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Quantum entanglement generating system and method, and quantum entanglement generating and detecting system and method

外国特許コード F110003515
整理番号 A291-02WO
掲載日 2011年6月28日
出願国 アメリカ合衆国
出願番号 67397208
公報番号 20110032532
公報番号 8228507
出願日 平成20年8月11日(2008.8.11)
公報発行日 平成23年2月10日(2011.2.10)
公報発行日 平成24年7月24日(2012.7.24)
国際出願番号 JP2008064436
国際公開番号 WO2009025195
国際出願日 平成20年8月11日(2008.8.11)
国際公開日 平成21年2月26日(2009.2.26)
優先権データ
  • 特願2007-213205 (2007.8.18) JP
  • 2008JP064436 (2008.8.11) WO
発明の名称 (英語) Quantum entanglement generating system and method, and quantum entanglement generating and detecting system and method
発明の概要(英語) A quantum entanglement generating system includes: a laser light source for producing a light beam of light frequency 2f0; a ring interferometer comprising a beam splitter into which the light beam of light frequency 2f0 is incident and a plurality of mirrors, the beam splitter and the mirrors forming an optical path in the form of a ring; a parametric amplifier inserted in the optical path of the ring interferometer for producing a beam of light of light frequency f0 upon receiving the light beam of light frequency 2f0 incident into the optical parametric amplifier; and a dispersive medium inserted in the optical path of the ring interferometer for varying relative optical path length for the light beam of light frequency 2f0 and the light beam of light frequency f0.
従来技術、競合技術の概要(英語) BACKGROUND ART
Quantum information techniques constitute a technology or a field of the technology that utilizes a quantum mechanical effect directly to achieve information processing performance unachievable so far.
Quantum entanglement is a most important resource in the quantum information techniques.
Utilization of the quantum entanglement permits actualizing absolutely safe communications and computation processing at a speed incommensurably higher than heretofore.
A quantum entangled state is a state that physical systems at a plurality of spatially separated locations are mutually correlated, thus the state that such a plurality of physical systems cannot be treated isolated.
If physical systems at two distant locations have a quantum entangled state in common, then measurements conducted at the two locations cause in their results a correlation which cannot be explained in the classical theory.
The term "quantum entanglement" is used in general to refer to a quantum entangled state itself, or a physical phenomenon which the entangled state exhibits and which is brought about peculiar in the quantum theory, or to state the concept that the quantum theory involves an inseparable characteristic.
The quantum entanglement is used herein, however, as the term to indicate a quantum entangled state.
Quantum information processing adopts mainly two approaches, one of which uses a discrete physical quantity and the other of which uses a continuous physical quantity (see, e.g., Non-Patent Reference 1).
In the case of light, use is generally made of the quadrature amplitude of an electric field as such a physical quantity taking a continuous physical value.
The quantum entanglement for continuous physical quantities is termed a continuous variable quantum entanglement.
Mention is made of conventional methods of generating a continuous variable quantum entanglement.
The method used most initially uses a non-degenerate parametric amplifier (see, e.g., Patent Reference 1).
Patent Reference 1 introduced an experiment in which potassium titanate phosphate (KTP) was used as a nonlinear medium and phase matching of type II was effected to generate a signal and an idler light beams which are in a mutually orthogonal polarized state.
The term "non-degenerate" refers to difference in the polarized state.
Such signal and idler light beams as generated by parametric amplification using phase matching of type II are quantum correlated and thus capable of generating a continuous variable quantum entanglement.
In a conventional method of using the phase matching of type II, however, a difference in index of reflection of the nonlinear medium to signal and idler light beams made it technically difficult to bring the light resonators into simultaneous resonance with these two light beams.
Further, the phase matching of type II in which beams tended in general to work off caused the quantum entanglement to deteriorate in quality.
In the method next performed, two squeezed light beams are generated and combined at a beam splitter with a transmissivity and a reflectance both of 50% to generate quantum entanglement.
Then, the two squeezed beams need to be precisely controlled so as to have their relative phase difference of pi /2.
For example, refer to Non-Patent Reference 2 in which a parametric amplifier placed in a ring resonator to effect phase matching of type 1 is used to generate squeezed beams which are traveling clockwise and anticlockwise along a ring and which are combined at a beam splitter laid outside of the ring to generate quantum entanglement.
This method has the problem that after leaving the ring resonator and then to be combined at the beam splitter, the two squeezed beams that follow the different paths make it difficult to maintain the relative optical path length between these two paths stably.
Patent Reference 1: H. J. Kimble et al., U.S. Pat. No. 5,339,182, Aug. 16, 1994
Non-Patent Reference 1: S. L. Braunstein and P. van Loock, Rev.
Mod. Phys. Vol. 77, p. 513, 2005
Non-Patent Reference 2: T. C. Zhang, et al., Phys. Rev. A. Vol. 67, p. 033802, 2003
Non-Patent Reference 3: Yujiro Eto, et al., Optics Letters, Vol. 32, pp. 1698-1700, 2007
Non-Patent Reference 4: L. M. Duan, et al., Physical Review Letters, Vol. 84, p. 2722, 2000

特許請求の範囲(英語) [claim1]
1. A quantum entanglement generating system comprising: a laser light source for producing a light beam of light frequency 2f0;
a ring interferometer comprising a beam splitter and a plurality of mirrors, the beam splitter and the minors forming an optical path in the form of a ring;
an optical parametric amplifier inserted in the optical path of the ring interferometer for producing a light beam of light frequency f0 upon receiving a light beam of light frequency 2f0 incident into the optical parametric amplifier; and
a dispersive medium inserted in the optical path of the ring interferometer,
wherein the light beam of light frequency 2f0 from the laser light source injects into the beam splitter,
the beam splitter splits the light beam of light frequency 2f0 into two light beams travelling mutually contrariwise in direction of advance in the ring interferometer, the two light beams injected into the optical parametric amplifier to generate a first and a second squeezed light beams traveling mutually contrariwise in direction of advance in the ring interferometer,
the dispersive medium adjusts the relative phase between the first and second squeezed light beams at a selected value, and
the beam splitter combines the first and second squeezed light beams, thereby generating quantum entangled beams.
[claim2]
2. A quantum entanglement generating system as set forth in claim 1 wherein the optical path of the ring interferometer is formed of the sides of a polygon of triangle or more angle in the ring interferometer in which the beam splitter is disposed at an apex of the polygon with the minors lying at its remaining apexes, respectively.
[claim3]
3. A quantum entanglement generating system as set forth in claim 1 wherein the optical path of the ring interferometer is a triangular optical path in which the beam splitter and a first and a second of the mirrors are arranged in turn anticlockwise, and wherein
the dispersive medium is disposed in the optical path between the beam splitter and the first minor in the ring interferometer, and
the optical parametric amplifier is disposed in the optical path between the first and second minors in the ring interferometer.
[claim4]
4. A quantum entanglement generating system as set forth in claim 1 wherein the optical path of the ring interferometer is a rectangular optical path in which the beam splitter and a first, a second and a third of the mirrors are arranged in turn anticlockwise, and wherein the optical parametric amplifier is disposed in the optical path between the first and second minors in the ring interferometer, and
the dispersive medium is disposed in the optical path between the beam splitter and the third minor in the ring interferometer.
[claim5]
5. A quantum entanglement generating system as set forth in claim 3 or claim 4 wherein on the optical axis there is disposed a condenser means, each between the optical parametric amplifier and the first minor and between the optical parametric amplifier and the second minor.
[claim6]
6. A quantum entanglement generating system as set forth in claim 1 wherein the optical parametric amplifier has an optical waveguide structure consisting of an electrooptic crystal.
[claim7]
7. A quantum entanglement generating system as set forth in claim 1 wherein the dispersive medium consists of two glass plates.
[claim8]
8. A quantum entanglement generating system as set forth in claim 1 wherein the laser light source comprises a light source for producing a light beam of light frequency f0 and a second harmonic generator for converting the incident light beam of light frequency f0 from the light source into a light beam of light frequency 2f0.
[claim9]
9. A quantum entanglement generating system as set forth in claim 8 wherein the second harmonic generator has an optical waveguide structure consisting of an electrooptic crystal.
[claim10]
10. A quantum entanglement generating system as set forth in claim 1 wherein the beam splitter has a transmissivity and a reflectance of about 50%, alike to both light beams of light frequency f0 and light frequency 2f0.
[claim11]
11. A quantum entanglement generating system as set forth in claim 1 wherein the ring interferometer is formed on a plane.
[claim12]
12. A quantum entanglement generating method comprising: producing a light beam of light frequency 2f0 from a laser light source;
injecting the light beam from the laser light source into a ring interferometer comprising a beam splitter and a plurality of mirrors, the beam splitter and mirrors forming an optical path in the form of a ring;
splitting the injected light beam at the beam splitter into two light beams traveling mutually contrariwise in direction of advance in the ring interferometer;
advancing one of the split light beams from an optical parametric amplifier disposed in the optical path of the ring interferometer into a dispersive medium disposed in the optical path of the ring interferometer, to generate a first squeezed light beam of light frequency f0; advancing the other of the split light beams from the dispersive medium into the optical parametric amplifier to generate a second squeezed light beam of light frequency f0; and
setting relative phase between the first and second squeezed light beams at a selected value through the dispersive medium, and
combining the first and second squeezed light beams at the beam splitter, thereby generating quantum entangled beams.
[claim13]
13. A quantum entanglement generating method as set forth in claim 12 wherein the relative phase between the first and second squeezed light rays is set at pi /2.
[claim14]
14. A quantum entanglement generating method as set forth in claim 12 wherein the quantum entangled beams comprises a first quantum entangled beam passing through the beam splitter and a second quantum entangled beam reflecting on the beam splitter.
[claim15]
15. A quantum entanglement generating and detecting system comprising: a light source part comprising a pulsed laser light source of light frequency f0 and a second harmonic generator into which the light beam of light frequency f0 is incident to produce a light beam of light frequency 2f0, the light source part emitting a pulsed laser light beam of light frequency f0 and a pulsed laser light beam of light frequency 2f0 on a common axis;
a ring interferometer comprising a beam splitter and a plurality of mirrors, the beam splitter and mirrors forming an optical path in the form of a ring;
an optical parametric amplifier inserted in the optical path of the ring interferometer for producing a light beam of light frequency f0 upon receiving a light beam of light frequency 2f0 incident into the optical parametric amplifier;
a dispersive medium inserted in the optical path of the ring interferometer ; and
a homodyne detector,
wherein the light beam of light frequency 2f0 from the laser light source injects into the beam splitter,
the beam splitter splits the light beam of light frequency 2f0 into two light beams travelling mutually contrariwise in direction of advance in the ring interferometer, the two light beams injected into the optical parametric amplifier to generate a first and a second linearly polarized, squeezed light beam of light frequency f0 traveling mutually contrariwise in direction of advance in the ring interferometer,
the dispersive medium adjusts the relative phase between the first and second squeezed light beams at a selected value,
the beam splitter combines the first and second squeezed light beams to generate a linearly polarized quantum entangled beam of light frequency f0,
as a signal light beam the linearly polarized quantum entangled beam of light frequency f0, and as a local-oscillator light beam the pulsed laser light beam of light frequency f0 emitted from the light source part and having a polarization orthogonal to the signal light beam, are both incident into the homodyne detector to detect a quadrature amplitude.
[claim16]
16. A quantum entanglement generating and detecting system as set forth in claim 15 wherein the quantum entangled beams comprises a first and a second quantum entangled beam and the homodyne detector comprises a first and a second homodyne detector, the first and second quantum entangled beams constituting signal light beams to the first and second homodyne detectors, respectively.
[claim17]
17. A quantum entanglement generating and detecting system as set forth in claim 15 wherein the beam splitter has a transmissivity and a reflectance of about 50%, alike to both a horizontally polarized light beam of light frequency f0 and a horizontally polarized light beam of light frequency 2f0, and has a reflectance of about 100% to a vertically polarized light ray of light frequency f0.
[claim18]
18. A quantum entanglement generating and detecting system as set forth in claim 15 wherein the homodyne detector comprises: an electrooptic crystal into which the signal light beam and the local-oscillator light beam are incident, a half wave plate for polarizing the light beams incident into the electrooptic crystal, a beam splitter for combining the light beams polarized at the half wave plate to split into a transmitted and a reflected light beam, detectors for sensing the two light beams split into by the beam splitter, respectively, and a means for providing a differential between outputs from the detectors.
[claim19]
19. A quantum entanglement generating and detecting system as set forth in claim 15 wherein the homodyne detector comprises a filter into which the signal light beam and the local-oscillator light beam are incident for transmitting the light frequency f0 and light frequency 2f0, a quarter wave plate for varying a phase between the light beams from the filter, a beam splitter for combining the light beams from the quarter wave plate and for splitting into a transmitted and a reflected light beam, detectors for sensing the two light beams split into by the beam splitter, respectively, and a means for providing a differential between outputs from the detectors.
[claim20]
20. A quantum entanglement generating and detecting system as set forth in claim 15, further comprising a dispersive medium disposed between the signal and local-oscillator light beams and the homodyne detector wherein the homodyne detector comprises a filter for transmitting a light beam of light frequency f0 and a light beam of light frequency 2f0 out of light beams passing through the dispersive medium, a beam splitter for combining light beams from the filter to split into a transmitted and a reflected light beam, detectors for sensing the two light beams split into by the beam splitter, respectively, and a means for providing a differential between outputs from the detectors.
[claim21]
21. A quantum entanglement generating and detecting system as set forth in claim 15 wherein the ring interferometer is formed on a plane.
[claim22]
22. A quantum entanglement generating and detecting method comprising: producing, on a common optical axis, a light beam of light frequency f0 from a laser light source and a light beam of light frequency 2f0 generated via a second harmonic generator from the laser light source;
injecting the light beam of light frequency 2f0 from the laser light source into a ring interferometer comprising a beam splitter and a plurality of mirrors ,the beam splitter and minors forming an optical path in the form of ring;
splitting the injected light beam at the beam splitter into two light beams traveling mutually contrariwise in direction of advance in the ring interferometer;
advancing one of the split light beams from an optical parametric amplifier disposed in the optical path of the ring interferometer into a dispersive medium disposed in the optical path of the ring interferometer, to generate a first linearly polarized, squeezed light beam of light frequency f0;
advancing the other of the split light beams from the dispersive medium into the optical parametric amplifier to generate a second linearly polarized, squeezed light beam of light frequency f0;
setting relative phase between the first and second squeezed light beams at a selected value through the dispersive medium; and
combining the first and second squeezed light beams at the beam splitter, thereby generating linearly polarized quantum entangled beams of light frequency f0;
deriving from the horizontally polarized quantum entangled beams of light frequency f0, a signal light beam for a homodyne detector;
passing the light beam of light frequency f0 from the laser light source through the ring interferometer via an optical path identical to that for the one light beam split into by the beam splitter, to provide a light beam of a polarization orthogonal to the signal light beam for use as a local-oscillator light beam for the homodyne detector; and
the homodyne detector detecting a quadrature amplitude of the signal light beam.
[claim23]
23. A quantum entanglement generating and detecting method as set forth in claim 22 wherein a filter for blocking the light beam of light frequency 2f0 is inserted on an optical axis, each in front and rear of the optical parametric amplifier to suspend generation of the quantum entangled beams.
  • 発明者/出願人(英語)
  • HIRANO TAKUYA
  • ETO YUJIRO
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • GAKUSHUIN SCHOOL
国際特許分類(IPC)
米国特許分類/主・副
  • 356/450
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