JP2016095440A - Multidimensional quantum entanglement state generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the formation of a multidimensional quantum entanglement state with fewer number of devices.SOLUTION: A light source 101 emits, for example, pulsed light. A splitter 102 splits the pump light emitted from the light source 101 into N pieces of input light beams (N is a natural number of two or more). The pump light is input into splitter 102 through an input optical waveguide 106. N pieces of non-linear optical waveguides 103 are made to have an identical optical waveguide length and receive the N pieces of input light beams split by the splitter 102, respectively. An array optical waveguide diffraction grating 104 has input terminals that are connected with the N pieces of non-linear optical waveguides 103, and has output ends that are connected with 2N pieces of output optical waveguides 105. In the non-linear optical waveguides 103 to which the pump light is incident, for example, a quantum correlated photon pair is generated by Spontaneous Four Wave Mixing (SFWM).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multidimensional entangled state generator in a cryptographic key exchange technique having security guaranteed by the principle of quantum mechanics.

  In recent years, research on quantum information processing technology that attempts to realize new information communication and signal processing by directly applying the basic properties of quantum mechanics has been actively conducted. For example, due to the uncertainty principle, it is not possible to completely measure what polarization state one photon is in. There is an encryption method that performs key distribution in the shared key encryption method using this, and is called “quantum encryption communication”.

  A plurality of photons (quantum entangled photons) having a quantum mechanical correlation are important elements in the quantum information communication system as described above. By sharing the quantum entangled photon pair between the sender and the receiver, it is possible to realize cryptographic key distribution having security guaranteed by a physical law that can reliably detect the presence of an eavesdropper.

  In the quantum information processing technology using photons, a superposition state encoded in some physical state of photons is used as a basic unit of information. As this physical quantity, polarization of light, spatial path (spatial position), time position, frequency, orbital angular momentum, and the like can be used. For example, when polarized light is used, a two-state system (number of states N = 2) of a transverse polarization state and a longitudinal polarization state can be configured, and a photon can take the above-described two-state linear superposition state. Such superposition of two states can be used as a qubit.

  When the time position is used, a qubit can be constituted by a two-state system using two time slots in which photons can exist. When a spatial path is used, a qubit can be configured by a two-state system using two spatially separated positions. A qubit is a basic resource in a quantum information protocol typified by quantum cryptography communication, and research on generation and control of a qubit is actively conducted.

Here, the entangled state constituted by the two-state system will be described. It is assumed that two photons exist simultaneously, and each photon is in a two-state superposition state. For example, when the degree of freedom of polarization is used, each photon takes a superposed state of horizontally polarized light and vertically polarized light. These two photons are called signal photons and idler photons. If these photons are in a entangled state, this state can be determined by using a wave function: “| quantum state> = (| 0> _s | 0> _i + | 1> _s | 1> _i ) / 2 ^1/2 ... (0) ”.

In Equation (0), | 0> _s represents a state where one signal photon exists in the 0th state, and | 0> _i represents a state where one idler photon exists in the 0th state. | 1> _s represents a state where one signal photon exists in the first state, and | 1> _i represents a state where one idler photon exists in the first state. For example, if the state is a photon polarization state, 0 can be assigned to horizontal polarization and 1 to vertical polarization. In this case, Equation (0) represents a state in which the polarization of each photon is not fixed, but the relationship between the polarizations of the two photons is fixed.

  In recent years, research using quantum states encoded in N> 3 superposition states, that is, quantum multistate systems, has attracted attention. By using a quantum multi-state system, for example, it is possible to improve the confidentiality of quantum cryptography communication compared to a two-state system (see Non-Patent Document 1). Therefore, a technique for generating a entangled state (multi-dimensional entangled state) based on a quantum multi-state system is extremely important for applications such as quantum cryptography communication.

  The state of the correlated two-photon represented by the wave function of the following equation (1) belongs to the N-dimensional quantum entangled state.

In Equation (1), m is a number for counting the overlapping states, N is the total number of overlapping states, and φ _m is a relative phase between the states (where φ ₀ = 0). | M> _s represents that the signal (s) photon forming the correlated two-photon is in the m-th quantum state, and | m> _i is the idler (i) photon forming the correlated two-photon Represents a quantum state.

  As a physical quantity for realizing such a multidimensional quantum entangled state, a light path (space position), a time position, a frequency, an orbital angular momentum, and the like can be used. Among these degrees of freedom, encoding to a spatial path is particularly important. This is because the quantum state encoded in the spatial path can be controlled relatively easily by using an optical circuit that combines an interferometer and a phase shifter (see Non-Patent Document 2).

In view of such a situation, a spatial path encoding type multi-dimensional quantum entangled photon pair source has been recently proposed (see Non-Patent Document 3). Hereinafter, this multidimensional entangled photon pair source will be described with reference to FIG. FIG. 5 shows FIG. 1. First, as shown in FIG. 5, an N × N coupler for branching λ, which is a common pump light, a nonlinear optical waveguide (ppLN _{1 to} ppLN _N ) for generating a correlated photon pair, and a correlated photon pair as a signal N wavelength separation filters (DWDM) that separate light into idler light.

  In this light source, each pair of correlated photons generated from a plurality of nonlinear optical waveguides is separated into different paths using a wavelength separation filter, and then a multidimensional quantum entangled state is obtained at the position of the broken line at the right end. The physical quantity that realizes the quantum multi-state system corresponds to the spatial position of the output waveguide in which the photons exist in the light source.

JP 2009-069513 A JP 2012-042849 A

N. J. Cerf et al., "Security of Quantum Key Distribution Using d-Level Systems", Physical Review Letters, vol.88, no.12, 127902, 2002. M. Reck and A. Zeilinger, "Experimental Realization of Any Discrete Unitary Operator", Physical Review Letters, vol.73, no.1, pp.58-61, 1994. C. Schaeff et al., "Scalable fiber integrated source for higherdimensional path-entangled photonic quNits", Optics Express, vol.20, no.15, pp.16145-16153, 2012. C. R. Doerr and K. Okamoto, "Advances in Silica Planar Lightwave Circuits", Journal of Lightwave Technology, vol.24, no.12, pp.4763-4789, 2006.

  However, in the technique of Non-Patent Document 3 described above, N wavelength separation filters are used to obtain the number of N entangled states, and the number of wavelength separation filters is the number of entangled states to be generated. Only needed. However, in order to further reduce the size and cost of the multidimensional quantum entangled state generator, it is required to significantly reduce the number of elements (= wavelength separation filters) required.

  The present invention has been made to solve the above problems, and an object of the present invention is to form a multidimensional entangled state with a smaller number of elements.

  The multidimensional quantum entangled state generator according to the present invention includes a light source capable of adjusting the light intensity of emitted pump light, and N (N is a natural number of 2 or more) input light from pump light emitted from the light source. , An N optical waveguide grating to which N input lights branched by the splitter are respectively input and the optical waveguide lengths are equal to each other, and an N optical waveguide diffraction grating to which the N nonlinear optical waveguides are connected And 2N output optical waveguides connected to the array optical waveguide diffraction grating.

  In the multidimensional quantum entangled state generator, the nonlinear optical waveguide may be any one that generates signal photons and idler photons from the input pump light by spontaneous emission four-wave mixing.

  In the multidimensional quantum entangled state generator, the signal photons and idler photons generated by one of the N nonlinear optical waveguides (by the input pump light) are quantum entangled photons having a quantum mechanical correlation. In addition, the signal photon, idler photon, and pump light may be input to the same input port of the arrayed waveguide grating, and the signal photon and idler photon may be output to different output ports of the arrayed waveguide grating. .

  In the multidimensional quantum entangled state generator, when a signal photon and an idler photon are generated in one nonlinear optical waveguide among the N nonlinear waveguides, the signal photon and idler are generated in the remaining N−1 nonlinear optical waveguides. What is necessary is just to make it adjust the light intensity of pump light in the state where a photon does not generate | occur | produce.

  In the multi-dimensional quantum entangled state generator, the signal photon and idler photon emitted from the output optical waveguide may have a normalized frequency overlap integral of 1% or less between them.

  As described above, according to the present invention, an excellent effect that a multi-dimensional quantum entangled state can be formed with a smaller number of elements can be obtained.

FIG. 1 is a configuration diagram showing a configuration of a multidimensional entangled state generation device according to an embodiment of the present invention. FIG. 2 is a configuration diagram for explaining the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 in the first embodiment. FIG. 3 is a configuration diagram for explaining the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 in the second embodiment. FIG. 4 is a configuration diagram for explaining the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 in the third embodiment. FIG. 5 is a configuration diagram showing the configuration of the multidimensional quantum entangled photon pair source shown in Non-Patent Document 3.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a configuration of a multidimensional entangled state generation device according to an embodiment of the present invention. The multidimensional quantum entangled state generator includes a light source 101, a splitter 102, N nonlinear optical waveguides 103, an array optical waveguide diffraction grating 104, and 2N output optical waveguides 105.

  The light source 101 can adjust the light intensity of the emitted pump light. The light source 101 emits pulsed light, for example. The splitter 102 branches the pump light emitted from the light source 101 into N (N is a natural number of 2 or more) input lights. The pump light is input to the splitter 102 via the input optical waveguide 106. The N nonlinear optical waveguides 103 each have the same optical waveguide structure and optical waveguide length. Further, N pieces of input light branched by the splitter 102 are input to the N nonlinear optical waveguides 103, respectively.

  The array optical waveguide diffraction grating 104 has N nonlinear optical waveguides 103 connected to its input end and 2N output optical waveguides 105 connected to its output end. The array optical waveguide diffraction grating 104 includes a first slab 111, an optical waveguide array 112, and a second slab 113.

  Pump light (pulse) as excitation light emitted from the light source 101 is input to the input optical waveguide 106 and is equally branched and incident on the N nonlinear optical waveguides 103 by the splitter 102. In each nonlinear optical waveguide 103 on which the pump light is incident, a time-correlated photon pair is generated by the nonlinear optical effect. Here, the pump light intensity is adjusted so that photon pairs are not simultaneously generated from two or more nonlinear optical waveguides 103.

  In order to generate a time-correlated photon pair, the second-order or third-order nonlinear optical waveguide 103 may be used. For example, as the third-order nonlinear optical waveguide 103, it is possible to generate a quantum correlation photon pair using a spontaneous emission four-wave mixing (SFWM) in a silicon optical waveguide (see Patent Document 1).

This spontaneous emission four-wave mixing process will be described. When pump light of optical frequency f _p is input to the third-order nonlinear optical waveguide 103, the signal photon and optical frequency of optical frequency f _s satisfying “2f _p = f _s + f _i (2)” idler photon of f _i occurs (where f _s> f _i). The photon pair composed of the signal photon and the idler photon has a quantum mechanical correlation with respect to the time position (occurrence time), and forms a time-correlated photon pair. Hereinafter, for the sake of simplicity, the case of the third-order nonlinear optical waveguide 103 will be described. SFWM is such that, for example, 0.1 photon is generated for one pulse of pump light. This generation efficiency is proportional to the square of the pump light intensity (peak intensity in the case of a pulse). Therefore, by adjusting the intensity of the pump light emitted from the light source 101, it is possible to set a state in which no photon pair is simultaneously generated from two or more nonlinear optical waveguides 103.

  The photon pair generated in any of the nonlinear optical waveguides 103 by the above-described SFWM is incident on the first slab 111 of the array optical waveguide diffraction grating 104 together with the pump light, and then diffuses in the first slab 111. Thereafter, the light is condensed on the output end side of the second slab 113 through the optical waveguide array 112. Due to the dispersion in the optical waveguide array 112, the condensing position on the output end side of the second slab 113 has optical frequency (wavelength) dependence.

  As a result, the pump light, the signal photon, and the idler photon having different frequencies are spatially separated and condensed at different positions on the output end of the second slab 113. If the output optical waveguide 105 connected to the second slab 113 is installed at a position where only the signal photon and idler photon are extracted from the light generated as described above, the signal photon and idler are removed except for the pump light. Photons can be taken out.

For example, N signal photon output optical waveguides S _m are arranged at positions where signal light generated from any one of the N nonlinear optical waveguides NLWG _m is collected, and the N idler photon output optical waveguides I _m. May be arranged at a position for collecting idler light generated from any one of N nonlinear optical waveguides NLWG _m (m = 1 to N). For example, m in the equation (1) may be made to correspond to the signal photon output optical waveguide S _m and the idler photon output optical waveguide I _m described above. Thereby, a multidimensional entangled state encoded in the optical path (space) can be obtained.

In the quantum entangled photon pair generating apparatus in the first embodiment, a quantum correlated photon pair (time correlated photon pair) is generated in the nonlinear optical waveguide 103 by SFWM. For example, a silicon optical waveguide can be used as the nonlinear optical waveguide 103. The nonlinear refractive index n2 of the silicon optical waveguide is 9 × 10 ⁻¹⁸ m ² / W, and the effective area Aeff of the core is 0.033 μm ² . In such a silicon optical waveguide, the optical waveguide length required to generate 0.1 pair of photons with a bandwidth of 25 GHz using a light pulse having a wavelength of 1550 nm, a pulse width of 100 ps, and a peak power of 100 mW as the pump light. Is about 2 mm. In some cases, the frequency difference between the signal photon and the idler photon is about 100 nm at maximum in terms of wavelength. This is about 17 THz when converted to a frequency difference.

  Hereinafter, an arrangement example of the nonlinear optical waveguide 103 and the output optical waveguide 105 will be described using an embodiment.

[Example 1]
First, the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 according to the first embodiment will be described with reference to FIG. FIG. 2 is a configuration diagram for explaining the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 in the first embodiment. In FIG. 2, the arrayed optical waveguide diffraction grating 104 is shown in a simplified manner.

Further, as shown in FIG. 2, a plurality (5) present in the nonlinear optical waveguide 103 is disposed at equal intervals D _i. Further, in practice, the input end face of the first slab 111 and the output end face of the second slab 113 shown in FIG. 1 are shaped to draw a curved arc, and the nonlinear optical waveguide 103 and the output optical waveguide 105 are It is installed along the normal of each arc, but is simplified in FIG.

In the first embodiment, the condensing position shift D ₀ at the output end of the second slab 113 between the pump light and the signal photon emitted from the same nonlinear optical waveguide 103 and the nonlinear optical waveguide 103 connected to the first slab 111. The relationship of “D ₀ <D _i / 2 (3)” is established with the interval D _i .

For simplicity, the first slab 111 and the second slab 113 are symmetrical. D ₀ is expressed by the following equation based on the difference Δλ = | c / f _p −c / f _s | between the pump light wavelength and the signal photon wavelength (see Non-Patent Document 4).

In Expression (4), N _c is the group refractive index of each optical waveguide constituting the optical waveguide array 112 part, R is the radius of curvature of each end face of the first and second slabs 113, and ΔL is the optical waveguide array 112. The difference in optical waveguide length between adjacent optical waveguides, n _s is the effective refractive index of the first and second slabs 113, and d is the connection between the first slab 111 and the second slab 113 and the array optical waveguide. Is an interval between the arrayed optical waveguides.

In addition, light having a wavelength λ ₀ that satisfies the condition of “λ ₀ = n _c ΔL / k” emitted from each nonlinear optical waveguide 103 (NLWG _{1 to} NLWG ₅ ) is symmetrically positioned at the output end of the second slab 113. (See Non-Patent Document 4). In the formula of the above conditions, n _c is the effective refractive index of the optical waveguides constituting the optical waveguide array 112 shown in FIG. 1, k is an integer. The optical waveguide array 112 is designed so that the pump light wavelength λ _p = c / f _p is equal to λ ₀ (c is the speed of light in vacuum).

In the first embodiment configured as described above, the pump light emitted from the nonlinear optical waveguide 103 is condensed at a symmetrical position of the output end of the second slab 113. In FIG. 2, the condensing position relationship between the AWG input end 141 and the AWG output end 142 of the pump light emitted from each of the nonlinear optical waveguides 103 of NLWG _{1 to} NLWG ₅ is indicated by a broken line. Due to the phase difference in the optical waveguide array 112, signal photons and idler photons having wavelengths different from those of the pump light are collected at different positions from the pump light. A condensing position relationship between the AWG input end 141 and the AWG output end 142 of the signal photon is indicated by a dotted line. Further, the light collection position relationship between the AWG input terminal 141 and the AWG output terminal 142 of the idler photon is indicated by a one-dot chain line.

Since D ₀ <D _i / 2 is satisfied, the signal photons and idler photons generated from any one of the nonlinear optical waveguides NLWG _{1 to} NLWG ₅ are pump light, signal photon and idler generated from the adjacent nonlinear optical waveguide 103. It is focused at a position that does not spatially overlap with the photon. By installing the output optical waveguide 105 in the order of S ₅ , I ₅ , S ₄ , I ₄ ,..., S ₁ , I ₁ from the top in a position where these are collected, the equation (1) is obtained. The multidimensional quantum entanglement state shown can be obtained.

In the first embodiment, the case of N = 5 is shown for the sake of simplicity. However, the present invention is not limited to this and can be realized in any N case. Further, although the center wavelength λ _p of the pump light coincides with the wavelength λ ₀ , the present invention is not limited to this condition. The same applies to the following embodiments.

[Example 2]
Next, the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 according to the second embodiment will be described with reference to FIG. FIG. 3 is a configuration diagram for explaining the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 in the second embodiment. Also in FIG. 3, the arrayed optical waveguide diffraction grating 104 is shown in a simplified manner.

Further, as shown in FIG. 3, five nonlinear optical waveguide 103 is disposed at equal intervals D _i. As described above, the input end face of the first slab 111 and the output end face of the second slab 113 shown in FIG. 1 have a curved arc shape, and the nonlinear optical waveguide 103 and the output optical waveguide 105 are , Installed along the normal of each arc, but is simplified in FIG.

In the second embodiment, the condensing position shift D ₀ at the output end of the second slab 113 between the pump light and the signal photon emitted from the same nonlinear optical waveguide 103 and the nonlinear optical waveguide 103 connected to the first slab 111. between the interval D _i of the relationship of _{"D i / 2 <D 0 <} D i ··· (5) " is satisfied.

Also in the second embodiment, the signal photon and idler photon generated from any one of the nonlinear optical waveguides NLWG _{1 to} NLWG ₅ are spatially separated from the pump light, signal photon and idler photon generated from the adjacent nonlinear optical waveguide 103. It is condensed at the position where it doesn't overlap.

However, in Example 2, the signal photon (or idler photon) generated from the same nonlinear optical waveguide 103 is generated from the adjacent nonlinear optical waveguide 103 with respect to the condensing position of the pump light emitted from the certain nonlinear optical waveguide 103. It is condensed at a position away from the idler photon (or idler photon). In order to collect these generated photons, the output optical waveguide 105 is installed in the order of S ₅ , S ₄ , I ₅ , S ₃ , I ₄ ,..., S ₁ , I ₂ , I _1. Thus, the multidimensional quantum entangled state shown in Expression (1) can be obtained.

[Example 3]
Next, the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 according to the third embodiment will be described with reference to FIG. FIG. 4 is a configuration diagram for explaining the arrangement of the nonlinear optical waveguide 103 and the output optical waveguide 105 in the third embodiment. 4 also shows the array optical waveguide diffraction grating 104 in a simplified manner.

Further, as shown in FIG. 4, five of the nonlinear optical waveguides 103 are arranged at equal intervals D _i. As described above, the input end face of the first slab 111 and the output end face of the second slab 113 shown in FIG. 1 have a curved arc shape, and the nonlinear optical waveguide 103 and the output optical waveguide 105 are , Installed along the normal of each arc, but is simplified in FIG.

In the third embodiment, the condensing position shift D ₀ at the output end of the second slab 113 between the pump light and the signal photon emitted from the same nonlinear optical waveguide 103 and the nonlinear optical waveguide 103 connected to the first slab 111. between the interval D _i of the relationship of _{"D 0> (N-1)} D i ··· (6) " is satisfied.

In the third embodiment in which the relationship of Expression (6) is established, the signal photon and the idler photon are condensed at a position outside the pump light emitted from any of the nonlinear optical waveguides NLWG _{1 to} NLWG _5. The Accordingly, as shown in FIG. 4, S _5, S ₄ from the top down output optical waveguide _{105, ···, S 1, I} 5, I 4, by installing ..., in the order of I _1, wherein The multidimensional entangled state shown in (1) can be obtained.

Note that the present invention is not limited to the above-described first to third embodiments. For example, even in a configuration in which the condition “D _i <D ₀ <(N−1) D _i (7)” is satisfied, In the case where the condition that all of the signal photons and idler photons are collected at spatially different positions is satisfied, the multi-dimensional quantum entangled state shown in Expression (1) can be obtained by appropriately installing the output optical waveguide 105. Can be obtained.

In the above embodiment, it is assumed that the optical frequencies f _s and f _i of the generated signal photons and idler photons are determined by the conditions of the spontaneous emission four-wave mixing process of the nonlinear optical waveguide 103 when the pump light frequency f _p is given. However, in practice, signal photons and idler photons may be generated over a wide band. In this case, the time-correlated photon pair can be extracted in the same manner as described above by installing the output optical waveguide 105 at a position that satisfies the condition of Expression (2) within the generation band of the photon pair.

In the above embodiment, the input optical waveguide 106 and the non-linear optical waveguide 103 may be configured such that the core cross-sectional structure satisfies the single mode condition at the pump light wavelength. Further, the output optical waveguides 105 for S _{1 to} S _N for condensing the signal photons and I _{1 to} I _N for condensing the idler light satisfy the single mode condition at the wavelengths of the signal photons and the idler photons. do it.

  In the above embodiment, it is assumed that the signal photons and idler photons output from the output optical waveguide 105 have a single frequency component. In practice, however, these photons are often output with a finite frequency bandwidth Δν (full width at half maximum). Δν is a transmission bandwidth determined by, for example, the condition of the spontaneous emission four-wave mixing process in the nonlinear optical waveguide 103 or the relationship between the core cross-sectional dimension of the output optical waveguide 105 and the structure of the array optical waveguide diffraction grating 104.

  Thus, even when the signal photon and the idler photon are output with a finite frequency bandwidth, the condition that the frequency overlap between the signal photon and the idler photon is small (for example, the normalized overlap integral is 1). If the output optical waveguide 105 is installed under the condition of% or less, a highly pure multidimensional quantum entangled state can be obtained.

More specifically, equation (3), equation (5), equation (6), and equation (7) may be changed as follows.
Equation _{(3) → 0 <D 0} <D i / 2-ΔD 0/2
Equation _{(5) → D i / 2} + ΔD 0/2 <D 0 <D i -ΔD 0/2
Equation _{(6) → D 0> (} N-1) D i + ΔD 0/2
Equation _{(7) → D i + ΔD} 0/2 <D 0 <(N-1) D i -ΔD 0/2

ΔD ₀ is a value obtained from Δν by the following equation (8).

  Further, a can arbitrarily take a value such that the normalized frequency overlap integral between the signal photon and the idler photon is 1% or less.

Next, the light source will be described. Light source 101 to obtain the pump light is, for example, a semiconductor laser, an optical frequency outputs pump light of f _p. The pump light may have a pulse shape. In general, since the intensity of the pump light is larger than the intensity of the signal photon and idler photon, the scattered light component of the pump light in the array optical waveguide diffraction grating 104 may be mixed into the output optical waveguide 105. In order to prevent this, each output optical waveguide 105 may be provided with pump light attenuation means for selectively attenuating pump light. What is necessary is just to comprise a pump light attenuation | damping part from a fiber Bragg grating etc., for example.

  Depending on the circuit layout design of each part including the arrayed optical waveguide diffraction grating 104, the optical length from each input part of the plurality of nonlinear optical waveguides 103 to each output part of the corresponding output optical waveguide 105 is different. There is. In this case, each output optical waveguide 105 may be provided with optical delay means having different lengths so as to eliminate the optical length difference. As the optical delay means, a bent optical waveguide, a spatial optical type optical delay line, or the like may be used.

  In the above description, the silicon optical waveguide is exemplified as the third-order nonlinear optical waveguide constituting the nonlinear optical waveguide 103. However, the present invention is not limited to this, and an optical waveguide whose core material is a semiconductor can be used. In particular, an optical waveguide having a core material of single crystal germanium, silicon / germanium mixed crystal, indium / gallium / arsenic mixed crystal (InGaAs), or the like is suitable.

  An optical waveguide having an amorphous structure as a core material can also be used. In particular, an optical waveguide having an amorphous silicon, chalcogenide glass, or quartz optical waveguide as a core material is suitable. An optical fiber can be used as the nonlinear optical waveguide 103. Examples of the cladding portion of these optical waveguides include organic substances such as silicon oxide, silicon nitride, silicon oxynitride, and polyimide, aluminum oxide, titanium oxide, resin, water, air, or a photonic crystal structure.

  The core materials constituting the elements other than the nonlinear optical waveguide 103 (the input optical waveguide 106, the splitter 102, the array optical waveguide diffraction grating 104, and the output optical waveguide 105) are also the core materials constituting the nonlinear optical waveguide 103 described above. You can choose from candidates. Further, it is not necessary to select the same core material as that of the nonlinear optical waveguide 103.

  Further, all the components of the multidimensional entangled state generator shown in FIG. 1 may be integrated on one optical circuit board. In this case, for example, integration can be performed by using a technique as described in Patent Document 1. By integrating all the elements on one substrate, a multidimensional quantum entangled state generating element with stable path length fluctuation can be obtained.

  As described above, according to the present invention, by using a plurality of nonlinear optical waveguides, time-correlated photon pairs are generated from the pump light, and wavelength separation is performed by the array optical waveguide diffraction grating. A multidimensional entangled state can be formed by the number of elements.

  In the multidimensional quantum entangled state generator shown in Non-Patent Document 3, it is necessary to prepare as many wavelength separation circuits as the number N of dimensions of quantum entanglement to be generated, which separate signal light and idler light into different paths. was there. On the other hand, according to the present invention, in order to increase the dimension number N of quantum entanglement to be generated, it is only necessary to increase the number of nonlinear optical waveguides and output waveguides, so that the increase in the number of elements can be suppressed, and the cost and size can be reduced. Can be reduced.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  DESCRIPTION OF SYMBOLS 101 ... Light source, 102 ... Splitter, 103 ... Nonlinear optical waveguide, 104 ... Array optical waveguide diffraction grating, 105 ... Output optical waveguide, 106 ... Input optical waveguide, 111 ... First slab, 112 ... Optical waveguide array, 113 ... Second Slab.

Claims (5)

A light source capable of adjusting the light intensity of the pump light to be emitted;
A splitter for branching the pump light emitted from the light source into N (N is a natural number of 2 or more) input lights;
N input light beams branched by the splitter are respectively input, and N nonlinear optical waveguides each having an equal optical waveguide length;
An array optical waveguide diffraction grating to which the N nonlinear optical waveguides are connected;
A multi-dimensional entangled state generating device comprising: 2N output optical waveguides connected to an arrayed optical waveguide diffraction grating. The multidimensional entangled state generator according to claim 1,
The non-linear optical waveguide generates a signal photon and an idler photon from the input pump light by spontaneous emission four-wave mixing. The multidimensional entangled state generator according to claim 1 or 2,
The signal photon and idler photon generated (by the input pump light) in one of the N nonlinear optical waveguides are entangled photons having a quantum mechanical correlation, and
The signal photon, the idler photon, and the pump light are input to the same input port of the arrayed waveguide grating,
The signal photon and the idler photon are output to different output ports of the arrayed waveguide diffraction grating. In the multidimensional quantum entangled state generator according to any one of claims 1 to 3,
When a signal photon and an idler photon are generated in one of the N nonlinear waveguides,
A multi-dimensional entangled state generator characterized in that the light intensity of pump light is adjusted so that no signal photons and idler photons are generated in the remaining N-1 nonlinear optical waveguides. In the multidimensional quantum entangled state generator according to any one of claims 1 to 3,
The signal photon and idler photon emitted from the output optical waveguide have a normalized frequency overlap integral between them of 1% or less. A multidimensional quantum entangled state generator.