Two-Photon Excitation Method and Device Based on Microcavity-Enhanced Solid-State Two-Photon Source, and Quantum Optical Device

Abstract

The present invention provides a two-photon excitation method and apparatus, as well as a quantum optical device, 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 reflective layer, a cavity center layer, and a second reflective layer, with semiconductor quantum dots disposed within the cavity center layer. The two-photon excitation method comprises: exciting the semiconductor quantum dots from a ground state to a first-shell bright biexciton state based on a preset excitation method and a phonon-assisted relaxation method; obtaining a first photon based on spontaneous emission from the first-shell bright biexciton state; resonating the first photon with the cavity membrane of the cavity center layer to generate a cavity photon, which is stimulated to radiate and excite a second photon, and the second photon and the first photon form a two-photon system.

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 key feature is that it leverages the properties of solid-state materials to generate and manipulate two-photons. It has significant application potential in fields such as quantum information processing, quantum communication, and quantum networking.

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

[0004] However, the inventors discovered that microlens-enhanced solid-state two-photon sources simply utilize a combination of microlenses on the top surface and Bragg reflectors on the substrate to improve two-photon collection efficiency from a geometric optics perspective. Therefore, this type of solid-state two-photon source cannot address the issues of low two-photon spontaneous emission rate and high lateral losses in 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 (referring to the degree of enhancement of the spontaneous emission rate in a specific optical environment) is lacking. Therefore, the two-photon spontaneous emission rate of this type of solid-state two-photon source is low, limiting the upper limit of the intrinsic two-photon yield. In addition, due to the low two-photon spontaneous emission coupling factor of this type of solid-state two-photon source, the side losses of the device account for a large proportion, which limits the two-photon collection efficiency. Summary of the Invention

[0006] According to one aspect of the present invention, a two-photon excitation method based on a microcavity-enhanced solid-state two-photon source is provided. The microcavity-enhanced solid-state two-photon source comprises at least a substrate layer, a first reflective layer, a cavity center layer, and a second reflective layer, wherein semiconductor quantum dots are disposed within the cavity center layer. The two-photon excitation method comprises: exciting the 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; obtaining a first photon based on spontaneous emission of the first-shell bright biexciton state; resonating the first photon with a cavity membrane of the cavity center layer to generate a cavity photon, which is stimulated to radiate and excite a second photon, and the second photon and the first photon form a two-photon system.

[0007] According to some embodiments of the present invention, exciting a 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 a 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 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, a two-photon excitation system based on a microcavity-enhanced solid-state two-photon source is provided, comprising the 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 comprises a substrate layer, a first reflective layer, a cavity center layer, and a second reflective layer, wherein a semiconductor quantum dot is disposed within the cavity center layer; a laser excitation device; and 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; wherein a first photon is obtained based on spontaneous emission 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, which is stimulated to radiate and excite a second photon, 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, a quantum optical device is provided, which includes the two-photon excitation device as described above.

[0015] Beneficial effects

[0016] 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 central layer of the cavity to generate a cavity photon. The cavity photon is stimulated to radiate and excite a second photon, so that the second photon and the first photon form a two-photon.

[0017] By resonantly coupling semiconductor quantum dots with a microcavity-enhanced solid-state two-photon source with a high Purcell enhancement effect, the present invention generates high-brightness energy-degenerate photon pairs through a zero-binding-energy biexciton-exciton radiative cascade. Due to the Purcell enhancement effect of the cavity membrane, the rate of the biexciton-exciton radiative cascade is significantly increased. Furthermore, the spontaneous emission coupling factor of two-photons to the cavity membrane is increased, reducing device lateral losses and improving two-photon collection efficiency.

[0018] Existing microlens-enhanced solid-state two-photon sources can achieve a two-photon detection count rate of 234 kHz under continuous light excitation of the P-shell. The microcavity-enhanced solid-state two-photon source provided by the present invention, however, can achieve a two-photon detection count rate of 64 MHz under continuous light excitation of the P-shell. The brightness of the two-photons collected by the present invention is at least two orders of magnitude higher than that of existing technologies. 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 structural diagram of a microcavity-enhanced solid-state two-photon source according to an embodiment of the present invention is shown;

[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 Schematic diagram showing an example of first shell bright biexciton state excitation 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 is shown.

[0025] Description of reference numerals:

[0026] Microcavity-enhanced solid-state two-photon source 1; substrate layer 10; first reflective layer 20; cavity center layer 30; second reflective layer 40; 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 embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the drawings represent like or similar parts, and thus repeated description thereof will be omitted.

[0028] The described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 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 methods, components, materials, devices, etc. may be employed. In these cases, well-known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0029] Furthermore, the terms "include," "comprise," and "have," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements, but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

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

[0031] The following is a clear and complete description of the technical solutions of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of the present invention.

[0032] Existing solutions generally rely on probabilistic nonlinear optical processes to generate two-photon states. For example, using down-converted photons and post-selection techniques can generate higher-quality entangled states. However, the inventors discovered that the probability of generating a two-photon state with this approach decreases exponentially as the number of photons increases. Furthermore, when each process in this approach generates photon pairs that follow a Poisson distribution, there is a non-zero probability of generating zero or more pairs.

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

[0034] Furthermore, based on the biexciton theory that semiconductor quantum dots have a finite binding energy, two-photon pairs can also be generated through spontaneous two-photon emission. For example, by fine-tuning the high-quality cavity membrane to resonate with the half-energy of the biexcitons, this setup can enhance the spontaneous two-photon emission rate while suppressing single-photon cascade emission. This process can therefore improve the efficiency and purity of the simultaneous emission of two photons into the cavity membrane.

[0035] It is understood that when the binding energy of the biexciton state of a 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. In other words, it can be characterized that semiconductor quantum dots with binding energy exhibit super-clustering behavior in the autocorrelation measurement of spontaneous emission photons 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 includes a substrate layer 10, a first reflective layer 20, a cavity center layer 30 and a second reflective layer 40. Semiconductor quantum dots 50 are disposed 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 predetermined number of pairs (e.g., 30 pairs). The second reflective layer 40 may include GaAs layers and AlGaAs layers grown alternately in a second predetermined 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 example embodiments, the semiconductor quantum dots 50 are quantum dots with zero binding energy. Figure 1 As shown, a 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 in the center of the cavity center layer 30 by molecular beam epitaxy (MBE).

[0041] Figure 2 FIG. 1 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 layers of semiconductor quantum dots are important components of their electronic structure. The S-shell is the lowest energy shell in a quantum dot and typically corresponds to the ground state of electrons. In a semiconductor quantum dot, electrons in the S-shell can tunnel to higher energy levels, such as the P-shell. This transfer process can be achieved through laser excitation. The P-shell, located above the S-shell, is one of the higher energy levels in a semiconductor quantum dot. Electrons in the P-shell can relax to the S-shell by releasing phonons.

[0045] For example, the preset excitation mode may be to use optical pumping based on pulsed laser to excite the ground state of semiconductor quantum dots; the phonon-assisted relaxation mode 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 mode and a phonon-assisted relaxation mode.

[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 Schematic diagram showing an example of first-shell bright biexciton state excitation according to an embodiment of the present invention.

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

[0049] In step S110 , a semiconductor quantum dot is excited from a ground state to a 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 S shell and the second shell as P shell, Figure 4 As shown, in response to user operation instructions, the semiconductor quantum dot is excited by a 5-picosecond pulse laser at 888nm to excite the P-shell dark exciton state. The P-shell dark exciton state is then relaxed to the S-shell dark exciton state through phonon-assisted relaxation.

[0054] Because the S-shell dark exciton state has a long lifetime, 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 recombines. Finally, the P-shell dark biexciton state can be relaxed to the S-shell bright biexciton state 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. The cavity photon is stimulated to radiate and generate a second photon. 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 is understood that efficient occupation of the biexciton state can be achieved by exciting a long-lived intermediate exciton state (the S-shell dark exciton state) in the P-shell. The indistinguishability of energy and polarization in the biexciton-singleton radiative cascade allows the first photon to stimulate the singlet exciton state to produce a second photon, which in turn generates 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 is shown.

[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 the biexciton lifetime under resonant conditions of the two-photon excitation method provided by the present invention is significantly higher than that under non-resonant conditions.

[0062] As an example, the diameter of the microcavity-enhanced solid-state two-photon source can be 2.4 μm, with a small mode volume and a quality factor Q of up to 9000. Therefore, the microcavity-enhanced solid-state two-photon source provided by the present invention has a large Purcell enhancement effect, such as a Purcell factor of up to 10.97.

[0063] For example, a superconducting nanowire single-photon detector records experimental data on the variation of count rate with power when detecting two orthogonal polarizations, H and V, of biexcitons. Based on this experimental data, the saturation count rates for the H and V radiation paths can reach 34.4 MHz and 29.6 MHz, respectively.

[0064] Under excitations below 3uW, the present invention can observe superbunching effects by arranging biexciton states through long-lived intermediate exciton states (such as S-shell dark exciton states), such as the maximum second-order autocorrelation function zero value can reach 1947. For example, when the semiconductor quantum dot reaches saturation, the second-order autocorrelation function zero 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 this 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 central layer of the cavity 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.

[0066] By resonantly coupling semiconductor quantum dots with a microcavity-enhanced solid-state two-photon source with a high Purcell enhancement effect, the present invention generates high-brightness energy-degenerate photon pairs through a zero-binding-energy biexciton-exciton radiative cascade. Due to the Purcell enhancement effect of the cavity membrane, the rate of the biexciton-exciton radiative cascade is significantly increased. Furthermore, the spontaneous emission coupling factor of two-photons to the cavity membrane is increased, reducing device lateral losses and improving two-photon collection efficiency.

[0067] The microlens-enhanced solid-state two-photon source can achieve a two-photon detection count rate of 234 kHz under continuous light excitation in 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 64 MHz under continuous light excitation in the P-shell. The two-photon brightness collected by the present invention is at least two orders of magnitude higher than that of existing technologies.

[0068] According to another aspect of the present invention, a two-photon excitation device based on a microcavity-enhanced solid-state two-photon source is provided. The two-photon excitation device includes 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, lattice vibration quanta) 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 layers of semiconductor quantum dots are important components of their electronic structure. The S-shell is the lowest energy shell in a quantum dot and typically corresponds to the ground state of electrons. In a semiconductor quantum dot, electrons in the S-shell can tunnel to higher energy levels, such as the P-shell. This transfer process can be achieved through laser excitation. The P-shell, located above the S-shell, is one of the higher energy levels in a semiconductor quantum dot. 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 a ground state to a second-shell dark exciton state using a preset laser. The phonon-assisted relaxation device relaxes the second-shell dark exciton state to a first-shell dark exciton state based on phonon assistance. The laser excitation device excites the first-shell dark exciton state to a second-shell dark biexciton state using 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 S shell and the second shell as P shell, Figure 4 As shown, in response to user operation instructions, the laser excitation device excites the semiconductor quantum dot with a 5-picosecond pulse laser at 888nm to excite the P-shell dark exciton state. The phonon-assisted relaxation device then relaxes the P-shell dark exciton state to the S-shell dark exciton state through phonon-assisted relaxation.

[0078] Because the S-shell dark exciton state has a long lifetime, the 888nm 5-picosecond pulsed laser can also excite the S-shell dark exciton state to the P-shell dark biexciton state before the S-shell dark exciton state recombines. Finally, the phonon-assisted relaxation device relaxes the P-shell dark biexciton state to the S-shell bright biexciton state through phonon-assisted relaxation.

[0079] According to example embodiments, 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 central layer to generate a cavity photon, which is stimulated to radiate and excite a second photon, and the second photon forms a two-photon with the first 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 a first photon. The first photon 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.

[0081] It is understood that efficient occupation of the biexciton state can be achieved by exciting a long-lived intermediate exciton state (the S-shell dark exciton state) in the P-shell. The indistinguishability of energy and polarization in the biexciton-singleton radiative cascade allows the first photon to stimulate the singlet exciton state to produce a second photon, which in turn generates 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 central layer of the cavity 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.

[0083] By resonantly coupling semiconductor quantum dots with a microcavity-enhanced solid-state two-photon source with a high Purcell enhancement effect, the present invention generates high-brightness energy-degenerate photon pairs through a zero-binding-energy biexciton-exciton radiative cascade. Due to the Purcell enhancement effect of the cavity membrane, the rate of the biexciton-exciton radiative cascade is significantly increased. Furthermore, the spontaneous emission coupling factor of two-photons to the cavity membrane is increased, reducing device lateral losses and improving two-photon collection efficiency.

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

[0085] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions of the aforementioned embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection 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 reflective layer, a cavity center layer, and a second reflective 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 emission of the first shell bright biexciton state; The first photon resonates with the cavity membrane of the central layer of the cavity 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; 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.

2. The two-photon excitation method according to claim 1, wherein The first shell is an S shell.

3. The two-photon excitation method according to claim 1, wherein: The second shell layer is a P shell layer.

4. 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 reflective layer, a cavity center layer, and a second reflective 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; wherein, a first photon is obtained based on spontaneous radiation of the bright biexciton state of the first shell, and the first photon resonates with the cavity membrane of the central layer of the cavity to generate a cavity photon, the cavity photon is stimulated to radiate and excite a second photon, and the second photon forms a two-photon with the first photon; The laser excitation device excites the semiconductor quantum dot from the ground state to the second shell dark exciton state through 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 assistance.

5. The two-photon excitation device according to claim 4, characterized in that: The first shell is an S shell.

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

7. A quantum optical device, characterized in that: It comprises a two-photon excitation device as described in any one of claims 4-6.

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