WO2023219002A1

WO2023219002A1 - Quantum wavelength converter, heralded single photon source

Info

Publication number: WO2023219002A1
Application number: PCT/JP2023/016812
Authority: WO
Inventors: 隆朗青木
Original assignee: 学校法人早稲田大学
Priority date: 2022-05-12
Filing date: 2023-04-28
Publication date: 2023-11-16
Also published as: JP2023167667A

Abstract

The present invention achieves a quantum wavelength converter that is easily coupled to an optical fiber. A quantum wavelength converter (2) comprises: an optical fiber (8) that contains a plurality of resonators (34, 36, 38, 40) that have a shared resonance optical path at at least a portion thereof; and a laser light source (6) that is connected to the optical fiber and inputs pump light that has one or more frequencies into the optical fiber. The plurality of resonators satisfy the law of conservation of energy and phase matching conditions for four-wave mixing or parametric conversion at the shared resonance optical path.

Description

Quantum wavelength converter, single photon source with messenger

The present disclosure relates to a quantum wavelength converter and a single photon source with a messenger equipped with the quantum wavelength converter.

As a quantum wavelength conversion technology for converting the wavelength of a photon, a method realized by a nonlinear optical process including parametric down conversion or a four-wave mixing process is generally known. These nonlinear optical processes are also used to generate photon pairs and are also important as the operating principle of single photon sources with messengers.

Non-Patent Document 1 and Non-Patent Document 2 disclose a method for realizing the above-described quantum wavelength conversion using a nonlinear optical crystal bulk such as a KTP crystal. Furthermore, Non-Patent Document 3 and Non-Patent Document 4 disclose a method of realizing the quantum wavelength conversion described above using a nonlinear optical crystal waveguide such as a PPLN waveguide. Furthermore, Non-Patent Document 5 and Non-Patent Document 6 disclose a method of realizing the above-mentioned quantum wavelength conversion using a ring-type microresonator on a chip.

The nonlinear optical crystal bulk, nonlinear optical crystal waveguide, and ring-shaped microresonator used in the quantum wavelength conversion techniques described in Non-Patent Documents 1 to 6 are all difficult to couple with an optical fiber. For this reason, when a quantum wavelength converter using the techniques described in Non-Patent Documents 1 to 6 is introduced into a device that uses an optical fiber as a quantum channel for propagating photons, the optical fiber and the quantum wavelength converter A mechanism is required to connect the two. Therefore, the above-mentioned quantum wavelength converter causes the complexity of the device provided with the quantum wavelength converter.

In order to solve the above problems, a quantum wavelength converter according to one aspect of the present disclosure connects an optical fiber including therein a plurality of resonators having at least a portion of a common resonant optical path, and the optical fiber. , a laser light source that inputs pump light having at least one frequency into the optical fiber, and the plurality of resonators include a first resonator having a first resonant frequency ω ₁ as a resonant frequency, and a second resonator having a first resonant frequency ω1. a second resonator having a resonant frequency ω ₂ as a resonant frequency; a third resonator having a third resonant frequency ω ₃ as a resonant frequency; the first resonant frequency ω ₁ , the second resonant frequency ω ₂ ; a fourth resonator having a fourth resonant frequency ω ₄ different from any of the third frequencies, where n _i is an effective refractive index inside the optical fiber for light having the i-th resonant frequency ω _i , and c is the speed of light, γ is the nonlinear parameter of the optical fiber, and P is the intensity of the pump light,

The above equations (1) and (2) hold true.

A quantum wavelength converter according to another aspect of the present disclosure connects an optical fiber including therein a plurality of resonators having at least a portion of a common resonant optical path, and the optical fiber, and transmits pump light to the optical fiber. the plurality of resonators include a first resonator having a first resonant frequency _ω1 as a resonant frequency, and a third resonator having a third resonant frequency _ω3 as a resonant frequency; a fourth resonator _having a fourth resonant frequency ω ₄ different from both the _first resonant frequency ω ₁ and the third resonant frequency ω ₃ ; The effective refractive index inside the optical fiber, c is the speed of light, γ is the nonlinear parameter of the optical fiber, P is the intensity of the pump light,

The above equations (3) and (4) hold true.

A quantum wavelength converter according to another aspect of the present disclosure connects an optical fiber including therein a plurality of resonators having at least a portion of a common resonant optical path, and the optical fiber, and transmits pump light to the optical fiber. the plurality of resonators include a first resonator having a first resonant frequency _ω1 as a resonant frequency, a second resonator having a second resonant frequency _ω2 as a resonant frequency, a fourth resonator having a fourth resonant frequency _ω4 different from both the first resonant frequency _ω1 and the second resonant frequency _ω2 , and n _i is the light having the i-th resonant frequency ω _i . where c is the speed of light, γ is the nonlinear parameter of the optical fiber, and P is the intensity of the pump light,

The above equations (5) and (6) hold true.

According to one aspect of the present disclosure, it is possible to achieve a quantum wavelength converter that can be easily coupled to an optical fiber and can reduce the complexity of the quantum device when it is introduced into a quantum device using an optical fiber.

FIG. 1 is a schematic plan view of a quantum wavelength converter and a schematic enlarged view of a resonator structure according to Embodiment 1 of the present disclosure. 1 is a schematic enlarged view of a single photon source according to Embodiment 1 of the present disclosure. FIG. 1A and 1B are a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 1 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. They are a schematic plan view of a quantum wavelength converter and a schematic enlarged view of a resonator structure according to Embodiment 2 of the present disclosure. They are a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 2 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG. 3 is a schematic plan view of a quantum wavelength converter and a schematic enlarged view of a resonator structure according to Embodiment 3 of the present disclosure. They are a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 3 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG. 3 is a schematic plan view of a quantum wavelength converter and a schematic enlarged view of a resonator structure according to Embodiment 4 of the present disclosure. They are a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 4 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG. 6 is a schematic plan view of a quantum wavelength converter and a schematic enlarged view of a resonator structure according to Embodiment 5 of the present disclosure. FIG. 7 is a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 5 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG. FIG. 7 is a schematic plan view of a single photon source with a messenger according to Embodiment 6 of the present disclosure. They are a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 6 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG. 7 is a schematic plan view of a single photon source with a messenger according to Embodiment 7 of the present disclosure. They are a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 7 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG. 7 is a schematic plan view of a single photon source with a messenger according to Embodiment 8 of the present disclosure. FIG. 7 is a schematic diagram showing input and output of photons in a resonator structure according to Embodiment 8 of the present disclosure, and an energy diagram showing energy transition in the resonator structure. FIG.

[Embodiment 1]
<Quantum wavelength converter>
For example, the quantum wavelength converter according to the present embodiment converts the wavelength of an input single photon having a specific wavelength and outputs a single photon having a wavelength different from the wavelength. This is a device that converts the wavelength of In particular, the quantum wavelength converter according to this embodiment converts a single photon from a single photon source and pump light from a laser light source into a resonator structure including a plurality of resonators having a common resonant optical path. This is a device that outputs a wavelength-converted single photon from the resonator structure upon input.

A quantum wavelength converter according to this embodiment and a resonator structure included in the quantum wavelength converter will be described with reference to FIG. 1. FIG. 1 is a schematic plan view of a quantum wavelength converter 2 according to the present embodiment, and an enlarged view of a resonator structure 4 included in the quantum wavelength converter 2 in the schematic plan view.

As shown in FIG. 1, the quantum wavelength converter 2 includes a resonator structure 4, a laser light source 6, and a single mode optical fiber 8. Further, the quantum wavelength converter 2 includes a single photon source 10, a dichroic mirror 12, and an optical terminator 14. Note that FIG. 1 also shows a quantum device X into which a wavelength-converted single photon generated by a quantum wavelength converter 2 by a method described later is input. As will be described in detail later, the quantum wavelength converter 2 according to the present embodiment converts a single photon input into the resonator structure 4 from the single photon source 10 into a single photon of a wavelength required by the quantum device This will be explained by taking as an example a quantum wavelength converter that converts .

<Resonator structure>
As shown in FIG. 1, the resonator structure 4 includes a nano-optical fiber portion 16 and both end portions 8A connected to the nano-optical fiber portion 16 via a tapered portion 18. Here, for example, both ends 8A are part of the optical fiber 8 included in the quantum wavelength converter 2. Further, the nano-optical fiber section 16 is heated by a method such as heating a part of the optical fiber 8 with a ceramic heater or various heating methods including oxygen-water flame, etc., and pulling the heated part from both ends. is formed in the heated portion of the . In other words, the resonator structure 4 includes the nano-optical fiber portion 16 and both end portions 8A as part of the optical fiber 8.

The resonator structure 4 further includes a common FBG (fiber Bragg grating) 20, a first FBG 22, a second FBG 24, a third FBG 26, and a fourth FBG 28 at both ends 8A or inside the nano-optical fiber section 16. In particular, in this embodiment, the above-described FBGs are formed in the core part 30 of the core part 30 through which photons propagate and the clad part 32 around the core part 30, which are included in both end parts 8A.

The common FBG 20, the first FBG 22, the second FBG 24, the third FBG 26, and the fourth FBG 28 reflect a portion of photons having a specific frequency. In this specification, the first FBG 22 has a first resonant frequency ω ₁ , the second FBG 24 has a second resonant frequency ω ₂ , the third FBG 26 has a third resonant frequency ω ₃ , and the fourth FBG 28 has a fourth resonant frequency ω ₄ . Reflect some of the photons. Further, the common FBG 20 partially reflects photons having any of the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ .

In this embodiment, the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ are all different frequencies. In other words, in this embodiment, at least the fourth resonant frequency ω ₄ is different from any of the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , and the third resonant frequency ω ₃ .

In this embodiment, of the two end portions 8A formed at both ends of the nano-optical fiber section 16, a common FBG 20 is formed at one end, and a first FBG 22, a second FBG 24, a third FBG 26, and a fourth FBG 28 are formed at the other end. There is. Therefore, a common optical path including at least the photon propagation path of the nano-optical fiber portion 16 is formed between the common FBG 20 and each of the first FBG 22 , the second FBG 24 , the third FBG 26 , and the fourth FBG 28 .

Therefore, in the resonator structure 4, the first resonator 34, the second resonator 36, the third resonator 38, and A fourth resonator 40 is formed. Here, in this embodiment, the first resonator 34, the second resonator 36, the third resonator 38, and the fourth resonator 40 each have a first resonant frequency ω ₁ , a second resonant frequency ω ₂ , The resonance frequency has a third resonance frequency ω ₃ and a fourth resonance frequency ω ₄ . In other words, in each resonator included in the resonator structure 4, photons having a corresponding resonant frequency resonate.

In particular, the first resonator 34, the second resonator 36, the third resonator 38, and the fourth resonator 40 share a propagation path of photons in the nano-optical fiber section 16, which is at least a part of the optical fiber 8. as a resonant optical path. In other words, the resonator structure 4 includes a plurality of resonators, at least some of which have a common resonant optical path.

Furthermore, each of the plurality of resonators has a pair of fiber Bragg gratings whose reflection bands include the respective resonant frequencies. In particular, the common FBG 20 is formed as the same fiber Bragg grating between the plurality of resonators. Note that at least one of the fiber Bragg gratings included in the plurality of resonators included in the resonator structure 4 may be a common FBG 20.

In this embodiment, as described above, the first FBG 22, the second FBG 24, the third FBG 26, and the fourth FBG 28 are individually formed at one both ends 8A. Therefore, in this embodiment, the resonator lengths L1, L2, L3, and L4 of the first resonator 34, the second resonator 36, the third resonator 38, and the fourth resonator 40 are Can be designed independently.

Note that in this embodiment, the first FBG 22, the second FBG 24, the third FBG 26, and the fourth FBG 28 are formed individually, but the invention is not limited to this. For example, in the present embodiment, a continuous fiber Bragg grating may be formed at one of both ends 8A, and chirps may be formed at each of a plurality of positions of the fiber Bragg grating. Accordingly, in this embodiment, each resonator may be formed by reflecting photons of a specific wavelength at the positions where each chirp is formed in the fiber Bragg grating.

<Laser light source, single photon source>
Referring back to the plan view of the quantum wavelength converter 2 in FIG. It is a light source for input. For example, the laser light source 6 may generate pump light that includes multiple frequency bands, or may generate multiple pump lights that include a specific frequency. In particular, in the present embodiment, the laser light source 6 generates a first pump light PL1 having a second resonant frequency ω ₂ and a second pump light PL2 having a third resonant frequency ω ₃ , and generates a first pump light PL1 having a third resonant frequency ω 3. And the second pump light PL2 is input to each resonator of the resonator structure 4.

Next, the single photon source 10 will be described in detail with reference to FIG. 2. FIG. 2 is an enlarged schematic diagram showing the single photon source 10 included in the quantum wavelength converter 2, out of the schematic plan view of the quantum wavelength converter 2 shown in FIG. As shown in FIG. 2, among the components included in the resonator structure 4, the single photon source 10 includes a nano-optical fiber section 16, and both ends connected to the nano-optical fiber section 16 via a tapered section 18. Contains 8A.

However, the single photon source 10 includes a common FBG 20 in the core part 30 at one end 8A of each fiber Bragg grating included in the resonator structure 4, and a first FBG 22 in the core part 30 at the other end 8A. Contains only. Therefore, the single photon source 10 includes only the first resonator 34 among the resonators included in the resonator structure 4 .

Furthermore, the single photon source 10 includes a quantum system 42 formed on the nano-optical fiber section 16. The quantum system 42 includes at least a ground level and an excited level that is a level higher than the ground level, and includes, for example, atoms, ions, diamond having nitrogen defects, quantum dots, and the like. Further, in this embodiment, the level difference between the ground level and the excited level of the quantum system 42 corresponds to the energy of a photon having the first resonance frequency _ω1 .

The single photon source 10 may generate a single photon having a first resonant frequency ω ₁ using, for example, a state transition between the ground level and the excited level of the quantum system 42 . In this case, the single photon source 10 may include, for example, a laser light source (not shown) that can irradiate the quantum system 42 with control light that causes a state transition between the ground level and the excited level of the quantum system 42. good.

The single photon source 10 uses, for example, the Purcell effect in which the spontaneous emission of a single photon accompanying a state transition between the ground level and the excited level is emphasized by the coupling between the quantum system 42 and the first resonator 34. A single photon having a first resonant frequency ω ₁ may be generated in the first resonator 34 based on ω 1 . In other words, the single photon source 10 generates a single photon by using the fact that a single photon is generated when the state of the quantum system 42 is excited by the control light from the laser light source and returns to the ground state again. You may.

Alternatively, the single photon source 10 may generate a single photon in the first resonator 34 by irradiating the quantum system 42 with control light whose amplitude gradually increases from 0. In this case, the waveform of a single photon can be controlled by controlling the temporal change in the amplitude of the control light.

Referring back to FIG. 1, the single photon source 10 is connected to the resonator structure 4 via an optical fiber 8. Therefore, the single photon source 10 inputs the generated single photon having the first resonance frequency ω ₁ to each resonator of the resonator structure 4 as an input single photon IF. The quantum wavelength converter 2 mixes the first pump light PL1 and the second pump light PL2 from the laser light source 6 and the input single photon IF from the single photon source 10 to convert each of the resonator structures 4 A confluencer 44 for inputting to the resonator may be provided.

<Four-wave mixing process>
As described above, in this embodiment, each resonator of the resonator structure 4 receives the first pump light PL1 and the second pump light PL2 from the laser light source 6, and the input single photon IF from the single photon source 10. is input. In this embodiment, the resonator structure 4 generates an output photon having a fourth resonant frequency ω ₄ by a four-wave mixing process using the input first pump light PL1, second pump light PL2, and input single photon IF. Generate OF. In this embodiment, the output photon OF is a single photon.

The generation of output photons OF by the resonator structure 4 will be explained in more detail with reference to FIG. 3. FIG. 3 is a schematic diagram 4A for explaining input and output of photons in the resonator structure 4, and an energy diagram D1 showing state transitions occurring in the resonator structure 4.

As shown in the schematic diagram 4A of FIG. 3, the resonator structure 4 includes a single input photon IF having a first resonant frequency ω ₁ , a first pump light PL1 having a second resonant frequency ω ₂ , and a third resonant Second pump light PL2 having a frequency ω ₃ is input. As a result, as shown in schematic diagram 4A, an output photon OF having a fourth resonant frequency ω ₄ is output from the resonator structure 4 by a method described below.

Here, in this embodiment, the following equations (1) and (2) are used for the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ holds true.

In the above two equations, n _i is the effective refractive index inside the nano-optical fiber section 16 for light having the i-th resonance frequency ω _i . In the above two equations, c is the speed of light, γ is the nonlinear coefficient of the nano-optical fiber section 16, and P is the total intensity of the pump light from the laser light source 6.

Here, in the nano-optical fiber section 16 included in the common optical path of each resonator of the resonator structure 4, as shown in the energy diagram D1 of FIG. Set. Further, the energy difference between the ground level g and the excited level e is made approximately equal to the total value of the energy of photons having the first resonance frequency ω ₁ and the energy of photons having the second resonance frequency ω ₂ . Note that from the above equation (1), ω ₁ +ω ₂ =ω ₃ +ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of a photon having the third resonance frequency ω ₃ . It is also approximately the same as the total value of the energy of photons having the fourth resonance frequency _ω4 .

When the above two equations hold true, a state transition shown in the energy diagram D1 occurs in the nano-optical fiber section 16 due to the single input photon IF, the first pump light PL1, and the second pump light PL2. Specifically, the single input photon IF and the first pump light PL1 cause excitation from the ground level g to the excited level e. In addition to the excitation, the second pump light PL2 causes a transition from the excitation level e to the middle of the two levels. As a result, an output photon OF having a fourth resonant frequency ω ₄ is generated, which has an energy corresponding to the difference between the energy of the second pump light PL2 and the energy difference between the ground level g and the excited level e. .

As a result of the above, a four-wave mixing process occurs in the nano-optical fiber section 16. In other words, each resonator of the resonator structure 4 according to the present embodiment satisfies the energy conservation law and phase matching conditions of the four-wave mixing process in the nano-optical fiber section 16, which is a common resonant optical path. Here, of the above two equations, equation (1) represents the energy conservation law of the four-wave mixing process, and equation (2) represents the phase matching condition of the four-wave mixing process.

Here, each resonator of the resonator structure 4 including the nano-optical fiber section 16 as a common resonant optical path has a first resonant frequency ω ₁ , a second resonant frequency ω ₂ , a third resonant frequency ω ₃ , and a fourth resonant frequency ω 3 . It couples with light having a resonant frequency ω ₄ . Therefore, each resonator of the resonator structure 4 promotes the above-mentioned four-wave mixing process in the nano-optical fiber section 16, and the generation of output photons OF in the resonator structure 4 is promoted.

<Free spectrum range design>
Here, the resonance condition of each resonator of the resonator structure 4 is expressed as (ni _· ω _i ·Li/c)+φ _i =m _i ·π. In the equation of the resonance condition, c is the speed of light, n _i is the group refractive index in the i-th resonator, Li is the resonator length of the i-th resonator, and φ _i reflects the photon having the i-th resonance frequency ω _i The phase change of the photon in the fiber Bragg grating, m _i , is a natural number. Here, in general, n _i and φ _i may depend on the frequency of the photon. Therefore, when the resonator length Li is the same and the dispersion of the fiber Bragg grating included in the resonator structure 4 is ignored, at the i-th resonance frequency ω _i that satisfies the resonance condition of each resonator of the resonator structure 4, , the above formula (2) generally does not hold.

Therefore, in the present embodiment, the resonator length Li of each resonator of the resonator structure 4 is individually designed, or the resonator length Li of each resonator is designed in consideration of the dispersion added by the fiber Bragg grating of each resonator. Design each resonator. Accordingly, in this embodiment, each resonator of the resonator structure 4 is designed so that the above formula (2) holds true. For example, as described above, by individually forming the first FBG 22, the second FBG 24, the third FBG 26, and the fourth FBG 28 for the common FBG 20, the resonator length Li of each resonator can be individually designed.

Thereby, in each resonator, it is possible to individually design a resonator length Li that satisfies the resonance condition (n _i ·ω _i ·Li/c)+φ _i =m _i ·π. Note that, as long as the above formula (2) is satisfied, the resonator length Li of each resonator included in the resonator structure 4 is not particularly limited. Therefore, the magnitude relationship of the resonator lengths Li of each resonator included in the resonator structure 4 is not limited to the magnitude relationship shown in FIG. 1 and the like.

Therefore, in the resonator structure 4 according to the present embodiment, each resonator can be easily designed to satisfy the above formula (2). In addition, since the resonator structure 4 individually forms one of the pair of fiber Bragg gratings for each resonator, the resonator length Li for each resonator is stable against disturbances such as temperature changes or vibrations. can be performed independently.

<Dichroic mirror, optical terminator>
With the above, the resonator structure 4 generates an output photon OF having the fourth resonant frequency ω ₄ . Returning to FIG. 1, the output photons OF output from the resonator structure 4 enter the dichroic mirror 12 via the optical fiber 8. However, the single input photon IF from the single photon source 10, the first pump light PL1 from the laser light source 6, and the second pump light PL2 are also emitted from the resonator structure 4, and enter the dichroic mirror 12. .

The dichroic mirror 12 is a mirror that transmits or reflects photons of a specific frequency. In this embodiment, the dichroic mirror 12 is installed so that the transmitted photons are incident on the quantum device X, and the reflected photons are incident on the optical terminator 14. Note that the quantum wavelength converter 2 according to this embodiment may include a plurality of dichroic mirrors 12 that transmit or reflect photons with different frequencies.

In this embodiment, the dichroic mirror 12 reflects photons having a first resonant frequency ω ₁ , a second resonant frequency ω ₂ , and a third resonant frequency ω ₃ and transmits photons having a fourth resonant frequency ω ₄ . Therefore, the dichroic mirror 12 receives a single input photon IF with a first resonant frequency ω ₁ , a first pump light PL1 with a second resonant frequency ω ₂ , and a second pump light PL2 with a third resonant frequency ω ₃ . It is reflected and made incident on the optical terminator 14. Furthermore, the dichroic mirror 12 transmits the output photon OF having the fourth resonance frequency ω ₄ and makes it incident on the quantum device X. In other words, the dichroic mirror 12 limits the photons that enter the quantum device X among the photons emitted from the resonator structure 4 to only the output photons OF.

Note that, instead of the dichroic mirror 12, the quantum wavelength converter 2 according to this embodiment may include a diffraction grating that diffracts the light emitted from the resonator structure 4 in different directions for each wavelength. Furthermore, the quantum wavelength converter 2 according to this embodiment may include a WDM filter that separates the light emitted from the resonator structure 4 instead of the dichroic mirror 12.

The optical terminator 14 is, for example, an optical element that converts the energy of incident photons into energy such as heat, thereby causing the photons to disappear without being reflected or dispersed. With the optical terminator 14, the quantum wavelength converter 2 reduces the output of the single input photon IF, the first pump light PL1, and the second pump light PL2 emitted from the resonator structure 4 to the outside.

However, the quantum wavelength converter 2 may further include another resonator structure 4 instead of the optical terminator 14, and the photons reflected by the dichroic mirror 12 may be incident on the resonator structure 4. good. Thereby, the quantum wavelength converter 2 may generate output photons OF in each of the plurality of resonator structures 4.

<Summary of Embodiment 1>
The quantum wavelength converter 2 according to the present embodiment converts a single input photon IF having a first resonance frequency ω ₁ generated by the single photon source 10 into a fourth resonance having a frequency different from the first resonance frequency ω ₁ . It can be converted into an output photon OF with frequency ω ₄ . Further, the quantum wavelength converter 2 inputs the output photon OF to the quantum device X. Thereby, even if there is a difference between the frequency of photons generated by the single photon source 10 and the frequency of photons required by the quantum device The frequency of the photon can be converted and input into the quantum device X.

In this embodiment, for example, as shown in the energy diagram D1 of FIG. 3, the fourth resonant frequency _ω4 is set to be a frequency lower than any of the other resonant frequencies. However, the present invention is not limited to this, and the fourth resonant frequency ω ₄ may be higher than any of the resonant frequencies. In this embodiment, for example, the fourth resonant frequency ω ₄ may be made larger than the third resonant frequency ω ₃ . In this embodiment, the frequencies of the first pump light PL1 and the second pump light PL2 and the resonator of each resonator included in the resonator structure 4 are set so that the above formulas (1) and (2) are satisfied. The fourth resonant frequency ω ₄ may be changed by changing the design such as length.

The quantum wavelength converter 2 according to the present embodiment includes, as part of the optical fiber 8, a common resonant optical path of each resonator into which pump light and the like are input and which generate photons after wavelength conversion. Therefore, even if a quantum device that emits photons before wavelength conversion or a quantum device that requires photons after wavelength conversion has an optical fiber, the quantum wavelength converter 2 according to the present embodiment can be used. , easily realizes coupling with the optical fiber. Therefore, even when the quantum wavelength converter 2 is incorporated into a quantum device including an optical fiber, the complexity of the structure of the quantum device is reduced.

Note that, although the quantum wavelength converter 2 converts the wavelength of the single input photon IF generated by the single photon source 10, the present invention is not limited thereto. For example, the quantum wavelength converter 2 may convert the wavelength of a photon having the first resonant frequency ω ₁ output from a quantum computing unit in a quantum computer or a quantum repeater in a quantum communication device. Alternatively, the quantum wavelength converter 2 may further convert the wavelength of the output photon OF generated by another quantum wavelength converter 2.

Generally, in a quantum processing unit or quantum repeater that includes atoms as a quantum system, when the atoms and photons interact, in order to ensure sufficient coherence time in the atoms, the excitation between the ground level of the atom and immediately above it is required. Transitions between levels are often used. In this case, the wavelength of the photon is generally required to be less than 1 μm in order to cause the atom to interact with the photon.

On the other hand, in order to perform further operations using photons used in operations in a certain quantum operation unit, to propagate the photons to other quantum operation units, or to propagate photons between multiple quantum repeaters. For this purpose, single mode optical fibers are generally used. Here, in general, in order to sufficiently reduce the loss of photons in an optical fiber, the wavelength of photons propagating through the optical fiber is included in the communication wavelength band, which is a wavelength band of 1.3 μm or more and 1.6 μm or less. There are many.

The quantum wavelength converter 2 according to the present embodiment converts photons with a wavelength of less than 1 μm, which are output from the quantum operation unit or quantum repeater described above, into photons with a wavelength of 1.3 μm or more and 1.6 μm or less, for example. However, it may also be propagated through an optical fiber. Then, another quantum wavelength converter 2 may convert the photon propagating in the optical fiber into a photon having a wavelength of less than 1 μm again, and then input the photon to another quantum processing unit or quantum repeater. In this case, the quantum wavelength converter 2 provides a low-loss propagation of photons in a plurality of quantum computing units or quantum repeaters.

In this embodiment, the common resonant optical path in each resonator of the resonator structure 4 includes a nano-optical fiber portion 16 having a smaller diameter than both end portions 8A. Therefore, due to the small mode cross section, the above-mentioned four-wave mixing process occurs more significantly in the nano-optical fiber portion 16 than in other portions of the optical fiber 8. Therefore, the quantum wavelength converter 2 according to this embodiment can improve the conversion efficiency from a single input photon IF to an output photon OF.

In this embodiment, each resonator of the resonator structure 4 has a pair of fiber Bragg gratings. Therefore, in the quantum wavelength converter 2, each resonator of the resonator structure 4 can be configured more simply than when the quantum wavelength converter 2 includes an optical element such as a pair of mirrors or a ring resonator. Furthermore, between the plurality of resonators, at least a portion of the fiber Bragg grating is the same common FBG 20. Therefore, in the quantum wavelength converter 2, each resonator of the resonator structure 4 can be configured more simply than when each resonator is provided with a pair of independent fiber Bragg gratings. As mentioned above, by forming one of the pair of fiber Bragg gratings in each resonator in common and forming the other individually, the quantum wavelength converter 2 can improve the design of the resonator length of each resonator. You can do it easily.

Note that the quantum wavelength converter 2 may input pump light having the first resonant frequency ω ₁ emitted from the laser light source 6 to the resonator structure 4 instead of the single input photon IF. In this case, by sufficiently increasing the intensity of each pump light emitted from the laser light source 6, the resonator structure 4 generates coherent photons having a fourth resonant frequency _ω4 . In other words, the quantum wavelength converter 2 may also function as an optical parametric oscillator. Note that the quantum wavelength converter according to each embodiment described in this specification, not limited to this embodiment, is an optical parametric converter that generates coherent photons having a fourth resonance frequency ω ₄ from pump light from a laser light source. It may also function as an oscillator.

[Embodiment 2]
<Wavelength conversion using parametric down conversion>
FIG. 4 is a schematic plan view of the quantum wavelength converter 46 according to the present embodiment, and an enlarged view of the resonator structure 48 included in the quantum wavelength converter 46 in the schematic plan view. The quantum wavelength converter 46 according to this embodiment differs in configuration from the quantum wavelength converter 2 according to the previous embodiment only in that it includes a resonator structure 48 instead of the resonator structure 4. In the following embodiments, unless otherwise specified, members that have the same configuration or perform the same functions in different embodiments will be designated by the same member numbers, and detailed explanations thereof will be omitted. do.

The resonator structure 48 according to this embodiment differs in configuration from the resonator structure 4 according to the previous embodiment in that it does not include the second FBG 24 and the second resonator 36. Therefore, the resonator structure 48 includes a first resonator 34, a third resonator 38, each having a first resonant frequency ω ₁ , a third resonant frequency ω ₃ , and a fourth resonant frequency ω ₄ as resonant frequencies, respectively. and a fourth resonator 40. Further, the resonator structure 48 includes at least the nano-optical fiber section 16 as a common resonant optical path of the first resonator 34, the third resonator 38, and the fourth resonator 40.

Further, in this embodiment, the laser light source 6 inputs the second pump light PL2 having the third resonance frequency ω ₃ to the resonator structure 48, and does not emit the first pump light PL1. Therefore, the second pump light PL2 from the laser light source 6 and the single input photon IF generated by the single photon source 10 are input to the resonator structure 48 according to this embodiment. In this embodiment, the resonator structure 48 generates an output photon OF having a fourth resonant frequency ω ₄ by parametric down-conversion using the input second pump light PL2 and the input single photon IF.

The generation of output photons OF by the resonator structure 48 will be explained in more detail with reference to FIG. 5. FIG. 5 is a schematic diagram 48A for explaining the input and output of photons in the resonator structure 48, and an energy diagram D2 showing state transitions occurring in the resonator structure 48.

As shown in the schematic diagram 48A of FIG. 5, a single input photon IF having a first resonant frequency ω ₁ and a second pump light PL2 having a third resonant frequency ω ₃ are input to the resonator structure 48. . As a result, as shown in schematic diagram 48A, an output photon OF having a fourth resonant frequency ω ₄ is output from the resonator structure 48 by a method described below. Also in this embodiment, the output photon OF is a single photon.

Here, in this embodiment, for the first resonant frequency ω ₁ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ , the above-mentioned equations (1) and (2) are replaced by the following equation (3). ) and the equation (4) is established.

In this embodiment, as shown in the energy diagram D2 of FIG. 5, the energy difference between the ground level g and the excited level e in the nano-optical fiber section ₁₆ is expressed as The energy is approximately the same as that of Note that from the above equation (3), ω ₁ = ω ₃ + ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of the photon having the third resonance frequency ω ₃ and the fourth It is also approximately the same as the total value of the energy of photons having a resonant frequency ω ₄ .

When the above two equations hold true, the state transition shown in the energy diagram D2 occurs in the nano-optical fiber section 16 due to the single input photon IF and the second pump light PL2. Specifically, a single input photon IF causes excitation from the ground level g to the excited level e. In addition to the excitation, the second pump light PL2 causes a transition from the excitation level e to the middle of the two levels. As a result, an output photon OF having a fourth resonant frequency ω ₄ is generated, which has an energy corresponding to the difference between the energy of the second pump light PL2 and the energy difference between the ground level g and the excited level e. .

As a result of the above, parametric downward conversion occurs in the nano-optical fiber section 16. In other words, each resonator of the resonator structure 48 according to this embodiment satisfies the energy conservation law and phase matching conditions for parametric down conversion in the nano-optical fiber section 16, which is a common resonant optical path. Here, of the above two equations, equation (3) represents the energy conservation law of parametric down transformation, and equation (4) represents the phase matching condition of parametric down transformation.

Here, the four-wave mixing process, which is a third-order nonlinear optical effect, occurs significantly even in materials with inversion symmetry, whereas the parametric down-conversion, which is a second-order nonlinear optical effect, occurs significantly even in materials with inversion symmetry. , occurs significantly in materials without inversion symmetry. Generally, for example, when a single mode optical fiber is made of silica glass, the optical fiber has inversion symmetry. However, in nano-optical fibers, the effect of the surface having no inversion symmetry as a structure becomes significant, and second-order nonlinear optical effects are observed. Therefore, in each resonator including the nano-optical fiber section 16 in a common resonant optical path, like the resonator structure 48 according to the present embodiment, not only the four-wave mixing process but also the parametric downward conversion significantly occurs. do.

As a result, the resonator structure 48 generates an output photon OF having a fourth resonant frequency ω ₄ . Returning to FIG. 4, the output photon OF output from the resonator structure 48 passes through the dichroic mirror 12 and enters the quantum device X. Furthermore, the single input photon IF from the resonator structure 48 and the second pump light PL2 are reflected by the dichroic mirror 12, enter the optical terminator 14, and disappear.

Like the quantum wavelength converter 2, the quantum wavelength converter 46 according to this embodiment receives a single input photon IF having a first resonant frequency ω ₁ generated by the single photon source 10 and a single input photon IF having a fourth resonant frequency ω _4. The output photon OF can be converted into an output photon OF and input into the quantum device X. Furthermore, the resonator structure 48 of the quantum wavelength converter 46 does not include the second resonator 36 compared to the resonator structure 4 of the quantum wavelength converter 2, and thus contains one fewer resonator. . Therefore, the quantum wavelength converter 46 can configure the resonator structure 48 more simply than the quantum wavelength converter 2, and also makes the design of the resonator structure 48 easier. The quantum wavelength converter 46 converts the wavelength of a photon using parametric down conversion, so compared to the quantum wavelength converter 2, the single photon input to the resonator structure 48 is converted into a photon with a longer wavelength and lower frequency. This is useful when you want to convert to .

[Embodiment 3]
<Wavelength conversion using parametric upward conversion>
FIG. 6 is a schematic plan view of the quantum wavelength converter 50 according to the present embodiment, and an enlarged view of the resonator structure 52 included in the quantum wavelength converter 50 in the schematic plan view. The quantum wavelength converter 50 according to the present embodiment differs in configuration from the quantum wavelength converter 2 according to the first embodiment only in that it includes a resonator structure 52 instead of the resonator structure 4.

The resonator structure 52 according to this embodiment differs in configuration from the resonator structure 4 in that it does not include the third FBG 26 and the third resonator 38. Therefore, the resonator structure 52 includes a first resonator 34, a second resonator 36, each having a first resonant frequency ω ₁ , a second resonant frequency ω ₂ , and a fourth resonant frequency ω ₄ as resonant frequencies, respectively. and a fourth resonator 40. Further, the resonator structure 52 includes at least the nano-optical fiber section 16 as a common resonant optical path of the first resonator 34, the second resonator 36, and the fourth resonator 40.

Furthermore, in this embodiment, the laser light source 6 inputs the first pump light PL1 having the second resonance frequency ω ₂ to the resonator structure 52, and does not emit the second pump light PL2. Therefore, the first pump light PL1 from the laser light source 6 and the single input photon IF generated by the single photon source 10 are input to the resonator structure 52 according to this embodiment. In this embodiment, the resonator structure 52 generates an output photon OF having a fourth resonant frequency ω ₄ by parametric upward conversion using the input first pump light PL1 and the input single photon IF.

The generation of output photons OF by the resonator structure 52 will be described in more detail with reference to FIG. 7. FIG. 7 is a schematic diagram 52A for explaining input and output of photons in the resonator structure 52, and an energy diagram D3 showing state transitions occurring in the resonator structure 52.

As shown in the schematic diagram 52A of FIG. 7, a single input photon IF having a first resonant frequency ω ₁ and a first pump light PL1 having a second resonant frequency ω ₂ are input to the resonator structure 52. . As a result, as shown in the schematic diagram 52A, an output photon OF having the fourth resonant frequency ω ₄ is output from the resonator structure 52 by a method described below. Also in this embodiment, the output photon OF is a single photon.

Here, in this embodiment, for the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , and the fourth resonant frequency ω ₄ , the above-mentioned equations (1) and (2) are replaced by the following equations (5 ) and the equation (6) is established.

In this embodiment, as shown in the energy diagram D3 of FIG. 7, the energy difference between the ground level g and the excited level e in the nano-optical fiber section ₁₆ is expressed as It is assumed that the energy of is almost the same as that of Note that from the above equation (5), ω ₁ +ω ₂ =ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of the photon having the first resonance frequency ω ₁ and the second It is approximately the same as the total value of the energy of a photon having a resonant frequency ω ₂ .

When the above two equations hold true, the state transition shown in the energy diagram D3 occurs in the nano-optical fiber section 16 due to the single input photon IF and the first pump light PL1. Specifically, the single input photon IF and the first pump light PL1 cause excitation from the ground level g to the excited level e. As a result, an output photon OF with a fourth resonant frequency ω ₄ is generated, which has an energy corresponding to the energy difference between the ground level g and the excited level e.

As a result of the above, parametric upward conversion occurs in the nano-optical fiber section 16. In other words, each resonator of the resonator structure 52 according to this embodiment satisfies the law of energy conservation and phase matching conditions for parametric upward conversion in the nano-optical fiber section 16, which is a common resonant optical path. Here, of the above two equations, equation (5) represents the energy conservation law of parametric upward transformation, and equation (6) represents the phase matching condition of parametric upward transformation.

Here, parametric upward conversion is a second-order nonlinear optical effect like parametric downward conversion, so it occurs significantly in a substance that does not have inversion symmetry. However, in the nano-optical fiber section 16 where the effect of the surface having no inversion symmetry as a structure is significant, parametric upward conversion also occurs significantly.

As a result, the resonator structure 52 generates an output photon OF having the fourth resonant frequency ω ₄ . Returning to FIG. 6, the output photon OF output from the resonator structure 52 passes through the dichroic mirror 12 and enters the quantum device X. Further, the single input photon IF from the resonator structure 52 and the first pump light PL1 are reflected by the dichroic mirror 12, enter the optical terminator 14, and disappear.

Like the quantum wavelength converter 2, the quantum wavelength converter 50 according to the present embodiment receives a single input photon IF having a first resonant frequency ω ₁ generated by the single photon source 10 and a single input photon IF having a fourth resonant frequency ω ₄ . The output photon OF can be converted into an output photon OF and input into the quantum device X. Furthermore, the resonator structure 52 of the quantum wavelength converter 50 does not include the third resonator 38 compared to the resonator structure 4 of the quantum wavelength converter 2, and thus contains one fewer resonator. . Therefore, the quantum wavelength converter 50 can configure the resonator structure 52 more simply than the quantum wavelength converter 2, and also makes the design of the resonator structure 52 easier. Quantum wavelength converter 50 converts the wavelength of a photon using parametric upward conversion, so compared to quantum wavelength converter 2 and quantum wavelength converter 46, quantum wavelength converter 50 converts a single photon input into resonator structure 52 more easily. This is useful when you want to convert photons with short wavelengths and high frequencies.

[Embodiment 4]
<Wavelength conversion of pump light>
FIG. 8 is a schematic plan view of the quantum wavelength converter 54 according to the present embodiment, and a schematic diagram showing an enlarged view of the resonator structure 56 included in the quantum wavelength converter 54 in the schematic plan view. Compared to the quantum wavelength converter 2 according to the first embodiment, the quantum wavelength converter 54 according to the present embodiment includes a resonator structure 56 instead of the resonator structure 4, and a single photon source 10. The configuration differs only in that it is not. Therefore, the quantum wavelength converter 54 does not need to include the combiner 44.

The resonator structure 56 according to this embodiment has the same configuration as the resonator structure 48 except for the relationship in size between the resonator lengths of the respective resonators. In particular, in this embodiment, L3 is longer than L1. For example, the resonator structure 56 corresponds to the resonator structure 4 in which the second FBG 24 is the same as the first FBG 22, and the first resonator 34 is the same as the second resonator 36. In this case, in this embodiment, the second resonant frequency ω ₂ can be considered to be the same as the first resonant frequency ω ₁ .

Therefore, the resonator structure 56 includes a first resonator 34, a third resonator 38, each having a first resonant frequency ω ₁ , a third resonant frequency ω ₃ , and a fourth resonant frequency ω ₄ as resonant frequencies, respectively. and a fourth resonator 40. Further, the resonator structure 56 includes at least the nano-optical fiber section 16 as a common resonant optical path of the first resonator 34, the third resonator 38, and the fourth resonator 40.

Further, in this embodiment, the laser light source 6 inputs the first pump light PL1 having the second resonant frequency ω ₂ and the second pump light PL2 having the third resonant frequency ω ₃ to the resonator structure 56 . Note that in this embodiment, since the second resonant frequency ω ₂ can be considered to be the same as the first resonant frequency ω ₁ , the first pump light PL1 can be considered to have the first resonant frequency ω ₁ . In this embodiment, the resonator structure 56 generates output photons OF having a fourth resonant frequency ω ₄ through a four-wave mixing process using the input first pump light PL1 and second pump light PL2.

The generation of output photons OF by the resonator structure 56 will be explained in more detail with reference to FIG. 9. FIG. 9 is a schematic diagram 56A for explaining the input and output of photons in the resonator structure 56, and an energy diagram D4 showing state transitions occurring in the resonator structure 56.

As shown in the schematic diagram 56A of FIG. 9, a first pump light PL1 having a first resonant frequency ω ₁ and a second pump light PL2 having a third resonant frequency ω ₃ are input to the resonator structure 56. . As a result, as shown in schematic diagram 56A, an output photon OF having a fourth resonant frequency ω ₄ is output from the resonator structure 56 by a method described below. In this embodiment, the output photon OF may be a single photon or may include multiple photons emitted from the resonator structure 56 substantially simultaneously.

Here, in this embodiment, for the first resonant frequency ω ₁ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ , in the above-mentioned equations (1) and (2), ω ₁ =ω ₂ The following formula holds true.

Here, in this embodiment _, as shown in the energy diagram D4 of FIG. The energy is approximately equal to twice the energy of . Note that from the above equation (5), 2ω ₁ =ω ₃ +ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of the photon having the third resonance frequency ω ₃ and the fourth It is also approximately the same as the total value of the energy of photons having a resonant frequency ω ₄ .

When the above two equations hold true, the state transition shown in the energy diagram D4 occurs in the nano-optical fiber section 16 due to the first pump light PL1 and the second pump light PL2. Specifically, the first pump light PL1 causes excitation from the ground level g to half the energy difference between the ground level g and the excited level e, and the excitation by the first pump light PL1 continues. occurs. Therefore, the first pump light PL1 causes excitation from the ground level g to the excitation level e. Excitation from the ground level g to the excited level e occurs more efficiently in proportion to the intensity of the first pump light PL1.

In addition to the excitation, the second pump light PL2 causes a transition from the excitation level e to the middle of the two levels. As a result, an output photon OF having a fourth resonant frequency ω ₄ is generated, which has an energy corresponding to the difference between the energy of the second pump light PL2 and the energy difference between the ground level g and the excited level e. .

As a result of the above, a four-wave mixing process occurs in the nano-optical fiber section 16. In other words, each resonator of the resonator structure 56 according to the present embodiment satisfies the energy conservation law and phase matching condition of the four-wave mixing process in the nano-optical fiber section 16, which is a common resonant optical path. Note that the four-wave mixing process in this embodiment is a degenerate four-wave mixing process that corresponds to the case where ω ₁ =ω ₂ in the four-wave mixing process in Embodiment 1. However, since the degenerate four-wave mixing process in this embodiment is a third-order nonlinear optical effect, like the non-degenerate four-wave mixing process in the first embodiment, it significantly occurs in the optical fiber 8.

As a result, the resonator structure 56 generates an output photon OF having a fourth resonant frequency ω ₄ . Returning to FIG. 8, the output photon OF output from the resonator structure 56 passes through the dichroic mirror 12 and enters the quantum device X. Further, the first pump light PL1 and the second pump light PL2 from the resonator structure 56 are reflected by the dichroic mirror 12, enter the optical terminator 14, and disappear.

The quantum wavelength converter 54 according to the present embodiment generates output photons OF having a fourth resonance frequency ω ₄ by converting the wavelength of the pump light from the laser light source 6, and can input them into the quantum device X. can.

Furthermore, the resonator structure 56 of the quantum wavelength converter 54 does not include the second resonator 36 compared to the resonator structure 4 of the quantum wavelength converter 2, and thus contains one fewer resonator. . Therefore, the quantum wavelength converter 54 can configure the resonator structure 56 more simply than the quantum wavelength converter 2, and also makes the design of the resonator structure 56 easier.

[Embodiment 5]
<Second harmonic generator>
FIG. 10 is a schematic plan view of the quantum wavelength converter 58 according to the present embodiment, and an enlarged view of the resonator structure 60 included in the quantum wavelength converter 58 in the schematic plan view. The quantum wavelength converter 58 according to this embodiment differs in configuration from the quantum wavelength converter 54 according to the previous embodiment only in that it includes a resonator structure 60 instead of the resonator structure 56.

The resonator structure 60 according to this embodiment differs in configuration from the resonator structure 4 in that it does not include the second FBG 24, the third FBG 26, the second resonator 36, and the third resonator 38. For example, the resonator structure 60 corresponds to the resonator structure 52 in which the second FBG 24 is the same as the first FBG 22, and the first resonator 34 is the same as the second resonator 36. In this case, in this embodiment, the second resonant frequency ω ₂ can be considered to be the same as the first resonant frequency ω ₁ .

Therefore, the resonator structure 60 includes a first resonator 34 and a fourth resonator 40, each having a first resonant frequency ω ₁ and a fourth resonant frequency ω ₄ as resonant frequencies. Further, the resonator structure 60 includes at least the nano-optical fiber section 16 as a common resonant optical path of the first resonator 34 and the fourth resonator 40.

Further, in this embodiment, the laser light source 6 inputs the first pump light PL1 having the second resonance frequency ω ₂ to the resonator structure 56 . Note that in this embodiment, since the second resonant frequency ω ₂ can be considered to be the same as the first resonant frequency ω ₁ , the first pump light PL1 can be considered to have the first resonant frequency ω ₁ . In this embodiment, the resonator structure 60 generates an output photon OF having a fourth resonant frequency ω ₄ through parametric upward conversion using the input first pump light PL1.

The generation of output photons OF by the resonator structure 60 will be explained in more detail with reference to FIG. 11. FIG. 11 is a schematic diagram 60A for explaining input and output of photons in the resonator structure 60, and an energy diagram D5 showing state transitions occurring in the resonator structure 60.

As shown in the schematic diagram 60A of FIG. 11, the first pump light PL1 having the first resonance frequency _ω1 is input to the resonator structure 60. As a result, as shown in the schematic diagram 60A, an output photon OF having the fourth resonant frequency ω ₄ is output from the resonator structure 60 by a method described below. In this embodiment, the output photon OF may be a single photon or may include multiple photons emitted from the resonator structure 56 substantially simultaneously.

Here, in this embodiment, the equations ω ₁ =ω 2 hold true in the above-mentioned equations (5) and ( ₆ ) for the first resonant frequency ω ₁ and the fourth resonant frequency ω ₄ .

Here, in this embodiment, as shown in the energy diagram D5 of FIG. 11, the energy difference between the ground level g and the excited level e in the nano-optical fiber section ₁₆ is expressed as The energy is approximately equal to twice the energy of . Note that from the above equation (5), since 2ω ₁ = ω ₄ holds, the energy difference between the ground level g and the excited level e is approximately the same as the energy of a photon having the fourth resonance frequency ω ₄ . .

When the above two equations hold true, the state transition shown in the energy diagram D5 occurs in the nano-optical fiber section 16 due to the first pump light PL1. Specifically, the first pump light PL1 causes excitation from the ground level g to an energy that is half the energy difference between the ground level g and the excited level e. Here, if the intensity of the first pump light PL1 is sufficiently strong, further excitation by the first pump light PL1 occurs continuously. Therefore, the first pump light PL1 causes excitation from the ground level g to the excitation level e. As a result, an output photon OF with a fourth resonant frequency ω ₄ is generated, which has an energy corresponding to the energy difference between the ground level g and the excited level e.

As a result of the above, parametric upward conversion occurs in the nano-optical fiber section 16. In other words, each resonator of the resonator structure 60 according to this embodiment satisfies the law of energy conservation and phase matching conditions for parametric upward conversion in the nano-optical fiber section 16, which is a common resonant optical path.

Accordingly, the resonator structure 60 generates an output photon OF having the fourth resonant frequency ω ₄ . Returning to FIG. 10, the output photon OF output from the resonator structure 60 passes through the dichroic mirror 12 and enters the quantum device X. Further, the first pump light PL1 from the resonator structure 60 is reflected by the dichroic mirror 12, enters the optical terminator 14, and disappears.

The quantum wavelength converter 58 according to this embodiment generates an output photon OF having a fourth resonance frequency ω ₄ by converting the wavelength of the pump light from the laser light source 6, and inputs the output photon OF to the quantum device X. can. In particular, since the fourth resonant frequency ω ₄ is twice the first resonant frequency ω ₁ , the parametric upconversion occurring in the resonator structure 60 is a so-called second harmonic generation. In other words, the quantum wavelength converter 58 functions as a second harmonic generator that generates output photons OF having a frequency twice the frequency of the pump light from the laser light source 6.

Further, the resonator structure 60 of the quantum wavelength converter 58 does not include the second resonator 36 and the third resonator 38 compared to the resonator structure 4 of the quantum wavelength converter 2, so the resonator structure 60 does not include the second resonator 36 and the third resonator 38. There are two fewer pieces. Therefore, the quantum wavelength converter 58 can configure the resonator structure 60 more simply than the quantum wavelength converter 2, and also makes the design of the resonator structure 60 easier.

[Embodiment 6]
<Single photon source with messenger>
Generating photon pairs and single photons with a messenger by converting the wavelength of pump light from a laser light source using a quantum wavelength converter including the resonator structure according to each of the embodiments described above. I can do it. Hereinafter, a single photon source with a messenger according to this embodiment, which is equipped with a quantum wavelength converter, will be described. FIG. 12 is a schematic plan view of the messenger-equipped single photon source 62 according to this embodiment.

As shown in FIG. 12, the single photon source with messenger 62 includes a quantum wavelength converter 64, a dichroic mirror 66, a single photon detector 68, a first output optical fiber 70, and a second output optical fiber 72. Equipped with. The quantum wavelength converter 64 differs in configuration from the quantum wavelength converter 2 according to the first embodiment only in that it does not include the single photon source 10.

However, in this embodiment, the dichroic mirror 12 transmits photons having a third resonant frequency ω ₃ in addition to photons having a fourth resonant frequency ω ₄ . Furthermore, the dichroic mirror 12 according to this embodiment reflects photons having a first resonant frequency ω ₁ and a second resonant frequency ω ₂ . Therefore, photons having the first resonant frequency ω ₁ and the second resonant frequency ω ₂ reflected by the dichroic mirror 12 enter the optical terminator 14 .

Dichroic mirror 66 differs in configuration from dichroic mirror 12 only in that it transmits photons having a fourth resonant frequency ω ₄ and reflects photons having a third resonant frequency ω ₃ . The dichroic mirror 66 is arranged so that photons transmitted through the dichroic mirror 12 are incident thereon.

The single photon detector 68 is an element for detecting an incident single photon. Single photon detector 68 is arranged so that photons reflected by dichroic mirror 66 are incident thereon. Therefore, the single photon detector 68 detects the photon having the third resonant frequency ω ₃ reflected by the dichroic mirror 66 .

In this embodiment, the quantum device X is arranged so that photons transmitted through the dichroic mirror 66 are incident thereon. Therefore, a photon having the fourth resonance frequency ω ₄ that has passed through the dichroic mirror 12 is incident on the single photon detector 68 .

The first output optical fiber 70 and the second output optical fiber 72 are single mode optical fibers, and may have the same configuration as the optical fiber 8. The first output optical fiber 70 is arranged so that photons reflected by the dichroic mirror 66 are incident thereon, and the second output optical fiber 72 is arranged so that photons transmitted through the dichroic mirror 66 are incident thereon.

Therefore, the first output optical fiber 70 propagates the photons having the third resonant frequency ω ₃ reflected at the dichroic mirror 66 to the single photon detector 68 . Further, the second output optical fiber 72 propagates the photon having the fourth resonance frequency ω ₄ that has passed through the dichroic mirror 66 to the quantum device X.

Further, in this embodiment, the laser light source 6 inputs the first pump light PL1 having the first resonant frequency ω ₁ and the second pump light PL2 having the second resonant frequency ω ₂ to the resonator structure 4 .

In this embodiment, the resonator structure 4 generates a first output photon OF1 having a third resonant frequency ω ₃ and a fourth resonant frequency ω ₄ through a four-wave mixing process using the input pump light, according to a method described later. A second output photon OF2 is generated having a second output photon OF2. In other words, the resonator structure 4 generates photon pairs having mutually different wavelengths from the input pump light. The first pump light PL1 and the second pump light PL2 emitted by the laser light source 6 according to the present embodiment are considered to be continuous pulse waves whose pulse length is the photon lifetime of each resonator of the resonator structure 4. be able to. Here, in the present embodiment, the probability that one photon pair is generated from one pulse wave of each of the first pump light PL1 and the second pump light PL2 is set to p which is sufficiently smaller than 1. do. Note that the laser light source 6 may intermittently emit pulse waves having respective resonance frequencies as the first pump light PL1 and the second pump light PL2.

The generation of photon pairs in the resonator structure 4 will be explained in more detail with reference to FIG. 13. FIG. 13 is a schematic diagram 4B for explaining input and output of photons in the resonator structure 4, and an energy diagram D6 showing state transitions occurring in the resonator structure 4.

As shown in the schematic diagram 4B of FIG. 13, a first pump light PL1 having a first resonant frequency ω ₁ and a second pump light PL2 having a second resonant frequency ω ₂ are input to the resonator structure 4. . As a result, as shown in schematic diagram 4B, a first output photon OF1 having a third resonant frequency ω ₃ and a second output photon OF2 having a fourth resonant frequency ω ₄ are output from the resonator structure 4 by the method described below. be done.

Here, in this embodiment, the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ are calculated using the above-mentioned equations (1) and (2). holds true. Also in this embodiment, the ground level g and the excited level e are virtually set in the nano-optical fiber section 16. In this embodiment, as shown in the energy diagram D6 of FIG. 13, the energy difference between the ground level g and the excited level e is the energy difference between the energy of a photon having a first resonant frequency _ω1 and the second resonant frequency _ω2. It is assumed that the total value of the photon energy is approximately the same as the total value of the photon energy. Note that from the above equation (1), ω ₁ +ω ₂ =ω ₃ +ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of a photon having the third resonance frequency ω ₃ . It is also approximately the same as the total value of the energy of photons having the fourth resonance frequency _ω4 .

When the above two equations hold true, the state transition shown in the energy diagram D6 occurs in the nano-optical fiber section 16 due to the first pump light PL1 and the second pump light PL2. Specifically, the first pump light PL1 and the second pump light PL2 cause excitation from the ground level g to the excitation level e.

In addition to the excitation, a state transition from the excited level e to the ground level g occurs. Here, the resonator structure 4 includes a third resonator 38 having a third resonant frequency ω ₃ as a resonant frequency, and a fourth resonator 40 having a fourth resonant frequency ω ₄ as a resonant frequency. Therefore, as shown in the energy diagram D6, in the nano-optical fiber portion 16, a state transition occurs from the excitation level e toward the ground level g by the energy of the photon having the third resonance frequency _ω3 . Furthermore, a state transition occurs by an amount equal to the energy of the photon having the fourth resonance frequency ω ₄ , thereby causing a state transition from the excitation level e to the ground level g.

Therefore, in the nano-optical fiber section 16 according to this embodiment, a four-wave mixing process significantly occurs as shown in the energy diagram D6. Due to the above-mentioned four-wave mixing process, photons that couple with the third resonator 38 and have a third resonant frequency ω ₃ are significantly generated in the third resonator 38 of the resonator structure 4 . Further, due to the above-mentioned four-wave mixing process, a photon having a fourth resonant frequency ω 4 coupled to the fourth resonator 40 of the resonator structure 4 is transmitted to the fourth resonator ₄₀ of the resonator structure 4 at the third resonant frequency It is generated almost simultaneously with the photon having ω ₃ .

Therefore, when the above-described four-wave mixing process occurs in the resonator structure 4, the first output photon OF1 is emitted from the third resonator 38, and the second output photon OF2 is emitted from the fourth resonator 40. . Referring back to FIG. 12, the first output photon OF1 emitted from the resonator structure 4 is transmitted through the dichroic mirror 12 and reflected at the dichroic mirror 66, thereby propagating through the first output optical fiber 70 and transmitting a single photon. It is detected by a one-photon detector 68. Further, the second output photon OF2 emitted from the resonator structure 4 transmits both the dichroic mirror 12 and the dichroic mirror 66, propagates through the second output optical fiber 72, and enters the quantum device X.

Here, as described above, the probability that one photon pair is generated from one pulse wave of each pump light by the four-wave mixing process is p. Therefore, the probability that two photon pairs are simultaneously generated from each pump light by the four-wave mixing process is the square of p. Therefore, when the single photon detector 68 detects a photon, the probability that two photons will enter the quantum device X is sufficiently smaller than one. In other words, when the single photon detector 68 detects a photon, the photon incident on the quantum device X is a single photon with a probability sufficiently close to 1. Specifically, when the single photon detector 68 detects the first output photon OF1, the probability that the second output photon OF2 includes a plurality of photons is sufficiently smaller than one. In other words, when the single photon detector 68 detects the first output photon OF1, the second output photon OF2 is a single photon with a probability sufficiently close to 1.

For the reasons described above, in this embodiment, when the single photon detector 68 detects the first output photon OF1, the second output photon OF2 almost certainly enters the quantum device X. In addition, the second output photon OF2 is a single photon with probability sufficiently close to 1. Therefore, the single photon source 62 with a messenger functions as a single photon source with a messenger that generates the second output photon OF2, which is a signal photon, using the detection of the first output photon OF1, which is an idler photon, as a messenger. The quantum device X may be, for example, a device including a quantum communicator that requires a single photon with a messenger, such as a quantum cryptographic communicator.

The single photon source 62 with a messenger according to the present embodiment is a quantum wavelength converter including a resonator structure 4, which generates a first output photon OF1 which is an idler photon and a second output photon OF2 which is a signal photon. 64 is used. Therefore, for the same reason as the quantum wavelength converter 2, even when the single photon source with messenger 62 is incorporated into a quantum device including an optical fiber, it reduces the complexity of the structure of the quantum device.

[Embodiment 7]
<Single photon source with messenger using degenerate four-wave mixing process>
FIG. 14 is a schematic plan view of the messenger-equipped single photon source 74 according to this embodiment. As shown in FIG. 12, compared to the single photon source 62 with a messenger, the single photon source 74 with a messenger includes the quantum wavelength converter 54 according to the fourth embodiment instead of the quantum wavelength converter 64. The only difference is in the configuration. However, in this embodiment, the dichroic mirror 12 included in the quantum wavelength converter 54 transmits photons having a third resonant frequency ω ₃ in addition to photons having a fourth resonant frequency ω ₄ , and transmits photons having a third resonant frequency ω 3 . ₁ and the photons with the second resonant frequency ω ₂ are reflected.

Further, in this embodiment, the laser light source 6 inputs the first pump light PL1 having the first resonance frequency ω ₁ to the resonator structure 4. In this embodiment, the resonator structure 4 generates a first output photon OF1 having a third resonant frequency ω ₃ and a fourth resonant frequency ω ₄ through a four-wave mixing process using the input pump light, according to a method described later. A second output photon OF2 is generated having a second output photon OF2.

Therefore, in this embodiment, it can be considered that the second resonant frequency ω ₂ is the same as the first resonant frequency ω ₁ in the previous embodiment. Further, in the single photon source 74 with a messenger according to the present embodiment, the second resonator 36 is the same as the first resonator 34 in the single photon source 62 with a messenger, and the second pump light PL2 is replaced with the first pump light. This corresponds to the same as PL1.

The generation of photon pairs in the resonator structure 56 will be explained in more detail with reference to FIG. 15. FIG. 15 is a schematic diagram 56B for explaining the input and output of photons in the resonator structure 56, and an energy diagram D7 showing state transitions occurring in the resonator structure 56.

As shown in the schematic diagram 56B of FIG. 15, the first pump light PL1 having the first resonance frequency _ω1 is input to the resonator structure 56. As a result, as shown in the schematic diagram 56B, a first output photon OF1 having a third resonant frequency ω ₃ and a second output photon OF2 having a fourth resonant frequency ω ₄ are output from the resonator structure 4 by the method described below. be done.

Here, in this embodiment, for the first resonant frequency ω ₁ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ , in the above-mentioned equations (1) and (2), ω ₁ =ω ₂ The following formula holds true. In this embodiment, the energy difference between the ground level g and the excited level e in the nano-optical fiber section 16 is approximately equal to twice the energy of the photon having the first resonance frequency _ω1 . Note that from the above equation (1), 2ω ₁ =ω ₃ +ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of the photon having the third resonance frequency ω ₃ and the fourth It is also approximately the same as the total value of the energy of photons having a resonant frequency ω ₄ .

When the above two equations hold true, the state transition shown in the energy diagram D7 occurs in the nano-optical fiber section 16 due to the first pump light PL1. Specifically, the first pump light PL1 causes excitation from the ground level g to an energy that is half the energy difference between the ground level g and the excited level e. Here, if the intensity of the first pump light PL1 is sufficiently strong, further excitation by the first pump light PL1 occurs continuously. Therefore, the first pump light PL1 causes excitation from the ground level g to the excitation level e.

In addition to the excitation, a state transition from the excited level e to the ground level g occurs. Also in this embodiment, the four-wave mixing process significantly occurs as shown in the energy diagram D7 for the same reason as explained in the previous embodiment. The four-wave mixing process that occurs in the nano-optical fiber section 16 according to this embodiment corresponds to the degenerate four-wave mixing process where ω ₁ = ω ₂ in the four-wave mixing process that occurs in the nano-optical fiber section 16 according to the previous embodiment. do. Due to the degenerate four-wave mixing process, the third resonator 38 of the resonator structure 4 receives a photon having the third resonant frequency _ω3 , and the fourth resonator 40 of the resonator structure 4 receives a photon having the fourth resonant frequency. Photons with ω ₄ are generated approximately simultaneously.

The first pump light PL1 can be regarded as a series of pulse waves whose pulse length is the photon lifetime of each resonator of the resonator structure 4. Here, in this embodiment, the probability that one photon pair is generated from one pulse wave of the first pump light PL1 is set to p, which is sufficiently smaller than 1. In this case, also in this embodiment, the probability that two photon pairs are simultaneously generated from the first pump light PL1 by the four-wave mixing process is the square of p. Therefore, when the single photon detector 68 detects a photon, the probability that two photons will enter the quantum device X is sufficiently smaller than one. In other words, in this embodiment as well, when the single photon detector 68 detects a photon, the photon incident on the quantum device X is a single photon with a probability sufficiently close to 1. Specifically, when the single photon detector 68 detects the first output photon OF1, the probability that the second output photon OF2 includes a plurality of photons is sufficiently smaller than one. In other words, when the single photon detector 68 detects the first output photon OF1, the second output photon OF2 is a single photon with a probability sufficiently close to 1.

Therefore, when the above-described four-wave mixing process occurs in the resonator structure 4, the first output photon OF1 is emitted from the third resonator 38, and the second output photon OF2 is emitted from the fourth resonator 40. . Returning to FIG. 14, the first output photon OF1 emitted from the resonator structure 56 is detected by the single photon detector 68, and the second output photon OF2 emitted from the resonator structure 56 is detected by the single photon detector 68. incident on quantum device X.

Also in this embodiment, for the same reason as explained in the previous embodiment, when a photon pair is generated from the resonator structure 56 and the single photon detector 68 detects the first output photon OF1, the quantum device The second output photon OF2 is almost certainly input to X. In addition, also in this embodiment, the second output photon OF2 is a single photon with a probability sufficiently close to 1. Therefore, the single photon source 74 with a messenger functions as a single photon source with a messenger that generates the second output photon OF2, which is a signal photon, using the detection of the first output photon OF1, which is an idler photon, as a messenger.

The single photon source 74 with a messenger according to the present embodiment is a quantum wavelength converter including a resonator structure 56 for generating a first output photon OF1, which is an idler photon, and a second output photon OF2, which is a signal photon. 54 is used. Therefore, for the same reason as the quantum wavelength converter 2, even when the single photon source 74 with a messenger is incorporated into a quantum device including an optical fiber, the complexity of the structure of the quantum device is reduced.

Furthermore, since the resonator structure 56 of the single photon source 74 with a messenger does not include the second resonator 36 compared to the resonator structure 4 of the single photon source 62 with a messenger, the number of resonators included is is one less. Therefore, the single photon source 74 with a messenger can configure the resonator structure 56 more simply than the single photon source 62 with a messenger, and also makes the design of the resonator structure 56 easier.

[Embodiment 8]
<Single photon source with messenger using parametric down conversion>
FIG. 16 is a schematic plan view of the single photon source 76 with messenger according to this embodiment. As shown in FIG. 16, the single photon source 76 with a messenger differs in configuration from the single photon source 62 with a messenger in that it includes a quantum wavelength converter 78 instead of the quantum wavelength converter 64. The quantum wavelength converter 78 differs in configuration from the quantum wavelength converter 46 according to the second embodiment only in that it does not include the single photon source 10. However, in this embodiment, the dichroic mirror 12 included in the quantum wavelength converter 78 transmits photons having a third resonant frequency ω ₃ in addition to photons having a fourth resonant frequency ω ₄ , and transmits photons having a third resonant frequency ω 3 . ₁ and the photons with the second resonant frequency ω ₂ are reflected.

Further, in this embodiment, the laser light source 6 inputs the first pump light PL1 having the first resonance frequency ω ₁ to the resonator structure 4. In this embodiment, the resonator structure 48 has a first output photon OF1 with a third resonant frequency ω ₃ and a fourth resonant frequency ω ₄ due to parametric down-conversion by the input pump light, according to the method described below. A second output photon OF2 is generated.

The generation of photon pairs in the resonator structure 48 will be explained in more detail with reference to FIG. 17. FIG. 17 is a schematic diagram 48B for explaining input and output of photons in the resonator structure 48, and an energy diagram D8 showing state transitions occurring in the resonator structure 48.

As shown in the schematic diagram 48B of FIG. 17, the first pump light PL1 having the first resonance frequency _ω1 is input to the resonator structure 48. As a result, as shown in schematic diagram 48B, a first output photon OF1 having a third resonant frequency ω ₃ and a second output photon OF2 having a fourth resonant frequency ω ₄ are output from the resonator structure 4 by the method described below. be done.

Here, in this embodiment, the above-described equations (3) and (4) hold for the first resonant frequency ω ₁ , the third resonant frequency ω ₃ , and the fourth resonant frequency ω ₄ . In this embodiment, the energy difference between the ground level g and the excited level e in the nano-optical fiber section 16 is made approximately equal to the energy of a photon having the first resonance frequency _ω1 . Note that from the above equation (3), ω ₁ = ω ₃ + ω ₄ holds, so the energy difference between the ground level g and the excited level e is equal to the energy of the photon having the third resonance frequency ω ₃ and the fourth It is also approximately the same as the total value of the energy of photons having a resonant frequency ω ₄ .

When the above two equations hold true, the state transition shown in the energy diagram D7 occurs in the nano-optical fiber section 16 due to the first pump light PL1. Specifically, the first pump light PL1 causes excitation from the ground level g to the excited level e.

In addition to the excitation, a state transition from the excited level e to the ground level g occurs. Also in this embodiment, parametric downward transformation occurs significantly as shown in the energy diagram D8 for the same reason as explained in the previous embodiment. Due to the parametric down-conversion described above, the third resonator 38 of the resonator structure 4 receives a photon having a third resonant frequency ω ₃ and the fourth resonator 40 of the resonator structure 4 receives a photon having a fourth resonant frequency ω ₄ photons are generated approximately simultaneously.

The first pump light PL1 can be regarded as a series of pulse waves whose pulse length is the photon lifetime of each resonator of the resonator structure 4. Here, in this embodiment, the probability that one photon pair is generated from one pulse wave of the first pump light PL1 is set to p, which is sufficiently smaller than 1. In this case, also in this embodiment, the probability that two photon pairs are simultaneously generated from the first pump light PL1 by parametric downward conversion is the square of p. Therefore, when the single photon detector 68 detects a photon, the probability that two photons will enter the quantum device X is sufficiently smaller than one. In other words, in this embodiment as well, when the single photon detector 68 detects a photon, the photon incident on the quantum device X is a single photon with a probability sufficiently close to 1. Specifically, when the single photon detector 68 detects the first output photon OF1, the probability that the second output photon OF2 includes a plurality of photons is sufficiently smaller than one. In other words, when the single photon detector 68 detects the first output photon OF1, the second output photon OF2 is a single photon with a probability sufficiently close to 1.

Therefore, when the above-mentioned parametric downward conversion occurs in the resonator structure 4, the first output photon OF1 is emitted from the third resonator 38, and the second output photon OF2 is emitted from the fourth resonator 40. Returning to FIG. 16, the first output photon OF1 emitted from the resonator structure 48 is detected by the single photon detector 68, and the second output photon OF2 emitted from the resonator structure 48 is detected by the single photon detector 68. incident on quantum device X.

Also in this embodiment, for the same reason as explained in the previous embodiment, when a photon pair is generated from the resonator structure 56 and the single photon detector 68 detects the first output photon OF1, the quantum device The second output photon OF2 is almost certainly input to X. In addition, also in this embodiment, the second output photon OF2 is a single photon with a probability sufficiently close to 1. Therefore, the single photon source 76 with a messenger functions as a single photon source with a messenger that uses the detection of the first output photon OF1, which is an idler photon, as a messenger to generate the second output photon OF2, which is a signal photon.

The single photon source 76 with a messenger according to the present embodiment is a quantum wavelength converter including a resonator structure 48 for generating first output photons OF1, which are idler photons, and second output photons OF2, which are signal photons. 78 is used. Therefore, for the same reason as the quantum wavelength converter 2, even when the single photon source 76 with a messenger is incorporated into a quantum device including an optical fiber, the complexity of the structure of the quantum device is reduced.

Further, since the resonator structure 48 of the single photon source 76 with a messenger does not include the second resonator 36 compared to the resonator structure 4 of the single photon source 62 with a messenger, the number of resonators included is is one less. Therefore, the single photon source 76 with a messenger can configure the resonator structure 48 more simply than the single photon source 62 with a messenger, and also makes the design of the resonator structure 48 easier.

(Additional notes)
All or part of the embodiments described above can also be expressed as follows.

(Aspect 1)
an optical fiber including therein a plurality of resonators having a common resonant optical path at least in part;
a laser light source connected to the optical fiber and inputting pump light having at least one frequency into the optical fiber;
The plurality of resonators include a first resonator having a first resonant frequency _ω1 as a resonant frequency, a second resonator having a second resonant frequency _ω2 as a resonant frequency, and a third resonant frequency _ω3 as a resonant frequency. and a fourth resonance having a fourth resonant frequency ω ₄ different from any of the first resonant frequency ω ₁ , the second resonant frequency ω ₂ , and the third resonant frequency ω ₃ . including vessels,
where n _i is the effective refractive index inside the optical fiber for light with the i-th resonance frequency ω _i , c is the speed of light, γ is the nonlinear coefficient of the optical fiber, and P is the intensity of the pump light,

A quantum wavelength converter that satisfies the above equations (1) and (2).

(Aspect 2)
further comprising a single photon source connected to the optical fiber and inputting input photons having the first resonant frequency ω ₁ to the plurality of resonators into the optical fiber,
the laser light source inputs a first pump light having the second resonant frequency ω ₂ and a second pump light having the third resonant frequency ω ₃ to the optical fiber;
The quantum wavelength converter according to aspect 1, wherein output photons having the fourth resonant frequency ω ₄ are emitted from the fourth resonator.

(Aspect 3)
the first resonant frequency ω ₁ is the same as the second resonant frequency ω ₂ ;
the first resonator is the same as the second resonator,
the laser light source inputs a first pump light having the first resonant frequency ω ₁ and a second pump light having the third resonant frequency ω ₃ to the optical fiber;
The quantum wavelength converter according to aspect 1, wherein output photons having the fourth resonant frequency ω ₄ are emitted from the fourth resonator.

(Aspect 4)
an optical fiber including therein a plurality of resonators having a common resonant optical path at least in part;
a laser light source connected to the optical fiber and inputting pump light into the optical fiber;
The plurality of resonators include a first resonator having a first resonant frequency ω ₁ as a resonant frequency, a third resonator having a third resonant frequency ω ₃ as a resonant frequency, and a third resonator having a resonant frequency ω 1 and a third resonant frequency ω ₃ . 3 resonant frequency ω ₃ and a fourth resonator having a different fourth resonant frequency ω ₄ as a resonant frequency,
where n _i is the effective refractive index inside the optical fiber for light with the i-th resonance frequency ω _i , c is the speed of light, γ is the nonlinear coefficient of the optical fiber, and P is the intensity of the pump light,

A quantum wavelength converter that satisfies the above equations (3) and (4).

(Aspect 5)
further comprising a single photon source connected to the optical fiber and inputting input photons having the first resonant frequency ω ₁ to the plurality of resonators into the optical fiber,
the laser light source inputs the pump light having the third resonant frequency ω ₃ to the optical fiber;
The quantum wavelength converter according to aspect 4, wherein output photons having the fourth resonant frequency ω ₄ are emitted from the fourth resonator.

(Aspect 6)
an optical fiber including therein a plurality of resonators having a common resonant optical path at least in part;
a laser light source connected to the optical fiber and inputting pump light into the optical fiber;
The plurality of resonators include a first resonator having a first resonant frequency ω ₁ as a resonant frequency, a second resonator having a second resonant frequency ω ₂ as a resonant frequency, and a second resonator having a second resonant frequency ω ₂ as a resonant frequency, and a fourth resonator having a fourth resonant frequency _ω4 different from both the second resonant frequency _ω2 ;
where n _i is the effective refractive index inside the optical fiber for light with the i-th resonance frequency ω _i , c is the speed of light, γ is the nonlinear coefficient of the optical fiber, and P is the intensity of the pump light,

A quantum wavelength converter that satisfies the above equations (5) and (6).

(Aspect 7)
further comprising a single photon source connected to the optical fiber and inputting input photons having the first resonant frequency ω ₁ to the plurality of resonators into the optical fiber,
the laser light source inputs the pump light having the second resonant frequency ω ₂ to the optical fiber;
The quantum wavelength converter according to aspect 6, wherein output photons having the fourth resonant frequency ω ₄ are emitted from the fourth resonator.

(Aspect 8)
the first resonant frequency ω ₁ is the same as the second resonant frequency ω ₂ ;
the first resonator is the same as the second resonator,
the laser light source inputs a first pump light having the first resonant frequency ω ₁ to the optical fiber;
7. The quantum wavelength converter according to aspect 6, having the fourth resonant frequency ω ₄ from the fourth resonator.

(Aspect 9)
The optical fiber includes a nano-optical fiber portion and both end portions that are larger in diameter than the nano-optical fiber portion and are connected to both ends of the nano-optical fiber portion via a tapered portion, and at least a portion of the resonant optical path. 9. The quantum wavelength converter according to any one of aspects 1 to 8, wherein the quantum wavelength converter is located in the nano-optical fiber section.

(Aspect 10)
The quantum wavelength converter according to any one of aspects 1 to 8, wherein each of the plurality of resonators includes a pair of fiber Bragg gratings whose reflection bands include the respective resonance frequencies.

(Aspect 11)
11. The quantum wavelength converter of aspect 10, wherein at least one of the fiber Bragg gratings is the same as any other of the fiber Bragg gratings.

(Aspect 12)
The quantum wavelength converter according to aspect 1,
a first output optical fiber connected to the optical fiber and configured to propagate a first single output photon having the third resonant frequency ω ₃ emitted from the third resonator;
a second output optical fiber connected to the optical fiber and configured to propagate a second single output photon having the fourth resonant frequency ω ₄ emitted from the fourth resonator;
further comprising a single photon detector connected to the first output optical fiber and detecting the first single output photon;
A single photon source with a messenger, wherein the laser light source inputs a first pump light having the first resonant frequency ω ₁ and a second pump light having the second resonant frequency ω ₂ to the optical fiber.

(Aspect 13)
the first resonant frequency ω ₁ is the same as the second resonant frequency ω ₂ ;
the first resonator is the same as the second resonator,
13. The single photon source with messenger according to aspect 12, wherein the second pump light is the same as the first pump light.

(Aspect 14)
The quantum wavelength converter according to aspect 4,
a first output optical fiber connected to the optical fiber and configured to propagate a first single output photon having the third resonant frequency ω ₃ emitted from the third resonator;
a second output optical fiber connected to the optical fiber and configured to propagate a second single output photon having the fourth resonant frequency ω ₄ emitted from the fourth resonator;
further comprising a single photon detector connected to the first output optical fiber and detecting the first single output photon;
A single photon source with a messenger, wherein the laser light source inputs the pump light having the first resonant frequency ω ₁ to the optical fiber.

(Aspect 15)
The optical fiber includes a nano-optical fiber portion and both end portions that are larger in diameter than the nano-optical fiber portion and are connected to both ends of the nano-optical fiber portion via a tapered portion, and at least a portion of the resonant optical path. 15. The single photon source with a messenger according to any one of aspects 12 to 14, wherein: is located in the nano-optical fiber section.

(Aspect 16)
The single photon source with a messenger according to any one of aspects 12 to 14, wherein each of the plurality of resonators has a pair of fiber Bragg gratings whose reflection bands include the respective resonance frequencies.

(Aspect 17)
17. The heralded single photon source of embodiment 16, wherein at least one of the fiber Bragg gratings is the same as any other of the fiber Bragg gratings.

The present disclosure is not limited to the embodiments described above, and various changes can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

2 Quantum wavelength converter 4 Resonator structure 6 Laser light source 8 Optical fiber 16 Nano optical fiber section 18 Tapered section 20 Common FBG
22 1st FBG
24 2nd FBG
26 3rd FBG
28 4th FBG
34 First resonator 36 Second resonator 38 Third resonator 40 Fourth resonator 62 Single photon source with messenger 68 Single photon detector 70 First output optical fiber 72 Second output optical fiber

Claims

an optical fiber including therein a plurality of resonators having a common resonant optical path at least in part;
a laser light source connected to the optical fiber and inputting pump light having at least one frequency into the optical fiber;
The plurality of resonators include a first resonator having a first resonant frequency ω1 as a resonant frequency, a second resonator having a second resonant frequency ω2 as a resonant frequency, and a third resonant frequency ω3 as a resonant frequency. and a fourth resonance having a fourth resonant frequency ω 4 different from any of the first resonant frequency ω 1 , the second resonant frequency ω 2 , and the third resonant frequency ω 3 . including vessels,
where n i is the effective refractive index inside the optical fiber for light with the i-th resonance frequency ω i , c is the speed of light, γ is the nonlinear coefficient of the optical fiber, and P is the intensity of the pump light,

A quantum wavelength converter that satisfies the above equations (1) and (2).
further comprising a single photon source connected to the optical fiber and inputting input photons having the first resonant frequency ω 1 to the plurality of resonators into the optical fiber,
the laser light source inputs a first pump light having the second resonant frequency ω 2 and a second pump light having the third resonant frequency ω 3 to the optical fiber;
The quantum wavelength converter according to claim 1, wherein output photons having the fourth resonant frequency ω4 are emitted from the fourth resonator.
the first resonant frequency ω 1 is the same as the second resonant frequency ω 2 ;
the first resonator is the same as the second resonator,
the laser light source inputs a first pump light having the first resonant frequency ω 1 and a second pump light having the third resonant frequency ω 3 to the optical fiber;
The quantum wavelength converter according to claim 1, wherein output photons having the fourth resonant frequency ω4 are emitted from the fourth resonator.
an optical fiber including therein a plurality of resonators having a common resonant optical path at least in part;
a laser light source connected to the optical fiber and inputting pump light into the optical fiber;
The plurality of resonators include a first resonator having a first resonant frequency ω 1 as a resonant frequency, a third resonator having a third resonant frequency ω 3 as a resonant frequency, and a third resonator having a resonant frequency ω 1 and a third resonant frequency ω 3 . 3 resonant frequency ω 3 and a fourth resonator having a different fourth resonant frequency ω 4 as a resonant frequency,
where n i is the effective refractive index inside the optical fiber for light with the i-th resonance frequency ω i , c is the speed of light, γ is the nonlinear coefficient of the optical fiber, and P is the intensity of the pump light,

A quantum wavelength converter that satisfies the above equations (3) and (4).
further comprising a single photon source connected to the optical fiber and inputting input photons having the first resonant frequency ω 1 to the plurality of resonators into the optical fiber,
the laser light source inputs the pump light having the third resonant frequency ω 3 to the optical fiber;
5. The quantum wavelength converter according to claim 4, wherein output photons having the fourth resonant frequency ω4 are emitted from the fourth resonator.
an optical fiber including therein a plurality of resonators having a common resonant optical path at least in part;
a laser light source connected to the optical fiber and inputting pump light into the optical fiber;
The plurality of resonators include a first resonator having a first resonant frequency ω 1 as a resonant frequency, a second resonator having a second resonant frequency ω 2 as a resonant frequency, and a second resonator having a second resonant frequency ω 2 as a resonant frequency, and a fourth resonator having a fourth resonant frequency ω4 different from both the second resonant frequency ω2 ;
where n i is the effective refractive index inside the optical fiber for light with the i-th resonance frequency ω i , c is the speed of light, γ is the nonlinear coefficient of the optical fiber, and P is the intensity of the pump light,

A quantum wavelength converter that satisfies the above equations (5) and (6).
further comprising a single photon source connected to the optical fiber and inputting input photons having the first resonant frequency ω 1 to the plurality of resonators into the optical fiber,
the laser light source inputs the pump light having the second resonant frequency ω 2 to the optical fiber;
7. The quantum wavelength converter according to claim 6, wherein output photons having the fourth resonant frequency ω4 are emitted from the fourth resonator.
the first resonant frequency ω 1 is the same as the second resonant frequency ω 2 ;
the first resonator is the same as the second resonator,
the laser light source inputs a first pump light having the first resonant frequency ω 1 to the optical fiber;
7. The quantum wavelength converter according to claim 6, having the fourth resonant frequency ω 4 from the fourth resonator.
The optical fiber includes a nano-optical fiber portion and both end portions that are larger in diameter than the nano-optical fiber portion and are connected to both ends of the nano-optical fiber portion via a tapered portion, and at least a portion of the resonant optical path. 9. The quantum wavelength converter according to claim 1, wherein: is located in the nano-optical fiber section.
The quantum wavelength converter according to any one of claims 1 to 8, wherein each of the plurality of resonators includes a pair of fiber Bragg gratings whose reflection bands include the respective resonant frequencies.
11. The quantum wavelength converter of claim 10, wherein at least one of the fiber Bragg gratings is the same as any other of the fiber Bragg gratings.
Quantum wavelength converter according to claim 1;
a first output optical fiber connected to the optical fiber and configured to propagate a first single output photon having the third resonant frequency ω 3 emitted from the third resonator;
a second output optical fiber connected to the optical fiber and configured to propagate a second single output photon having the fourth resonant frequency ω 4 emitted from the fourth resonator;
further comprising a single photon detector connected to the first output optical fiber and detecting the first single output photon;
A single photon source with a messenger, wherein the laser light source inputs a first pump light having the first resonant frequency ω 1 and a second pump light having the second resonant frequency ω 2 to the optical fiber.
the first resonant frequency ω 1 is the same as the second resonant frequency ω 2 ;
the first resonator is the same as the second resonator,
13. The single photon source with messenger according to claim 12, wherein the second pump light is the same as the first pump light.
Quantum wavelength converter according to claim 4,
a first output optical fiber connected to the optical fiber and configured to propagate a first single output photon having the third resonant frequency ω 3 emitted from the third resonator;
a second output optical fiber connected to the optical fiber and configured to propagate a second single output photon having the fourth resonant frequency ω 4 emitted from the fourth resonator;
further comprising a single photon detector connected to the first output optical fiber and detecting the first single output photon;
A single photon source with a messenger, wherein the laser light source inputs the pump light having the first resonant frequency ω 1 to the optical fiber.
The optical fiber includes a nano-optical fiber portion and both end portions that are larger in diameter than the nano-optical fiber portion and are connected to both ends of the nano-optical fiber portion via a tapered portion, and at least a portion of the resonant optical path. The single photon source with a messenger according to any one of claims 12 to 14, wherein the single photon source is located in the nano-optical fiber section.
The single photon source with a messenger according to any one of claims 12 to 14, wherein each of the plurality of resonators has a pair of fiber Bragg gratings whose reflection bands include the respective resonant frequencies.
17. The messenger single photon source of claim 16, wherein at least one of the fiber Bragg gratings is the same as any other of the fiber Bragg gratings.