JP5340684B2 - Photon generator and method - Google Patents

Description

  The present invention relates to a photon generator used for quantum cryptography and the like. More specifically, the present invention relates to a photon generator that can freely control the emission position and emission pattern in a narrow spectrum using exciton recombination.

  With the recent development of Internet technology, the safety of commercial transactions and personal information exchanged over a network is required, and the demand for security in data transmission is increasing. Quantum cryptography has attracted attention as a technology that meets this demand. Many experiments have been started to realize a quantum cryptography system using quantum cryptography, and the possibility of data transmission by high-speed and long-distance cryptocommunication has been studied energetically.

  One important component technology that supports quantum cryptography systems is the photon generator. In order to realize ideal quantum cryptography communication, a single photon generator that can limit the number of photons contained in one pulse to one is essential. In order to reduce the generation probability of multiple photons, turn-style elements, quantum dots, and the like have been studied.

  Conventionally, as disclosed in Non-Patent Document 1, for example, LED or LD element elements arranged in a matrix have been used as a photon generator. These element devices utilize light emission by electron-hole pair recombination. In the above-described photon generator, control for generating a single photon is performed by lowering the injection amount of LED and LD drive currents. In this method, when generating a photon from an electron-hole pair by reducing the injection amount, a single photon is realized by lowering the quantum mechanical probability distribution of the photon by reducing the intensity of the light. The time of occurrence will be extremely indeterminate. As a result, it has been difficult to generate single photons at the desired time and position. That is, it has been difficult to perform stable control so that photons are generated from a photon generator at an arbitrary time and by an arbitrary spatial position or spatial pattern.

  In addition, in order to support a higher-speed quantum cryptography system, it was difficult to generate a time-series photon sequence having a high bit rate.

“A single-photon turnstile device”, J. Kim, O. Benson, H. Kan and Y. Yamamoto, Nature vol. 397, p.500-503 (1999)

  The present invention has been made in view of such problems, and an object of the present invention is to realize a photon generation method capable of stably controlling generation of a single photon temporally and spatially. An object of the present invention is to realize a photon generator capable of generating an arbitrary time, an arbitrary place, or an arbitrary space pattern. Another object of the present invention is to realize a photon generator capable of generating a photon train on a time axis at higher speed.

In order to achieve the above object, the present invention provides an exciton generation unit that generates excitons and a generation of the exciton generation unit by changing a dielectric constant. was able bind the exciton has a plurality of barrier regions, from the barrier region at a predetermined position, the by recombining said exciton by reducing the dielectric constant of the barrier region, excitons controlled to generate a photon The plurality of barrier regions are made of a material having an energy gap different from that of the peripheral region excluding the plurality of barrier regions, and the dielectric constants of the barrier regions are sequentially increased with respect to adjacent barrier regions. The photon generator is characterized in that the exciton is spatially moved to a predetermined position of the exciton control unit by changing relative to the dielectric constant of the peripheral region .

The invention according to claim 2 includes an exciton generation unit that generates excitons, and a plurality of barrier regions that can bind excitons generated in the exciton generation unit by changing a dielectric constant, An exciton control unit that recombines the excitons by reducing the dielectric constant of the barrier region from a predetermined position to generate photons, and the exciton control unit has a lattice shape A plurality of barrier regions disposed in a well region and a well region having a dielectric constant different from that of the barrier region, and the dielectric constant of the barrier region is changed relative to the dielectric constant of the well region. The photon generator is characterized in that the exciton is spatially moved to a barrier region at a predetermined position by the above and photons are generated by recombination of the excitons at a predetermined time.

A third aspect of the present invention is the photon generation device according to the first or second aspect , wherein a plurality of excitons generated in the exciton generation unit are applied to the plurality of barrier regions forming a predetermined spatial pattern. A plurality of photons are generated in a predetermined spatial pattern by moving in space.

The invention according to claim 4 is the photon generating device according to any one of claims 1 to 3 , wherein the exciton control unit is formed in a film shape and includes a plurality of exciton control layers each including a plurality of barrier regions. Each of the plurality of barrier regions in the plurality of exciton control layers are arranged at the same position in the film formation surface, and each excitation in the predetermined barrier region position. The present invention is characterized in that the photons are generated in a predetermined time series pattern by controlling the dielectric constant of the plurality of barrier regions over the child control layer.

The invention according to claim 5 is the photon generating device according to any one of claims 1 to 4 , wherein the dielectric constant of the barrier region uses a light pulse to irradiate the barrier region, and the electric field of the barrier region Or is controlled by using a nanomachine that travels in the nanotube structure.

The invention according to claim 6 includes an exciton generation unit and a plurality of barrier regions that can be bound by changing the dielectric constant of the exciton generated in the exciton generation unit, and the barrier at a predetermined position. In a method for controlling photon generation in a photon generator including an exciton controller that generates photons by recombination of the excitons from a region, the exciton generator generates excitons; and Changing the dielectric constant of one of the barrier regions to bind the excitons to the one barrier region, and changing the dielectric constant of the one barrier region to release the binding. Changing the dielectric constant of another barrier region adjacent to the one barrier region and constraining it to move the exciton in space, and moving the exciton to the barrier region in a predetermined position. The elevators, an invention of a method of controlling the photon generation, characterized in that it comprises a step of recombination by varying the dielectric constant of the barrier region at a given time.

The invention according to claim 7 is the method according to claim 6 , wherein the exciton control unit includes a plurality of barrier regions arranged in a lattice shape and a well region having a different dielectric constant from the barrier regions. The step of constraining and the step of spatially moving are performed by changing a dielectric constant of the barrier region relative to a dielectric constant of the well region.

The invention according to claim 8 is the method according to claim 7 , wherein the dielectric constant of the barrier region in the vicinity of the boundary between the exciton generation unit and the exciton control unit is larger than the dielectric constant of the well region. In this case, the method further comprises a step of controlling intrusion of excitons into the exciton control unit.

  As described above, according to the photon generator of the present invention, a method for stably controlling the generation of a single photon in time and space can be realized, and a single photon can be controlled at an arbitrary time, an arbitrary place, or an arbitrary It is possible to realize a photon generator that can generate a spatial pattern of A photon generator capable of generating a higher-speed photon train can be realized, which can be adjusted to a predetermined arbitrary time pulse pattern and arbitrary pulse interval. Realization of higher speed and higher functionality of the quantum cryptography system.

  One feature of the photon generator of the present invention is that (1) a mechanism for spatially moving excitons by controlling the dielectric constant is used. Further, by using one or more of the following mechanisms (2) to (4) in combination, generation of a single photon at an arbitrary time, an arbitrary location, and an arbitrary spatial pattern is realized. That is, (2) exciton generation control, (3) photon generation control from excitons by permittivity control, and (4) time-series single photon string generation control by a multilayered structure. Hereinafter, the present invention will be described in detail with reference to the drawings.

  In the following description, “space” in terms of space movement, space pattern, and the like is used to mean a space that forms a plurality of points in a two-dimensional plane that generates photons, as compared to photons generated from one point. Has been. Therefore, it does not mean a space composed of air as a medium or a vacuum space.

FIG. 1 is a conceptual diagram showing a basic configuration of a photon generator of the present invention. The photon generator 1 according to the present invention includes an exciton generator 2 and an exciton controller 3. The exciton generation unit 2 is made of a semiconductor and generates excitons by being irradiated with light generated by an excitation light source 9 connected to the outside of the photon generator or formed as a part of the photon generator. To do. As is well known, excitons are electron-hole pairs that are in a bound state due to Coulomb attractive interaction.

The excitons generated by the exciton generation unit 2 are controlled by the exciton control unit 3 so as to generate photons through exciton spatial movement and exciton emission (emission recombination). As will be described later in detail, the exciton control unit 3 is composed of two or more types of semiconductors. In FIG. 1, the excitation light source 9, the exciton generation unit 2, and the exciton control unit 3 are described as separate blocks. However, since any block can be composed of one or more kinds of semiconductor materials, it can be integrally formed as an element patterned on a semiconductor substrate. That is, it should be noted that FIG. 1 represents the photon generator of the present invention as a functional block. Whereas the prior art used light emission by electron-hole pair recombination for photon generation, the photon generator of the present invention is different in that it uses excitons. Please pay attention to. The configuration and operation of the exciton control unit that is a characteristic component of the present invention will be described in more detail.

  2A and 2B show an enlarged view of the exciton control unit and a part thereof. In FIG. 2A, the exciton control unit 3 has a plurality of barrier regions 5 formed of a semiconductor material having a larger band gap in a well region 4 formed of one semiconductor material in a matrix. It has an embedded structure. A major feature of this matrix structure is that the dielectric constant ε1 of the material of the buried barrier region 5 can be controlled from a value smaller than the dielectric constant ε2 of the semiconductor material of the surrounding well region 5 to a larger value. FIG. 2A is a top view of a well region formed on a semiconductor substrate as viewed from a direction perpendicular to the substrate surface.

FIG. 2B shows an enlarged view near one barrier region. In the photon generation device of the present invention, the dielectric constant of the barrier region 5 is controlled to attract and trap excitons to move to a desired position, and the dielectric constant of the barrier region is controlled to achieve a desired timing. To generate photons. The present invention is also characterized in that a small number of photons are generated and controlled not by controlling the material of the well region where excitons are present but by controlling the barrier layer material where excitons are not present. The control by the well region is advantageous in controlling the barrier region as in the present invention in that the stability of excitons may be deteriorated. As shown in FIG. 2B, excitons 8 composed of pairs of electrons 7 and holes 6 can be trapped in the vicinity of one barrier region 5 by controlling the dielectric constant of the barrier region 5. .

  FIGS. 3A and 3B are diagrams illustrating an exemplary method for controlling the dielectric constant of the barrier region. The dielectric constant of the barrier region can be controlled by: (1) applying an electric field to the embedded material, (2) irradiating light, and (3) making the barrier region hollow and placing a dielectric in it. It is possible to realize this by using a method of moving automatically. FIG. 3A is an illustrative diagram of a method for controlling the dielectric constant by applying an electric field. A cross-sectional view of the exciton control unit viewed from the side surface of the substrate constituting the well region 4 is shown. A cylindrical barrier region 5 having a dielectric constant ε1 is embedded in a well region 4 having a dielectric constant ε2. Barrier layers 11 a and 11 b made of a material having a large band gap are formed above and below the well region 4. Furthermore, electrodes 10a and 10b are formed in portions corresponding to the barrier regions 5 above and below the barrier layers 11a and 11b, respectively. By applying a voltage between the upper and lower electrodes 10a and 10b to generate an electric field (electric field), the effective dielectric constant of the barrier region under the electric field can be changed.

  As one of the methods of irradiating light, for example, there is a method of controlling the dielectric constant of a material using an optical pulse. The dielectric constant changes depending on the intensity of light irradiated on the material (non-linear polarization = due to non-linear optical effect). By utilizing this property, the dielectric constant of the barrier region can be controlled by controlling the light applied to the barrier region.

  The light irradiation method can be realized by the following procedure, for example. 1) An LD, an LED, or the like is formed on a layer above (or below) each barrier region. 2) An optical fiber is brought close to (or below) each barrier region. 3) A spatial light pattern corresponding to the matrix formed by the barrier region is imaged on a layer having the barrier region (a mechanism like a projector).

  Further, as shown in FIG. 3B, a hollow space 13 is formed inside the well region 4 and, for example, a cylindrical dielectric 15 is disposed in this space. The location of the hollow space 13 corresponds to the barrier region 5. The position of the dielectric 15 in the hollow can be changed up and down, for example, in the normal direction of the formation surface of the well region 4 by the driving mechanism 12 using a micromachine technique or the like. By changing the position of the dielectric 15 up and down, the effective dielectric constant of the barrier region can be changed. The dielectric 15 may have any shape and configuration as long as a change in the dielectric constant can be caused by a change in its position. For example, a nanomachine that travels in a nanotube structure can be used. Next, the principle of moving the excitons in space by controlling the dielectric constant will be described in more detail.

  FIG. 4 is a diagram for explaining the principle of exciton spatial movement by permittivity control. FIG. 4 schematically illustrates the relationship between the dielectric constant of the barrier region and the exciton binding energy Eb, together with the graph, in two states. As described above, excitons are those in which electrons and holes form a bound state by clonal interaction. The energy of the exciton changes depending on the dielectric constant of the space where the exciton exists. Consider changing the dielectric constant ε1 of the barrier region.

  When ε1 is smaller than the dielectric constant ε2 of the well region (ε1 <ε2), the exciton is present in the vicinity of the barrier region, particularly so as to surround the barrier region, and the Coulomb attractive force between electrons and holes becomes stronger. The energy of excitons is low. As a result, excitons surround the barrier region, and the centroid motion is localized, that is, bound to the barrier region.

  On the other hand, when ε1 is larger than the dielectric constant ε2 of the well region (ε1> ε2), the Coulomb attractive force between electrons and holes is weak in the vicinity of the barrier region, and the exciton energy becomes large. Therefore, the exciton freely moves in the center of gravity in the outer peripheral region of the barrier region.

  The behavior of excitons depending on the dielectric constant of the barrier region near and around the barrier region is similar to the behavior of bound excitons in a material containing impurity atoms. Hereinafter, an exciton in a state where the exciton surrounds the barrier region is referred to as “in a bound state”, and an unexcited exciton is referred to as “in a free state”. In the case of ε1> ε2, excitons leave the barrier region and are in a free state. The effects of the two states described above can be used for exciton movement. Further, the exciton moving method will be described in detail.

  FIG. 5 is a diagram for explaining the principle of exciton spatial movement by permittivity control together with spatial energy. 5A and 5B, the well region 4 including only two adjacent barrier regions 5a and 5b is described for the sake of simplicity. Below each figure, the spatial dependence of exciton energy is also conceptually shown. In the energy diagram, C represents conduction band energy, V represents valence band energy, and ex represents exciton energy. The process of spatially moving the excitons 8 from the left barrier region 5a to the right barrier region 5b by changing the dielectric constant from the state (A) to the state (B) will be described.

  FIG. 5A shows a state before the exciton is spatially moved. In this state, the dielectric constant of the left barrier region 5a is set to ε2 smaller than the dielectric constant ε1 of the well region 4, and the dielectric constant of the right barrier region 5b is set to the same dielectric constant ε2 as that of the well region 4.

  On the other hand, FIG. 5B shows a state after the exciton is spatially moved by the dielectric constant control of the present invention. Here, the dielectric constant of the left barrier region 5a is set to ε3 larger than the dielectric constant ε2 of the well region 4, and the dielectric constant of the right barrier region 5b is set to ε1 smaller than the dielectric constant ε2 of the well region 4. In the case of (A), the exciton energy is low around the left barrier region 5a and high at other locations. In the case of (B), the exciton energy is high around the left barrier region 5a and low around the right barrier region 5b. For the exciton 8, this energy acts as an effective potential energy V, and the exciton 8 feels a force F corresponding to the reverse direction of the gradient.

  Accordingly, in the state of FIG. 5A, the excitons 8 in the vicinity of the left barrier region 5a are attracted to the left barrier region 5a and bound thereto. By controlling the dielectric constants of the two barrier regions 5a and 5b at a predetermined timing, each dielectric constant of each barrier region is changed to the state (B). At this time, the excitons 8 bound to the left barrier region 5b receive a repulsive force from the left barrier region 5a and are attracted by an attractive force from the right barrier region 5b due to the above-described energy gradient. . As a result, the exciton 8 moves from the left barrier region 5a to the right barrier region 5b and is bound there. Thus, exciton spatial movement can be implemented by controlling the dielectric constant of the barrier region. In addition to the exciton spatial movement, the exciton control unit 3 executes another dielectric constant control mechanism.

  FIG. 6 is a graph showing the relationship between the dielectric constant of the barrier region near the excitons and the normalized vibrator strength f. The horizontal axis of FIG. 6 shows the effective dielectric constant ε * of the barrier region. The vertical axis represents the normalized vibrator strength f. As is well known, the oscillator strength is a material constant that represents the likelihood of an emission transition. Therefore, the light emission transition is more likely to occur as the vibrator strength increases. Here, the oscillator strength (oscillator strength normalized by the oscillator strength of the bulk material) when the oscillator strength of the well layer material (bulk state) having no artificial structure is 1 is shown. Please be careful.

  The effective dielectric constant perceived by the excitons is determined from the dielectric constant of the barrier region, the dielectric constant of the well region, and the structure of the barrier region (see, for example, FIG. 3A). If the other parameters are constant, the effective dielectric constant can be reduced by reducing the dielectric constant of the barrier region 5. From the relationship between the theoretical calculation values shown in FIG. 6, it can be seen that the probability of light emission increases dramatically as the effective dielectric constant decreases. Therefore, after realizing the spatial movement of the exciton to a desired position by controlling the dielectric constant of the barrier region 5 described above, the dielectric constant of the barrier region to which the exciton is constrained is further reduced to thereby reduce the exciton. The generation of photons from can be promoted. As described above, the photon generator of the present invention is characterized in that it includes a mechanism for promoting the generation of photons from excitons in addition to a mechanism for spatially moving excitons by means of permittivity control of the barrier region.

  Furthermore, since the emission from the exciton is essentially only a single photon emission, there is no need for a process of generating a single photon with a lower probability distribution as in the conventional single photon light source. For this reason, it is also characterized in that photons can be efficiently generated at an arbitrary time.

  Example 1 Next, a more specific operation of the exciton control unit will be described using an example.

  FIG. 7 is a conceptual diagram showing the configuration of the photon generator of Example 1 of the present invention. FIG. 7 also conceptually focuses on the exciton spatial movement method of the present invention, and is a diagram for explaining the actual shape and configuration of a photon generator that can be manufactured of a semiconductor element or the like. Note that this is not the case. The photon generator of the first embodiment has a configuration in which an exciton generator 2 displayed with a small rectangle on the left side is connected to an exciton control unit 3 displayed with a large rectangle on the right. The exciton generator 2 is irradiated with excitation light, and excitons 8 indicated by a ring are generated. The exciton control unit 3 includes a plurality of circular barrier regions 5 arranged in a lattice pattern in the well region with the well region 4 as a base. The barrier regions are all composed of the semiconductor material 1, and each barrier region is numbered sequentially from the left end of the figure. In the following description, the barrier region (1) and the barrier region (2) are called and distinguished. The well region is constituted by another semiconductor material 2. The exciton generation unit 2 is composed of the same semiconductor material 2 as the well region 4 and is connected to the exciton control unit 3.

  Hereinafter, with respect to the operation of the photon generator of the present embodiment, one exciton is moved from the exciton generator 2 to the barrier region (17), and then a single photon is generated from the barrier region (17). Will be described as an example. The dielectric constant of each part used in the following description is assumed to have a relation of ε1 << ε2 <ε3 <ε4, and the dielectric constant of the well region 4 is ε3.

  FIG. 8 is a diagram for explaining how the excitons are spatially moved by permittivity control. Along with FIGS. 8A to 8D, how the excitons 8 are sequentially moved from the exciton generator 2 to the barrier region (17) will be described in the following steps 1) to 4). Is done. For simplicity, only the exciton control unit 3 is shown in each figure. In the initial state, the dielectric constants from the barrier region (1) to the barrier region (21) are all ε4.

  1) One or a plurality of excitons are generated in the exciton generator 2 by irradiating the exciton generator 2 with excitation light. In this state, since the dielectric constant (ε4) of the barrier region (2) near the entrance of the exciton control unit 3 is larger than the dielectric constant ε3 of the well region 4, the exciton 8 cannot enter the exciton control unit 3. .

  2) Here, as shown in FIG. 8A, the dielectric constant of the barrier region (2) is set from ε4 to ε2. As a result, only one of the excitons in the exciton generation part moves toward the barrier region (2) and is bound around the barrier region (2).

  3) Next, as shown in FIG. 8B, the dielectric constant of the barrier region (6) is set to ε2, and subsequently the dielectric constant of the barrier region (2) is set to ε4. This causes excitons to move around the barrier region (6) where they are bound.

  4) Similarly, as shown in FIG. 8C, the dielectric constant of the barrier region (10) is set to ε2, and subsequently the dielectric constant of the barrier region (6) is set to ε4. This causes excitons to move around the barrier region (10) where they are bound. As described above, the excitons can be moved to a desired position of the exciton control unit 3 by sequentially changing the dielectric constant of the barrier region to move the excitons. Next, photon emission control will be described.

  FIG. 9 is a diagram for explaining the final stage of generating photons in the photon generator of the first embodiment. A description will be given following each step described in FIG.

  5) Following (D) of FIG. 8, as shown in (A) of FIG. 9, the dielectric constant of the barrier region (17) is set to ε2, and subsequently the dielectric constant of the barrier region (13) is set to ε4. To do. This causes excitons to move around the barrier region (17) where they are bound. Finally, the spatial movement to the barrier region (17) which is the target position is completed.

  6) Here, the dielectric constant of the barrier region (17) is set from ε2 to ε1. By further reducing the dielectric constant, the excitons recombine and single photons are emitted from the barrier region (17) as described in FIG. Single photons jump out in the direction perpendicular to the paper surface of FIG. As described in detail above, in this embodiment, the dielectric constant of the barrier region is sequentially controlled to move excitons and move to a desired spatial position to generate a single photon at an arbitrary time. Can do.

  Regarding the dielectric constant control in this embodiment, since the barrier region is made of the semiconductor material 1, the dielectric constant control by the electric field or the dielectric constant control by light explained in FIG. Specifically, a pair of insulating films are formed so as to sandwich the entire semiconductor layer (well region), and a pair of independent electrodes are formed on the insulating film so as to sandwich each barrier region. Form. By changing the voltage applied between the pair of electrodes in time series, the dielectric constant of the sandwiched barrier region is controlled. Further, as described in FIG. 3B, by installing a cylindrical micromachine in which the barrier region portion is hollow and a dielectric multilayer film is formed in the hollow portion, and moved in the normal direction of the surface, A method of controlling the dielectric constant of the barrier region is also effective. In this case, the cylindrical axis of the cylindrical micromachine is set in the normal direction of the semiconductor layer (well region), and the dielectric multilayer film is laminated in parallel with the semiconductor layer.

  As an example of a method for manufacturing the photon generator of this embodiment, first, a layer of the semiconductor material 2 is grown on a substrate by epitaxial growth. Thereafter, a portion to be a barrier region is removed by etching. Furthermore, the barrier region can be formed of the semiconductor material 1 by regrowth.

  When a more specific structure of the exciton control unit is taken as an example in which the material of the well region layer is GaAs, the size of the exciton is 1 to 5 nm (10 nm for bulk GaAs) and the size of the barrier region is the diameter. It is preferably 1-5 nm and slightly smaller than the exciton. The thickness of the barrier region, that is, the thickness of the well region can be set to about submicron to several microns. Moreover, the space | interval of barrier regions can be 2-10 nm larger than the magnitude | size of an exciton. However, it should be noted that if it is too large, it takes too much time to move excitons. If the material of the well region layer changes, the size of the exciton also changes, so the lattice shape and dimensions of the barrier region described above vary depending on the material constant. Examples of the material for the well region include GaAs, AlGaAs, InP, and GaN. Further, the material of the barrier region is required to have an energy gap larger than that of the material of the well region, and AlGaAs, AlAs, GaInP, AlGaN, etc. are conceivable as corresponding to the above-described material examples of the well region.

Embodiment 2 FIG. 10 is a conceptual diagram showing a configuration of a photon generator according to Embodiment 2 of the present invention. In this embodiment, by controlling the spatial positions of a plurality of excitons, photons can be generated with an arbitrary spatial light emission pattern. Basic operations related to exciton spatial movement and generation of photons are the same as those in the first embodiment. Here, the operation will be described focusing on the differences from the first embodiment.

  Similar to the first embodiment, the exciton generation unit 2 and the exciton control unit 3 are continuously configured. The exciton control unit 3 includes a plurality of barrier regions 5 arranged in a lattice pattern in a well region 4 having a dielectric constant ε3. In the initial state, all the barrier regions are set to a dielectric constant ε4. Here, it is assumed that the relationship of ε3 <ε4 holds. In the following description, different barrier regions are referred to as a barrier region (1), a barrier region (2), and the like.

  The barrier regions (1)-(3) are designed to move excitons in space in order to bind the exciton groups generated in the exciton generation unit 2 to the barrier regions of the barrier regions (4)-(7) one by one. It is used for the purpose of controlling smoothly. Therefore, it is not essential from the viewpoint of forming the spatial pattern in the present embodiment. Accordingly, exciton binding may or may not be performed in the barrier regions (1) to (3). The present embodiment is characterized in that excitons are spatially moved so as to form a spatial pattern in which arbitrary photon generation points are distributed.

  FIG. 11 is a diagram illustrating a state in which a spatial pattern of excitons is formed in the second embodiment. 11A to 11F, the exciton generator 2 moves a plurality of excitons to desired barrier region positions to form a spatial pattern, and further generates a plurality of photons. The process to make is demonstrated. Hereinafter, it is assumed that the dielectric constant of each part used in the description has a relationship of ε1 << ε2 <ε3 <ε4.

  When the exciton binding is not performed in the barrier regions (1) to (3), a 4 × 4 lattice formed by the 16 barrier regions (4) to (19) in the exciton control unit 3 of FIG. The photons can be generated in an arbitrary pattern. For example, consider the case where the following spatial pattern is formed by the number of the barrier region.

4 12 16
5 9 17
10 14
7 19

  The pattern formation of the exciton distribution is excited with a desired pattern in the first row of the barrier regions (4)-(7) at a time interval (τ) longer than the speed of exciton movement between adjacent lattices. The introduced excitons (groups) are divided into the second row of barrier regions (8)-(11), the third row of barrier regions (12)-(15), the barrier region ( 16)-(19) by sequentially moving to the fourth column.

  1) At time t = 0 in the initial state, the dielectric constants of the barrier regions are all set to ε4.

  2) First, at time t = τ1, the dielectric constants of the barrier regions (4), (5), and (7) are set from ε4 to ε2, and the excitons are bound. (See (A) in FIG. 11)

  3) At time t = τ2, first, the dielectric constants of the barrier regions (8), (9), and (11) are changed from ε4 to ε2, and the dielectric constants of the barrier regions (4), (5), and (7) are changed. From ε2 to ε4, the excitons in the barrier regions (4), (5), and (7) are translated into the barrier regions (8), (9), and (11). (See (B) in FIG. 11)

  4) At time t = τ3, the dielectric constants of the barrier regions (4) and (6) are set from ε4 to ε2, and the excitons are bound. At this point, excitons are arranged in the first and second rows. (See (C) in FIG. 11)

  5) At time t = τ4, the excitons in the barrier regions (8), (9), (11) are moved to the barrier regions (12), (13), (15), and the barrier regions (4), (15) The excitons of (6) translate in the barrier regions (8) and (10), respectively. (See (D) in FIG. 11)

  6) As a result of the parallel movement of the exciton group at time t = τ5, the barrier regions (4), (7), (7), and the barrier region (9) are obtained from the first column to the fourth column. , (10), the barrier regions (12), (14), and the barrier regions (16), (17), (19) are arranged with excitons to form a desired spatial pattern. At this time, the dielectric constant of the barrier region where the excitons are bound is set to ε2. (See (E) in FIG. 11)

  7) Finally, at time t = τ6, the dielectric constant of all the barrier regions is set to ε1, and photons are simultaneously generated from the respective barrier regions.

  In the above description of the series of steps, the relationship between the times is not specified, but any timing may be used as long as exciton movement is performed smoothly and reliably. Further, since the exciton translation process is the same between the barrier regions, the excitons can be translated at equal time intervals. Needless to say, the photon generation stage in the final process can be set at an arbitrary time. As described above, according to the present embodiment, a single photon can be generated with an arbitrary spatial position pattern in the plane of the exciton control unit.

FIG. 12 is a conceptual diagram showing the configuration of the photon generator of Example 3 of the present invention. The photon generator of the present embodiment includes a structure in which the exciton control units of the photon generator of Embodiment 2 are stacked in multiple layers. That is, the first exciton control unit 20-1, the second exciton control unit 20-2,..., The sixth exciton control unit 20-6, and the seventh exciton control unit 20-7 The structure is sequentially stacked in the x direction. In FIG. 12, only the exciton control unit 3 is illustrated, but it goes without saying that the exciton control unit of each layer is provided or a common exciton generation unit is provided. One exciton control unit is formed along the yz plane. The arrangement configuration pattern of the plurality of barrier regions is the same as that of the second embodiment, but is not limited thereto. Any arrangement pattern may be used as long as exciton can be spatially moved on the yz plane of one exciton control layer. FIG. 12 conceptually shows the operation of the present embodiment, and the dimensions in the x, y, and z directions in an actual apparatus (device) are not displayed in proportion.

  Each exciton control unit 20-1,..., 20-7 includes a well region 4 having a dielectric constant ε3 and a plurality of barrier regions 5. The barrier regions of each layer are all cylindrical, and the position is common to each layer. In FIG. 12, for simplicity, a mechanism such as an electrode for controlling the dielectric constant for the barrier region of each layer is not described. In each exciton control layer, the exciton can be spatially moved in the yz plane by independent dielectric constant control.

  Interlayer separation layers 21-1, 21-2,..., 21-6 made of a material having a large band gap are formed between the layers of each exciton control unit. According to the structure of the photon generator of the present embodiment, photons emitted from each exciton control unit layer propagate as a waveguide through a cylinder serving as a barrier region, and excite the top layer as a time-series photon sequence. Output from the child control unit layer 20-1. Next, generation of the time-series photon sequence will be further described.

  FIG. 13 is a diagram illustrating a mechanism for generating photons in time series in the third embodiment. Focusing on one barrier region, a cross-sectional view of the xz plane including one barrier region is shown. The exciton control layers 20-1, 20-2,... 20-N have N layers, and interlayer separation layers 21-1,..., 21-N-1 are formed between the exciton control layers. ing. Let L be the repetition pitch in the x direction of each exciton control unit. Since the barrier region of each layer is formed at the same position on the yz plane, an optical waveguide is formed in the x direction. Each exciton control unit can independently control the dielectric constant of the barrier region, and at a certain point in time, all the barrier regions 5-1, 5-2,. On the other hand, the exciton can be set in a bound state. At this time, the dielectric constant of the barrier region is ε2 as described in the second embodiment with reference to FIG.

  FIG. 13A shows a state in which excitons are bound to the barrier region at the same position in the yz plane of each exciton control layer. Here, by simultaneously reducing the dielectric constant ε2 to ε1 of each barrier region, photons are generated simultaneously from each barrier region. Each photon jumps out in the x-axis direction and is emitted as a photon string from the uppermost barrier region 5-1. As described above, since the barrier region of each layer forms an optical waveguide in the x-axis direction, photons are time-series photon pulses having time intervals determined by the repetitive pitch L of the exciton control layer. As output. FIG. 13B is a conceptual diagram illustrating a photon train pulse.

  Hereinafter, a more specific configuration will be described by way of example. One exciton control part layer can have a thickness of 1-2 nm, and the thickness of the interlayer separation layer can be 10 μm. At this time, the periodic pitch of the multilayer structure is approximately 10 μm. Here, the reason why the thickness of the interlayer separation layer is much larger than the thickness of the exciton control layer is to set the interval between the light pulses relatively long.

  The required time required to execute each operation in the present embodiment is as follows. The time taken to move between the barrier regions in one exciton control layer is about 1 nsec. This time depends on the distance between the barrier regions. On the other hand, the time required for light to move between exciton control layers having a periodic structure of pitch L is 0.1 psec. For example, when the refractive index of GaAs is 3.1 and L is 10 μm, approximately 0.1 psec is obtained.

  Since the interval between the optical pulses is as short as about 0.1 psec, more time-series optical pulses (signals) can be used by increasing the number of layers. For example, if the number of layers is increased to 100, modulation having 100 optical pulses in a burst period of 10 nsec can be performed. Further, if the layer interval L is made smaller, an optical pulse having a shorter period can be generated. Conversely, if the layer spacing L is made larger, light pulses having a longer period can be generated.

  In the above description, photon emission of each layer is performed simultaneously. However, if the timing for setting the dielectric constant of each layer from ε2 to ε1 is set separately, an arbitrary pulse pattern can be formed on the time axis. It will also be readily understood that the pulse interval can be adjusted. In addition, the number of layers in the multilayer structure and the layer spacing vary depending on the selection of the semiconductor material. Further, it is not necessary to configure the intervals between the exciton control units at equal intervals, and they can be set at unequal intervals. It is also possible to set some layers as a certain interval and other layers as another interval. By doing so, it is possible to generate a predetermined arbitrary time pulse pattern only by simultaneously controlling the dielectric constant of the photon emission of each layer. Moreover, it can adjust to arbitrary pulse intervals.

  As described above, according to the photon generation device of the third embodiment, it is possible to generate an arbitrary time series light pulse. A time-series photon pulse train can be generated independently from each barrier region of the uppermost exciton control layer. As described in the second embodiment, not only can photons be generated in an arbitrary spatial pattern, but also arbitrary time-series optical pulses can be generated. The photon generation device having the configuration of the third embodiment enables parallel processing of a plurality of signal sequences. Through parallel processing, the quantum cryptography system can be further increased in speed and multifunction.

  According to the photon generator of the present invention, a method for stably controlling the generation of a single photon temporally and spatially using an exciton is realized, and a single photon can be controlled at any time and at any place. Alternatively, it is possible to realize a photon generator that can generate an arbitrary spatial pattern. The excitonic transition with high frequency purity can be used. Furthermore, it is possible to realize a photon generator capable of generating a faster photon train. Realization of higher speed and higher functionality of the quantum cryptography system.

  The present invention can be used in a quantum cryptography system. In particular, it can be used for a photon generator of a quantum cryptosystem.

It is the conceptual diagram which showed the basic composition of the photon generator of this invention. It is a figure which shows the structure of the exciton control part in the photon generator of this invention, and the one part expansion. FIG. 6 illustrates an exemplary method for controlling the dielectric constant of a barrier region of an exciton controller. It is a figure explaining the space movement principle of the exciton by dielectric constant control. It is another figure explaining the space movement principle of the exciton by dielectric constant control. It is a figure which shows the graph of the relationship between the dielectric constant of the barrier area | region near an exciton, and the normalized vibrator | oscillator strength f. It is a conceptual diagram which shows the structure of the photon generator of Example 1 of this invention. In Example 1, it is a figure explaining a mode that an exciton is spatially moved by dielectric constant control. It is a figure explaining the last step which generates a photon in the photon generator of Example 1. It is a conceptual diagram which shows the structure of the photon generator of Example 2 of this invention. In Example 2, it is a figure explaining a mode that the space pattern of an exciton is formed. It is a conceptual diagram which shows the structure of the photon generator of Example 3 of this invention. It is a figure explaining the mechanism which generates a photon in time series in Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photon generator 2 Exciton generation part 3 Exciton control part 4 Well area | region 5, 5a, 5b, 5-1, ..., 5-N barrier area | region 6 Hole 7 Electron 8 Exciton 9 Excitation light source 10a, 10b Control electrode 11a, 11b Barrier region layer 12 Drive mechanism 13 Hollow space 20-1, 20-2, ..., 20-N Exciton control part layer 21-1, 21-2, ... 20-N-1 interlayer separation layer

Claims (8)

An exciton generator for generating excitons;
By changing the dielectric constant, it has a plurality of barrier regions that can bind the excitons generated in the exciton generator, and by reducing the dielectric constant of the barrier region from the barrier region at a predetermined position and recombining the exciton, and a excitons controller for generating photons,
The plurality of barrier regions are made of a material having an energy gap different from that of the peripheral region excluding the plurality of barrier regions, and the dielectric constants of the barrier regions are sequentially set with respect to adjacent barrier regions. The exciton is moved spatially to a predetermined position of the exciton control unit by changing relative to the photon generator. An exciton generator for generating excitons;
By changing the dielectric constant, it has a plurality of barrier regions that can bind the excitons generated in the exciton generator, and by reducing the dielectric constant of the barrier region from the barrier region at a predetermined position An exciton control unit that recombines the excitons to generate photons;
With
The exciton control unit includes the plurality of barrier regions arranged in a lattice shape and a well region having a dielectric constant different from that of the barrier region, and the dielectric constant of the barrier region is set to the dielectric constant of the well region. The exciton is spatially moved to a barrier region at a predetermined position by changing relative to the photon, and a photon is generated by recombination of the excitons at a predetermined time. The plurality of excitons generated in the exciton generation unit are spatially moved to the plurality of barrier regions forming a predetermined space pattern, and a plurality of photons are generated with the predetermined space pattern. Item 3. The photon generator according to Item 1 or 2 . The exciton control unit has a multilayer structure in which a plurality of exciton control layers each including a plurality of barrier regions formed in a film shape are stacked, and the plurality of barriers in the plurality of exciton control layers The regions are arranged at the same position in the film formation surface, and the photons are controlled in a predetermined time-series pattern by controlling the dielectric constant of the plurality of barrier regions over each exciton control layer at the predetermined barrier region position. The photon generator according to any one of claims 1 to 3 , wherein the photons are generated. The dielectric constant of the barrier region is controlled by using a light pulse that irradiates the barrier region, by using an electric field of the barrier region, or by using a nanomachine that travels in a nanotube structure. The photon generator according to any one of claims 1 to 4 . An exciton generator and a plurality of barrier regions that can be bound by changing the dielectric constant of the excitons generated in the exciton generator, and recombination of the excitons from the barrier region at a predetermined position In a method for controlling photon generation in a photon generator having an exciton control unit for generating photons,
A step of generating excitons in the exciton generator;
Changing the dielectric constant of one of the plurality of barrier regions to bind the excitons to the one barrier region;
Changing the dielectric constant of the one barrier region to release the binding, and changing the dielectric constant of another barrier region adjacent to the one barrier region to bind and excitonally move the space; ,
Recombining excitons spatially moved to a barrier region at a predetermined position by changing a dielectric constant of the barrier region at a predetermined time. The exciton control unit includes the plurality of barrier regions arranged in a lattice shape, and a well region having a dielectric constant different from that of the barrier region, and the binding step and the spatially moving step include the step The method of claim 6 , wherein the method is performed by changing a dielectric constant of a barrier region relative to a dielectric constant of the well region. By controlling the dielectric constant of the barrier region near the boundary between the exciton generation unit and the exciton control unit to be larger than the dielectric constant of the well region, the exciton intrusion into the exciton control unit is controlled. The method of claim 7 , further comprising a step.

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