JP2017161619A - Photon generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate photons having an extremely narrow spectrum spread more efficiently. SOLUTION: A parametric guiding unit 103 inputs a first light 151, a second light 152, and a third light 153, each guided by a different optical path, and a first light 151, a second light 152, by a guided parametric process. And the third light 153 interacts with each other to change the quantum state of the first light 151 and output it to the first optical path 131. The phase shifter 107 gives a phase difference of π / 2 between the fifth light and the fourth light. The combined wave unit 108 combines (interferes with) the fourth light and the fifth light whose phase is given by the phase shifter 107, and outputs them to the first output port 134 and the second output port 135. [Selection diagram] Fig. 1

Description

  The present invention relates to a photon generator that efficiently generates photons having a very narrow spectral spread.

  Controlling the quantum state of light and atoms by the interaction of light and atoms is not only the basis of today's precision spectroscopy technology, but also important for quantum information processing technologies (quantum computers, etc.) that are expected in the future Elemental technology. In particular, when the frequency difference between the quantum levels of atoms and ions coincides with the frequency of light, in the case of so-called resonance, the effect of interaction is greatly increased, and the quantum state can be controlled efficiently. However, the spectral width of atomic resonance is usually very narrow, about several MHz or less, and the frequency of light must be precisely matched. Furthermore, in quantum optical communication and quantum light measurement, it is necessary to prepare photons with a very narrow frequency spectrum.

  For applications that do not require resonance with material atoms, single photon generators with a messenger that supply single photons with a broad spectrum spread with a guaranteed generation time (with a messenger) have already been developed. This uses the nonlinear optical effect of certain substances, where the energy of a high-frequency photon splits into two low-frequency photons, one as a messenger and the other as a signal photon. To supply. This splitting is a phenomenon that occurs stochastically and is called a natural parametric transformation process.

Since the spectrum width of photons is as wide as about several hundred GHz to 1 THz, the above-described conversion probability is relatively good, and the conversion probability is about 10 ⁻⁶ to 10 ⁻⁵ per high-energy photon. Also, by inputting a large number of photons, the probability of the generation of net signal photons can be increased to about 0.1.

  On the other hand, it is understood that if the spectral width of the signal photon is narrowed to 1 MHz in order to match the resonance line of the atom, the generation efficiency decreases by 5 to 6 digits by itself. As described above, the conventional method using the natural parametric conversion process cannot be used as a single photon generator having a narrow line width as it is.

  In order to solve the above problem, a method using an atomic resonance transition in the generation of photons has been proposed and an experiment has been conducted (see Non-Patent Document 1). Specifically, this process is called a Raman scattering process. First, a three-level system having two ground state pairs (states 1 and 2) in which energy is extremely close to each other and an excited state (state 3) by light is prepared first. Next, this group of atoms is sufficiently cooled so as not to be affected by thermal noise. Next, an initial state of electrons is prepared so that electrons are present at level 1 and no electrons are present at levels 2 and 3 regardless of which atom is seen. This initial state is also prepared by intense light irradiation.

  After the above-described initial state is prepared, the atomic group is irradiated with a laser beam having a narrow spectral width and an optical frequency that resonates with the transition frequency between level 3 and level 1 and an appropriate intensity. By this irradiation, electrons move from level 1 to level 2 in a very small proportion of atoms. This process is called natural Raman scattering. Along with this movement, a number of photons corresponding to the number of atoms in which the movement has occurred are emitted. The frequency of the photons emitted here is equal to the transition frequency between level 3 and level 2. Here, attention is paid to the case where one photon is emitted in a specific orientation. This corresponds to the situation where there is only one atom with electrons at level 2.

  After selecting the conditions so far, next, the above-mentioned atomic group is irradiated with a laser beam having an optical frequency that resonates with the transition frequency between level 3 and level 2 and an appropriate intensity and a narrow spectral width. . This light interacts only with atoms whose electrons are at level 2 and moves the electrons from level 2 to level 1. At this time, one photon having a frequency matching the transition frequency between level 3 and level 1 is always generated in a specific direction.

  Thus, only when one photon can be observed in the first process, it can be guaranteed that only one photon is generated at the irradiation stage in the next process. The spectral width of the photons generated at this time is only about the width of the resonance of atoms, and is extremely narrow. Also note that the first observed photon plays the role of a so-called messenger photon.

  By using the Raman scattering process described above, it is possible to supply a single photon with a narrow spectral width with a messenger photon.

  However, the probability of the occurrence of the Raman scattering process is not sufficiently high, and even if this method is adopted, the actual number of photons that can be supplied per second is about 0.1. However, the method of Non-Patent Document 1 has a great advantage that the problem of noise in the spectral region can be avoided because the frequency of generated photons is limited to two.

T. Chaneliere et al., "Storage and retrieval of single photons transmitted between remote quantum memories", Nature, vol.438, pp.833-836, 2005. Co-authored by Tadanobu Kojima, Kazuko Kojima, “The Quantum Theory of the Light of Light”, published by Uchida Otsukaku Shinsha Co., Ltd., first edition, pages 172-173, March 5, 1978. H. Zhang et al., "Preparation and storage of frequency-uncorrelated entangled photons from cavity-enhanced spontaneous parametric downconversion", Nature Photonics, vol.5, pp.628-632, 2011.

  As explained above, the nonlinear optical effect (natural parametric conversion process) that was suitable for supplying photons with a wide spectral spread with a messenger is necessary for supplying photons having a spectral width of only several MHz. The generation efficiency is too low to be used. In addition, the method using the Raman scattering process in the cooled atomic group does not function as an efficient photon generator because the probability of natural Raman scattering is small. As described above, any of the conventional techniques has a problem that it is difficult in principle to efficiently generate photons having a very narrow spectrum spread.

  The present invention has been made to solve the above-described problems, and an object thereof is to more efficiently generate photons having a very narrow spectrum spread.

  The photon generator according to the present invention includes a first light, a second light, and a third light through coherent first light, second light, and third light having different optical frequencies f1, f2, and f3 through a guided parametric process. The light generation unit that generates the fourth light and the fifth light having the optical frequency f1 by changing the quantum state of the first light by causing an interaction between the light, and the fifth light generated by the light generation unit On the other hand, a phase shifter that gives a phase difference of π / 2 with the fourth light, and a fifth light that has been phased by the fourth light and the phase shifter are combined to provide a first output port and a second output port A multiplexing unit that outputs to the second output port from the multiplexing unit, a demultiplexing unit that outputs to the third output port and the detection port, and a multiplexed light that is output from the demultiplexing unit to the detection port A photodetection unit that detects the number of photons of the photon, and that the photodetection unit has detected one photon. And a notifying unit for, first light is weaker intensity than the second light, and third light, there is a f1 + f2 = f3.

  In the photon generator, the first light, the second light, and the third light, which are respectively guided by different optical paths, are input, and an interaction between the first light, the second light, and the third light is performed by a guided parametric process. And a parametric guiding unit that changes the quantum state of the first light and outputs it to the first optical path, and transmits light of the optical frequency f1 from the light that is arranged in the first optical path and exits the parametric guiding unit. An optical filter that outputs the fourth light, an optical switch that divides the fourth light emitted from the optical filter into a second optical path and a third optical path at predetermined time intervals, and a switching in the optical switch that is disposed in the third optical path. And an optical delay line that provides a delay equal to the time interval and serves as a fifth light, and a light generation unit includes a parametric guiding unit, a first optical path, an optical filter, a second optical path, a third optical path, an optical switch, and an optical delay line. It is configured It may be set to cormorants.

  In the photon generation device, the light generation unit includes a first light generation unit that generates fourth light and a second light generation unit that generates fifth light, and the first light generation units are guided by different optical paths. The first light, the second light, and the third light are input, and the quantum state of the first light is changed by causing an interaction between the first light, the second light, and the third light by a guided parametric process. A first parametric guiding unit that outputs to the first optical path and a fourth light that is disposed in the first optical path and transmits the light having the optical frequency f1 from the light emitted from the first parametric guiding unit and outputs the fourth light. And a second light generation unit that inputs the first light, the second light, and the third light, respectively, guided by different optical paths, and performs the first light, the second light, and the light by a guided parametric process. An interaction occurs between the third light to change the quantum state of the first light and enter the second optical path. And a second optical filter that is disposed in the second optical path and that transmits the light having the optical frequency f1 from the light emitted from the second parametric guidance unit and outputs the fifth light. It may be.

  The photon generator includes a first light source that generates the first light, a second light source that generates the second light, and a third light source that generates the third light, the first light source generated by the first light source. The light is branched and led to each of the first parametric guiding unit and the second parametric guiding unit, and the second light generated from the second light source is branched and led to each of the first parametric guiding unit and the second parametric guiding unit. The third light generated from the third light source may be branched and guided to each of the first parametric guide unit and the second parametric guide unit.

  As described above, according to the present invention, it is generated by changing the quantum state of the first light by causing an interaction between the first light, the second light, and the third light by the induced parametric process. Since the fourth light and the fifth light having the optical frequency f1 are caused to interfere with each other by giving a phase difference of π / 2 to the other, it is possible to more efficiently generate photons having an extremely narrow spectrum spread. An excellent effect that it can be obtained.

FIG. 1 is a configuration diagram showing the configuration of the photon generator in Embodiment 1 of the present invention. FIG. 2 is a configuration diagram showing the configuration of the photon generator in Embodiment 2 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram showing the configuration of the photon generator in Embodiment 1 of the present invention. The photon generator includes a light source 101, a phase adjustment unit 102, a parametric induction unit 103, an optical filter 104, an optical switch 105, an optical delay line 106, a phase shifter 107, a multiplexing unit 108, a demultiplexing unit 109, and a light detection unit 110. And a notification unit 111.

  The light source 101 supplies the first light 151 that is weak coherent light having a stable optical frequency f1 and a stable phase. For example, the light source 101 can be composed of a frequency stabilized laser and an optical attenuator. The phase adjustment unit 102 appropriately adjusts the phase of the first light 151 supplied from the light source 101 to a desired state.

  The parametric guide unit 103 receives the first light 151, the second light 152, and the third light 153, which are guided by different optical paths, and receives the first light 151, the second light 152, and the third light through a guided parametric process. An interaction is generated during 153 to change the quantum state of the first light 151 and output it to the first optical path 131. In the first embodiment, the first light 151 is guided to the first optical path 131. Here, the first light 151 is weaker than the second light 152 and the third light 153. In addition, there is a relationship of f1 + f2 = f3 between optical frequencies.

  The parametric guiding unit 103 may be configured from a second-order nonlinear optical medium that can obtain a second-order nonlinear optical effect. The parametric induction unit 103 is composed of a crystal having non-linear optical characteristics such as lithium niobate, and is composed of a plurality of regions connected in series with a periodic pitch length. (The nonlinear constant is periodically inverted).

  The optical filter 104 is disposed in the first optical path 131, and transmits the light having the optical frequency f1 from the light emitted from the parametric guiding unit 103, and outputs the fourth light. The optical filter 104 is a narrow-band optical filter that transmits only a narrow spectral range centered on the frequency f1. The optical filter 104 removes noise photons, idler light, and pump light leakage generated during the parametric interaction in the parametric guiding unit 103.

  The optical switch 105 splits the fourth light emitted from the optical filter 104 into the second optical path 132 and the third optical path 133 at predetermined time intervals. The optical delay line 106 is arranged in the third optical path 133 and gives a delay equal to the switching time interval in the optical switch 105 to be the fifth light. The phase shifter 107 gives a phase difference of π / 2 between the fifth light and the fourth light.

  In the first embodiment, the third optical path 133 includes the reflecting portions 112 and 113. The fourth light separated into the third optical path 133 by the optical switch 105 is changed in the traveling direction by the reflection unit 112 and enters the optical delay line 106. The fifth light output after being delayed by the optical delay line 106 is incident on the phase shifter 107 while the traveling direction is changed by the reflection unit 113.

  The multiplexing unit 108 combines (interfers with) the fourth light and the fifth light whose phase is given by the phase shifter 107 and outputs the combined light to the first output port 134 and the second output port 135. The multiplexing unit 108 is, for example, a semi-reflecting mirror having a transmittance of 50% (a reflectance of 50%). The demultiplexing unit 109 outputs the multiplexed light output from the multiplexing unit 108 to the second output port 135 to the third output port 136 and the detection port 137. The demultiplexing unit 109 is, for example, a semi-reflecting mirror having a transmittance of 50% (a reflectance of 50%).

  The light detection unit 110 discriminates the photons of the combined light output from the demultiplexing unit 109 to the detection port 137 and detects the number. The notification unit 111 notifies that the light detection unit 110 has detected one photon. In a state where the photodetection unit 110 detects one photon, a single photon is output from the third output port 136 with a probability of 1.

  In the present invention, in the light generation unit, the first light, the second light, and the third light are generated from the coherent first light, second light, and third light respectively having different optical frequencies f1, f2, and f3 by a guided parametric process. An interaction is generated between the lights to change the quantum state of the first light to generate the fourth light and the fifth light having the optical frequency f1, and the fourth light is generated with respect to the fifth light generated by the light generation unit. A phase difference of π / 2 is given to the light by the phase shifter 107, and the fourth light and the fifth light to which the phase is given by the phase shifter 107 are multiplexed by the multiplexing unit 108, and the first output port 134. It is important that the multiplexed light that is output to the second output port 135 and output from the multiplexing unit 108 to the second output port 135 is output to the third output port 136 and the detection port 137 by the demultiplexing unit 109. .

  In the first embodiment, the above-described light generation unit includes the parametric guiding unit 103, the first optical path 131, the optical filter 104, the second optical path 132, the third optical path 133, the optical switch 105, and the optical delay line 106. .

  This will be described in more detail below.

  In the parametric guiding unit 103, the first light 151, which is weak coherent light having a fixed frequency f1 and phase, is used as the signal light, and the second light 152 as the intense idler light that is simultaneously input and the third light as the pump light. It causes a parametric interaction involving three light waves with the light 153, manipulates the physical properties related to the photon number distribution in the signal light, and changes the signal light (first to a non-classical state different from the coherent state). The quantum mechanical state of the light) is modulated to be the fourth light (fifth light).

  Here, the quantum state of the first light 151 before being modulated is represented by a coherent state | α>, and the non-classical state after being modulated is represented by | ψ>. | Ψ> is a state vector generally describing a quantum state, and a photon number definite state | n> having n photons is represented by basis sets {| 0>, | 1>, | 2>, | 3>, | 4>,...}, And describes the quantum mechanical characteristics of the light wave by linear combination | Ψ> = a | 0> + b | 1> + c | 2> + d | 3> + e | 4> +. (See Non-Patent Document 2). The states | α> and | ψ> are the same in that they are composed of a group of single-mode photons having the frequency f1, but the difference in the coefficients of the linear combination causes a difference in the physical properties of the light wave. .

The light wave output from a normal laser light source is in a coherent state (classical state), and _assuming that the average number of photons is | α | ² , each coefficient C _n is “C _n = exp (| α | ² / 2) α ⁿ / √n! ”. α is a complex number | α | exp (iφ), | α | is an amplitude, and φ is a phase when a light wave is represented by a sin wave. The purpose of the aforementioned parametric interaction is to change the values of these coefficients a, b, c, d, e, from C _n to the required values to create a non-classical state | ψ>. This is physically possible by appropriately selecting the phase relationship between the first light 151, the second light 152, and the third light 153 and the intensity of the second light 152 and the third light 153.

  As described above, in order to cause the weak fourth light modulated and prepared in the quantum state | ψ> to interfere with itself (fifth light), the optical switch 105 causes the second optical path 132 and the second optical light in the time domain. After splitting into three optical paths 133, the first half of the pulse is delayed by a delay corresponding to the pulse width through the optical delay line 106 to be the fifth light, and the second half of the pulse (fourth) is transmitted by a translucent mirror having a transmittance of 50%. Superimpose with light). In this superposition, the phase of the fifth light is adjusted by the phase shifter 107 so that the phase difference between the fourth light and the fifth light becomes π / 2.

  Of the two first output ports 134 and second output ports 135 of the multiplexing unit 108, the reflected portion of the fifth light pair and the transmitted portion of the fourth light are output to the first output port 134, and the fifth light pair The portion of the transmitted and reflected fourth light is output to the second output port 135. Whether the photon of the first light 151 is output to the first output port 134 or the second output port 135 depends on the quantum state | ψ> of the first light 151.

  The light wave (combined light) output from the second output port 135 is further split into two by the branching unit 109, and the photons of the reflected light are output from the third output port 136. Photons transmitted through the demultiplexing unit 109 and output to the detection port 137 are detected by the photodetection unit 110 capable of photon number discrimination. Only when the number of photons detected by the light detection unit 110 is one, the notification unit 111 notifies (notifies) the detection of photons.

  At this time, the fact that one photon is always output from the third output port 136 that is the reflection port of the demultiplexing unit 109 defines the principle of quantum mechanics (the behavior of a system composed of a plurality of photons). Guaranteed by Bose statistics).

The feature of the present invention described above is that the optical frequency of the signal photon is determined by the frequency f1 of the first light (coherent state) to be input, and this spectral spread is uniquely determined by the reciprocal (ΔT) ⁻¹ of the pulse time width ΔT. It is decided. Therefore, by setting the time width ΔT so that (ΔT) ⁻¹ falls within the target resonance line width, it becomes possible to supply a single photon with a messenger signal that matches the resonance line.

The quantum state | ψ> of the signal light is superposed on the photon number determined state | n>: | ψ> = a | 0> + b | 1> + c | 2> + d | 3> + e | 4> +. In the light quantum state | Φ> _AB generated as a result of interference in the multiplexing unit 108, the number of photons guided to the first output port 134 and the second output port 135 is determined to be k and l, respectively. Using the state | k> _A | l> _B , it can be expressed as follows.

  If the signal light remains in the coherent state | α> (classical state), the value of the following equation or the like becomes exactly zero, and no photon is guided to the second output port 135.

  The output light from the first output port 134 is also in a coherent state.

  In contrast to the state described above, when | ψ> is a non-classical state, values such as the following equations can take a finite value, and a finite number of photons are guided to the second output port 135. There is a probability.

Here, when photons are guided to the second output port 135, the photons always act as an even number of groups as in | 2> _B and | 4> _B , and the photons alone are the second output port 135. It is essential not to be guided by If one photon is detected by the light detection unit 110, it can be ensured by the messenger signal (notification) from the notification unit 111 that another photon is output from the third output port 136. . That is, the output timing of the photon can be known from the messenger signal.

Considering that the probability that two photons guided to the second output port 135 are reflected and transmitted by the demultiplexing unit 109 is ½, the arrival and output of a single photon per pulse is transmitted. The probability P _total that can be known with the addition is given by the following equation (2).

On the other hand, in the eighth term on the right side of Expression (1), when four photons are guided to the second output port 135 as in | 4> _B and one photon is detected by the light detection unit 110, the third photon There is a non-zero probability that three photons are emitted from the output port 136.

Therefore, in order to increase the probability that a single photon is generated with a messenger signal and to reduce the probability that an extra photon is generated, the value of the following equation (3) is increased and the value of equation (4) is increased. The quantum state | ψ> = a | 0> + b | 1> + c | 2> + d | 3> + e | 4> + may be appropriately prepared so that is sufficiently small.

As will be described later, when the average photon number | α | ^{2 in} the coherent state (classical state) of the input signal light is about 0.1, the value of the expression (3) is ˜2 (| α | ^{2) 2} degrees of the value of the time equation (4) is to 2 (| a degree of ^{2) 4} | alpha. Therefore, it is possible to provide a single photon with messenger at a rate of once per 100 times, and the rate of mixing a plurality of photons can be reduced to nearly 1%.

When 10 MHz is required as the spectrum width of the photon, the time width of the corresponding pulse is 100 ns, and 10 ⁷ signal pulse lights are supplied per second. Among these, if a single photon with messenger is provided once in 400 times, it can be seen that a high supply rate of 2 × 10 ⁴ times per second can be achieved. This value is a significant improvement of nearly 4 to 5 digits compared to the prior art. This significant improvement in feed rate is a significant effect of the means of the present invention.

  When the present invention is specifically implemented, the first light 151 that is a weak signal light is changed from a coherent state | α> to a desired non-classical quantum state | ψ> by parametric interaction in the parametric induction unit 103. In order to convert to, we adopt guided parametric interaction as the physical process described below.

  In the induced parametric interaction, the photon of the pump light (third light) having the frequency f3 = f1 + f2 is converted into the signal photon of the optical frequency f1 and the idler photon of the optical frequency f2 by the second-order nonlinear optical effect. It consists of a process and a reverse process in which signal photons and idler photons are simultaneously absorbed and converted to pump photons.

  When the value of the sum φ1 + φ2 of the phase of the signal light (first light) and idler light (second light) is shifted by π with respect to the phase φ3 of the pump light (in the case of reverse phase), the reverse The process becomes dominant, the photon is extracted from the signal light, and the quantum state of the light wave becomes non-classical.

  The quantum state of the light wave is represented by | ψ> = a | 0> + b | 1> + c | 2> + d | 3> + e | 4> +, and the initial state is | α>, and the number of photons associated with the interaction is determined. Approximate changes in the coefficients a, b, c, d, and e with respect to the state | n> are as follows.

  In equation (5), μ is a parameter of the parametric interaction. μ = 0 corresponds to the state where the interaction has not started, and the value of each coefficient actually gives the initial state coherent state | α>.

The interaction parameter μ can be expressed by the following equation (6) using the interaction coefficient l, the length L _{NL of} the nonlinear medium, the light wave propagation velocity v _g in the nonlinear medium, and the Planck constant.

The interaction coefficient λ is the dielectric constant ε _{0 of the} vacuum, the second-order nonlinear optical constant χ ^{2) of} the nonlinear medium, the cross-sectional area a and the length L _{NL of the} nonlinear medium, the real number amplitude | A ₃ | of the pump light, the idler Using the real light amplitude | A ₂ |, the relative permittivity κ _NL of the nonlinear medium, the pulse time width ΔT of the signal light, and the frequency f1 of the signal light, the following expression (7) is given.

  Even when the pulse time width ΔT is increased corresponding to the narrow bandwidth, it is possible to increase the value of the interaction coefficient λ by sufficiently strengthening the pump light and the idler light to achieve the desired μ value. Is possible.

  In this way, the supply rate of the single photon with messenger in the means of the present invention can be evaluated.

  The background noise light mixed in the signal light can be sufficiently weakened by introducing the following device in addition to the narrow-band optical filtering centered on the frequency f1 by the optical filter 104.

  In the nonlinear medium constituting the parametric guiding unit 103, a natural parametric process in which the photons of the pump light are spontaneously converted into the photons of the signal light and the idler light is generated in parallel with the above-described guided parametric process. Since the signal light and idler light generated in this process have a wide spectrum spread including f1 and f2, narrowband optical filtering is effective for this removal.

Since the probability amplitude at which a natural parametric process occurs is proportional only to the pump light amplitude | A ₃ |, the product | A ₃ || A ₂ | value of | A ₃ | and idler light amplitude | A ₂ | If | A ₂ | is increased and | A ₃ | is decreased at the same time while keeping constant, it is possible to reduce the background noise light by suppressing only the natural parametric process while maintaining the induced parametric process.

  For the above reasons, the means of the present invention have a significant advantage compared to a method using only a natural parametric process (see Non-Patent Document 3).

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a configuration diagram showing the configuration of the photon generator in Embodiment 2 of the present invention. The photon generator includes a first light generation unit 200a, a second light generation unit 200b, a phase shifter 207, a multiplexing unit 208, a demultiplexing unit 209, a light detection unit 210, and a notification unit 211.

  The first light generation unit 200a includes a first light source 201a, a first phase adjustment unit 202a, a first parametric guidance unit 203a, and a first optical filter 204a. The second light generation unit 200b includes a second light source 201b, a second phase adjustment unit 202b, a second parametric guidance unit 203b, and a second optical filter 204b.

  The first light source 201a supplies the first light 251a which is weak coherent light having a stable optical frequency f1 and a stable phase. For example, the first light source 201a can be composed of a frequency stabilized laser and an optical attenuator. The first phase adjustment unit 202a appropriately adjusts the phase of the first light 251a supplied from the first light source 201a to a desired state.

  The first parametric guiding unit 203a inputs the first light 251a, the second light 252a, and the third light 253a, which are guided by different optical paths, respectively, and performs the first light 251a, the second light 252a, and the first light by the guided parametric process. An interaction is generated between the three lights 253a to change the quantum state of the first light 251a and output it to the first optical path 231. In the second embodiment, the first light 251 a is guided to the first optical path 231. Here, the first light 251a is weaker than the second light 252a and the third light 253a. In addition, there is a relationship of f1 + f2 = f3 between optical frequencies.

  The first parametric guiding unit 203a may be configured from a second-order nonlinear optical medium that can obtain a second-order nonlinear optical effect. The first parametric induction unit 203a is composed of a crystal having nonlinear optical characteristics such as lithium niobate, and is composed of a plurality of regions connected in series with a periodic pitch length. Inverted (nonlinear constant is periodically inverted).

  The first optical filter 204a is disposed in the first optical path 231 and transmits the light having the optical frequency f1 from the light emitted from the first parametric guiding unit 203a to output the fourth light. The first optical filter 204a is a narrow-band optical filter that transmits only a narrow spectral range centered on the frequency f1. The first optical filter 204a removes leakage of noise photons, idler light, and pump light generated during the parametric interaction in the first parametric guiding unit 203a.

  The second light generation unit 200b includes a second light source 201b, a second phase adjustment unit 202b, a second parametric guidance unit 203b, and a second optical filter 204b. The second light generation unit 200b includes a second light source 201b, a second phase adjustment unit 202b, a second parametric guidance unit 203b, and a second optical filter 204b.

  The second light source 201b supplies the first light 251b which is weak coherent light having a stable optical frequency f1 and a stable phase. For example, the second light source 201b can be composed of a frequency stabilized laser and an optical attenuator. The first phase adjustment unit 202a appropriately adjusts the phase of the first light 251b supplied from the second light source 201b to a desired state.

  The second parametric guiding unit 203b receives the first light 251b, the second light 252b, and the third light 253b, which are guided by different optical paths, respectively, and performs the first light 251b, the second light 252b, and the first light by a guided parametric process. An interaction is generated between the three lights 253b to change the quantum state of the first light 251b and output the second light path 232. In the second embodiment, the first light 251 b is guided to the second optical path 232. Here, the first light 251b is weaker than the second light 252b and the third light 252c. In addition, there is a relationship of f1 + f2 = f3 between optical frequencies.

  The second parametric guiding unit 203b may be configured from a second-order nonlinear optical medium that can obtain a second-order nonlinear optical effect. The second parametric induction unit 203b is composed of a crystal having nonlinear optical characteristics such as lithium niobate, and is composed of a plurality of regions connected in series with a periodic pitch length. Inverted (nonlinear constant is periodically inverted).

  The second optical filter 204b is disposed in the second optical path 232, and transmits the light having the optical frequency f1 out of the light emitted from the second parametric guiding unit 203b and outputs the fifth light. The second optical filter 204b is a narrow band optical filter that transmits only a narrow spectral range centered on the frequency f1. The second optical filter 204b removes leakage of noise photons, idler light, and pump light generated during the parametric interaction in the second parametric guiding unit 203b.

  In the second embodiment, the phase shifter 207 gives a phase difference of π / 2 between the fourth light and the fifth light generated by the first light generation unit 200b.

  The multiplexing unit 208 multiplexes (interfers with) the fourth light and the fifth light whose phase is given by the phase shifter 207 and outputs the combined light to the first output port 134 and the second output port 135. The multiplexing unit 208 is, for example, a semi-reflecting mirror having a transmittance of 50% (a reflectance of 50%). The demultiplexing unit 209 outputs the multiplexed light output from the multiplexing unit 208 to the second output port 135 to the third output port 136 and the detection port 137. The demultiplexing unit 209 is, for example, a semi-reflecting mirror having a transmittance of 50% (a reflectance of 50%).

  The light detection unit 210 discriminates the photons of the combined light output from the demultiplexing unit 209 to the detection port 137 and detects the number. The notification unit 211 notifies that the light detection unit 210 has detected one photon. In a state where the light detection unit 210 detects one photon, a single photon is output from the third output port 136 with a probability of 1.

  In the present invention, in the light generation unit, the first light, the second light, and the third light are generated from the coherent first light, second light, and third light respectively having different optical frequencies f1, f2, and f3 by a guided parametric process. An interaction is generated between the lights to change the quantum state of the first light to generate the fourth light and the fifth light having the optical frequency f1, and the fourth light is generated with respect to the fifth light generated by the light generation unit. A phase shift of π / 2 is given to the light by the phase shifter 207, and the fourth light and the fifth light to which the phase is given by the phase shifter 207 are multiplexed by the multiplexing unit 208, and the first output port 134 It is important that the multiplexed light that is output to the second output port 135 and output from the multiplexing unit 208 to the second output port 135 is output to the third output port 136 and the detection port 137 by the demultiplexing unit 209. .

  In the second embodiment, the above-described light generation unit includes the first light generation unit 200a and the second light generation unit 200b. In the second embodiment, two non-classical signal lights (fourth light and fifth light) having the same state prepared separately are caused to interfere with each other. Other configurations are the same as those of the first embodiment, and details are omitted.

  A first light source that generates the first light, a second light source that generates the second light, and a third light source that generates the third light, and branches the first light generated from the first light source. To the first parametric guide unit and the second parametric guide unit, branch the second light generated from the second light source, and guide it to each of the first parametric guide unit and the second parametric guide unit. The generated third light may be branched and guided to each of the first parametric guiding unit and the second parametric guiding unit.

  As described above, according to the present invention, an induced parametric process generates an interaction between the first light, the second light, and the third light to change the quantum state of the first light. The fourth light and the fifth light having the optical frequency f1 thus made interfere with each other by giving a phase difference of π / 2 to the other. According to the present invention, it is possible to efficiently generate a single photon having a very narrow spectral width about the width of the resonance line of an atom, with a messenger signal notifying the generation. The improvement in efficiency is 5 orders of magnitude over the prior art. As a result, photons with a very narrow spectrum can be generated more efficiently, and quantum states can be controlled efficiently using the resonant interaction process between single photons and atoms. It becomes possible.

  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 ... Phase adjustment part, 103 ... 103, 104 ... Parametric induction part, 105 ... Optical switch, 106 ... Optical delay line, 107 ... Phase shifter, 108 ... Multiplexing part, 109 ... Demultiplexing part, 110 ... Light detecting unit 111 ... Notification unit 112 ... Reflecting unit 113 113 Reflecting unit 131 ... First optical path 132 ... Second optical path 133 ... Third optical path 134 ... First output port 135 ... Second output port 136, third output port, 137, detection port, 151, first light, 152, second light, 153, third light.

Claims (4)

Interaction between the first light, the second light, and the third light from the coherent first light, second light, and third light, each having a different optical frequency f1, f2, and f3, through a guided parametric process. Generating a fourth light and a fifth light having an optical frequency f1 by changing the quantum state of the first light,
A phase shifter that gives a phase difference of π / 2 between the fifth light generated by the light generation unit and the fourth light;
A multiplexing unit that combines the fourth light and the fifth light phased by the phase shifter, and outputs the combined light to the first output port and the second output port;
A demultiplexing unit that outputs the multiplexed light output from the multiplexing unit to the second output port to a third output port and a detection port;
A light detection unit that detects the number of photons of the combined light output from the branching unit to the detection port;
A notification unit for notifying that the photodetection unit has detected one photon,
The first light has a weaker intensity than the second light and the third light, and f1 + f2 = f3. The photon generator according to claim 1, wherein
The first light, the second light, and the third light, which are respectively guided by different optical paths, are input, and an interaction between the first light, the second light, and the third light is performed by a guided parametric process. A parametric induction unit that changes the quantum state of the first light and outputs it to the first optical path;
An optical filter that is disposed in the first optical path and transmits the light of the optical frequency f1 from the light emitted from the parametric guiding unit and outputs the fourth light;
An optical switch that separates the fourth light emitted from the optical filter into a second optical path and a third optical path at a predetermined time interval;
An optical delay line disposed in the third optical path and giving a delay equal to a switching time interval in the optical switch to be a fifth light,
The photogenerator includes the parametric guide unit, the first optical path, the optical filter, the second optical path, the third optical path, the optical switch, and the optical delay line. . The photon generator according to claim 1, wherein
The light generation unit includes a first light generation unit that generates the fourth light and a second light generation unit that generates the fifth light,
The first light generation unit includes:
The first light, the second light, and the third light, which are respectively guided by different optical paths, are input, and an interaction between the first light, the second light, and the third light is performed by a guided parametric process. Generating a first parametric induction unit that changes the quantum state of the first light and outputs it to the first optical path;
A first optical filter that is disposed in the first optical path and that transmits the light having the optical frequency f1 from the light emitted from the first parametric guiding unit and outputs the fourth light;
The second light generator is
The first light, the second light, and the third light, which are respectively guided by different optical paths, are input, and an interaction between the first light, the second light, and the third light is performed by a guided parametric process. A second parametric induction unit that changes the quantum state of the first light and outputs it to the second optical path;
And a second optical filter arranged in the second optical path and transmitting the light having the optical frequency f1 from the light emitted from the second parametric guiding section and outputting the fifth light. Generator. The photon generator according to claim 3,
A first light source for generating the first light;
A second light source for generating the second light;
A third light source for generating the third light,
Branching the first light generated from the first light source to each of the first parametric guiding unit and the second parametric guiding unit;
Branching the second light generated from the second light source to each of the first parametric guiding unit and the second parametric guiding unit;
The photon generator, wherein the third light generated from the third light source is branched and guided to each of the first parametric guide unit and the second parametric guide unit.

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