JP3999752B2 - Entangled photon pair generating apparatus and method - Google Patents

Description

  The present invention relates to an entangled photon pair generating apparatus and method, and more particularly to a quantum cryptographic key transmission technique in quantum cryptographic communication, and an entangled photon pair generating apparatus and method for generating a photon pair having a quantum correlation. In particular, the present invention relates to an entangled photon pair generating apparatus and method for generating an entangled photon pair having a correlation between polarization states.

  In recent years, a new type of information communication system using photon pairs having a quantum mechanical correlation has been proposed. More specifically, quantum key distribution using quantum correlation, quantum teleportation, and the like can be given. Quantum cryptographic key distribution is a cryptographic communication system that supplies cryptographic keys for performing cryptographic communications to two remote parties. Ultimately secure cryptographic keys are guaranteed by the principles of quantum mechanics. It is a cryptographic communication system.

There are various methods for quantum key distribution, but those using quantum correlation are most suitable for long-distance transmission. Quantum teleportation is a system that transfers quantum states and is used for signal transfer between quantum information processing devices such as quantum computers. A photon pair having a quantum correlation used in these quantum information communication systems is called a quantum entangled photon pair or simply an entangled photon pair. Quantum correlation can be considered for various physical quantities, and various types of entangled photon pairs exist accordingly. The entangled photon pair for the polarization state will be described below in accordance with the present invention.
In general, the polarization state of a single photon is expressed as | Ψ> = α | H> + β | V> as a superposition of a horizontal linear polarization state and a vertical linear polarization state. Here, | H> represents a state where the photon is a horizontal linear polarization, and | V> represents a state where the photon is a vertical linear polarization. α and β are weighting coefficients for each state, and | α | ² and | β | ² are the probabilities that the result will be horizontal or vertical when measured by a system that determines whether the photon is laterally polarized or longitudinally polarized. Represents. Specifically, the coefficient when a classical photoelectric field is displayed after being decomposed into a horizontal linear vibration component and a vertical linear vibration component is used as it is. For example, a clockwise circularly polarized photon is

  The counterclockwise circularly polarized photon is

  It is expressed as

  The above is a description of one photon, but when this is expanded to a two-photon state, a quantum entangled photon pair can be described. Suppose that there is a light source that simultaneously generates two photons. The two photons are collectively considered as one quantum state, and from this light source,

Is output. Here, subscripts a and b are used to identify two photons. When the two-photon measurement is performed to determine whether the two-photon is in a horizontal linear polarization state or a longitudinal polarization state, | H> _a | H> _b or | V> _a | V> It means that the state _b is observed. Here, | H> _a | H> _b represents a state in which photon a is horizontally polarized and photon b is horizontally polarized, and | V> _a | V> _b is photon a is vertically polarized and photon b. Represents the state of longitudinal polarization.

  For example, it is assumed that the generated two photons are sent to two persons (referred to as Alice and Bob), and both perform measurements on the respective photons. If Alice obtains the measurement result of horizontal polarization | H>, the measurement result that Bob obtains for the photon that is paired with it is always horizontal polarization | H>, and Alice obtains the measurement result of vertical polarization | V>. This means that the measurement result Bob obtains for the paired photons is always vertically polarized light | V>. Two photons having such a correlation are called a quantum entangled photon pair. In the case of the above-mentioned example, since it is a correlation about a polarization state, it is also called a polarization entangled photon pair.

  The feature of quantum entanglement is that the correlation is established even if the measurement system is changed. In the above description, the measurement is performed to determine whether the two-photon is in the horizontal linear polarization state or the vertical polarization state. However, the measurement is performed to determine whether it is a clockwise circular polarization state or a counterclockwise circular polarization state. However, the same correlation can be obtained. In order to see the situation, rewriting equation (2) using equations (1a) and (1b) described above,

  It becomes. When this equation (3) is used to determine whether two-photons are clockwise or counterclockwise circularly polarized, if one is clockwise, the other is counterclockwise and the other is counterclockwise. If this is the case, the other means clockwise rotation, indicating that the correlation holds even in circular polarization measurement. Although not described in detail here, if such a property is skillfully used, an ultimately secure quantum cryptography system or quantum teleportation can be implemented.

As means for generating the above-described polarization entangled photon pair, a method using a second-order optical nonlinear effect is known (for example, see Non-Patent Document 1). When pump light of wavelength λ _p is input to the second-order nonlinear optical crystal, a signal photon of wavelength λ _s and an Andler of wavelength λ _i satisfying the relationship 1 / λ _p = 1 / λ _s + 1 / λ _i It has the property of generating photons simultaneously. This phenomenon is known as parametric down conversion.

Further, at this time, in a certain type of crystal, if the direction of the crystal axis is set appropriately, the signal photon and the idler photon can be generated as the same linear polarization with respect to the linearly polarized pump light input. Since the signal photon and the idler photon are always generated in pairs, this generation state is described as | φ> = | H> _s | H> _i (or | V> _s | V> _i ). Here, the subscripts s and i represent a signal photon and an idler photon, respectively.

  In order to obtain a polarization entangled photon pair by parametric down conversion phenomenon, a signal photon and idler photon of the same polarization as the pump light are generated for a linearly polarized pump light input in a specific axial direction. Two non-linear crystals that do not generate anything are prepared for the input of pump light orthogonal thereto.

  FIG. 1 is a diagram for explaining a conventional method for generating an entangled photon pair, in which two nonlinear crystals 1a and 1b are arranged in series with their crystal axes inclined by 90 °. The first nonlinear crystal 1a generates a signal photon and an idler photon having the same polarization with respect to an input of linearly polarized pump light in the direction of 0 °, and an input of pump light orthogonal thereto. Assume that nothing is arranged. Then, since the crystal axis of the second nonlinear crystal 1b is shifted by 90 ° from that of the first nonlinear crystal 1a, the same polarization is applied to the input of the linearly polarized pump light in the 90 ° direction. Signal photons and idler photons. The linearly polarized pump light inclined by 45 ° is input to this series configuration.

  Such pump light can be considered by dividing it into a vertical polarization component and a horizontal polarization component. In the first nonlinear crystal 1a, a vertically polarized signal photon and an idler photon are generated from the vertical pump light component. In the second nonlinear crystal 1b, horizontal component signal photons and idler photons are generated from the horizontal pump light component.

Here, η is the efficiency with which one set of signal / idler photon pairs is generated from one nonlinear crystal. Then, the efficiency with which photon pairs are generated from either of the two nonlinear crystals arranged in series is η ² . The generation efficiency of the photon pair depends on the power of the pump light. Therefore, if the power of the pump light is adjusted so that η >> η ² , the efficiency of generating photon pairs from either of the two nonlinear crystals becomes negligibly low, and one set from the series arrangement. Of photons can be output.

  Whether the output photon pair is generated by the first nonlinear crystal 1a or the second nonlinear crystal 1b is unknown until measurement. Such a photon pair state is described as the superposition of the photon pair state generated in the first nonlinear crystal 1a and the photon pair state generated in the second nonlinear crystal 1b as follows.

This equation (4) represents that the output is in the polarization entangled state. That is, with the configuration shown in FIG. 1, a polarization entangled photon pair can be obtained. It should be noted that the entangled photon pair state of Equation (4) needs to have the same probability that | H> _s | H> _i and the probability that | V> _s | V> _i . For this purpose, the generation efficiency of photon pairs in the first nonlinear crystal 1a must be equal to the generation efficiency of photon pairs in the second nonlinear crystal 1b.

Paul G Kwiat. Et. Al. “Ultrabright source of polarization-entangled photons,” Physical Review A. vol. 60. No.2 pp. R773-R776,1999

  The conventional entangled photon pair generation method described above has a problem that it is difficult to obtain a photon pair in a long wavelength band (1.3 μm or 1.5 μm). In order to generate an entangled photon pair, it is necessary to match the phase velocities of the pump light, the signal photon, and the idler photon in the nonlinear crystal (phase matching condition). Considering the application of entangled photon pairs, it is desirable to generate photon pairs in the long wavelength band where the transmission loss of the optical fiber is small, but with conventional bulk nonlinear crystals, it is difficult to satisfy the phase matching condition in the long wavelength band. It has become. Even if a crystal that satisfies the phase matching condition is developed, it is necessary to couple the photon emitted from the crystal to the optical fiber in order to apply it to the optical fiber transmission system, and there is a problem in the efficiency and stability of the coupling system. It becomes.

Thus, in the conventional entangled photon pair generation method, 1 / λ _p = 1 / λ _s + 1 / λ _i generated simultaneously by inputting pump light (wavelength λ _p ) to the second-order nonlinear optical crystal. The signal photons (wavelength λ _s ) and idler photons (wavelength λ _i ) satisfying the above are used as entangled photon pairs, but the three phase velocities of pump light, signal light, and idler light are matched in the nonlinear optical crystal. (Phase matching condition).

  Therefore, for quantum cryptography applications using optical fiber transmission, long wavelength band photon pairs with low optical fiber transmission loss are desired, but bulk nonlinear crystals are difficult to satisfy phase matching conditions in the long wavelength band. There is a problem.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an entangled photon pair generation device capable of outputting a polarization entangled photon pair in a communication wavelength band in an all-optical fiber system, and It is to provide such a method.

The present invention has been made to achieve such an object. The invention according to claim 1 is directed to a polarization beam splitter having four input / output terminals and a first terminal of the polarization beam splitter. the input means for inputting the pumping light of the optical frequency f _p, and the second terminal of the polarization beam splitter horizontally polarized wave component of the pump light input to the polarization beam splitter is output, the pump light vertical and optical fiber connecting the third and the terminal of the polarization beam splitter polarization component is output, generated in the optical fiber, the signal photon of light frequency fs that satisfies 2f p = _f s _{+ f i} of and the idler photons of light frequency f _i, and output means for outputting to the fourth terminal of the polarization beam splitter, a phase difference between two orthogonal polarization of the output light from the fourth terminal by the output means Compensate It is characterized by comprising phase compensation means, and acquisition means for taking out the signal photons and Andler photons output from the phase compensation means.

  The invention according to claim 2 is the invention according to claim 1, wherein the acquisition means is a wavelength filter.

The invention according to claim 3, a polarization beam splitter having at least three input and output terminals, input means for inputting the pumping light of the optical frequency f _p to a first terminal of said polarization beam splitter, A second terminal of the polarization beam splitter from which the transverse polarization component of the pump light input to the polarization beam splitter is output; and a polarization beam splitter of the polarization beam splitter from which the longitudinal polarization component of the pump light is output. an optical fiber for connecting the third and terminals, occurs within the optical fiber, the idler photons 2f p = _f s ₊ signal photon of light frequency fs satisfying f _i and the optical frequency f _i, said first terminal Output means for outputting to the output means, acquisition means for taking out the signal photons and the Andler photons output from the first terminal by the output means, and the polarization beam taken out by the acquisition means. And phase compensation means for compensating for a phase difference between two orthogonal polarizations of the output light from the beam splitter.

  The invention according to claim 4 is the invention according to claim 3, characterized in that the acquisition means is an optical circulator.

The pump an invention according to claim 5, which is entered by four first input step and, input step of inputting pump light of the optical frequency f _p at the terminals of a polarization beam splitter having input and output terminals The horizontal polarization component of light is output to the second terminal of the polarization beam splitter, and the longitudinal polarization component of the pump light connected to the second terminal by an optical fiber is converted to the polarization beam splitter. a first output step of outputting to the third terminal, generated within the optical fiber, the idler photons 2f p = _f s ₊ signal photon of the optical frequency f _s that satisfies f _i and the optical frequency f _i, the polarized A second output step for outputting to the fourth terminal of the wave beam splitter, and a phase compensation step for compensating for a phase difference between two orthogonally polarized waves of the output light from the fourth terminal by the second output step. When, characterized by comprising a obtaining step of removing said Andora photons and the signal photon output from the phase compensation step.

The invention of claim 6 includes the steps of: inputting pump light of the optical frequency f _p to a first terminal of the polarization beam splitter having at least three input-output terminals, is input by the input step The transversely polarized component of the pump light is output to the second terminal of the polarization beam splitter, and the longitudinally polarized component of the pump light connected to the second terminal by an optical fiber is converted to the polarized beam splitter. of a first output step of outputting to the third terminal, occurs within the optical fiber, the idler photons 2f p = _f s ₊ signal photon of the optical frequency f _s that satisfies f _i and the optical frequency f _i, the A second output step for outputting to the first terminal; an acquisition step for extracting the signal photon and the Andler photon output from the first terminal by the second output step; To compensate for the phase difference between two orthogonal polarization of the output light from the polarization beam splitter extracted by resulting step is characterized in that a phase compensation step.

  According to the present invention, it is possible to generate a polarization entangled photon pair that is stable and suitable for a fiber transmission system in a fiber communication wavelength band.

  In addition, the present invention generates entangled photon pairs not by the second-order nonlinear optical effect of the bulk type nonlinear crystal but by the parametric amplification phenomenon that is the third-order nonlinear optical effect of the optical fiber that is different from the conventional one in principle. Therefore, the conventional problem is solved, and at the same time, there is an effect that it is suitable for fiber transmission of photons.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a block diagram for explaining the first embodiment of the entangled photon pair generating apparatus of the present invention, in which reference numeral 31 is a pump light source, 32 is a polarization beam splitter (PBS), 32a to 32d are input / output terminals, Reference numeral 33 denotes an optical fiber, 34 denotes a phase compensation circuit, and 35 denotes a wavelength filter.

In the entangled photon pair generating apparatus according to the first embodiment, the polarization beam splitter 32 has four input / output terminals 32 a to 32 d, and an input portion of the polarization beam splitter 32 transmits light to the first terminal 32 a of the polarization beam splitter 32. It is configured to enter the pump light frequency f _p. The optical fiber 33 also outputs the second terminal 32b of the polarization beam splitter 32 from which the transverse polarization component of the pump light input to the polarization beam splitter 32 is output, and the longitudinal polarization component of the pump light. The third terminal 32c is connected.

The output unit of the polarization beam splitter 32, generated in the optical fiber _33, the idler photons 2f _{p =} f s + signal photon of the optical frequency _{f s} that satisfies _{f i} and the optical frequency _{f i,} the polarization beam splitter It is comprised so that it may output to 32 4th terminal 32d. The phase compensation circuit 34 compensates for a phase difference between two orthogonal polarizations of light output from the fourth terminal 32 d of the polarization beam splitter 32. The wavelength filter 35 is for extracting signal photons and Andler photons output from the phase compensation circuit 34.

In the present invention, a polarization entangled photon pair is generated by utilizing a parametric amplification phenomenon that is a third-order optical nonlinear effect of an optical fiber. Parametric amplification means that when signal light (frequency f _s ) having the same polarization state as the pump light is input to an optical fiber to which strong pump light (frequency f _p ) is input, the optical fiber is This is a phenomenon in which signal light is amplified and output when the dispersion and the input optical frequency have an appropriate relationship. At this time, at the same time that the signal light is _amplified, the light of a frequency _{f i} satisfying 2f _{p = f} s + f _i is also output. Light polarization state also pump light frequency f _i, which is the same as the signal light.

The signal light to be amplified f _i frequency light signal light, generated are called idler light. As shown in FIG. 2, this phenomenon can be regarded as a phenomenon in which a signal photon and an idler photon are generated one by one from two pump photons when light is viewed as a photon. Since this phenomenon is an optical amplification process, spontaneous emission light is generated in the same manner as in normal optical amplification. That is, even if only pump light is input to the optical fiber, signal light and idler light are spontaneously output. Two lights are generated simultaneously, and their polarization state is the same as that of the pump light. In the present invention, a pair of polarization entangled photons is generated using the parametric spontaneous emission light from the optical fiber.

  As shown in FIG. 3, the pulsed light from the pump light source 31 is input to the first port 32 a of the 2 × 2 polarization beam splitter (PBS) 32. The PBS 32 has a characteristic of transmitting the horizontally polarized wave and reflecting the vertically polarized wave. The horizontally polarized wave component is output to the second port 32b, and the vertically polarized wave component is output to the third port 32c. Here, it is assumed that the input polarization state of the pump light is set so that the horizontal component and the vertical component have the same power.

  The second port 32b and the third port 32c of the PBS 32 are connected in a loop via an optical fiber 33 for generating parametric light. Longitudinal polarization pump light propagates clockwise in the loop and transverse polarization pump light propagates counterclockwise. While the pump light goes around the loop, signal photons and idler photons are generated by the parametric spontaneous emission phenomenon. The polarization state of the generated photons is the same as that of the pump light. The clockwise rotation is longitudinal polarization and the counterclockwise rotation is horizontal polarization. The generated photons are input to the second port 32b and the third port 32c of the PBS 32.

  Due to the transmission characteristics of the PBS 32, the longitudinally polarized light input to the second port 32b and the laterally polarized light input to the third port 32c are output to the fourth port 32d. That is, both clockwise light and counterclockwise light are output to the fourth port 32d. The signal light and idler light output from the PBS 32 are separated by the wavelength filter 35 and output as signal light and idler light, respectively.

With the configuration as described above, a polarization entangled photon pair can be obtained. As described above, the polarization state of the signal photon and idler photon generated in the loop fiber is the same as that of the positive light, that is, the clockwise rotation is longitudinal polarization and the counterclockwise rotation is transverse polarization. If you write in the formula,
| Φ> _R = | V> _s | V> _i
In the counterclockwise direction,
| Φ> _L = | H> _s | H> _i
Each state occurs. Here, since the power of the pump light is the same clockwise and counterclockwise, the generation efficiency of the parametric photon pair is the same for both directions. The generated photon pair is output to the fourth port 32d of the PBS 32. Here, similarly to the conventional example, it is assumed that the generation efficiency η of photon pairs is η >> η ² by adjusting the power of the pump light. That is, the probability that two or more photon pairs are output from the PBS 32 is negligibly small, and one set of photon pairs is generally output from the PBS 32. This photon pair cannot be discriminated without measuring whether it is generated clockwise or counterclockwise in the loop. Such a state is a superposition of the two states,

  Is written. The phase difference θ between the first term and the second term is a constant determined by the polarization state of the pump light input to the PBS 32, the birefringence of the loop fiber, and the like. This phase difference can be compensated at the output stage of the fourth port 32d of the PBS 32 by a phase compensation circuit 34 that provides a phase difference between longitudinally polarized waves and transversely polarized waves, for example, a Babinet Soleil phase plate. By adjusting so that θ = 0, the output state is

  This is a polarization entangled photon pair state. If the input of the pump light to the PBS 32 is in a 45 ° linearly polarized state and the birefringence of the loop fiber is negligible, θ = 0 at the output stage of the PBS 32 and phase compensation is not necessary. .

  A polarization entangled photon pair can be obtained as described above. If the generated signal photons / idler photons are to be taken out separately, they can be demultiplexed by a wavelength filter.

  In the above description, it is assumed that the polarization state of light is maintained even during propagation of the loop fiber. This condition is satisfied if a polarization-maintaining fiber is used, but in general, for example, light input to the loop fiber as a transverse polarization from the second port 32b of the PBS 32 is converted into a longitudinal polarization while going around the loop. It may rotate and be output from the third port 32c of the PBS 32 to the first port 32a. In order to avoid this, a polarization control circuit may be inserted in the loop as necessary, and adjusted so that the same polarization is input again to the PBS 32 after propagation through the loop.

  By the way, in order for the parametric process to occur efficiently, it is necessary to satisfy the phase matching condition. In an optical fiber, it is known that the phase matching condition is satisfied when the wavelength of the pump light is matched with the zero dispersion wavelength of the optical fiber. A normal optical transmission fiber has a zero dispersion wavelength in the 1.3 μm band or 1.5 μm band. If these are used as a loop fiber, a polarization entangled photon pair in the optical fiber communication wavelength band can be generated.

  The feature of the first embodiment is that the entire system can be constituted by optical fibers. For this reason, the structure is more stable and suitable for optical fiber transmission than the conventional method using a bulk crystal.

  FIG. 4 is a block diagram for explaining the embodiment 2 of the entangled photon pair generating apparatus of the present invention, in which reference numeral 41 is a pump light source, 42 is a polarization beam splitter (PBS), 42a to 42c are input / output terminals, Reference numeral 43 denotes an optical fiber, 44 denotes a phase compensation circuit, 45 denotes a wavelength filter, and 46 denotes an optical circulator.

In the entangled photon pair generating apparatus according to the second embodiment, the polarization beam splitter 42 has at least three input / output terminals 42 a to 42 c, and the input portion has an optical frequency connected to the first terminal 42 a of the polarization beam splitter 42. It is configured to enter the pumping light of f _p. Further, the optical fiber 43 outputs the second terminal 42b of the polarization beam splitter 42 from which the transverse polarization component of the pump light input to the polarization beam splitter 42 is output, and the longitudinal polarization component of the pump light. The third terminal 42c is connected.

The output unit of the polarization beam splitter 42, generated in the optical fiber _43, the idler photons 2f _{p =} f s + signal photon of the optical frequency _{f s} that satisfies _{f i} and the optical frequency _{f i,} the polarization beam splitter It is configured to output to 42 first terminals 42a.

  The optical circulator 46 takes out signal photons and Andler photons output from the first terminal 42 a of the polarization beam splitter 42. The phase compensation circuit 44 compensates for a phase difference between two orthogonal polarizations of output light from the polarization beam splitter 42 extracted by the wavelength filter 45. The wavelength filter 45 is for separating the signal photon and the Andler photon output from the phase compensation circuit 44.

  The basic principle of entangled photon pair generation is the same as that of the first embodiment described above, but the photon pair generated by the loop fiber is output from the first port 42a of the PBS 42. Such output characteristics can be realized by connecting the second port 42b and the third port 42c of the PBS 42 by twisting the polarization maintaining axis by 90 ° when a polarization maintaining fiber is used as the loop fiber. It is. In addition, when a normal optical fiber is used, it can be realized by adjusting the polarization state by inserting a polarization control circuit in the loop as necessary. Thus, if the signal photon and idler photon output from the first port 42a of the PBS 42 are extracted by the optical circulator 46, a polarization entangled photon pair can be obtained in the same manner as in the first embodiment.

It is a figure for demonstrating the conventional entangled photon pair generation method. It is a figure which shows the photon image of the parametric amplification phenomenon by 3rd-order optical nonlinearity. It is a block diagram for demonstrating Example 1 of the entangled photon pair generator of this invention. It is a block diagram for demonstrating Example 2 of the entangled photon pair generator of this invention.

Explanation of symbols

1a, 1b Nonlinear crystal 31, 41 Pump light source 32, 42 Polarization beam splitter (PBS)
32a to 32d, 42a to 42c Input / output terminals 33 and 43 Optical fibers 34 and 44 Phase compensation circuits 35 and 45 Wavelength filter 46 Optical circulator

Claims (6)

A polarization beam splitter having four input / output terminals;
Input means for inputting the pumping light of the optical frequency f _p to a first terminal of said polarization beam splitter,
A second terminal of the polarization beam splitter from which the transverse polarization component of the pump light input to the polarization beam splitter is output; and a polarization beam splitter of the polarization beam splitter from which the longitudinal polarization component of the pump light is output. An optical fiber connecting the third terminal;
Generated in the optical fiber, and an output means for the idler photons 2f p = _f s ₊ signal photon of the optical frequency f _s that satisfies f _i and the optical frequency f _i, and outputs it to the fourth terminal of the polarization beam splitter ,
Phase compensation means for compensating for a phase difference between two orthogonal polarizations of output light from the fourth terminal by the output means;
An entangled photon pair generation device comprising: the signal photon output from the phase compensation unit; and an acquisition unit that extracts the Andler photon.   2. The entangled photon pair generating apparatus according to claim 1, wherein the acquisition means is a wavelength filter. A polarization beam splitter having at least three input / output terminals;
Input means for inputting the pumping light of the optical frequency f _p to a first terminal of said polarization beam splitter,
A second terminal of the polarization beam splitter from which the transverse polarization component of the pump light input to the polarization beam splitter is output; and a polarization beam splitter of the polarization beam splitter from which the longitudinal polarization component of the pump light is output. An optical fiber connecting the third terminal;
Generated in the optical fiber, and an output means for the idler photons 2f p = _f s ₊ signal photon of the optical frequency f _s that satisfies f _i and the optical frequency f _i, and outputs it to the first terminal,
Obtaining means for taking out the signal photons and the Andler photons output from the first terminal by the output means;
An entangled photon pair generation device comprising: phase compensation means for compensating for a phase difference between two orthogonally polarized waves of output light from the polarization beam splitter extracted by the acquisition means.   The entangled photon pair generating apparatus according to claim 3, wherein the acquisition means is an optical circulator. An input step of inputting the pumping light of the optical frequency f _p to a first terminal of the polarization beam splitter having four input terminals,
The transversely polarized component of the pump light input in the input step is output to the second terminal of the polarization beam splitter, and the longitudinally polarized light of the pump light connected to the second terminal by an optical fiber. A first output step of outputting a component to a third terminal of the polarization beam splitter;
Generated within the optical fiber, 2f the idler photons p = _f s ₊ signal photon of the optical frequency f _s that satisfies f _i and the optical frequency f _i, the second output to the fourth terminal of the polarization beam splitter An output step;
A phase compensation step for compensating for a phase difference between two orthogonally polarized lights of output light from the fourth terminal in the second output step;
An entangled photon pair generation method comprising: the signal photon output from the phase compensation step and an acquisition step of extracting the Andler photon. An input step of inputting the pumping light of the optical frequency f _p to a first terminal of the polarization beam splitter having at least three input and output terminals,
The transversely polarized component of the pump light input in the input step is output to the second terminal of the polarization beam splitter, and the longitudinally polarized light of the pump light connected to the second terminal by an optical fiber. A first output step of outputting a component to a third terminal of the polarization beam splitter;
Generated within the optical fiber, and a second output step of the idler photons 2f p = _f s ₊ optical frequency satisfies the f _i f _s signal photon and an optical frequency f _i, and outputs to the first terminal,
Obtaining the signal photon and the Andler photon output from the first terminal in the second output step;
An entangled photon pair generation method comprising: a phase compensation step of compensating for a phase difference between two orthogonally polarized waves of output light from the polarization beam splitter extracted in the acquisition step.

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