JP2011141477A - Wavelength converting device and wavelength converting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent decrease in a signal-to-noise ratio in wavelength conversion for a single photon. <P>SOLUTION: A wavelength converting device is provided, including: a coupled quantum dot having a first quantum dot and a second quantum dot; an optical resonator encapsulating the coupled quantum dot; and a voltage controlling unit controlling a voltage applied to the coupled quantum dot. The energy difference between an energy level of one carrier and an energy level of the other carrier, in the carriers having different polarities in the first quantum dot, is equal to the energy of an incident single photon. The energy difference between an energy level of one carrier and an energy level of the other carrier in the carriers having different polarities in the second quantum dot, or the energy difference between an energy level of one of the carriers in the first quantum dot and an energy level of one of the carrier in the second quantum dot, having different polarity from that of the carrier in the first quantum dot, is equal to the resonance energy of the optical resonator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wavelength conversion device and a wavelength conversion method, and more particularly to a single photon wavelength conversion device and a wavelength conversion method.

  With the recent penetration of the electronic information society, research on information and communication technology has been actively conducted. However, since the computerized information is easy to duplicate and does not deteriorate, security against eavesdropping and duplication becomes a problem. Therefore, in order to realize a next-generation information society including e-government and e-commerce, secure and reliable encryption communication is required.

  A public encryption key method and a secret encryption key method are used as encryption communication. As an example, in the RSA public encryption key method, security is guaranteed based on the computational aspect that enormous time is required for factoring a very large number. However, it has been proved that the prime factorization can be calculated in parallel based on the Shor algorithm by using a quantum computer that is currently being studied. When the quantum computer reaches a practical level, the time required to decrypt the RSA cipher is drastically reduced, and the security of the RSA cipher is not guaranteed. Therefore, the security of the public encryption key method and the secret encryption key method currently used cannot be said to be perfect.

  As a means for solving such security problems, expectations for quantum cryptography communication are increasing. A well-known scheme for quantum cryptography is the “BB84” protocol. In this protocol, information is loaded on one quantum state (for example, polarization state) and transmitted. In order to eavesdrop on this, it is necessary to observe the one-photon state and return the observed photon to the transmission line. However, according to the no-cloning theorem (no-cloning theorem), it is impossible to extract or duplicate information without destroying the quantum state. Therefore, when correct bit information is taken out, it is revealed that it has been wiretapped (that is, the photon state has been destroyed).

  In order to put quantum cryptography communication into practical use, it is important to realize a single photon generator that regularly generates one photon as an information medium. As physical system candidates that can be used as a single photon generator, for example, InAs self-formed quantum dots (Non-Patent Document 1), nitrogen defect color centers in diamond crystals (Non-Patent Document 2), CdSe colloidal quantum dots (Non-Patent Document 1) Patent document 3) is mentioned.

JP 2006-098130 A

P. Michler et al. , “A Quantum Dot Single-Photon Turnstile Device,” Science 290, 2282 (2000). C. Kurtsiefer et al. "Stable Solid-State Source of Single Photos," Physical Review Letters 85, 290 (2000). X. Brokmann et al. , “Highly effective triggered emission of singles by colloidal CdSe / ZnS nanocrystals,” Applied Physics Letters 85, 712 (2004).

  It is conceivable to use an optical fiber network that forms the backbone of the current information network as a single photon transmission path used in quantum cryptography communication. In order to reduce the transmission loss in the optical fiber, it is desirable that the wavelength of the single photon is 1.3 μm band or 1.55 μm band (hereinafter referred to as “communication wavelength band”).

  In quantum cryptography in the communication wavelength band, a technique for efficiently detecting weak light called a single photon is also required. As a general detection technique, a technique using an InGaAs avalanche photodiode (APD) can be cited.

  However, according to this method, (1) the quantum efficiency is as low as about 10%, (2) only photons synchronized with the gate pulse can be detected, and (3) dark count that erroneously counts even if no photons have come. (4) The detection cannot be repeated at high speed due to an overcurrent called afterpulse after photon detection.

  As a method for solving these problems, there is a photon detection method based on wavelength conversion. In this method, a single photon in the optical communication wavelength band is converted into a wavelength having a detection sensitivity by silicon APD. Specifically, the wavelength is set to 1 μm or less, and considering the quantum efficiency, the wavelength is set to about 700 to 800 nm. According to this method, (1) the quantum efficiency can be 50% or more, (2) no gate operation is required, (3) the dark count is as low as several tens of counts per second, (4 ) The after-pulse generation probability is negligibly small. Therefore, according to the photon detection method based on wavelength conversion, the above-mentioned problems can be solved.

  As an example of wavelength conversion, the case where the communication wavelength band is converted to about 800 nm has been described, but the present invention is not limited to this. In general, it is preferable that the transmission line in long-distance transmission is an optical fiber. However, at a short distance of about several meters to several tens of meters, the propagation loss is small, and rather the connection loss of the measuring device based on the optical fiber may be large. Therefore, it may be better to use a measuring instrument or spatial transmission based on a spatial optical system, and in this case, visible light is often used as the wavelength. A wavelength conversion function at a single photon level is required in a portion connecting such a short distance spatial transmission and a long distance optical fiber transmission.

  In order to widen the bandwidth of quantum cryptography, a wavelength division multiplexing (WDM) system is also being studied. This is because when N wavelengths are used, the bandwidth can be increased N times compared to the case of one wavelength. Even in this case, a wavelength conversion technique is required when converting a signal between channels (wavelengths).

  From the above, it can be seen that a single photon wavelength converter is required in quantum information communication.

As a conventional technique related to wavelength conversion of a single photon, a method using a nonlinear optical crystal is known (Patent Document 1). FIG. 8 shows a configuration for realizing the wavelength conversion method described in Patent Document 1. An input single photon (frequency ω _IN , corresponding to a wavelength of 1550 nm) and pump light (frequency ω _p ) are superimposed on the same axis using a beam splitter, an optical coupler or the like, and incident on the nonlinear optical crystal 40. . As the nonlinear optical crystal 40, periodically poled lithium niobate (PPLN) or the like is used. The input single photon 43 in the communication wavelength band is wavelength-converted into an output single photon 44 (frequency ω _OUT ) in the visible light region by generating a sum frequency that is a second-order nonlinear optical effect in the crystal. Here, from the energy conservation law, each frequency satisfies ω _OUT = ω _IN + ω _p .

  It is known that the efficiency of wavelength conversion becomes 80% or more by optimizing the polarization inversion of the nonlinear optical crystal 40. By converting the wavelength into the visible light wavelength band in this way, single photon detection with high quantum efficiency and low dark count using the above-described silicon APD becomes possible.

  However, according to this method, a problem arises regarding separation of the converted signal light and pump light. The efficiency of the sum frequency generation is proportional to the product of the pump light intensity and the input single photon intensity. However, since the single photon is very weak, the pump light intensity is required to achieve a quantum efficiency of 80% or more. Need to be considerably stronger. However, when the pump light 45 is mixed with the wavelength-converted output single photon 44, the signal-to-noise ratio (S / N ratio) is lowered, so that it is necessary to avoid the mixing of the pump light 45.

  Since the signal light and the pump light 45 propagate in the same direction as shown in FIG. 8, the strong pump light 45 must be removed by using a plurality of prisms 41 and bandpass filters 42 in the subsequent stage of the nonlinear optical crystal 40. I must. When the pump light 45 is mixed into the output single photon 44, the S / N ratio is lowered, so that precise optical path adjustment is required. Further, since optical components such as a filter have a finite optical loss with respect to the output single photon 44, the wavelength conversion efficiency of the entire apparatus is lowered as a result.

  Further, in an apparatus based on an optical fiber, the S / N ratio may be lowered due to Raman scattering of pump light. When strong pump light propagates through the optical fiber, it is scattered by light having the same wavelength as the output single photon by inelastic scattering via phonons called Raman scattering. Since the light of the same wavelength cannot be removed by the prism or the band pass filter, the S / N ratio is lowered by generating photons that should not be generated.

  Thus, a method for performing wavelength conversion of weak light at the level of one photon without complicating the apparatus and lowering the S / N ratio has not been known so far.

  Therefore, in the wavelength conversion of single photons, it is a problem to prevent a decrease in signal-to-noise ratio (S / N ratio). The objective of this invention is providing the wavelength converter and wavelength conversion method which solve this subject.

The wavelength converter according to the first aspect of the present invention is:
A coupled quantum dot having a first quantum dot and a second quantum dot coupled to each other;
An optical resonator containing the coupled quantum dots;
A voltage controller for controlling a voltage applied to the coupled quantum dots,
The energy difference between the energy level of one of the carriers of different polarity in the first quantum dot and the energy level of the other carrier matches the energy of the incident single photon,
The energy difference between the energy level of one of the carriers of different polarity in the second quantum dot and the energy level of the other carrier, or the energy level of the carrier in the first quantum dot And the energy level of the carrier in the second quantum dot having a polarity different from that of the carrier is equal to the resonance energy of the optical resonator.

The wavelength conversion method according to the second aspect of the present invention is:
Controlling a voltage applied to a coupled quantum dot having a first quantum dot and a second quantum dot coupled to each other;
Absorbing the incident single photon into the first quantum dot to generate one electron and one hole each.
The energy difference between the energy level of one of the carriers of different polarity in the second quantum dot and the energy level of the other carrier, or the energy level of the carrier in the first quantum dot And the energy level of a carrier having a polarity different from that of the carrier in the second quantum dot is equal to the resonance energy of the optical resonator containing the coupled quantum dot.

  According to the wavelength conversion device and the wavelength conversion method according to the present invention, it is possible to prevent a decrease in signal-to-noise ratio (S / N ratio) in wavelength conversion of a single photon.

1 is a diagram schematically showing a configuration of a wavelength conversion device according to a first embodiment of the present invention. It is a figure for demonstrating operation | movement of the wavelength converter which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the wavelength conversion method which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating the wavelength conversion method which concerns on the 3rd Embodiment of this invention. It is a figure for demonstrating the wavelength conversion method which concerns on the 4th Embodiment of this invention. It is a figure for demonstrating the wavelength conversion method which concerns on the 7th Embodiment of this invention. It is a figure which shows schematically the structure of the wavelength converter which concerns on the 10th Embodiment of this invention. It is a figure which shows the structure of the wavelength converter described in patent document 1 as an example.

  According to the first development form of the present invention, the wavelength conversion device according to the first aspect is provided.

  Here, the coupled quantum dots (coupled quantum dots) are a wave function of electrons or holes bound to one quantum dot and a wave function of electrons or holes bound to the other quantum dot. A plurality of quantum dots that are close enough to each other to overlap.

  When an input single photon is absorbed by a coupled quantum dot, a single photon of the same wavelength is usually emitted on a time scale of about 1 ns. However, an optical resonator containing coupled quantum dots inside suppresses light emission at this wavelength, and electrons generated by light absorption and holes injected before light absorption or generated by light absorption. In order to promote luminescence recombination between holes and electrons injected before light absorption, an output single photon with a wavelength different from the input single photon is obtained.

  According to the second development form of the present invention, one hole is injected into the second quantum dot, and the input single photon is absorbed so that one electron and hole is contained in the first quantum dot. When generated one by one, electrons in the first quantum dot and holes in the second quantum dot are recombined to generate an output single photon having energy equal to the resonance energy. A wavelength converter is provided.

  According to the third embodiment of the present invention, one electron is injected into the second quantum dot, and one electron and a hole are absorbed in the first quantum dot by absorbing the input single photon. When generated one by one, holes in the first quantum dot and electrons in the second quantum dot are recombined to generate an output single photon having energy equal to the resonance energy. A wavelength converter is provided.

  According to the fourth embodiment of the present invention, one hole is injected into the second quantum dot, the input single photon is absorbed, and one electron and hole are contained in the first quantum dot. When the electrons in the first quantum dot are made to coincide with each other and the energy levels of the electrons in the first and second quantum dots are made to coincide with each other, the electrons in the first quantum dot are moved to the second quantum dot by a resonance tunnel. Provides a wavelength conversion device in which electrons and holes in the second quantum dot are recombined to generate an output single photon having an energy equal to the resonance energy.

  After electrons and holes are generated in the coupled quantum dot by light absorption, electrons are moved between the dots by a resonant tunnel, and the recombination with the optical resonator promotes the luminescence recombination of electrons and holes in the same dot. Thus, an output single photon having a wavelength different from that of the input single photon can be obtained.

  The number of quantum dots constituting the coupled quantum dot is not limited to two, and may be three or more. At this time, the electrons sequentially resonate between adjacent quantum dots.

  According to the fifth development of the present invention, one electron is injected into the second quantum dot, the input single photon is absorbed, and one electron and one hole are contained in the first quantum dot. And the energy levels of the holes in the first and second quantum dots are matched so that the holes in the first quantum dot are moved to the second quantum dot through a resonant tunnel. In some cases, a wavelength conversion device is provided in which electrons and holes in the second quantum dot are recombined to produce an output single photon having an energy equal to the resonance energy.

  According to the sixth development of the present invention, the input single photon is absorbed to generate one electron and one hole in the first quantum dot, and in the first and second quantum dots When the energy levels of the electrons are matched and the electrons in the first quantum dot are moved to the second quantum dot by a resonant tunnel, the holes in the first quantum dot and the first quantum dot are moved. A wavelength conversion device is provided that recombines with electrons in two quantum dots to produce an output single photon having an energy equal to the resonance energy.

  According to a seventh development of the present invention, the input single photon is absorbed to generate one electron and one hole in the first quantum dot, and in the first and second quantum dots When holes in the first quantum dot are moved to the second quantum dot through a resonance tunnel by matching the energy levels of the holes, the electrons in the first quantum dot and the electron in the first quantum dot A wavelength conversion device is provided that recombines with holes in a second quantum dot to produce an output single photon having an energy equal to the resonance energy.

  According to an eighth development of the present invention, in the optical resonator, the i-type semiconductor layer including the coupled quantum dots includes a p-type distributed Bragg reflector having two types of semiconductor multilayer films having different refractive indexes and an n-type. There is provided a wavelength converter sandwiched between distributed Bragg reflectors.

  According to the ninth embodiment of the present invention, the optical resonator can be moved independently of the coupled quantum dots and the n-type or p-type distributed Bragg reflector integrated with the coupled quantum dots. There is provided a wavelength conversion device including a reflecting mirror.

  According to a tenth embodiment of the present invention, there is provided a wavelength conversion method according to the second aspect.

  According to the present invention, an output single photon having a wavelength different from that of an input single photon can be generated by a combination of a coupled quantum dot and an optical resonator. Since the S / N ratio of a single photon does not decrease in principle, it is possible to perform quantum cryptography communication with a higher communication speed and higher reliability than before. According to the present invention, it is possible to obtain a single photon wavelength conversion device without reducing the S / N ratio, and it is possible to expand the bandwidth of quantum cryptography communication.

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

(Embodiment 1)
FIG. 1 is a schematic diagram illustrating a wavelength conversion apparatus according to the first embodiment.

  In FIG. 1, the wavelength conversion device includes an n-type DBR (distributed Bragg reflector (DBR) 14 doped to n-type), a first quantum dot 10 and a second quantum dot 11. It comprises an intrinsic resonator layer 15, a p-type DBR 16, a lower electrode 13 disposed so as to sandwich them, and an upper electrode 17. In the upper electrode, a minute opening 18 for inputting and outputting a single photon through a lens 19 is formed. The semiconductor portion shown here is formed on the n-type substrate 12 from the lower portion of the drawing by a molecular beam epitaxy (MBE) method, a metal organic chemical vapor deposition (MOCVD) method, or the like. Be filmed.

  Referring to FIG. 1, the semiconductor has a pillar shape in order to confine light in the stacking plane, and its diameter is about 2 to 10 μm. It can be processed into such a shape by electron beam lithography or an optical exposure method and a dry etching technique.

  As an example, the n-type substrate is Si-doped GaAs, the n-type DBR is a multilayer film in which Si-doped GaAs and AlAs are alternately stacked, the i-type resonator is non-doped GaAs, and the quantum dots are The p-type DBR may be a multilayer film in which GaAs doped with Be and AlAs are alternately stacked.

  The first quantum dot 10 is formed by self-growth at a substantially central portion of the i-type resonator layer 15, and the second quantum dot 11 is formed thereon by self-growth. The first quantum dot 10 and the second quantum dot are adjacent to each other and are coupled to each other to form a coupled quantum dot 100. Here, the two quantum dots are coupled to each other between the wave function of electrons or holes bound to one quantum dot and the wave function of electrons or holes bound to the other quantum dot. This means that the quantum dots are close enough that a finite overlap occurs between them. A typical distance between quantum dots is about 5 to 10 nm.

  The DBR has a structure in which media having different refractive indexes (referred to as n1 and n2) are alternately stacked with film thicknesses of λ / 4n1 and λ / 4n2 with respect to the light wavelength λ desired to be reflected. As the number of layers is increased, a higher reflectance can be obtained. In this embodiment, assuming GaAs and AlAs as the constituent media, about 10 to 20 pairs (20 to 40 layers) are required.

  The n-type DBR 14 and the p-type DBR 16 constitute an optical resonator that strongly confines light in the i-type resonator layer 15, and the resonator energy determined by the pillar diameter and the thickness of the i-type resonator layer will be described later. Designed to match the energy of the output single photon. At this time, it is necessary to arrange the coupled quantum dots in the vicinity of the maximum position of the electric field amplitude so that the resonator electric field and the coupled quantum dots 100 interact with each other.

  The upper electrode 17 is produced on the p-type DBR 16 by metal vapor deposition or the like. The lower electrode 13 is in contact with the n-type substrate 12. By appropriately controlling the voltage applied between the upper electrode 17 and the lower electrode 13, one electron is injected from the n-type DBR 14 into the first quantum dot 10, or from the p-type DBR 16 to the second quantum dot 11. One hole can be injected into the. Moreover, the electron energy or hole energy of the 1st quantum dot 10 and the 2nd quantum dot 11 can also be made to correspond by this applied voltage control. Furthermore, electrons or holes remaining in the coupled quantum dots after wavelength conversion can be removed (that is, carriers in the coupled quantum dots are initialized).

  Next, the principle of operation will be described. Various variations are conceivable depending on the relationship between the energy of the electron or hole of the quantum dot and the energy of the input single photon, and the presence or absence of the movement of the carrier between the quantum dots.

  FIG. 2 is a diagram for explaining the operation of the wavelength conversion device according to the first embodiment. FIG. 2 shows an energy diagram of electrons and holes in the vicinity of the coupled quantum dot 100. In addition, about the part which is not required in order to demonstrate operation | movement, the structure of the energy diagram was simplified and shown. The valence band 20 and the conduction band 21 are inclined because of the built-in voltage in the pin structure and the voltage applied between the upper electrode 17 and the lower electrode 13. White circles indicate holes 22 and black circles indicate electrons 23.

  The energies of electrons and holes bound to the first quantum dots are EC1 and EV1, respectively. In addition, the energy of electrons and holes bound to the second quantum dots are EC2 and EV2, respectively. Here, it is assumed that the resonance energy of the optical resonator is ΔE = EC1−EV2.

  The single photon wavelength conversion (energy conversion) operation is performed by the following procedure.

  (A) One hole is injected into the second quantum dot 11 by setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value.

  (B) The input single photon 24 whose energy coincides with EC1-EV1 is absorbed by the first quantum dots 10, whereby one electron and one hole are generated.

  (C) The optical resonator suppresses light emission of energy EC1-EV1 deviating from resonator resonance and promotes light emission of resonant energy EC1-EV2 (Parcel effect). The electrons and the holes in the second quantum dot 11 are recombined to generate an output single photon 25 with energy EC1-EV2.

  (D) By setting a voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value, one hole remaining in the first quantum dot 10 is removed from the coupled quantum dot 100. Or move to the second quantum dot 11.

  By repeating the above operation, the input single photon of energy EC1-EV1 is converted into the output single photon of energy EC1-EV2. At this time, the energy change amount of the single photon becomes EV1-EV2, and the wavelength change of the single photon corresponding to this is realized.

  According to the above operation, since the strong pump light as in the conventional case is not used, it is possible to prevent the S / N ratio from being lowered. Further, by adopting the resonator structure, it is possible to increase the efficiency with which the input photons are absorbed by the quantum dots and the efficiency with which the output photons are extracted.

  As can be seen from the operating principle, the wavelength of wavelength conversion is determined by the energy level of the quantum dots. The energy level of a quantum dot is determined by the material and size of the dot. Therefore, the operating wavelength of the wavelength conversion device can be controlled by selecting the substance and designing the shape.

(Embodiment 2)
FIG. 3 is a diagram for explaining a wavelength conversion method according to the second embodiment of the present invention. FIG. 3 shows an energy diagram of electrons and holes in the vicinity of the coupled quantum dot 100. The wavelength conversion method of this embodiment is different from the operation of the wavelength conversion device according to the first embodiment in that the roles of electrons and holes are interchanged.

  The energies of electrons and holes bound to the first quantum dots are EC1 and EV1, respectively. In addition, the energy of electrons and holes bound to the second quantum dots are EC2 and EV2, respectively. Here, it is assumed that the resonance energy of the optical resonator is ΔE = EC1−EV2.

  (A) One electron is injected into the second quantum dot 11 by setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value.

  (B) The input single photon 24 whose energy coincides with EC1-EV1 is absorbed by the first quantum dots 10, whereby one electron and one hole are generated.

  (C) The optical resonator suppresses light emission of energy EC1-EV1 deviating from resonator resonance and promotes light emission of energy EC2-EV1 that resonates, so that the electrons in the second quantum dots 11 and the first Are recombined with the holes in the quantum dot 10 to generate an output single photon 25 of energy EC2-EV1.

  (D) By setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value, one electron remaining in the first quantum dot 10 is removed from the coupled quantum dot 100. Or move to the second quantum dot 11.

  By repeating the above operation, an input single photon of energy EC1-EV1 is converted into an output single photon of energy EC2-EV1. At this time, the energy change amount of the single photon becomes EC2-EC1, and the wavelength change of the single photon corresponding to this is realized.

(Embodiment 3)
FIG. 4 is a diagram for explaining a wavelength conversion method according to the third embodiment of the present invention. FIG. 4 shows an energy diagram of electrons and holes in the vicinity of the coupled quantum dot 100.

  The energies of electrons and holes bound to the first quantum dots are EC1 and EV1, respectively. In addition, the energy of electrons and holes bound to the second quantum dots are EC2 and EV2, respectively. Here, it is assumed that the resonance energy of the optical resonator is ΔE = EC2−EV2.

  (A) One hole is injected into the second quantum dot 11 by setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value.

  (B) The input single photon 24 whose energy coincides with EC1-EV1 is absorbed by the first quantum dots 10, whereby one electron and one hole are generated.

  (C) By setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value, the electron energies of the first quantum dot 10 and the second quantum dot 11 are made to coincide with each other. Electrons in the quantum dot are moved to the second quantum dot by a resonant tunneling phenomenon.

  (D) The optical resonator suppresses the emission of energy EC1-EV1 and EC1-EV2 deviating from the resonator resonance, and promotes the emission of the resonant energy EC2-EV2. The electrons and holes recombine to generate an output single photon 25 of energy EC2-EV2.

  (E) Removing one hole left in the first quantum dot 10 from the coupled quantum dot 100 by setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value. Or move to the second quantum dot 11.

  By repeating the above operation, an input single photon of energy EC1-EV1 is converted into an output single photon of energy EC2-EV2. At this time, the energy change amount of the single photon is EC2−EC1 + EV1−EV2, and the wavelength change of the single photon corresponding to this is realized.

(Embodiment 4)
FIG. 5 is a diagram for explaining a wavelength conversion method according to the fourth embodiment of the present invention. FIG. 5 shows an energy diagram of electrons and holes in the vicinity of the coupled quantum dot 100. The wavelength conversion method of this embodiment is different from the wavelength conversion method according to the third embodiment in that the roles of electrons and holes are interchanged.

  The energies of electrons and holes bound to the first quantum dots are EC1 and EV1, respectively. In addition, the energy of electrons and holes bound to the second quantum dots are EC2 and EV2, respectively. Here, it is assumed that the resonance energy of the optical resonator is ΔE = EC1−EV1.

  (A) One electron is injected into the second quantum dot 11 by setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value.

  (B) The input single photon 24 whose energy coincides with EC1-EV1 is absorbed by the first quantum dots 10, whereby one electron and one hole are generated.

  (C) By setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value, the hole energies of the first quantum dot 10 and the second quantum dot 11 are matched, and the first The holes in the quantum dots 10 are moved to the second quantum dots 11 by the resonant tunneling phenomenon.

  (D) The optical resonator suppresses the emission of energy EC1-EV1 and EC1-EV2 deviating from the resonator resonance, and promotes the emission of the resonant energy EC2-EV2. The electrons and holes recombine to generate an output single photon 25 of energy EC2-EV2.

  (E) removing one electron remaining in the first quantum dot 10 from the coupled quantum dot 100 by setting an applied voltage between the upper electrode 17 and the lower electrode 13 to an appropriate value, or Move to the second quantum dot 11.

  By repeating the above operation, an input single photon of energy EC1-EV1 is converted into an output single photon of energy EC2-EV2. At this time, the energy change amount of the single photon is EC2−EC1 + EV1−EV2, and the wavelength change of the single photon corresponding to this is realized.

(Embodiment 5)
In Embodiment 3, the number of quantum dots constituting the coupled quantum dot 100 is two, but the same operation is possible even in a system in which three or more adjacent quantum dots are coupled to each other. The quantum dots are first, second,..., Nth quantum dots from the n-type doped layer side. However, N is an integer greater than or equal to 3.

  The electron energy in the Nth quantum dot is ECN, and the hole energy is ECV. Here, the resonance energy of the optical resonator is ΔE = ECN−EVN.

  (A) A state in which holes are injected into the Nth quantum dot is prepared, and an input single photon whose energy coincides with EC1-EV1 is absorbed by the first quantum dot 10, whereby electrons and holes are absorbed. One by one is generated.

  (B) Using the resonant tunneling phenomenon, electrons in the first quantum dot are repeatedly moved to the second quantum dot, the third dot,..., And moved to the Nth quantum dot.

  (C) Since the optical resonator promotes only light emission of the resonant energy ECN-EVN, electrons and holes in the Nth quantum dot are recombined to generate an output single photon of energy ECN-EVN. appear.

  Thus, an input single photon with energy EC1-EV1 is converted to an output single photon with energy EC2-EV2. At this time, the energy change amount of the single photon is ECN−EC1 + EV1−EVN, and the single photon wavelength change corresponding to this is realized.

(Embodiment 6)
A wavelength conversion method according to the sixth embodiment of the present invention will be described. The wavelength conversion method of this embodiment is obtained by switching the roles of electrons and holes in the wavelength conversion method according to the fifth embodiment. In addition, this embodiment can also be considered that the wavelength dot which concerns on 4th Embodiment expands the quantum dot which comprises a coupled quantum dot from 2 pieces to 3 or more quantum dots.

(Embodiment 7)
FIG. 6 is a diagram for explaining a wavelength conversion method according to the seventh embodiment of the present invention. FIG. 6 shows an energy diagram of electrons and holes in the vicinity of the coupled quantum dot 100. In the present embodiment, unlike the first to sixth embodiments, it is not necessary to inject electrons or holes into the coupled quantum dots in advance.

  The energies of electrons and holes bound to the first quantum dots are EC1 and EV1, respectively. In addition, the energy of electrons and holes bound to the second quantum dots are EC2 and EV2, respectively. Here, it is assumed that the resonance energy of the optical resonator is ΔE = EC2−EV1.

  (A) The input single photon 24 whose energy coincides with EC1-EV1 is absorbed by the first quantum dot 10, whereby one electron and one hole are generated.

  (B) By setting the voltage applied between the upper electrode 17 and the lower electrode 13 to an appropriate value, the electron energies of the first quantum dot 10 and the second quantum dot 11 are matched, and the first Electrons in the quantum dot are moved to the second quantum dot by a resonant tunneling phenomenon.

  (C) The optical resonator suppresses the emission of energy EC1-EV1 or the like deviating from the resonator resonance, and promotes the emission of the resonant energy EC2-EV1. The holes recombine to generate an output single photon 25 of energy EC2-EV1.

  This operation converts the input single photon of energy EC1-EV1 into an output single photon of energy EC2-EV1. At this time, the energy change amount of the single photon becomes EC2-EC1, and the wavelength change of the single photon corresponding to this is realized.

(Embodiment 8)
In the seventh embodiment, the roles of the first quantum dot and the second quantum dot may be interchanged. The carriers moved by the resonant tunnel may be electrons or holes. At this time, the resonance energy of the optical resonator must be designed to match the energy of the desired output single photon.

(Embodiment 9)
In the first to eighth embodiments, the input is a single photon. When there are two or more input photons, one photon is absorbed by the quantum dot to generate electrons and holes, but no more input photons are absorbed. This is because fermions such as electrons and holes cannot occupy the same quantum state due to Pauli exclusion. Therefore, other than the absorbed photons pass through the quantum dot. Even in this case, the output is a single photon wavelength-converted. Therefore, in the first to eighth embodiments, the input photon is not limited to a single photon.

(Embodiment 10)
FIG. 7 is a diagram schematically showing the configuration of the wavelength conversion device according to the tenth embodiment of the present invention.

  Referring to FIG. 7, the wavelength converter includes an n-type DBR 14, an i-type resonator layer 15 including the first quantum dots 10 and the second quantum dots 11, a lower electrode 13 disposed so as to sandwich these, The upper electrode 17 and the reflecting mirror 30 are included. The upper electrode is formed with a minute opening 18 through which an input / output single photon is transmitted. The difference from the first embodiment is that an optical resonator is constituted by an n-type DBR 14 integrated with an i-type resonator layer 15 and a reflecting mirror 30 that is not integrated (independent) with these. Is a point. Also in the wavelength conversion device of this embodiment, by injecting electrons or holes into the coupled quantum dots and absorbing the input single photons, the same methods as those described in the first to ninth embodiments are performed. A wavelength-converted output single photon is obtained.

  The resonant frequency of the resonator must match the predetermined energy difference of the coupled quantum dots. According to the wavelength conversion device of the present embodiment, the reflecting mirror 30 can be moved independently of the n-type DBR 14 formed on the same substrate as the coupled quantum dots 100, and between the reflecting mirror 30 and the n-type DBR 14. Can be finely adjusted mechanically. Therefore, according to the wavelength conversion device of the present embodiment, it is possible to finely adjust an error generated in the manufacturing process.

  Since this embodiment uses an n-type substrate and an n-type DBR, it can be applied to the second, fourth, and sixth embodiments in which electrons need to be injected into the coupled quantum dots. When applied to the first, third and fifth embodiments where holes need to be injected into the coupled quantum dots, a p-type substrate and a p-type DBR are used instead of the n-type substrate and the n-type DBR. Use it.

  Each disclosure of the above non-patent document is incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Various combinations and selections of various disclosed elements are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

  The single photon wavelength conversion device and the wavelength conversion method according to the present invention can be used in quantum cryptography communication.

  The present invention also includes the inventions appended below.

(Appendix 1) A coupled quantum dot having a first quantum dot and a second quantum dot coupled to each other;
An optical resonator containing the coupled quantum dots;
A voltage controller for controlling a voltage applied to the coupled quantum dots,
The energy difference between the energy level of one of the carriers of different polarity in the first quantum dot and the energy level of the other carrier matches the energy of the incident single photon,
The energy difference between the energy level of one of the carriers of different polarity in the second quantum dot and the energy level of the other carrier, or the energy level of the carrier in the first quantum dot Difference between the energy level of the second quantum dot and the energy level of the carrier having a polarity different from that of the carrier is equal to the resonance energy of the optical resonator.

  (Appendix 2) When one hole is injected into the second quantum dot and one input photon is absorbed to generate one electron and one hole in the first quantum dot. The electron in the first quantum dot and the hole in the second quantum dot are recombined to generate an output single photon having an energy equal to the resonance energy, 2. The wavelength converter according to 1.

  (Supplementary Note 3) When one electron is injected into the second quantum dot and the input single photon is absorbed to generate one electron and one hole in the first quantum dot, The hole in the first quantum dot and the electron in the second quantum dot are recombined to generate an output single photon having an energy equal to the resonance energy. The wavelength converter described in 1.

  (Supplementary Note 4) One hole is injected into the second quantum dot, the input single photon is absorbed to generate one electron and one hole in the first quantum dot, and When the energy levels of the electrons in the first and second quantum dots are matched, and the electrons in the first quantum dot are moved to the second quantum dot by a resonant tunnel, the second quantum dot The wavelength conversion apparatus according to appendix 1, wherein an electron and a hole in the quantum dot are recombined to generate an output single photon having an energy equal to the resonance energy.

  (Supplementary Note 5) One electron is injected into the second quantum dot, the input single photon is absorbed to generate one electron and one hole in the first quantum dot, and the first quantum dot And when the holes in the first quantum dot are moved to the second quantum dot through a resonance tunnel by matching the energy levels of the holes in the second quantum dot, the second quantum dot The wavelength converter according to appendix 1, wherein electrons and holes in the quantum dots are recombined to generate an output single photon having an energy equal to the resonance energy.

(Additional remark 6) It further has the 3rd quantum dot couple | bonded with the said 1st quantum dot and the said 2nd quantum dot,
The energy level of the electrons in the third quantum dot is matched with the energy level of the electrons in the first and second quantum dots, and the electrons in the first quantum dot are The wavelength conversion device according to appendix 4, wherein the wavelength conversion device is moved to the second quantum dot via a third quantum dot.

(Supplementary note 7) Further comprising a third quantum dot coupled to the first quantum dot and the second quantum dot,
The energy level of holes in the third quantum dot is matched with the energy level of holes in the first and second quantum dots, and the holes in the first quantum dot are resonant tunneled. The wavelength converter according to appendix 5, wherein the wavelength converter is moved to the second quantum dot via the third quantum dot.

  (Supplementary Note 8) The input single photon is absorbed to generate one electron and one hole in the first quantum dot, and the energy levels of the electrons in the first and second quantum dots are matched. Thus, when electrons in the first quantum dot are moved to the second quantum dot by a resonant tunnel, holes in the first quantum dot and electrons in the second quantum dot are And recombining with each other to generate an output single photon having an energy equal to the resonance energy.

  (Supplementary Note 9) The input single photon is absorbed to generate one electron and one hole in the first quantum dot, and the energy level of the hole in the first and second quantum dots is determined. When the holes in the first quantum dot are moved to the second quantum dot by a resonance tunnel, the electrons in the first quantum dot and the electrons in the second quantum dot The wavelength conversion device according to appendix 1, wherein an output single photon having an energy equal to the resonance energy is generated by recombination with holes.

  (Supplementary Note 10) The hole injection is present in the p-type semiconductor layer by controlling the voltage between the p-type semiconductor layer adjacent to the coupled quantum dot and the electrode provided so as to sandwich the coupled quantum dot. The wavelength conversion device according to any one of appendices 2, 4 and 6, wherein the wavelength conversion device is performed by moving holes to the coupled quantum dots.

  (Additional remark 11) The injection | pouring of the said electron controls the voltage between the electrode provided so that the n type semiconductor layer and the said coupling quantum dot which adjoin the said coupling quantum dot may be pinched | interposed, The wavelength conversion device according to any one of appendices 3, 5 and 7, wherein the wavelength conversion device is performed by moving the coupled quantum dots to the coupled quantum dots.

  (Supplementary note 12) The energy levels of electrons or holes in each quantum dot are matched by applying an electric field in a direction parallel to the coupling direction of the coupled quantum dots. The wavelength converter as described in any one.

  (Supplementary Note 13) In the optical resonator, the i-type semiconductor layer including the coupled quantum dots is sandwiched between a p-type distributed Bragg reflector and an n-type distributed Bragg reflector having two types of semiconductor multilayer films having different refractive indexes. The wavelength conversion device according to any one of appendices 1 to 12, wherein the wavelength conversion device is characterized in that:

(Supplementary note 14) The optical resonator includes an n-type or p-type distributed Bragg reflector integrated with the coupled quantum dot;
The wavelength converter according to any one of appendices 1 to 12, further comprising a reflecting mirror that can be moved independently of the coupled quantum dots.

(Supplementary note 15) a step of controlling a voltage applied to a coupled quantum dot having a first quantum dot and a second quantum dot coupled to each other;
Absorbing the incident single photon into the first quantum dot to generate one electron and one hole each.
The energy difference between the energy level of one of the carriers of different polarity in the second quantum dot and the energy level of the other carrier, or the energy level of the carrier in the first quantum dot Difference between the energy level of a carrier having a polarity different from that of the carrier in the second quantum dot is equal to a resonance energy of an optical resonator containing the coupled quantum dot. Method.

(Supplementary Note 16) Injecting one hole into the second quantum dot;
Further comprising recombining electrons in the first quantum dots and holes in the second quantum dots to generate an output single photon having an energy equal to the resonance energy. 16. The wavelength conversion method according to appendix 15, which is a feature.

(Supplementary note 17) Injecting one electron into the second quantum dot;
Further comprising the step of recombining holes in the first quantum dots and electrons in the second quantum dots to generate output single photons having an energy equal to the resonance energy. 16. The wavelength conversion method according to appendix 15, which is a feature.

(Supplementary note 18) Injecting one hole into the second quantum dot;
Matching the energy levels of the electrons in the first and second quantum dots and moving the electrons in the first quantum dots to the second quantum dots by a resonant tunnel;
The method of claim 15, further comprising: recombining electrons and holes in the second quantum dot to generate an output single photon having an energy equal to the resonance energy. Wavelength conversion method.

(Supplementary note 19) Injecting one electron into the second quantum dot;
Matching the energy levels of the holes in the first and second quantum dots and moving the holes in the first quantum dots to the second quantum dots by a resonant tunnel;
The method of claim 15, further comprising: recombining electrons and holes in the second quantum dot to generate an output single photon having an energy equal to the resonance energy. Wavelength conversion method.

(Appendix 20) The step of causing the energy levels of the electrons in the first and second quantum dots to coincide and moving the electrons in the first quantum dots to the second quantum dots by a resonant tunnel;
Further comprising the step of recombining holes in the first quantum dots and electrons in the second quantum dots to generate output single photons having an energy equal to the resonance energy. 16. The wavelength conversion method according to appendix 15, which is a feature.

(Additional remark 21) The process of making the energy level of the hole in the said 1st and 2nd quantum dot correspond, and moving the hole in the said 1st quantum dot to the said 2nd quantum dot by a resonance tunnel When,
Further comprising the step of recombining electrons in the first quantum dots and holes in the second quantum dots to generate an output single photon having an energy equal to the resonance energy. 16. The wavelength conversion method according to appendix 15, which is a feature.

(Supplementary note 22) A wavelength conversion device that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first and second quantum dots coupled together;
Means for injecting holes into the second quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator matches the energy difference between the energy level of the electrons in the first quantum dot and the energy level of the holes in the second quantum dot;
When one hole is injected into the second quantum dot and the input single photon is absorbed by the first quantum dot to generate an electron and a hole one by one in the first quantum dot Is characterized in that an electron in the first quantum dot and a hole in the second quantum dot are recombined to generate an output single photon having energy equal to the resonance energy. Wavelength converter.

(Supplementary Note 23) A wavelength converter that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first and second quantum dots coupled together;
Means for injecting electrons into the second quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator matches the energy difference between the energy level of holes in the first quantum dot and the energy level of electrons in the second quantum dot;
When one electron is injected into the second quantum dot and the input single photon is absorbed into the first quantum dot to generate an electron and a hole one by one in the second quantum dot Is characterized in that a hole in the first quantum dot and an electron in the second quantum dot are recombined to generate an output single photon having an energy equal to the resonance energy. Conversion device.

(Supplementary Note 24) A wavelength converter that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first and second quantum dots coupled together;
Means for injecting holes into the second quantum dots;
Means for matching the energy levels of the electrons of the first and second quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator coincides with the energy difference between the energy level of electrons and the energy level of holes in the second quantum dot,
Injecting one hole into the second quantum dot and absorbing the input single photon to generate one electron and one hole in the first quantum dot, and the first quantum dot When the electrons in the second quantum dot are moved to the second quantum dot by a resonance tunnel, the electrons and holes in the second quantum dot are recombined to have an output unit having energy equal to the resonance energy. A wavelength converter that generates one photon.

(Supplementary Note 25) A wavelength conversion device that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first and second quantum dots coupled together;
Means for injecting electrons into the first quantum dots;
Means for matching the energy levels of the holes in the first and second quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator matches the energy difference between the energy level of electrons and the energy level of holes in the first quantum dot,
Injecting one electron into the second quantum dot, absorbing the input single photon to generate one electron and one hole in the first quantum dot, and in the first quantum dot Are transferred to the second quantum dot by a resonant tunneling, electrons and holes in the second quantum dot are recombined, and an output unit having energy equal to the resonance energy is obtained. A wavelength converter that generates one photon.

(Supplementary note 26) A wavelength conversion device that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first to Nth (N is a natural number of 3 or more) quantum dots in which adjacent quantum dots are coupled to each other;
Means for injecting holes into the Nth quantum dot;
Means for matching the energy levels of the electrons of the adjacent quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator coincides with the energy difference between the energy level of electrons and the energy level of holes in the Nth quantum dot,
Injecting one hole into the Nth quantum dot and absorbing the input single photon to generate one electron and one hole in the first quantum dot, and the first quantum dot In the case where the electrons in the Nth quantum dot are finally moved to the Nth quantum dot through the second quantum dot and the third quantum dot by the resonance tunnel, the electrons and holes in the Nth quantum dot are Recombining to generate an output single photon having an energy equal to the resonance energy.

(Supplementary note 27) A wavelength conversion device that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first to Nth (N is a natural number of 3 or more) quantum dots in which adjacent quantum dots are coupled to each other;
Means for injecting electrons into the first quantum dots;
Means for matching the energy levels of the holes of the adjacent quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator coincides with the energy difference between the energy level of electrons and the energy level of holes in the Nth quantum dot,
Injecting one electron into the Nth quantum dot, absorbing the input single photon to generate one electron and one hole in the first quantum dot, and in the first quantum dot When the holes are moved to the Nth quantum dot through the second quantum dot and the third quantum dot by the resonant tunneling, the electrons and holes in the Nth quantum dot are Recombining to generate an output single photon having an energy equal to the resonance energy.

(Supplementary note 28) A wavelength converter for generating output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first and second quantum dots coupled together;
Means for matching the energy levels of the electrons of the first and second quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator matches the energy difference between the energy level of electrons in the second quantum dot and the energy level of holes in the first quantum dot;
The input single photon is absorbed to generate one electron and one hole in the first quantum dot, and the electron in the first quantum dot is moved to the second quantum dot through a resonance tunnel. If so, the holes in the first quantum dot and the electrons in the second quantum dot are recombined to generate an output single photon having energy equal to the resonance energy. A featured wavelength converter.

(Supplementary note 29) A wavelength conversion device that generates output single photons having different wavelengths with respect to input single photons,
A coupled quantum dot having first and second quantum dots coupled together;
Means for matching the hole energies of the first and second quantum dots;
An optical resonator including the coupled quantum dot therein,
The resonance energy of the optical resonator matches the energy difference between the energy level of the electrons in the first quantum dot and the energy level of the holes in the second quantum dot;
The input single photon is absorbed to generate one electron and one hole in the first quantum dot, and the hole in the first quantum dot is transferred to the second quantum dot by a resonance tunnel. When moved, electrons in the first quantum dot and holes in the second quantum dot are recombined to generate an output single photon having energy equal to the resonance energy. A wavelength converter characterized by the above.

  (Supplementary Note 30) The means for injecting holes controls a voltage between a p-type semiconductor layer adjacent to the coupled quantum dot and an electrode provided so as to sandwich the coupled quantum dot, and the p-type semiconductor layer 27. The wavelength conversion device according to any one of appendices 22, 24, or 26, wherein an existing hole is moved to the coupled quantum dot.

  (Supplementary Note 31) The means for injecting electrons is present in the n-type semiconductor layer by controlling a voltage between an n-type semiconductor layer adjacent to the coupled quantum dot and an electrode provided so as to sandwich the coupled quantum dot. The wavelength conversion device according to any one of appendices 23, 25, or 27, wherein electrons to be moved are moved to the coupled quantum dots.

  (Supplementary note 32) Any one of Supplementary notes 24 to 29, wherein an energy of electrons or holes in each quantum dot is made to coincide by applying an electric field in a direction parallel to a coupling direction of the coupled quantum dots. The wavelength converter as described in one.

  (Supplementary note 33) In the optical resonator, the i-type semiconductor layer including the coupled quantum dots is formed by a p-type distributed Bragg reflector having two types of semiconductor multilayer films having different refractive indexes and an n-type distributed Bragg reflector. 33. The wavelength conversion device according to any one of appendices 22 to 32, wherein the wavelength conversion device is sandwiched.

(Supplementary Note 34) The optical resonator includes an n-type or p-type distributed Bragg reflector integrated with the coupled quantum dot;
33. The wavelength converter according to any one of appendices 22 to 32, further comprising a reflecting mirror that can be moved independently of the coupled quantum dots.

10 first quantum dot 11 second quantum dot 12 n-type substrate 13 lower electrode 14 n-type DBR
15 i-type resonator 16 p-type DBR
17 Upper electrode 18 Micro hole 19 Lens 20 Valence band 21 Conductive band 22 Hole 23 Electron 24 Input single photon 25 Output single photon 26 Resonant energy 30 of optical resonator 30 Reflector 40 Nonlinear optical crystal 41 Prism 42 Band pass Filter 43 Input single photon 44 Output single photon 45 Pump light 100 Coupled quantum dot

Claims (10)

A coupled quantum dot having a first quantum dot and a second quantum dot coupled to each other;
An optical resonator containing the coupled quantum dots;
A voltage controller for controlling a voltage applied to the coupled quantum dots,
The energy difference between the energy level of one of the carriers of different polarity in the first quantum dot and the energy level of the other carrier matches the energy of the incident single photon,
The energy difference between the energy level of one of the carriers of different polarity in the second quantum dot and the energy level of the other carrier, or the energy level of the carrier in the first quantum dot Difference between the energy level of the second quantum dot and the energy level of the carrier having a polarity different from that of the carrier is equal to the resonance energy of the optical resonator.   When one hole is injected into the second quantum dot and the input single photon is absorbed to generate one electron and one hole in the first quantum dot, the first quantum dot 2. The electron in the quantum dot and the hole in the second quantum dot are recombined to produce an output single photon having an energy equal to the resonance energy. Wavelength converter.   When one electron is injected into the second quantum dot and the input single photon is absorbed to generate one electron and one hole in the first quantum dot, the first quantum dot The hole in a quantum dot and the electron in the second quantum dot are recombined to produce an output single photon having an energy equal to the resonance energy. Wavelength converter.   Injecting one hole into the second quantum dot and absorbing the input single photon to generate one electron and one hole in the first quantum dot, and the first and second When the energy levels of the electrons in the quantum dots are matched and the electrons in the first quantum dots are moved to the second quantum dots by a resonance tunnel, 2. The wavelength converter according to claim 1, wherein electrons and holes are recombined to generate an output single photon having energy equal to the resonance energy.   Injecting one electron into the second quantum dot and absorbing the input single photon to generate one electron and one hole in the first quantum dot, and the first and second When the energy levels of the holes in the quantum dots are matched and the holes in the first quantum dots are moved to the second quantum dots by a resonant tunnel, The wavelength conversion device according to claim 1, wherein an electron and a hole are recombined to generate an output single photon having energy equal to the resonance energy.   Absorbing the input single photon to generate one electron and one hole in the first quantum dot, and matching the energy level of the electrons in the first and second quantum dots, When electrons in the first quantum dot are moved to the second quantum dot by a resonance tunnel, holes in the first quantum dot and electrons in the second quantum dot are recombined. The wavelength converter according to claim 1, wherein an output single photon having energy equal to the resonance energy is generated.   Absorbing the input single photon to generate one electron and one hole in the first quantum dot, and matching the energy levels of the holes in the first and second quantum dots, When holes in the first quantum dot are moved to the second quantum dot by a resonance tunnel, electrons in the first quantum dot and holes in the second quantum dot are 2. The wavelength converter according to claim 1, wherein recombination generates an output single photon having an energy equal to the resonance energy.   In the optical resonator, the i-type semiconductor layer including the coupled quantum dots is sandwiched between a p-type distributed Bragg reflector and an n-type distributed Bragg reflector having two types of semiconductor multilayer films having different refractive indexes. The wavelength conversion device according to claim 1, wherein: The optical resonator includes an n-type or p-type distributed Bragg reflector integrated with the coupled quantum dot;
The wavelength conversion device according to claim 1, further comprising a reflecting mirror that can be moved independently of the coupled quantum dots. Controlling a voltage applied to a coupled quantum dot having a first quantum dot and a second quantum dot coupled to each other;
Absorbing the incident single photon into the first quantum dot to generate one electron and one hole each.
The energy difference between the energy level of one of the carriers of different polarity in the second quantum dot and the energy level of the other carrier, or the energy level of the carrier in the first quantum dot Difference between the energy level of a carrier having a polarity different from that of the carrier in the second quantum dot is equal to a resonance energy of an optical resonator containing the coupled quantum dot. Method.

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