CN104579499A - Interferometer and sub-natural linewidth polarization-entangled twin photon generation method thereof - Google Patents

Abstract

The invention discloses an interferometer and a method for generating subnatural linewidth polarization-entangled photon pairs. The interferometer includes a vacuum system, a first laser, a second laser, a third laser, a photodetector, and a first polarization splitter. Prism, second polarization beam splitter prism, first mirror and second mirror; the center of the vacuum system generates cold atomic groups, the first laser is used to generate reference light, the second laser is used to generate coupling light, and the third laser is used to generate pump light. The method is to build a vacuum system first, obtain cold atomic groups in the center of the vacuum system, use the reference light to stabilize the phase difference of the interferometer, and then use the spontaneous emission four-wave mixing process to generate Stokes Stokes photons and anti-Stokes photons; adjust the phase difference between the two channels of the interferometer, set the polarization of the pump light and the coupling light, and obtain subnatural linewidth polarization-entangled photon pairs. The photon pairs produced by the invention are suitable for long-distance quantum communication and quantum storage.

Description

An interferometer and its method for generating subnatural linewidth polarization-entangled photon pairs

technical field

The present invention relates to an interferometer and its method for generating subnatural linewidth polarization-entangled photon pairs, in particular to a Mach-Zehnder interferometer and its method for generating subnatural linewidth polarization-entangled photon pairs, belonging to photon transmission and storage technology field.

Background technique

Photon is the basic particle that transmits electromagnetic interaction and the carrier of electromagnetic radiation. In quantum field theory, photon is the mediator of electromagnetic interaction. In quantum communication system, it is considered as an ideal information transmission carrier. However, the photon in the channel decays exponentially with the transmission distance, which limits the communication distance. Long-distance quantum communication requires the use of quantum relay based on quantum memory, and the photon linewidth that can be stored in quantum memory cannot be greater than the natural linewidth (MHz order of magnitude), so subnatural linewidth photons are critical to the source.

The polarization state of photons, as an internal state, has the advantages of easy encoding and reading, strong anti-interference ability during flight, etc., and is an ideal transmission carrier for flying bits.

At present, the spontaneous parametric down-conversion process is often used to generate polarization-entangled photon pairs, but the linewidth of the polarization-entangled photon pair generated by the spontaneous parametric down-conversion process is still larger than the natural linewidth of most atomic transitions, resulting in the storage of the photon polarization state. Inefficient and difficult to use in quantum memory.

Contents of the invention

The object of the present invention is to solve the above-mentioned defects in the prior art, and provide an interferometer with simple structure, convenient operation and high feasibility, which is suitable for long-distance quantum communication and quantum storage.

Another object of the present invention is to provide a method for the above-mentioned interferometer to generate polarization-entangled photon pairs with subnatural linewidths, and the method generates polarization-entangled photon pairs with subnatural linewidths.

The purpose of the present invention can be achieved by taking the following technical solutions:

An interferometer, which is a Mach-Zehnder interferometer, is characterized in that: it comprises a vacuum system, a first laser, a second laser, a third laser, a photodetector, a first polarization beam splitter, and a second polarization beam splitter Prism, first mirror and second mirror; the center of the vacuum system produces cold atomic groups, the first laser is used to generate reference light, the second laser is used to generate coupling light, and the first laser generates Both the reference light and the coupling light generated by the second laser are aimed at the first polarization beam splitter prism, and the optical path direction of the reference light is perpendicular to the optical path direction of the coupling light; the third laser is used to generate pumping light, and the generated The pumping light is aimed at the second polarization beam splitting prism, and the photodetector is arranged at the output end of the light path of the beam combination of the second polarization beam splitting prism and detects the light intensity; the first reflector is arranged at the first polarization beam splitting prism In one of the optical paths of the beam, the second reflecting mirror is arranged in one of the optical paths of the second polarization beam splitting prism, and the first polarization beam splitting prism and the first reflecting mirror are respectively connected with the second polarization beam splitting prism and the second polarization beam splitting prism. The mirrors are symmetrical about the vacuum system.

As a preferred solution, it also includes four half-wave plates and four 1/4 wave plates, the four half-wave plates are respectively the first half-wave plate, the second half-wave plate, the third half-wave plate and the fourth half-wave plate wave plate, the four 1/4 wave plates are respectively the first 1/4 wave plate, the second 1/4 wave plate, the third 1/4 wave plate and the fourth 1/4 wave plate, the first half wave The plate is arranged between the first laser and the first polarization beam splitter, the second half wave plate is arranged between the second laser and the first polarization beam splitter, and the third half wave plate is arranged between the third laser and the first polarization beam splitter Between the second polarization beam splitter, the fourth half-wave plate is arranged between the photodetector and the second polarization beam splitter, and the first 1/4 wave plate is arranged between the first polarization beam splitter and the first reflector Between, the second 1/4 wave plate is arranged between the first polarizing beam splitter and the vacuum system, and the third 1/4 wave plate is arranged between the second polarizing beam splitting prism and the second mirror, so The fourth 1/4 wave plate is arranged between the second polarization beam splitter and the vacuum system.

As a preferred solution, the first polarizing beam splitter and the second polarizing beam splitting prism serve as an optical path beam splitter or an optical path beam combiner, and the first reflective mirror and the second reflective mirror are used for adjusting the direction of the optical path and phase compensation.

As a preferred solution, the vacuum system is a vacuum chamber.

As a preferred solution, the first laser, the second laser and the third laser are all DL100 semiconductor lasers.

Another object of the present invention can be achieved by taking the following technical solutions:

A method for producing subnatural linewidth polarization-entangled photon pairs, characterized in that it comprises the following steps:

1) Build a vacuum system, obtain cold atomic groups in the center of the vacuum system, and prepare to the ground state of four-wave mixing;

2) The reference light generated by the first laser is injected into the interferometer, first passes through the first half-wave plate, and then is divided into two paths by the first polarizing beam splitter prism, one of which passes through the first mirror and the second mirror in turn, and the other One path is synthesized by the second polarization beam splitter prism, and enters the photodetector to detect the light intensity; according to the signal of the photodetector, the piezoelectric ceramic is controlled by the feedback circuit to adjust the position of the first reflector and the second reflector, and stabilize the interferometer Two-way phase difference;

3) The coupled light generated by the second laser passes through the second half-wave plate, and then is divided into two paths by the first polarization beam splitter. The light is recombined and injected into the cold atomic group. The two optical paths form a small angle with the long axis of the cold atomic group; the pump light generated by the third laser passes through the third half-wave plate, and then is divided into two paths by the second polarizing beam splitter. The optical path passes through the third 1/4 wave plate and the fourth 1/4 wave plate respectively, and is relatively incident with the coupling light, and the optical path overlaps;

4) The coupled light and the pump light interact with the cold atom groups respectively to form a four-wave mixing process, and emit a Stokes photon and an anti-Stokes photon. According to the four-wave mixing process, energy conservation, angle Conservation of momentum, conservation of momentum, time and frequency entanglement of Stokes photons and anti-Stokes photons generated in pairs, polarization matching with coupling light and pump light; at the same time, the three pairs of coupled light and anti-Stokes photons The energy-level electromagnetically induced transparency effect will narrow the linewidth of the generated entangled photon pairs, and obtain subnatural linewidth entangled photon pairs;

5) When two channels of coupling light and pumping light exist at the same time, adjust the phase difference between the two channels of the interferometer, set the polarization of coupling light and pumping light, and obtain the required subnatural linewidth polarization-entangled photon pairs.

As a preferred solution, the step 4) forms a four-wave mixing process, and emits a Stokes photon and an anti-Stokes photon, as follows:

In the direction of the long axis of the cold atomic cluster, under the action of pump light, an atom transitions from the atomic ground state to the excited state, and emits a Stokes single photon through spontaneous emission, and the atom returns to another ground state, under the action of coupled light Under the Raman transition process, the atom immediately transitions to another excited state and emits an anti-Stokes photon.

As a preferred option, the method also includes:

Before the cold atomic group diffuses, stop emitting coupling light and pump light by turning off the second laser and the third laser, and return to step 1) for the next preparation.

As a preferred solution, the cold atomic groups are obtained by generating cooling light with a laser, and the laser for generating cooling light is turned off before step 3), so that the cold atomic groups can freely diffuse and create a photon pair generation window.

As a preferred solution, the laser that generates the cooling light is a TA100 semiconductor laser.

Compared with the prior art, the present invention has the following beneficial effects:

1. The interferometer of the present invention is a Mach-Zehnder interferometer, which can generate photon-to-polarization entanglement through a four-wave mixing process, and the anti-Stokes photon linewidth is lower than the natural linewidth, and subnatural The linewidth polarization entangled photon pair is suitable for long-distance quantum communication and quantum storage, and solves the problem of low storage efficiency of photon polarization state in the prior art and difficulty in being used in quantum storage.

2. The subnatural linewidth polarization-entangled photon pairs produced by the interferometer of the present invention have long coherence time and codable photon polarization states, and are ideal flying bit carriers in long-distance quantum communication networks.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the interferometer of the present invention.

Fig. 2 is a schematic diagram of four-wave mixing energy levels of the present invention.

Among them, 1-vacuum system, 2-first laser, 3-second laser, 4-third laser, 5-photodetector, 6-first polarization beam splitter, 7-second polarization beam splitter, 8-th One mirror, 9-second mirror, 10-first half-wave plate, 11-second half-wave plate, 12-third half-wave plate, 13-fourth half-wave plate, 14-first 1/4 Wave plate, 15-second 1/4 wave plate, 16-third 1/4 wave plate, 17-fourth 1/4 wave plate, 18-cold atomic group, 19-pump light, 20-ground state, 21- Excited state, 22-coupled light, 23-another ground state, 24-another excited state, 25-Stokes photon, 26-anti-Stokes photon.

Detailed ways

Example 1:

As shown in Figure 1, the interferometer of this embodiment is a Mach-Zehnder interferometer, comprising a vacuum system 1, a first laser 2, a second laser 3, a third laser 4, a photodetector 5, and a first polarization beam splitter 6. The second polarizing beam splitter prism 7, the first reflector 8, the second reflector 9, four half-wave plates and four 1/4 wave plates, the four half-wave plates are respectively the first half-wave plate 10, the second half-wave plate The second half-wave plate 11, the third half-wave plate 12, and the fourth half-wave plate 13, and the four 1/4 wave plates are respectively the first 1/4 wave plate 14, the second 1/4 wave plate 15, and the third 1/4 wave plate. /4 wave plate 16 and the fourth 1/4 wave plate 17;

The center of the vacuum system 1 produces cold atomic groups 18, the first polarizing beam splitting prism 6 and the second polarizing beam splitting prism 7 are used as an optical path beam splitter or an optical path beam combiner; the first laser 2 is used to generate reference light, The second laser 3 is used to generate coupled light, the reference light generated by the first laser 2 and the coupled light generated by the second laser 3 are aligned with the first polarization beam splitter prism 6, and the optical path direction of the reference light is the same as that of the coupled light The optical path directions are perpendicular to each other; the third laser 4 is used to generate pumping light, and the generated pumping light is aligned with the second polarization beam splitter prism 7, and the photodetector 5 is arranged on the second polarization beam splitter prism 7 for beam combining The output end of the light path and detect the light intensity;

The first reflector 8 is arranged in one of the beam paths of the first polarization beam splitter 6, and the second reflector 9 is arranged in one of the beam paths of the second polarization beam splitter 7. The first reflector 8 and the second reflector 9 are used to adjust the direction of the optical path and phase compensation, the first polarization beam splitter prism 6, the first reflector 8 are respectively symmetrical with the second polarization beam splitter prism 7, the second reflector 9 with respect to the vacuum system 1 .

The first half-wave plate 10 is arranged between the first laser 2 and the first polarization beam-splitting prism 6, and the second half-wave plate 11 is arranged between the second laser 3 and the first polarization beam-splitting prism 6, so The third half-wave plate 12 is arranged between the third laser 4 and the second polarization beam splitter prism 7, and the fourth half-wave plate 13 is arranged between the photodetector 5 and the second polarization beam splitter prism 7, and the first A 1/4 wave plate 14 is arranged between the first polarization beam splitting prism 6 and the first reflection mirror 8, and the second 1/4 wave plate 15 is arranged between the first polarization beam splitting prism 6 and the vacuum system 1, so The third 1/4 wave plate 16 is arranged between the second polarization beam splitter 7 and the second reflector 9, and the fourth 1/4 wave plate 17 is arranged between the second polarization beam splitter 7 and the vacuum system 1 .

As shown in Figure 2, in the four-wave mixing process of this embodiment, the pump light 19 acts on the energy level 20 of the ground state to transition the atoms to the energy level 21 of the excited state, and the coupling light 22 acts on another energy level 23 of the ground state and Between the energy levels of another excited state 24 , two energy levels are coupled to cause a Raman transition process, thereby generating Stokes photons 25 and anti-Stokes photons 26 .

As shown in Fig. 1 and Fig. 2, the interferometer of the present embodiment produces the method for subnatural linewidth polarization entangled photon pair, comprises the following steps:

1) Build a vacuum system 1, generate cooling light through a laser (not shown in the figure), obtain long cold atomic groups 18 in the center of the vacuum system 1, and prepare to the ground state 20 of four-wave mixing, this embodiment adopts rubidium atom;

2) The reference light generated by the first laser 2 is injected into the interferometer, first passes through the first half-wave plate 10, and then is divided into two paths by the first polarizing beam splitter prism 6, wherein one path passes through the first reflector 8 and the second reflector in turn After 9, one road is combined with another road through the second polarization beam splitter prism 7, and enters the photodetector 5 to detect the light intensity, and its optical path is shown as the dotted line in Figure 1; according to the signal of the photodetector 5, the voltage is controlled by the feedback circuit Electric ceramics are used to adjust the positions of the first reflector 8 and the second reflector 9, and stabilize the phase difference between the two paths of the interferometer;

3) Turn off the laser that generates the cooling light, so that the cold atomic groups 18 can diffuse freely, and create a photon pair generation window;

4) The coupling light 22 produced by the second laser 3 passes through the second half-wave plate 11, and then is divided into two paths by the first polarization beam splitter prism 6, and the two optical paths pass through the first 1/4 wave plate 14 and the second 1/4 wave plate 14 respectively. The wave plate 15 coincides with the reference light and is injected into the cold atomic group 18. The two optical paths form a small angle with the long axis of the cold atomic group 18; the pump light 19 generated by the third laser 4 passes through the third half-wave plate 12, and then Divided into two paths through the second polarization beam splitter 7, the two paths of light pass through the third 1/4 wave plate 16 and the fourth 1/4 wave plate 17 respectively, and are relatively incident with the coupling light 22, and the light paths overlap; the light paths of the coupling light 22 and the pump The optical path of Puguang 19 is shown as the hollow line in Figure 1;

5) The coupling light 22 and the pumping light 19 respectively interact with the cold atomic group 18 to form a four-wave mixing process, and emit a Stokes photon 25 and an anti-Stokes photon 26, specifically:

In the direction of the long axis of the cold atomic group 18, under the action of the pump light 19, an atom transitions from the atomic ground state 20 to the excited state 21, emits a Stokes single photon 25 through spontaneous emission, and the atom returns to another ground state 23 , under the action of coupling light 22, a Raman transition process is caused, the atom immediately transitions to another excited state 24, and emits an anti-Stokes photon 26;

Since the entire four-wave mixing process must satisfy energy conservation, angular momentum conservation, and momentum conservation, the paired Stokes photons 25 and anti-Stokes photons 26 are entangled in time and frequency, and the polarization and coupling light 22 and the pump The light 19 is matched; at the same time, due to the three-level electromagnetically induced transparency effect formed by the coupled light 22 and the anti-Stokes photon 26, the linewidth of the generated entangled photon pair will be narrowed, and a subnatural linewidth entangled photon pair will be obtained;

6) When two paths of coupling light 22 and pumping light 19 exist at the same time, adjust the phase difference between the two paths of the interferometer, set the polarization of coupling light 22 and pumping light 19, and obtain the required subnatural linewidth polarization-entangled photon pairs ;

7) Before the cold radical 18 diffuses, turn off the second laser 3 and the third laser 4, stop emitting the coupling light 22 and the pumping light 19, and return to step 1) for the next preparation, which can be repeated.

The Stokes photons and anti-Stokes photons prepared in the above steps are subnatural linewidth polarization-entangled photon pairs, which are suitable for long-distance quantum communication and quantum storage.

In the above embodiment, the vacuum system is a vacuum cavity, the laser for generating cooling light is a TA100 semiconductor laser, and the first laser, the second laser and the third laser are all DL100 semiconductor lasers.

The above is only a preferred embodiment of the patent of the present invention, but the scope of protection of the patent of the present invention is not limited thereto, as the cold atomic group can also be an atomic gas, and any person familiar with the technical field is described in the patent of the present invention Within the scope of the disclosure, any equivalent replacement or change according to the technical solution of the patent of the present invention and its inventive concept all belong to the protection scope of the patent of the present invention.

Claims (10)

1. A kind of interferometer, this interferometer is Mach-Zehnder interferometer, it is characterized in that: comprise vacuum system, the first laser device, the second laser device, the 3rd laser device, photodetector, the first polarization beam splitter prism, the second Polarizing beam splitter, first reflector and second reflector; the center of the vacuum system produces cold atomic groups, the first laser is used to generate reference light, the second laser is used to generate coupling light, and the first Both the reference light generated by the laser and the coupled light generated by the second laser are aligned with the first polarization beam splitter, and the optical path direction of the reference light is perpendicular to the optical path direction of the coupled light; the third laser is used to generate pumping light, and The generated pumping light is aimed at the second polarization beam splitter, and the photodetector is arranged at the output end of the beam path of the second polarization beam splitter to detect the light intensity; the first reflector is arranged at the first polarization beam splitter In one of the optical paths of the beam splitting by the prism, the second reflector is arranged in one of the optical paths of the second polarizing beam splitting prism, and the first polarizing beam splitting prism and the first reflecting mirror are respectively connected with the second polarizing beam splitting prism, The second mirror is symmetrical about the vacuum system. 2. A kind of interferometer according to claim 1, it is characterized in that: also comprise four half-wave plates and four 1/4 wave plates, four half-wave plates are respectively the first half-wave plate, the second half-wave plate wave plate, the third half wave plate and the fourth half wave plate, the four 1/4 wave plates are the first 1/4 wave plate, the second 1/4 wave plate, the third 1/4 wave plate and the fourth 1/4 wave plate, the first half wave plate is arranged between the first laser and the first polarization beam splitter, and the second half wave plate is arranged between the second laser and the first polarization beam splitter, so The third half-wave plate is arranged between the third laser and the second polarization beam-splitting prism, the fourth half-wave plate is arranged between the photodetector and the second polarization beam-splitting prism, and the first 1/4 wave plate Set between the first polarization beam splitter and the first reflector, the second 1/4 wave plate is set between the first polarization beam splitter and the vacuum system, and the third 1/4 wave plate is set on the second Between the polarization beam splitting prism and the second reflection mirror, the fourth 1/4 wave plate is arranged between the second polarization beam splitting prism and the vacuum system. 3. A kind of interferometer according to claim 1 or 2, characterized in that: the first polarization beam splitter and the second polarization beam splitter are used as an optical path beam splitter or an optical path beam combiner, and the first reflector And the second mirror is used to adjust the light path direction and phase compensation. 4. An interferometer according to claim 1 or 2, characterized in that: the vacuum system is a vacuum chamber. 5. An interferometer according to claim 1 or 2, characterized in that: the first laser, the second laser and the third laser are all DL100 semiconductor lasers. 6. the method for producing subnatural linewidth polarization entangled photon pairs based on the interferometer described in claim 2, is characterized in that comprising the following steps: 1) Build a vacuum system, obtain cold atomic groups in the center of the vacuum system, and prepare to the ground state of four-wave mixing; 2) The reference light generated by the first laser is injected into the interferometer, first passes through the first half-wave plate, and then is divided into two paths by the first polarizing beam splitter prism, one of which passes through the first mirror and the second mirror in turn, and the other One path is synthesized by the second polarization beam splitter prism, and enters the photodetector to detect the light intensity; according to the signal of the photodetector, the piezoelectric ceramic is controlled by the feedback circuit to adjust the position of the first reflector and the second reflector, and stabilize the interferometer Two-way phase difference; 3) The coupled light generated by the second laser passes through the second half-wave plate, and then is divided into two paths by the first polarization beam splitter. The light is recombined and injected into the cold atomic group. The two optical paths form a small angle with the long axis of the cold atomic group; the pump light generated by the third laser passes through the third half-wave plate, and then is divided into two paths by the second polarizing beam splitter. The optical path passes through the third 1/4 wave plate and the fourth 1/4 wave plate respectively, and is relatively incident with the coupling light, and the optical path overlaps; 4) The coupled light and the pump light interact with the cold atom groups respectively to form a four-wave mixing process, and emit a Stokes photon and an anti-Stokes photon. According to the four-wave mixing process, energy conservation, angle Conservation of momentum, conservation of momentum, time and frequency entanglement of Stokes photons and anti-Stokes photons generated in pairs, polarization matching with coupling light and pump light; at the same time, the three pairs of coupled light and anti-Stokes photons The energy-level electromagnetically induced transparency effect will narrow the linewidth of the generated entangled photon pairs, and obtain subnatural linewidth entangled photon pairs; 5) When two channels of coupling light and pumping light exist at the same time, adjust the phase difference between the two channels of the interferometer, set the polarization of coupling light and pumping light, and obtain the required subnatural linewidth polarization-entangled photon pairs. 7. according to claim 6, produce subnatural linewidth polarization entangled photon pair method, it is characterized in that: step 4) described formation four-wave mixing process, emits a Stokes photon and an anti-Stokes Si photon, the details are as follows: In the direction of the long axis of the cold atomic cluster, under the action of pump light, an atom transitions from the atomic ground state to the excited state, and emits a Stokes single photon through spontaneous emission, and the atom returns to another ground state, under the action of coupled light Under the Raman transition process, the atom immediately transitions to another excited state and emits an anti-Stokes photon. 8. The method for producing subnatural linewidth polarization-entangled photon pairs according to claim 6, is characterized in that said method also includes: Before the cold atomic group diffuses, stop emitting coupling light and pump light by turning off the second laser and the third laser, and return to step 1) for the next preparation. 9. The method for generating subnatural linewidth polarization-entangled photon pairs according to any one of claims 6-8, characterized in that: the cold atomic group is obtained by generating cooling light with a laser, and the generation is turned off before step 3). Lasers that cool light allow free diffusion of cold atomic clusters, creating photon-pair-generating windows. 10. The method for generating subnatural linewidth polarization-entangled photon pairs according to claim 9, characterized in that: the laser for generating the cooling light is a TA100 semiconductor laser.