7, further comprising:

an optically linear fiber, wherein;

the light source includes;

an optically non-linear fiber corresponding to a non-linear fiber piece arranged by being one of inserted into and added onto the optically linear fiber,

a pumping light source producing a pump light, and

an optical filter for suppressing the pump light at an output of at

least one of the optically non-linear fiber and the optically linear fiber, and

the photon pair is generated in at least one of the optically non-linear fiber and the optically linear fiber by a parametric fluorescence.

12. The device according to claim 11, wherein:

the pumping light source corresponds to a laser.

13. The device according to claim 7, wherein:

the light source is formed by one of one output of at least a further device and by a combination of a plurality of outputs of a plurality of further devices.

14. The device according to claim 7, wherein:

the arrangement for separating the photon pair includes one of a wavelength-selective mirror, a polarizer, and a polarizing beam splitter.

15. The device according to claim 7, wherein:

at least one of the optical path lengths δ

1_F, δ

1_S, and δ

1 is capable of being varied by at least one of at least one mechanical adjustment element and at least one electro-optical adjustment element.

16. The device according to claim 15, wherein:

each one of the at least one mechanical adjustment element and the at least one electro-optical adjustment element is remote-controlled.

17. The device according to 15, claim wherein:

each one of the at least one mechanical adjustment element and the at least one electrooptical adjustment element includes one of electronically controllable liquid-crystal cells and electro-optical crystal modulators.

18. The device according to claim 7, wherein:

the interferometer includes one of a Mach-Zehnder interferometer, a Michelson interferometer, a Fabry-Perot interferometer, and an Echelon.

19. The device according to claim 7, wherein:

the interferometer includes a linearly birefringent crystal having an optical path difference δ

1_F−

δ

1_S that is enlarged by one of an additional compensator and an electrically tunable delay plate corresponding to one of a liquid-crystal cell and a Kerr cell, such that the optical path difference δ

1_F−

δ

1_S is variable by more than one half wavelength of the photon coupled into a corresponding one of the plurality of beam-component paths.

20. The device according to claim 19, wherein:

the linearly birefringent crystal includes a quartz plate, and

the additional compensator includes a Babinet-Soleil compensator.

21. The device according to claim 7, wherein:

the beam splitter includes an optical fiber coupler having a division ratio of 1;

1.

22. The device according to claim 7, wherein mounted in at least one of the plurality of beam-component paths are at least one of:

at least one intensity-altering absorber for influencing a quantity of the photons,

at least one polarization-altering adjustment element for influencing a polarization of the photons,

at least one phase-altering adjustment element for influencing a phase of the photons, and

at least one frequency-altering adjustment element for influencing a frequency of the photons.

23. The device according to claim 7, further comprising:

at least one optical storage device inserted into at least one of the plurality of beam-component paths.

24. The device according to claim 23, wherein the at least one optical storage device includes one of a glass-fiber loop and a Fabry-Perot resonator.