JP6296548B2 - Photon generator and photon generation method - Google Patents

Description

  The present invention relates to a photon generator and a photon generation method for generating a single photon.

  In recent years, there is an increasing expectation for quantum information technology that manipulates the quantum state and uses it for information processing by precisely controlling the interaction between light and materials. Typical applications of quantum information technology are quantum cryptography (quantum key distribution) and quantum computation. By realizing these, it is possible to realize highly secure information communication and high-speed computation with a specific algorithm. The technology underlying quantum information technology is the creation of controlled quantum states. In particular, it is important to generate single-photon and entangled photon pairs with good controllability because the possibility of application to quantum cryptography communication is expanded.

  Many single-photon generators using semiconductor quantum dots have been studied from the viewpoint of solid materials, stable operation, and emission wavelength control. To date, single-photon generators have been realized mainly by optical excitation from the near-ultraviolet wavelength region to the wavelength band of optical fiber communications.

When using a single photon generator for the most basic quantum key distribution, as a performance index, the secondary photon correlation value g ⁽²⁾ (0) reflecting the degree of multiple photon generation, the light extraction efficiency h, Parameters such as repetition frequency and jitter are used. Among these, g ⁽²⁾ (0) is a parameter that directly represents the difference between a single photon generator and another light source. For typical light sources, g ⁽²⁾ (0) never falls below 1, but below 1 for a single photon generator and 0 for an ideal single photon generator. In practice, however, it is difficult to achieve g ⁽²⁾ (0) = 0 even if single photons are generated using a quantum two-level system such as a quantum dot. The cause is that light emission (background light emission) that cannot be removed from something other than the desired quantum dot occurs and is observed as if multiple photons have been generated, and one photoexcitation. An example is when a photon is generated multiple times from one quantum dot.

It is known that quasi-resonant excitation is effective as a technique for increasing the single photon property to approach g ⁽²⁾ (0) = 0 (see, for example, Non-Patent Documents 1 to 4). Quasi-resonant excitation refers to p-shell excitons of quantum dots (excitons consisting of one electron in the first excitation level of a conductor and one hole in the first excitation level of the valence band), etc. Energy of one LO phonon from s-shell excitons (excitons consisting of one electron in the ground level of the conductor and one hole in the ground level of the valence band) In this method, s-shell excitons relaxed from these levels to the ground state are irradiated as single photons.

FIG. 1 shows, as an example, the operation of a single photon generator by quasi-resonant excitation when the p-shell state is optically excited resonantly. When an excitation pulse having the same energy as the energy E _ex of the p-shell exciton is irradiated, a p-shell exciton is generated in the quantum dot with the time width τ _pulse of the excitation pulse. Thereafter, the p-shell excitons are relaxed to s-shell excitons with a relaxation time τ _relax and a single photon is generated with a recombination lifetime τ _X. By this method, excessive carrier generation can be suppressed and only the quantum dots used as a single photon generator can be selectively photoexcited. Light emission from other light emission sources (such as other quantum dots) that are excited simultaneously when the quantum dots are photoexcited is suppressed, and background light emission is reduced.

  In addition, a technique has been proposed in which quantum dots are arranged in a resonator so that emitted photons are made into a single spatial mode, thereby increasing the coupling efficiency with an optical element such as an optical fiber (for example, see Patent Document 1). This method uses an energy-tunable pump laser to optically excite excited excitons such as the p-shell, and to recombine s-shell excitons whose energy is relaxed to the ground state. Or used to generate entangled photon pairs.

Special table 2004-518275 gazette

Santori et al., Phys. Rev. Lett. 86, 1504 (2001) Malko et al., APL 88 081905 (2006) Kumano et al., J. Nanoelectron. Optoelectron. 1 p.39 (2006) K. Takemoto, et al., Phys.stat.sol. (C) 5, No. 9, 2699 (2008)

Even if quasi-resonant excitation such as p-shell exciton state is used, g ⁽²⁾ (0) = 0 is not generated in actual single photon generation, and multiple photons are generated. It is a problem to suppress the generation of multiple photons.

The reason why multiple photons are generated even when quasi-resonant excitation is used is considered to be that two or more photons are generated for one excitation light irradiation event from the s-shell state used as a single photon. The reason why two or more photons are generated by a single excitation pulse irradiation event in the single photon generator may be a re-excitation process that occurs within one excitation pulse irradiation. The process of re-excitation refers to the generation of excited excitons (for example, p-shell excitons) by the absorption of excitation light and the excited states before one irradiation of an excitation pulse having a specific time width τ _pulse is completed. Is the process in which the exciton of s is relaxed to the s-shell state exciton, recombination emission of the s-shell exciton, and p-shell exciton generation by reabsorption of excitation light. Since this re-excitation process occurs stochastically, there is a possibility that this process occurs once or a plurality of times depending on the excitation event, which causes the generation of a plurality of photons. While the transition time τ _relax of intraband transition (for example, relaxation from p-shell to s-shell) is about 10 ps, the time width τ _pulse of the excitation _pulse (typically 10 to 20 ps) is about the same. Alternatively, since it is more than that, a re-excitation process may occur. When reexcitation occurs, the single photon generation purity decreases.

  Therefore, as a means of solving the problem, in order to suppress the re-excitation process, the s-shell exciton molecular state (two electrons in the ground level of the conduction band and two positive states in the ground level of the valence band). Two s-shell exciton states consisting of holes) and the resonator effect are used. The energy of the excitation pulse from the outside is adjusted to an energy that enables generation of s-shell exciton molecules by two-photon absorption described later, and irradiation is performed. Using the resonator effect, the recombination lifetime of the first s-shell exciton molecular emission that occurs in the photo-excited s-shell exciton molecule state is controlled to be long, and subsequently By controlling the recombination lifetime of the s-shell exciton emission that occurs in a short time, the recombination lifetime of the s-shell exciton molecular emission that is sufficiently longer than the irradiation time of the excitation pulse is realized. The effect can be suppressed. This enhances the generation purity of single photons within a single excitation pulse irradiation event.

In this specification and claims, the term “s-shell exciton molecular state” means that two excitons exist in the s-shell state of a quantum dot, and “s-shell exciton state” "Means that one exciton exists in the s-shell state in the quantum dot. When the s-shell exciton molecule state emits recombination, a photon of E _BX , which is the recombination energy of the s-shell exciton molecule, is generated, and then the recombination energy of s-shell exciton, E _X Photons are generated. This is called recombination emission of s-shell excitons. S-shell exciton molecular recombination energy E _BX and s-shell exciton recombination energy E _X take different values due to Coulomb interaction between electrons and holes in the quantum dot. -Shell exciton recombination emission and s-shell exciton recombination emission have different wavelengths. Since the energy E _p of the excitation pulse is intermediate between E _X and E _BX , the quantum dot absorbs two photons in the excitation pulse, thereby generating an s-shell exciton molecular state. At this time, since E _X and E _BX and E _p take different energies, the photons have different wavelengths, and therefore can be identified by a filter.

From the above, the photon generator is
A single quantum dot formed on a semiconductor substrate;
An excitation light source that irradiates the quantum dots with excitation light to resonantly excite the s-shell exciton molecular state of the quantum dots;
Of the two s-shell excitons that form the s-shell exciton molecular state, the resonance energy resonates with the recombination energy of the s-shell exciton and does not resonate with the recombination energy of the s-shell exciton molecule. A resonator having
An optical filter for separating recombination emission of the s-shell exciton from recombination emission of the excitation light and the s-shell exciton molecule;
Is provided.

It is a figure which shows the single photon generation process by quasi-resonance excitation. It is a figure explaining the principle of single photon generation of a 1st embodiment. It is the schematic of the single photon generator of 1st Embodiment. It is a figure which shows an example of the resonator used with a single photon generator. It is a figure explaining the principle of single photon generation of 2nd Embodiment. It is the schematic of the single photon generator of 2nd Embodiment. It is a figure which shows the modification 1 of 1st Embodiment and 2nd Embodiment. 10 is a diagram showing an element structure used in Modification 1. FIG. It is a figure which shows the element structure used in the modification 2 of 1st Embodiment and 2nd Embodiment. 10 is a diagram showing another example of an element structure used in Modification 2. FIG.

<First Embodiment>
FIG. 2 is a diagram for explaining the principle of single photon generation according to the first embodiment. FIG. 2A shows the generation of s-shell exciton molecular states to a single quantum dot by irradiation with an excitation pulse that resonantly excites the s-shell exciton molecular states. The energy Ep of the excitation pulse is an intermediate energy between the recombination energy E _x of the s-shell exciton and the recombination energy E _BX of the s-shell exciton molecule, and Ep = (E _x + E _BX ) / 2 Fulfill.

In the embodiment, as will be described later, a small resonator is disposed around a single quantum dot to realize optical confinement. Resonator has a resonance energy that resonates with s- shell exciton energy E _X. When the resonance energy of the resonator and _{E cavity, E cavity = E X} , and satisfies the condition of E _cavity ≠ E _BX.

In FIG. 2 (B), of the s-shell exciton pairs excited to the s-shell exciton molecule state, the s-shell exciton molecule that recombines first (recombination energy is E _BX ) is recombined. Recombines with a lifetime (or emission lifetime) T _BX to generate a single photon. The recombination lifetime T _BX of the s-shell exciton molecule is several times longer than the recombination lifetime τ _BX of the s-shell exciton molecule without the resonator due to the resonator effect. How long it can be made depends on the pulse width τ _pulse of the excitation light, the material of the quantum dots, and the configuration of the resonator, but in the embodiment, T _BX is about three times t _BX . By increasing the recombination lifetime T _BX of the s-shell exciton molecule, re-excitation within the irradiation time τ _pulse is suppressed.

In FIG. 2C and FIG. 2D, the s-shell excitons with recombination energy E _X recombine with recombination lifetime T _X to generate a second single photon. The recombination lifetime T _X of the s-shell exciton is shorter than the recombination lifetime τ _X of the s-shell exciton without the resonator due to the resonator effect. In the embodiment, it is about 1/5. By discriminating two single photons having different energies with an optical filter, only a single photon having a desired energy can be extracted. In an embodiment, the second recombined s-shell exciton emission is extracted as a single photon.

Immediately after the recombination lifetime T _BX of the extended s-shell exciton molecule, the exciton emission is generated quickly, thereby suppressing the re-excitation within a single excitation pulse irradiation event. It can be produced with high purity.

Next, the effect of the resonator will be described. Placing a resonator around the single quantum dot that resonates with the recombination energy E _X of the s-shell exciton reduces the density of states of the photon with energy E _BX . On the other hand, the state density of photons with energy E _X increases. As a result, the emission lifetime T _BX of the s-shell exciton molecule is long and the recombination lifetime T _X of the s-shell exciton is short.

When there is no resonator effect, the recombination lifetime τ _X of a typical s-shell exciton is about 1 ns, and the recombination lifetime τ _BX of an s-shell exciton molecule is about 0.5 ns. By designing the resonance energy E _cavity of the resonator so that E _cavity = E _X and E _cavity ≠ E _BX , the recombination lifetime T _X of the s-shell exciton is shortened to about 0.2 ns, The recombination lifetime T _BX of the s-shell exciton molecule can be extended to about 1.5 ns.

When the transition time T _BX from the s-shell exciton molecule to the s-shell exciton extends to 1.5 ns due to the resonator effect, compared with the time width τ _pulse = 10 to 20 ps of a general excitation pulse light A sufficiently large value. The possibility of being re-excited within the time that the excitation pulse remains is negligibly small, and single photon purity is improved.

  FIG. 3 is a schematic configuration diagram of a single photon generator 10A using the s-shell exciton molecular state and the resonator effect. The single photon generator 10A includes an element unit 13 having a single quantum dot 15 and a resonator 14, an excitation pulse generator 11 that irradiates the quantum dot 15 with excitation light, and a single photon generated from the quantum dot 15. And an optical filter 12 for extracting a single photon having a desired energy.

The energy Ep of the excitation light is intermediate between the recombination energy E _X of the s-shell exciton in the s-shell exciton molecule state and the recombination energy E _BX of the s-shell exciton molecule as described above, and Ep = (E _X + E _BX ) / 2. The angle θ between the optical path of the excitation pulse generator 11 and the detection path of the optical filter 12 that detects a single photon can be set to any angle as long as optical excitation is realized. The excitation path and the detection path may be coaxial, such as θ = 0 °. The excitation pulse generator 11 is, for example, a pulse light source using a semiconductor laser diode.

The optical filter 12, in the example of FIG. 3, taken out only a single photon energy E _X. As a result, the output of the single-photon generator 10A is a single photon energy E _X.

  FIG. 4 shows a configuration example of the element unit 13. The element unit 13 includes a post-type resonator 14 as the resonator 14. The post-type resonator 14 has a configuration in which a resonator layer (cavity layer) 32 is sandwiched between a lower DBR (distributed Bragg reflector) 35 a and an upper DBR 35 b on a GaAs substrate 31. The quantum dot layer 33 having the quantum dots 15 is located in the central portion of the resonator layer 32 where the electric field strength is highest.

  The quantum dot layer 33 has, for example, InAs / GaAs quantum dots 15. Instead of the GaAs substrate 31, an InP substrate may be used, and InAs / InP quantum dots 15 may be used.

  The lower DBR 35a and the upper DBR 35b are obtained by alternately stacking crystal films having different refractive indexes. The stack of the lower DBR 35a and the upper DBR 35b may be an epitaxially grown GaAs / AlGaAs multilayer film or a multilayer film structure with an oxide film such as Si / SiO2 or SiO2 / TiO2. Process the stack into cylindrical posts using appropriate mask and dry etch conditions. The diameter of the post structure (diameter in the XY plane) is, for example, 2 μm or less.

The film thickness of the resonator layer 32 is a thickness that matches the emission wavelength (one wavelength) of the s-shell excitons. Film speed of the lower DBR35a upper BDR35b also resonates in s- shell exciton energy (recombination energy) E _x of the quantum dots 15, and the number of reflectance can be realized a high reflectivity of greater than about 99% Is set.

The condition imposed on the post-type resonator 14 is that the resonance energy E _cavity is equal to the s-shell exciton energy E _X of the quantum dot 15 and is different from the s-shell exciton molecular energy E _BX. . Since the s-shell excitons excited in the quantum dot 15 are affected by the Coulomb interaction between carriers, the luminescence reactivation is performed in the s-shell exciton state and in the s-shell exciton molecular state. The binding energy changes. This amount of energy change is called s-shell exciton molecular binding energy (ΔE _BX ). In a typical InAs / GaAs quantum dot or InAs / InP quantum dot, ΔE _BX has an energy of about 1 meV to several meV.

Due to the presence of the energy difference ΔE _BX , resonance excitation of the s-shell exciton molecular state is possible with energy separated by ΔE _BX / 2 from the recombination energy of the s-shell exciton. As described above, for excitation to the s-shell exciton molecular state, an excitation pulse having an energy Ep = (E _X + E _BX ) / 2 between s-shell exciton emission and s-shell exciton emission is used. use. By using the resonator 14, the transition time T _BX to the s-shell exciton state (see FIG. 2) is lengthened, and the transition time (recombination lifetime) T _X from the s-shell exciton state is controlled to be short. Can do. This improves the purity of single photons generated by one excitation pulse irradiation.

Second Embodiment
FIG. 5 is a diagram for explaining the principle of single photon generation according to the second embodiment. In the second embodiment, after irradiation of the excitation light (Ep) (FIG. 5A), a control pulse is irradiated after a time several times the pulse width τ _pulse (FIG. 5B) (FIG. 5B). FIG. 5C). The energy Ec of the control pulse is equal to the recombination energy E _BX of the s-shell exciton molecule (Ec = E _BX ). Upon receiving the control pulse Ec, the s-shell exciton molecule is recombined among the exciton pairs in the s-shell exciton molecule state to generate the first single photon. The duration (pulse width) of the control pulse is, for example, the same τ _{pulse as} that of the excitation pulse.

By irradiating the control pulse Ec with a time several times longer than the τ _pulse after the excitation pulse Ep, the s-shell is irradiated within the control pulse irradiation time (typical value is about τ _pulse = 10 to 20 ps). A coherent transition is made from the exciton molecular state (FIG. 5B) to the s-shell exciton state (FIG. 5D).

In the first embodiment, the transition time T _BX from the s-shell exciton molecule to the s-shell exciton state transits steadily with a time constant of about 1.5 ns after irradiation with the excitation pulse Ep. In the second embodiment, the transition time T _BX from the s-shell exciton molecule to the s-shell exciton state is definitely determined by the irradiation time τ _pulse of the control pulse Ec.

  FIG. 6 is a schematic configuration diagram of a single photon generator 10B of the second embodiment. The single photon generator 10B is obtained by adding a control pulse generator 16 to the single photon generator 10A of the first embodiment. The same components as those of the single photon generator 10A of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

The control pulse generator 16 emits a control pulse Ec at a level of the recombination energy E _BX of the s-shell exciton molecule. The condition imposed on the angle φ between the optical path of the control pulse generator 16 and the photon detection path by recombination light emission is that light irradiation is realized, and the excitation path and the detection path are such that φ = 0. It does not matter if it is coaxial. Further, the excitation pulse generator 11 and the control pulse generator 16 may be combined with one laser. In this case, it is possible to use a laser whose output level is variable and switch between the excitation light (Ep) for exciting the S-shell exciton molecular state and the control pulse (Ec = E _BX ). The resonator 14 may be a post-type resonator 14 as in the first embodiment.

In the method of the second embodiment, the recombination lifetime of the s-shell exciton molecule can be reduced from T _BX (for example, about 1.5 ns) to the control pulse time width τ _pulse (for example, 10 to 20 ps). Therefore, the repetition rate is improved.

Moreover, the jitter of the single photon generator 10B can be reduced. The jitter of a single photon is a deviation for each event of the emission time of a single photon that is determined probabilistically. In normal single photon generation, it is about the emission lifetime τ _X of an s-shell exciton. In the first embodiment, the sum of the lifetime T _X of the s-shell exciton shortened by the resonator effect and the lifetime T _BX of the s-shell exciton molecule lengthened by the resonator effect is the single photon generator 10A. Jitter. In the second embodiment, the transition to the s-shell exciton state occurs coherently by the introduction of the control pulse Ec. Therefore, the jitter of the single photon generator 10B is only about the lifetime T _x of the s-shell exciton shortened by the resonator effect.

<Modification 1>
FIG. 7 shows a first modification of the single photon generator of the first embodiment and the second embodiment. FIG. 7A is a schematic configuration diagram of a single photon generator 10C which is a modification of the single photon generator 10A of the first embodiment, and FIG. 7B is a single photon generator of the second embodiment. It is a schematic block diagram of single photon generator 10D which is a modification of apparatus 10B.

  In these modified examples, the element unit 23 includes a quantum dot 15, a resonator 14, and a pair of electrodes 27 that are arranged with the quantum dot 15 interposed therebetween. The electrode 27 controls the electric field of the energy of the s-shell excitons of the quantum dots 15.

  By applying a voltage to the pair of electrodes 27, the Stark effect is used to finely adjust the s-shell exciton energy in the quantum dots 15. By applying an appropriate electric field, the s-shell exciton energy and the resonance energy of the resonator 14 are matched, and the resonator effect (the recombination lifetime of the s-shell exciton molecule is prolonged, Ensure recombination life is shortened).

In the quantum dots 15 formed in a self-forming manner by a technique such as the Stranski krastanow method, the energy becomes non-uniform due to size variation. In this case, even if the resonator 14 designed in accordance with the recombination energy of the s-shell excitons of the quantum dots 15 is arranged, the recombination energy E _x of the s-shell excitons due to the size variation of the quantum dots 15. There is a possibility that a slight energy difference exists between the resonance energy E _cavity of the resonator 14. Therefore, the resonance condition is realized by finely adjusting the s-shell exciton energy by applying an external electric field.

  FIG. 8 is a diagram showing a configuration example of the element unit 23 using the electrode 27 structure of FIG. 8A is a cross-sectional view, and FIG. 8B is a plan view.

  In the element portion 23, the post-type resonator 14 is formed on the GaAs substrate 41 via the doped layer 42. The doped layer 42 is a semiconductor layer doped with n-type or p-type impurities. A quantum dot 15 is disposed in the center of the post-type resonator 14.

  An insulating film 43 having a low refractive index is formed around the post-type resonator 14 and processed into a predetermined shape. A top electrode 27 a is formed on the insulating film 43. The top electrode 27 a has a ring electrode 27 b that contacts the post-type resonator 14. When light is taken out in the vertical direction of the substrate 41 (upward on the paper surface), it is desirable to remove reflection and shielding around the central axis of the post-type resonator 14 having a strong electric field strength. Therefore, a ring electrode 27b connected to the upper electrode 27a is provided. A bottom electrode 27 c is disposed on the doped layer 42. The dielectric layer at the upper end and the lower end of the DBR portion (see FIG. 4) of the post resonator 14 may be doped with p-type or n-type impurities.

By applying a voltage between the top electrode 27a and the bottom electrode 27c, for detecting the voltage value of the E _cavity = E _X. The single photon generators 10C and 10D are operated with the detected voltage value. Thus, shift and resonant energy E _cavity by production error of the element portion 23, the recombination energy E _X due to the shape variation of the quantum dots 15, even when deviation of E _BX, by adjusting the E _X by an external electric field The conditions of E _cavity = E _X and E _cavity ≠ E _BX can be realized.

<Modification 2>
FIG. 9 shows a second modification of the first embodiment and the second embodiment. In the second modification, a two-dimensional slab slab-shaped photonic crystal 50 is used as the resonator 14. The photonic crystal 50 has periodic holes 52. By designing the diameter and interval of the holes 52 and the shape / size of the defect structure, the conditions of E _cavity = E _X and E _cavity ≠ E _BX can be achieved.

  The photonic crystal 50 has a resonator layer 51. The resonator layer 51 has a p-i-n doped structure. Although not shown, the defect structure in the photonic crystal 50 functions as the resonator 14. Similarly, although not shown, a quantum dot layer having quantum dots 15 is arranged at the center of the i layer where the electric field strength is considered to be maximum in the resonator layer 51.

  As the resonator layer 51, a GaAs-based or InP-based material can be used. An etching sacrificial layer 72 made of a different semiconductor material is disposed between the substrate 71 and the p-i-n type resonator layer 51. As the etching sacrificial layer 71, for example, an AlGaAs layer can be used if the resonator layer 51 is a GaAs-based material, and an InGaAs layer can be used if the resonator layer 51 is an InP-based material. After resist patterning by electron beam exposure, the etching sacrificial layer 72 is selectively etched to create an air portion (cavity) 74, thereby realizing a slab type structure.

  FIG. 10 shows a configuration example in which the electrode structure 75 is provided in the photonic crystal 60. The photonic crystal 60 has a configuration in which an n-type doped layer 61n, a non-doped layer 61i, and a p-type doped layer 61p are stacked in this order as the resonator layer 61. A quantum dot layer having the quantum dots 15 is arranged at the center of the non-doped layer 61 i that is considered to have the maximum electric field strength in the resonator layer 61. The material of the resonator layer 61 and the arrangement of the etching sacrificial layer are the same as those in FIG.

Around the defect (not shown) of the phytonic crystal 60, a ring electrode 75b as a top electrode and an electrode line 75a connected thereto are formed. In addition, the bottom electrode 75c is arranged at a location away from the resonator on the n-type doped layer 61n. By applying an electric field between the ring electrode 75a and the bottom electrode 75c, detects a voltage value to be E _cavity = E _X, single photon generator 10C, it is possible to operate the 10D in the voltage value.

  The above-described embodiments and modifications realize a single photon generator with high purity.

  The present invention is not limited to the above-described embodiments and modifications, and various modifications can be made. For example, the optical filter 12 derives recombination emission of s-shell excitons (second generated single photon) from excitation light and recombination emission of s-shell exciton molecules (first single photon). It is good also as a structure which takes out separately. In addition, the recombination emission of the s-shell exciton molecule (first generated single photon) is separated and extracted from the excitation light and the recombination emission of the s-shell exciton (second single photon). It is good.

The following notes are presented for the above explanation.
(Appendix 1)
A single quantum dot formed on a semiconductor substrate;
An excitation light source that irradiates the quantum dots with excitation light to resonantly excite the s-shell exciton molecular state of the quantum dots;
Of the two s-shell excitons that form the s-shell exciton molecular state, the resonance energy resonates with the recombination energy of the s-shell exciton and does not resonate with the recombination energy of the s-shell exciton molecule. A resonator having
An optical filter for separating recombination emission of the s-shell exciton from recombination emission of the excitation light and the s-shell exciton molecule;
A photon generator characterized by comprising:
(Appendix 2)
The recombination energy E _X of the s- shell _excitons, the recombination d E energy of E _BX of the s- shell _biexciton, when the energy of the excitation light and E _P, the excitation light,
E _P = (E _X + E _BX ) / 2
The photon generator according to appendix 1, wherein:
(Appendix 3)
A control light source that generates control light having an energy equal to the recombination energy E _BX of the s-shell exciton molecule;
The control light source irradiates the quantum dots with the control light after a period of several times the pulse width of the excitation light after the excitation light irradiation. The photon generator according to appendix 1 or 2.
(Appendix 4)
The excitation light source is a variable light source capable of switching between the excitation light for resonantly exciting the s-shell exciton molecule state and a control light equal to the recombination energy of the s-shell exciton molecule,
The supplementary light source 1 or 2, wherein the excitation light source irradiates the quantum dots with the control light after a time several times the pulse width of the excitation light after the excitation light irradiation. Photon generator.
(Appendix 5)
A pair of electrodes for applying an electric field to the quantum dots;
The photon generator according to any one of appendices 1 to 4, further comprising:
(Appendix 6)
The photon according to any one of appendices 1 to 5, wherein the resonator is a post-type resonator, and the quantum dot is disposed at a position where the electric field strength is strongest in the post-type resonator. Generator.
(Appendix 7)
The resonator is a resonator using a photonic crystal, and the quantum dot is arranged at a position where the electric field strength is the strongest in the photonic crystal. The photon generator as described.
(Appendix 8)
A resonator having a resonance energy around a single quantum dot that resonates with the recombination energy of the s-shell exciton of the quantum dot and does not resonate with the recombination energy of the s-shell exciton molecule of the quantum dot And place
The quantum dot is irradiated with excitation light and resonantly excited into the s-shell exciton molecular state,
Separating the recombination emission of the s-shell exciton from the recombination emission of the excitation light and the s-shell exciton molecule;
A photon generation method characterized by the above.
(Appendix 9)
The recombination energy E _X of the s- shell _excitons, the recombination energy of E _BX of the s- shell _biexciton, when the energy of the excitation light and E _P, the excitation light,
E _P = (E _X + E _BX ) / 2
The photon generation method according to appendix 8, wherein:
(Appendix 10)
After the irradiation of the excitation light, after a time several times the pulse width of the excitation light, the quantum dot is irradiated with a control pulse equal to the recombination energy of the s-shell exciton molecule,
Then separating the recombination emission of the s-shell exciton from the excitation light and the recombination emission of the s-shell exciton molecule;
10. The photon generation method according to appendix 8 or 9, wherein
(Appendix 11)
Using a variable energy light source, the quantum dots are irradiated with the excitation light,
The energy of the light source is switched after the irradiation of the excitation light, and after a time several times the pulse width of the excitation light, a control pulse equal to the recombination energy of the s-shell exciton molecule is applied to the quantum dot. Irradiate
Then separating the recombination emission of the s-shell exciton from the excitation light and the recombination emission of the s-shell exciton molecule;
The photon generating method according to any one of appendices 8 to 10, characterized in that:
(Appendix 12)
Applying an electric field to the quantum dots to match the recombination energy of the s-shell excitons of the quantum dots with the resonance energy of the resonator;
The photon generation method according to any one of appendices 8 to 11, characterized in that:

10A, 10B, 10C, 10D Single photon generator 11 Excitation pulse generator (excitation light source)
DESCRIPTION OF SYMBOLS 12 Optical filter 13, 23 Element part 14 Resonator 15 Quantum dot 16 Control pulse generator 27, 75 electrode 27a Top electrode 27b, 75b Ring electrode 27c, 75c Bottom electrode 31, 41, 71 Semiconductor substrate 32, 51, 61 Resonator Layer 33 Quantum dot layer 50, 60 Photonic crystal

Claims (8)

A single quantum dot formed on a semiconductor substrate;
An excitation light source that irradiates the quantum dots with excitation light to resonantly excite the s-shell exciton molecular state of the quantum dots;
Of the two s-shell excitons that form the s-shell exciton molecular state, the resonance energy resonates with the recombination energy of the s-shell exciton and does not resonate with the recombination energy of the s-shell exciton molecule. A resonator having
An optical filter for separating recombination emission of the s-shell exciton from recombination emission of the excitation light and the s-shell exciton molecule;
A photon generator characterized by comprising: The recombination energy E _X of the s- shell _excitons, the recombination d E energy of E _BX of the s- shell _biexciton, when the energy of the excitation light and E _P, the excitation light,
E _P = (E _X + E _BX ) / 2
The photon generator according to claim 1, wherein: A control light source that generates control light having an energy equal to the recombination energy of the s-shell exciton molecule;
The control light source irradiates the quantum dots with the control light after waiting for several times the pulse width of the excitation light after irradiation with the excitation light. Item 3. The photon generator according to Item 1 or 2. The excitation light source is a variable light source capable of switching between the excitation light for resonantly exciting the s-shell exciton molecule state and a control light equal to the recombination energy of the s-shell exciton molecule,
The said excitation light source irradiates the said quantum dot with the said control light, after the time of several times the pulse width of the said excitation light after irradiation of the said excitation light, It is characterized by the above-mentioned. The photon generator as described. A resonator having a resonance energy around a single quantum dot that resonates with the recombination energy of the s-shell exciton of the quantum dot and does not resonate with the recombination energy of the s-shell exciton molecule of the quantum dot And place
The quantum dot is irradiated with excitation light and resonantly excited into the s-shell exciton molecular state,
Separating the recombination emission of the s-shell exciton from the recombination emission of the excitation light and the s-shell exciton molecule;
A photon generation method characterized by the above. The recombination energy E _X of the s- shell _excitons, the recombination energy of E _BX of the s- shell _biexciton, when the energy of the excitation light and E _P, the excitation light,
E _P = (E _X + E _BX ) / 2
The photon generation method according to claim 5, wherein: After the irradiation of the excitation light, after a time several times the pulse width of the excitation light, the quantum dot is irradiated with a control pulse equal to the recombination energy of the s-shell exciton molecule,
Then separating the recombination emission of the s-shell exciton from the excitation light and the recombination emission of the s-shell exciton molecule;
The photon generation method according to claim 5 or 6, wherein Using a variable energy light source, the quantum dots are irradiated with the excitation light,
The energy of the light source is switched after the irradiation of the excitation light, and after a time several times the pulse width of the excitation light, a control pulse equal to the recombination energy of the s-shell exciton molecule is applied to the quantum dot. Irradiate
Then separating the recombination emission of the s-shell exciton from the excitation light and the recombination emission of the s-shell exciton molecule;
The photon generating method according to any one of claims 5 to 7, wherein

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