Two-photon excitation method and device based on microcavity enhanced solid-state two-photon source, and quantum optical device

Abstract

The invention provides a two-photon excitation method and device based on a microcavity enhanced solid-state two-photon source and a quantum optical device. The microcavity enhanced solid-state two-photon source at least comprises a substrate layer, a first reflecting layer, a cavity center layer and a second reflecting layer, and the semiconductor quantum dots are arranged in the cavity center layer. The two-photon excitation method comprises the following steps: exciting a semiconductor quantum dot from a ground state to a first shell bright double-exciton state based on a preset excitation mode and a phonon-assisted relaxation mode; obtaining a first photon based on spontaneous radiation of a bright double-exciton state of the first shell layer; the first photons and a cavity film of the cavity center layer resonate to generate cavity photons, the cavity photons are excited and radiated to obtain second photons, and the second photons and the first photons form two photons.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state two-photon sources, and in particular to a two-photon excitation method and device based on a microcavity enhanced solid-state two-photon source, and a quantum optical device. Background Art

[0002] A solid-state two-photon source is a quantum optical device that generates entangled two-photon states in a solid-state system. Its main feature is that it uses the properties of solid-state materials to achieve the generation and manipulation of two photons. Solid-state two-photon sources have important application potential in the fields of quantum information processing, quantum communication, and quantum networks.

[0003] Existing solid-state two-photon sources may include microlens-enhanced solid-state two-photon sources, which can generate two-photons based on the radiation cascade of zero-binding-energy biexcitons-excitons in semiconductor quantum dots (QDs) of solid-state materials such as In(Ga)As. This type of solid-state two-photon source can reduce the light field leakage of the underlying substrate based on a Bragg reflector, and can increase the photon extraction efficiency by using a microlens on the upper surface.

[0004] However, the inventors found that the microlens-enhanced solid-state two-photon source only uses the microlens on the upper surface and the Bragg reflector on the substrate to improve the two-photon collection efficiency from the perspective of geometric optics. Therefore, this type of solid-state two-photon source cannot solve the problems of low two-photon spontaneous emission rate and large side loss of the device.

[0005] For example, due to the relatively weak coupling between the light field and the semiconductor quantum dots, the Purcell enhancement effect of the cavity membrane is lacking (referring to the degree of enhancement of the spontaneous emission rate in a specific optical environment), so the two-photon spontaneous emission rate of this type of solid-state two-photon source is low, limiting the upper limit of the intrinsic yield of two-photons. In addition, due to the low two-photon spontaneous emission coupling factor of this type of solid-state two-photon source, the side loss of the device accounts for a large proportion, which limits the collection efficiency of two-photons. Summary of the invention

[0006] According to one aspect of the present invention, the present invention provides a two-photon excitation method based on a microcavity enhanced solid-state two-photon source. The microcavity enhanced solid-state two-photon source comprises at least a substrate layer, a first reflection layer, a cavity center layer and a second reflection layer, and a semiconductor quantum dot is arranged in the cavity center layer. The two-photon excitation method comprises: based on a preset excitation mode and a phonon-assisted relaxation mode, the semiconductor quantum dot is excited from a ground state to a first shell bright biexciton state; based on the spontaneous radiation of the first shell bright biexciton state, a first photon is obtained; the first photon resonates with a cavity membrane of the cavity center layer to generate a cavity photon, the cavity photon is stimulated to radiate, and a second photon is excited, and the second photon and the first photon form a two-photon.

[0007] According to some embodiments of the present invention, exciting semiconductor quantum dots from a ground state to a first-shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode includes: exciting semiconductor quantum dots from a ground state to a second-shell dark exciton state by a preset laser; relaxing the second-shell dark exciton state to a first-shell dark exciton state based on phonon assistance; exciting the first-shell dark exciton state to a second-shell dark biexciton state by a preset laser; and relaxing the second-shell dark biexciton state to a first-shell bright biexciton state based on phonon assistance.

[0008] According to some embodiments of the present invention, the first shell is an S shell.

[0009] According to some embodiments of the present invention, the second shell layer is a P shell layer.

[0010] According to another aspect of the present invention, the present invention provides a two-photon excitation system based on a microcavity-enhanced solid-state two-photon source, including a microcavity-enhanced solid-state two-photon source, a laser excitation device, and a phonon-assisted relaxation device. The microcavity-enhanced solid-state two-photon source includes a substrate layer, a first reflection layer, a cavity center layer, and a second reflection layer, wherein semiconductor quantum dots are arranged in the cavity center layer; a laser excitation device; and a phonon-assisted relaxation device, wherein the laser excitation device excites the semiconductor quantum dots from the ground state to the first shell bright biexciton state based on a preset excitation mode and the phonon-assisted relaxation device; wherein, a first photon is obtained based on spontaneous radiation of the first shell bright biexciton state, and the first photon resonates with the cavity membrane of the cavity center layer to generate a cavity photon, the cavity photon is stimulated to radiate, and a second photon is excited, and the second photon forms a two-photon with the first photon.

[0011] According to some embodiments of the present invention, the laser excitation device excites the semiconductor quantum dot from the ground state to the second shell dark exciton state by a preset laser; the phonon-assisted relaxation device relaxes the second shell dark exciton state to the first shell dark exciton state based on phonon assistance; the laser excitation device excites the first shell dark exciton state to the second shell dark biexciton state by a preset laser; and the phonon-assisted relaxation device relaxes the second shell dark biexciton state to the first shell bright biexciton state based on phonon assistance.

[0012] According to some embodiments of the present invention, the first shell is an S shell.

[0013] According to some embodiments of the present invention, the second shell layer is a P shell layer.

[0014] According to another aspect of the present invention, the present invention provides a quantum optical device, which comprises the two-photon excitation device as described above.

[0015] Beneficial Effects

[0016] The present invention can excite semiconductor quantum dots from a ground state to a first-shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode, and obtain a first photon based on spontaneous radiation of the first-shell bright biexciton state. The first photon resonates with a cavity membrane of a cavity center layer to generate a cavity photon. The cavity photon is stimulated to radiate and excites a second photon, so that the second photon and the first photon form a two-photon.

[0017] The present invention resonantly couples semiconductor quantum dots with a microcavity-enhanced solid-state two-photon source with a high Purcell enhancement effect, and can generate high-brightness energy degenerate photon pairs through a zero-binding-energy biexciton-exciton radiation cascade. Due to the Purcell enhancement effect of the cavity membrane, the rate of the biexciton-exciton radiation cascade is also significantly improved. In addition, the spontaneous radiation coupling factor of the two-photon to the cavity membrane is increased, the side loss of the device is reduced, and the collection efficiency of the two-photon is improved.

[0018] The existing microlens-enhanced solid-state two-photon source can achieve a two-photon detection count rate of 234KHz under the condition of continuous light excitation of the P shell. The microcavity-enhanced solid-state two-photon source provided by the present invention can achieve a two-photon detection count rate of 64MHz under the condition of continuous light excitation of the P shell. The brightness of the two-photons collected by the present invention is at least 2 orders of magnitude higher than that of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A schematic diagram showing the structure of a microcavity enhanced solid-state two-photon source according to an embodiment of the present invention;

[0021] Figure 2 A schematic diagram showing a flow chart of a two-photon excitation method according to an embodiment of the present invention;

[0022] Figure 3 A schematic diagram showing the process of first shell bright biexciton state excitation according to an embodiment of the present invention;

[0023] Figure 4 An exemplary schematic diagram showing the excitation of the first shell bright biexciton state according to an embodiment of the present invention;

[0024] Figure 5 A schematic diagram showing a comparison of biexciton lifetimes in a resonant situation and a non-resonant situation according to an embodiment of the present invention.

[0025] Description of reference numerals:

[0026] A microcavity enhanced solid-state two-photon source 1; a substrate layer 10; a first reflection layer 20; a cavity center layer 30; a second reflection layer 40; and a semiconductor quantum dot 50. DETAILED DESCRIPTION

[0027] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present invention will be comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0028] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices, etc. may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0029] In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or devices.

[0030] The terms "first", "second" and the like in the specification, claims and the above drawings of the present invention are used to distinguish different objects rather than to describe a specific order.

[0031] The technical solution of the present invention is described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0032] The prior art generally relies on probabilistic nonlinear optical processes to generate two-photon states. For example, by using down-converted photons and post-selection techniques, higher-quality entangled states can be generated. However, the inventors found that as the number of photons increases, the probability of generating two-photon states in this way decreases exponentially. And when each process in this way generates photon pairs that follow Poisson distribution statistics, there is a non-zero probability of generating zero or more pairs.

[0033] In the prior art solution, bi-photons can also be generated by spontaneous radiation of bi-exciton states in semiconductor quantum dots (QDs). The bi-exciton state of semiconductor quantum dots consists of two bound electron-hole pairs. Due to Coulomb interaction and exchange interaction, the bi-exciton state of semiconductor quantum dots has limited binding energy compared to two unbound exciton states. In solid-state materials such as InGaAs or GaAs material systems, the binding energy can generally be several millielectron volts. Based on the larger binding energy of the bi-exciton state, the bi-exciton state can be prepared by coherent two-photon excitation, and then the bi-exciton-exciton radiation cascade single-photon process can be used to generate indistinguishable entangled photon pairs.

[0034] In addition, based on the biexciton state theory that the biexciton state of semiconductor quantum dots has a limited binding energy, two-photon pairs can also be generated through spontaneous two-photon radiation. For example, the high-quality factor cavity membrane can be fine-tuned to resonate with half the energy of the biexciton. This setting can enhance the spontaneous two-photon emission rate and suppress the single-photon cascade emission. Therefore, this process can improve the efficiency and purity of emitting two photons simultaneously to the cavity membrane.

[0035] It is understandable that when the binding energy of the biexciton state of the semiconductor quantum dot disappears, the binding energy of the biexciton state in the semiconductor quantum dot can be adjusted to zero by fine-tuning the aspect ratio of the semiconductor quantum dot size through growth conditions, or by using an external strain field. That is, it can be characterized that the semiconductor quantum dots with binding energy have super-aggregation behavior in the photon autocorrelation measurement of spontaneous radiation under low-speed non-resonant optical pumping, and have the potential for effective two-photon states.

[0036] According to one aspect of the present invention, the present invention provides a two-photon excitation method based on a microcavity enhanced solid-state two-photon source. Figure 1 A schematic structural diagram of a microcavity enhanced solid-state two-photon source according to an embodiment of the present invention is shown.

[0037] According to an example embodiment, Figure 1 As shown, the microcavity enhanced solid-state two-photon source 1 comprises a substrate layer 10, a first reflective layer 20, a cavity center layer 30 and a second reflective layer 40. The semiconductor quantum dot 50 is arranged in the cavity center layer 30.

[0038] For example, Figure 1As shown, the substrate layer 10 may be a GaAs layer. The first reflective layer 20 may include GaAs layers and AlGaAs layers grown alternately in a first preset number of pairs (e.g., 30 pairs). The second reflective layer 40 may include GaAs layers and AlGaAs layers grown alternately in a second preset number of pairs (e.g., 18 pairs).

[0039] Exemplarily, the thickness d of the GaAs layer and the AlGaAs layer may be a quarter of the dielectric wavelength.

[0040] According to an example embodiment, the semiconductor quantum dot 50 is a quantum dot with zero binding energy. Figure 1 As shown, the semiconductor quantum dot 50 is disposed in the cavity center layer 30. The semiconductor quantum dot 50 may be an In(Ga)As quantum dot. The In(Ga)As quantum dot may be grown at the center of the cavity center layer 30 by molecular beam epitaxy (MBE).

[0041] Figure 2 FIG. 2 is a flow chart showing a two-photon excitation method according to an embodiment of the present invention. Figure 2 As shown, the two-photon excitation method may include steps S100-S300.

[0042] According to an example embodiment, in step S100 , a semiconductor quantum dot is excited from a ground state to a first shell biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode.

[0043] Optionally, the first shell layer may be an S shell layer, and the second shell layer may be a P shell layer.

[0044] The S shell and P shell of semiconductor quantum dots are important components of their electronic structure. The S shell is the lowest energy shell in quantum dots and usually corresponds to the ground state of electrons. In semiconductor quantum dots, electrons in the S shell can be transferred to higher energy levels, such as the P shell, through the tunneling effect. This transfer process can be achieved through laser excitation. The P shell is located above the S shell and is one of the higher energy levels in semiconductor quantum dots. Electrons in the P shell can relax to the S shell by releasing phonons.

[0045] For example, the preset excitation method may be to use optical pumping based on pulsed laser to excite the ground state of semiconductor quantum dots; the phonon-assisted relaxation method may be that in certain physical systems, phonons (quantized form of lattice vibrations) participate in and promote the relaxation of electrons or other particles.

[0046] Based on the quantum physics properties of semiconductor quantum dots, semiconductor quantum dots can be excited from the ground state to the S-shell bright biexciton state (i.e., the first-shell bright biexciton state) based on a preset excitation method and a phonon-assisted relaxation method.

[0047] Figure 3 A schematic diagram showing the process of first shell bright biexciton state excitation according to an embodiment of the present invention; Figure 4 An exemplary schematic diagram showing the first shell bright biexciton state excitation according to an embodiment of the present invention.

[0048] Alternatively, if Figure 3 As shown, step S100 may also include steps S110 to S140.

[0049] In step S110, the semiconductor quantum dot is excited from the ground state to the second shell dark exciton state by a preset laser.

[0050] In step S120 , the second shell dark exciton state is relaxed to the first shell dark exciton state based on phonon assistance.

[0051] In step S130 , a first shell dark exciton state is excited to a second shell dark biexciton state by a preset laser.

[0052] In step S140 , the second shell dark biexciton state is relaxed to the first shell bright biexciton state based on phonon assistance.

[0053] For example, taking the first shell as the S shell and the second shell as the P shell, Figure 4 As shown, in response to the user's operation instruction, the semiconductor quantum dots are excited by 888nm 5 picosecond pulse laser to excite the P shell dark exciton state, and then the P shell dark exciton state is relaxed to the S shell dark exciton state by phonon-assisted relaxation.

[0054] Since the S-shell dark exciton state has a long lifespan, the 888nm 5-picosecond pulse laser can also excite the S-shell dark exciton state to the P-shell dark biexciton state before the S-shell dark exciton state recombine. Finally, the P-shell dark biexciton state can be relaxed to the S-shell bright biexciton state again through phonon-assisted relaxation.

[0055] According to example embodiments, in step S200 , a first photon is obtained based on spontaneous emission of a first shell bright biexciton state.

[0056] For example, Figure 4 As shown, the S-shell bright biexciton state to the S-shell bright single exciton state can radiate a single photon to the cavity membrane 30 in the cavity center layer through spontaneous radiation, thereby obtaining the first photon.

[0057] According to an example embodiment, in step S300, a first photon resonates with a cavity membrane of the cavity central layer 30 to generate a cavity photon, and the cavity photon is stimulated to radiate and excite a second photon, and the second photon and the first photon form a double photon.

[0058] For example, the first photon generated in step S200 is collected by the cavity membrane. Since the frequency of the first photon is the same as the frequency of the cavity membrane (the frequency of the cavity membrane is determined by the structure of the microcavity enhanced solid-state two-photon source), the first photon resonates with the cavity membrane, thereby generating a cavity photon and obtaining a second photon in the form of stimulated radiation.

[0059] It can be understood here that the efficient occupation of the biexciton state can be achieved by exciting the long-lived intermediate exciton state (S shell dark exciton state) of the P shell. The indistinguishability of energy and polarization in the biexciton-single exciton radiation cascade can make the first photon stimulate the stimulated radiation of the single exciton state to produce a second photon, so that the second photon and the first photon can form two-photon radiation.

[0060] Figure 5 A schematic diagram showing a comparison of biexciton lifetimes in a resonant situation and a non-resonant situation according to an embodiment of the present invention.

[0061] like Figure 5 As shown, based on the comparison of the biexciton lifetime under resonant conditions and the biexciton lifetime under non-resonant conditions, it is obvious that in the two-photon excitation method provided by the present invention, the biexciton lifetime under resonant conditions is significantly higher than that under non-resonant conditions.

[0062] As an embodiment, the diameter of the microcavity-enhanced solid-state two-photon source can be 2.4 um, with a small mode volume, and the quality factor Q can reach 9000, so the microcavity-enhanced solid-state two-photon source provided by the present invention has a large Purcell enhancement effect. For example, the Purcell factor can reach 10.97.

[0063] For example, the superconducting nanowire single-photon detector records the experimental data of the counting rate changing with power when detecting the two orthogonal polarizations of H and V of biexcitons. According to the experimental data of the present invention, the saturation counting rates of the two radiation paths of H and V can reach 34.4MHZ and 29.6MHZ respectively.

[0064] Under the excitation of less than 3uw, the present invention can observe the superbunching effect by arranging the biexciton state through the long-lived intermediate exciton state (such as the S shell dark exciton state), such as the maximum second-order autocorrelation function zero point value can reach 1947. Exemplarily, when the semiconductor quantum dot reaches saturation, the second-order autocorrelation function zero point value is 2.5, and the corresponding two-photon emission probability is 0.2. It can be seen that the two-photon radiation rate and extraction efficiency of the microcavity enhanced solid-state two-photon source are significantly improved.

[0065] Through the above embodiments, the present invention can excite semiconductor quantum dots from the ground state to the first shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode, and obtain a first photon based on the spontaneous radiation of the first shell bright biexciton state. The first photon resonates with the cavity membrane of the cavity center layer to generate a cavity photon. The cavity photon is stimulated to radiate and excites to obtain a second photon, so that the second photon and the first photon form a two-photon.

[0066] The present invention resonantly couples semiconductor quantum dots with a microcavity-enhanced solid-state two-photon source with a high Purcell enhancement effect, and can generate high-brightness energy degenerate photon pairs through a zero-binding-energy biexciton-exciton radiation cascade. Due to the Purcell enhancement effect of the cavity membrane, the rate of the biexciton-exciton radiation cascade is also significantly improved. In addition, the spontaneous radiation coupling factor of the two-photon to the cavity membrane is increased, the side loss of the device is reduced, and the collection efficiency of the two-photon is improved.

[0067] The microlens-enhanced solid-state two-photon source can achieve a two-photon detection count rate of 234KHz under the condition of continuous light excitation of the P shell. The microcavity-enhanced solid-state two-photon source provided by the present invention can achieve a two-photon detection count rate of 64MHz under the condition of continuous light excitation of the P shell. The brightness of the two-photons collected by the present invention is at least 2 orders of magnitude higher than that of the prior art.

[0068] According to another aspect of the present invention, the present invention provides a two-photon excitation device based on a microcavity enhanced solid-state two-photon source. The two-photon excitation device comprises a microcavity enhanced solid-state two-photon source, a laser excitation device and a phonon-assisted relaxation device.

[0069] The specific structure of the microcavity enhanced solid-state two-photon source has been described in detail above and will not be repeated here.

[0070] The laser excitation device can be a device that emits a target laser, such as optical pumping. The phonon-assisted relaxation device can be a device that uses phonons (ie, quanta of lattice vibrations) to accelerate or regulate the relaxation process of electrons or other particles in a material.

[0071] According to example embodiments, the laser excitation device excites the semiconductor quantum dot from a ground state to a first shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation device.

[0072] Optionally, the first shell layer may be an S shell layer, and the second shell layer may be a P shell layer.

[0073] The S shell and P shell of semiconductor quantum dots are important components of their electronic structure. The S shell is the lowest energy shell in quantum dots and usually corresponds to the ground state of electrons. In semiconductor quantum dots, electrons in the S shell can be transferred to higher energy levels, such as the P shell, through the tunneling effect. This transfer process can be achieved through laser excitation. The P shell is located above the S shell and is one of the higher energy levels in semiconductor quantum dots. Electrons in the P shell can relax to the S shell by releasing phonons.

[0074] Based on the quantum physical properties of semiconductor quantum dots, semiconductor quantum dots can be excited from the ground state to the S shell bright biexciton state (i.e., the first shell bright biexciton state) based on a laser excitation device and a phonon-assisted relaxation device.

[0075] Optionally, the laser excitation device excites the semiconductor quantum dot from the ground state to the second shell dark exciton state by a preset laser. The phonon-assisted relaxation device relaxes the second shell dark exciton state to the first shell dark exciton state based on phonon-assisted relaxation. The laser excitation device excites the first shell dark exciton state to the second shell dark biexciton state by a preset laser.

[0076] The phonon-assisted relaxation device relaxes the second shell dark biexciton state to the first shell bright biexciton state based on phonon-assisted relaxation.

[0077] For example, taking the first shell as the S shell and the second shell as the P shell, Figure 4 As shown, in response to the user's operation instruction, the laser excitation device excites the semiconductor quantum dot through a 5-picosecond pulse laser of 888nm to excite the P-shell dark exciton state. Then, the phonon-assisted relaxation device relaxes the P-shell dark exciton state to the S-shell dark exciton state through phonon-assisted relaxation.

[0078] Since the S-shell dark exciton state has a long lifespan, the 888nm 5 picosecond pulse laser can also excite the S-shell dark exciton state to the P-shell dark biexciton state before the S-shell dark exciton state recombine. Finally, the phonon-assisted relaxation device can relax the P-shell dark biexciton state to the S-shell bright biexciton state through phonon-assisted relaxation.

[0079] According to an example embodiment, a first photon is obtained based on spontaneous radiation of a bright biexciton state of a first shell layer, and the first photon resonates with a cavity membrane of a cavity center layer to generate a cavity photon, the cavity photon is stimulated to radiate and excite a second photon, and the second photon and the first photon form a double photon.

[0080] For example, Figure 4As shown, the S-shell bright biexciton state to the S-shell bright single exciton state can radiate a single photon to the cavity membrane 30 in the center layer of the cavity through spontaneous radiation, thereby obtaining the first photon. And the first photon is collected by the cavity membrane, and since the frequency of the first photon is the same as the frequency of the cavity membrane (the frequency of the cavity membrane is determined by the structure of the microcavity enhanced solid-state two-photon source), the first photon resonates with the cavity membrane, thereby generating cavity photons, and obtaining the second photon in the form of stimulated radiation.

[0081] It can be understood here that the efficient occupation of the biexciton state can be achieved by exciting the long-lived intermediate exciton state (S shell dark exciton state) of the P shell. The indistinguishability of energy and polarization in the biexciton-single exciton radiation cascade can make the first photon stimulate the stimulated radiation of the single exciton state to produce a second photon, so that the second photon and the first photon can form two-photon radiation.

[0082] Through the above embodiments, the present invention can excite semiconductor quantum dots from the ground state to the first shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode, and obtain a first photon based on the spontaneous radiation of the first shell bright biexciton state. The first photon resonates with the cavity membrane of the cavity center layer to generate a cavity photon. The cavity photon is stimulated to radiate and excites to obtain a second photon, so that the second photon and the first photon form a two-photon.

[0083] The present invention resonantly couples semiconductor quantum dots with a microcavity-enhanced solid-state two-photon source with a high Purcell enhancement effect, and can generate high-brightness energy degenerate photon pairs through a zero-binding-energy biexciton-exciton radiation cascade. Due to the Purcell enhancement effect of the cavity membrane, the rate of the biexciton-exciton radiation cascade is also significantly improved. In addition, the spontaneous radiation coupling factor of the two-photon to the cavity membrane is increased, the side loss of the device is reduced, and the collection efficiency of the two-photon is improved.

[0084] The existing microlens-enhanced solid-state two-photon source can achieve a two-photon detection count rate of 234KHz under the condition of continuous light excitation of the P shell. The microcavity-enhanced solid-state two-photon source provided by the present invention can achieve a two-photon detection count rate of 64MHz under the condition of continuous light excitation of the P shell. The brightness of the two-photons collected by the present invention is at least 2 orders of magnitude higher than that of the prior art.

[0085] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions of the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A two-photon excitation method based on a microcavity enhanced solid-state two-photon source, characterized in that: The microcavity enhanced solid-state two-photon source comprises at least a substrate layer, a first reflection layer, a cavity center layer and a second reflection layer, wherein semiconductor quantum dots are arranged in the cavity center layer, and the two-photon excitation method comprises: Exciting the semiconductor quantum dot from a ground state to a first shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode; Obtaining a first photon based on spontaneous radiation of the bright biexciton state of the first shell; The first photon resonates with the cavity membrane of the cavity center layer to generate a cavity photon, and the cavity photon is stimulated to radiate and excite a second photon, and the second photon and the first photon form a double photon.

2. The two-photon excitation method according to claim 1, characterized in that: The method of exciting the semiconductor quantum dot from a ground state to a first shell bright biexciton state based on a preset excitation mode and a phonon-assisted relaxation mode includes: Exciting the semiconductor quantum dot from a ground state to a second shell dark exciton state by a preset laser; Relaxing the second shell dark exciton state to the first shell dark exciton state based on phonon assistance; Exciting the first shell dark exciton state to the second shell dark biexciton state by the preset laser; The second shell dark biexciton state is relaxed to the first shell bright biexciton state based on phonon assistance.

3. The two-photon excitation method according to claim 1, characterized in that: The first shell is an S shell.

4. The two-photon excitation method according to claim 2, characterized in that: The second shell layer is a P shell layer.

5. A two-photon excitation device based on a microcavity enhanced solid-state two-photon source, characterized in that: include: A microcavity enhanced solid-state two-photon source comprises a substrate layer, a first reflection layer, a cavity center layer and a second reflection layer, wherein semiconductor quantum dots are arranged in the cavity center layer; Laser excitation device; A phonon-assisted relaxation device, wherein the laser excitation device excites the semiconductor quantum dot from a ground state to a first-shell bright biexciton state based on a preset excitation mode and the phonon-assisted relaxation device; Among them, a first photon is obtained based on the spontaneous radiation of the bright biexciton state of the first shell layer, and the first photon resonates with the cavity membrane of the cavity center layer to generate a cavity photon, the cavity photon is stimulated to radiate and excite a second photon, and the second photon and the first photon form a two-photon.

6. The two-photon excitation device according to claim 5, characterized in that: The laser excitation device excites the semiconductor quantum dot from the ground state to the second shell dark exciton state by using a preset laser; The phonon-assisted relaxation device relaxes the second shell dark exciton state to the first shell dark exciton state based on phonon assistance; The laser excitation device excites the first shell dark exciton state to the second shell dark biexciton state through the preset laser; The phonon-assisted relaxation device relaxes the second shell dark biexciton state to the first shell bright biexciton state based on phonon-assisted relaxation.

7. The two-photon excitation device according to claim 5, characterized in that: The first shell is an S shell.

8. The two-photon excitation device according to claim 6, characterized in that: The second shell layer is a P shell layer.

9. A quantum optical device, characterized in that: It comprises a two-photon excitation device as described in any one of claims 5-8.

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