CN109004508B

CN109004508B - Single photon source based on quantum dots

Info

Publication number: CN109004508B
Application number: CN201810722562.5A
Authority: CN
Inventors: 叶寒; 王芋晶; 俞重远; 刘玉敏; 王叶; 张春雨
Original assignee: Beijing University of Posts and Telecommunications
Current assignee: Beijing University of Posts and Telecommunications
Priority date: 2018-07-03
Filing date: 2018-07-03
Publication date: 2020-01-17
Anticipated expiration: 2038-07-03
Also published as: CN109004508A

Abstract

The embodiment of the invention provides a single photon source based on quantum dots, which comprises: the device comprises a substrate (1), quantum dots (2), a metal micro-nano structure (3) and a gain medium layer (4); the quantum dots (2) and the metal micro-nano structures (3) are respectively arranged on the substrate (1); the metal micro-nano structure (3) comprises: the quantum dot structure comprises two identical semiellipsoids which are cut along the long axis in half, the planes of the semiellipsoids are attached to the substrate (1), and the quantum dots (2) are positioned between the two semiellipsoids and respectively have intervals with the two semiellipsoids; the gain medium layer (4) covers the substrate (2) and wraps the quantum dots (2) and the metal micro-nano structure (3). According to the embodiment of the invention, the loss of the metal micro-nano structure is reduced by adding the gain medium layer, and the problem that single photons are not easy to obtain is solved.

Description

Single photon source based on quantum dots

Technical Field

The invention relates to the technical field of single photon sources, in particular to a single photon source based on quantum dots.

Background

Quantum communication is a novel communication mode for information transmission by using quantum entanglement effect. One of the three core technologies of quantum communication is a single photon source technology. A single photon source, i.e. a light source that generates only one photon at a time.

Existing single photon sources can excite quantum dots with energy, producing only one photon at a time. The photons are called single photons, and the energy may include electrical energy or optical energy, wherein the optical energy may be, for example, planar optical waves (hereinafter referred to as planar light).

The mutual action between the planar light and the quantum dots is weak because of the large size mismatching between the planar light and the quantum dots. Localized Surface Plasmons (LSPs) near the metal nanoparticles can realize a mode volume much smaller than the diffraction limit, and can confine the optical field of planar light near the quantum dots and increase the light intensity there, so that it can be used as an effective medium for enhancing the interaction between light and quantum dots. Therefore, the metal micro-nano structure can be used as a transition medium for interaction between the plane light and the quantum dots. Wherein the surface plasmon is: when light waves enter the metal nano particles, free electrons on the surface of the metal nano particles are subjected to collective oscillation, the light waves and the free electrons on the surface of the metal nano particles are coupled to form a near-field light wave which propagates along the surface of the metal, when the oscillation frequency of electrons is consistent with the frequency of incident light waves, resonance is generated, the energy of the light waves is effectively converted into collective oscillation energy of the free electrons on the surface of the metal nano particles in a resonance state, and then a special mode is formed: the optical field is limited in a small range on the surface of the metal nano-particle and enhanced, and the phenomenon is the surface plasmon phenomenon.

That is, the process of generating a single photon by using the existing single photon source may be as follows: the metal micro-nano structure is excited by plane light, receives energy and generates heat, so that electrons of the metal micro-nano structure become hot electrons of the metal micro-nano structure, the hot electrons of the metal micro-nano structure do not reach an electron work function, and LSPs are generated near metal nano particles of the metal micro-nano structure. When the LSPs and the local oscillation frequency of the quantum dots resonate, the LSPs transfer energy to the quantum dots to generate single photons.

However, when a single photon source is actually prepared, in a coupling system based on a quantum dot-metal micro-nano structure, energy exchange occurs between LSPs of the metal micro-nano structure and the external environment, so that energy loss is large, that is, the attenuation rate is high. For the quantum dot-metal micro-nano structure, the larger the loss is, the more difficult it is to obtain a single photon.

Disclosure of Invention

The embodiment of the invention aims to provide a single photon source based on quantum dots, which solves the problems that the loss of a quantum dot-metal micro-nano structure is large and a single photon is not easy to obtain in the prior art by adding a gain medium layer. The specific technical scheme is as follows:

in a first aspect, an embodiment of the present invention provides a single photon source based on quantum dots, where the single photon source includes: the device comprises a substrate 1, quantum dots 2, a metal micro-nano structure 3 and a gain medium layer 4;

the quantum dots 2 and the metal micro-nano structures 3 are respectively arranged on the substrate 1;

the metal micro-nano structure 3 comprises: the quantum dot structure comprises two same semi-ellipsoids which are split in half along a long axis, wherein the planes of the semi-ellipsoids are attached to the substrate 1, and the quantum dot 2 is positioned between the two semi-ellipsoids and is respectively spaced from the two semi-ellipsoids;

the gain medium layer 4 covers the substrate 2 and wraps the quantum dots 2 and the metal micro-nano structure 3.

Optionally, the gain medium layer is made of silicon dioxide SiO₂Doped with rare earth element ions.

In a second aspect, an embodiment of the present invention provides a method for determining a gain factor of a gain medium layer, where the method is used for the gain medium layer in the single-photon source in the first aspect, and the method includes:

determining a structural object to be calculated, the structural object to be calculated comprising: a target structure object;

carrying out value taking on the gain coefficients within a preset range according to a preset rule, and sequentially selecting the gain coefficients with different values as candidate gain coefficients;

under the candidate gain coefficient, determining a basic parameter of the target structure object corresponding to the candidate gain coefficient;

determining a target structure object model based on the basic parameters, and calculating a coherence function of the target structure object model;

and if the coherent functions of the target structure object models corresponding to the candidate gain coefficients of all the selected values are obtained by calculation, determining the candidate gain coefficients corresponding to the coherent functions meeting the preset judgment conditions as the target gain coefficients.

Optionally, the structural object to be calculated further includes: a first structural object and a second structural object; under the candidate gain coefficient, determining the basic parameters of the target structure object corresponding to the candidate gain coefficient, including:

establishing a frequency domain model corresponding to each structural object to be calculated aiming at the determined structural object to be calculated by using a finite element method, and calculating a first absorption cross section of each structural object to be calculated under a candidate gain coefficient;

based on the cavity quantum electrodynamics CQED, establishing a steady-state model corresponding to each structural object to be calculated aiming at the determined structural object to be calculated, and calculating a second absorption cross section of each structural object to be calculated under a steady-state condition candidate gain coefficient;

and fitting each first absorption cross section and each second absorption cross section obtained by calculation, and determining basic parameters of the target structure object corresponding to the candidate gain coefficients.

Optionally, the structural object to be calculated further includes: a first structural object and a second structural object; the step of establishing a frequency domain model corresponding to each structural object to be calculated by using a finite element method aiming at the determined structural object to be calculated, and calculating a first absorption cross section of each structural object to be calculated under a candidate gain coefficient comprises the following steps:

establishing a frequency domain model corresponding to each structural object to be calculated aiming at the determined structural object to be calculated by using a finite element method;

exciting each structural object to be calculated by adopting a planar light wave 5;

calculating a first absorption section of each structural object to be calculated under the candidate gain coefficient by using a calculation formula of the first absorption section;

wherein the calculation formula of the first absorption cross section is as follows:

σ_abs1(ω)＝Q_rh(ω)/S₀

wherein σ_abs1(ω) is a first absorption cross section at an incident frequency ω of the planar lightwave 5, Q_rh(omega) is the corresponding heat loss when the incident frequency of the planar lightwave 5 is omega, S₀Is the energy density of the planar lightwave 5.

Optionally, the structural object to be calculated further includes: a first structural object and a second structural object; the method comprises the following steps of establishing a steady-state model corresponding to each structural object to be calculated aiming at the determined structural object to be calculated based on the cavity quantum electrodynamics CQED, and calculating a second absorption cross section of each structural object to be calculated under a steady-state condition candidate gain coefficient, wherein the step comprises the following steps of:

based on CQED, aiming at the determined structural objects to be calculated, establishing JC models, Hamilton quantities and quantum principal equations corresponding to the structural objects to be calculated;

calculating a second absorption cross section of each structural object to be calculated under the steady-state condition candidate gain coefficient by using a calculation formula of the second absorption cross section;

wherein, the calculation formula of the second absorption cross section is as follows:

σ_abs2(ω)＝(ω/2)Im[μ_ωE₀*]/S₀

μ_ω＝<μ|ρ>

wherein σ_abs2(ω) is a second absorption cross section of the planar lightwave 5 at an incident frequency ω, where ω is the incident frequency μ of the planar lightwave 5_ωRepresents an expected value of mu obtained in rho for a dipole moment when the incident frequency of the planar lightwave 5 is omega, mu is a total dipole operator, rho is a density matrix corresponding to the incident frequency of the planar lightwave 5, E₀ ^*For the excitation intensity E of the planar lightwave 5₀Conjugation of (1).

Optionally, the structural object to be calculated further includes: a first structural object and a second structural object; the step of fitting each of the first absorption cross sections and the second absorption cross sections obtained by calculation and determining the basic parameters of the target structure object corresponding to the candidate gain coefficients includes:

fitting a frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the first structural object;

fitting a frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the second structural object;

fitting a frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the target structure object;

and determining basic parameters of the target structure object corresponding to the candidate gain coefficients based on the fitting of the frequency domain curves of all the first absorption cross sections and the steady-state frequency domain curve of the second absorption cross section.

Optionally, the basic parameters of the target structure object include:

surface plasmon field eigenfrequency, cavity mode dissipation rate, quantum dot eigenfrequency, pure dephasing, quantum dot dipole moment, surface plasmon dipole moment, dot-cavity coupling strength, and quantum dot spontaneous emissivity.

Optionally, the step of determining a target structure object model based on the basic parameters and calculating a coherence function of the target structure object model includes:

applying the basic parameters to a Hamiltonian quantity and a quantum principal equation of a target structure object to determine a target structure object model;

calculating a coherence function of the target structure object model by using a calculation formula of the coherence function;

wherein, the calculation formula of the coherence function is as follows:

wherein, g²(0) Is a coherence function of the object of the target structure,

an operator is generated/annihilated for photons of the surface plasmon field.

Optionally, the step of determining a gain coefficient corresponding to the coherence function that satisfies the preset determination condition as a target gain coefficient includes:

acquiring the minimum value of each coherent function as the minimum value of the coherent function;

judging whether the minimum value of each coherent function meets a preset judgment condition, and determining the coherent function meeting the preset judgment condition as a candidate coherent function;

and comparing all the candidate coherence function minimum values, and determining the candidate gain coefficient corresponding to the candidate coherence function corresponding to the minimum value in the candidate coherence function minimum values as the target gain coefficient.

The embodiment of the invention provides a single photon source based on quantum dots, which comprises: the device comprises a substrate 1, quantum dots 2, a metal micro-nano structure 3 and a gain medium layer 4; the quantum dots 2 and the metal micro-nano structures 3 are respectively arranged on the substrate 1; the metal micro-nano structure 3 comprises: the quantum dot structure comprises two same semi-ellipsoids which are split in half along a long axis, wherein the planes of the semi-ellipsoids are attached to the substrate 1, and the quantum dot 2 is positioned between the two semi-ellipsoids and is respectively spaced from the two semi-ellipsoids; the gain medium layer 4 covers the substrate 2 and wraps the quantum dots 2 and the metal micro-nano structure 3.

According to the embodiment of the invention, the substrate is covered with the gain medium layer, and the quantum dots and the metal micro-nano structure are wrapped in the gain medium layer, the metal micro-nano structure can limit the incident light field of the planar light wave near the quantum dots to enhance the interaction between light and substances, the gain medium layer wraps the quantum dots and the metal micro-nano structure, the attenuation of LSPs near the metal micro-nano structure can be limited, single photons can be better obtained, and the problems that the loss of the quantum dots-metal micro-nano structure is large and the single photons are not easy to obtain in the prior art are solved.

Of course, it is not necessary for any product or method of practicing the invention to achieve all of the above-described advantages at the same time.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic view of a single photon source based on quantum dots according to an embodiment of the present invention;

fig. 2 is a schematic flowchart of a method for determining a gain factor of a gain medium layer according to an embodiment of the present invention;

FIG. 3 is a flow chart of one embodiment of determining the basic parameters of the target structure object in the embodiment shown in FIG. 2;

FIG. 4 is a flowchart of one embodiment of step S303 in the embodiment shown in FIG. 3;

FIG. 5a is a schematic diagram of a frequency domain curve of a first absorption cross section and a steady-state frequency domain curve of a second absorption cross section corresponding to a first structural object according to an embodiment of the present invention;

FIG. 5b is a schematic diagram of another steady-state frequency domain curve of the first absorption cross section and the second absorption cross section corresponding to the first structural object according to an embodiment of the present invention;

FIG. 6a is a schematic diagram of a frequency domain curve of a first absorption cross section and a steady-state frequency domain curve of a second absorption cross section corresponding to a second structure object according to an embodiment of the present invention;

FIG. 6b is a schematic diagram of another frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the second structure object according to the embodiment of the present invention;

FIG. 7a is a schematic diagram of a frequency domain curve of a first absorption cross section and a steady-state frequency domain curve of a second absorption cross section corresponding to a fitting target structure object according to an embodiment of the present invention;

FIG. 7b is a schematic diagram of another frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the object of the target structure according to another embodiment of the present invention;

FIG. 8 is a flow diagram of one embodiment of determining a coherence function in the embodiment of FIG. 2;

FIG. 9 is a flow diagram of one embodiment of determining a target gain factor in the embodiment of FIG. 2;

FIG. 10a is a diagram illustrating a coherence function curve of an object model of a target structure according to an embodiment of the present invention;

fig. 10b is a schematic diagram of a coherence function curve of another object model of the target structure according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention provides a single photon source based on quantum dots, and aims to solve the problems in the prior art that the loss of a metal micro-nano structure is large and a single photon is not easily obtained in the coupling system based on the quantum dots and the metal micro-nano structure.

In order to solve the problems in the prior art, an embodiment of the present invention provides a single photon source based on quantum dots, including: the device comprises a substrate 1, quantum dots 2, a metal micro-nano structure 3 and a gain medium layer 4;

the quantum dots 2 and the metal micro-nano structures 3 are respectively arranged on the substrate 1; the metal micro-nano structure 3 comprises: the quantum dot structure comprises two same semi-ellipsoids which are split in half along a long axis, wherein the planes of the semi-ellipsoids are attached to a substrate 1, and quantum dots 2 are positioned between the two semi-ellipsoids and respectively have intervals with the two semi-ellipsoids; the gain medium layer 4 covers the substrate 2 and wraps the quantum dots 2 and the metal micro-nano structure 3.

In the embodiment of the invention, the substrate is covered with the gain medium layer, and the quantum dot and the metal micro-nano structure are wrapped in the gain medium layer, the metal micro-nano structure can limit the incident light field of the plane light wave near the quantum dot so as to enhance the interaction between light and substances, the gain medium layer wraps the quantum dot and the metal micro-nano structure, the attenuation of LSPs near the metal micro-nano structure can be limited, single photons can be better obtained, and the problems that the loss of the quantum dot-metal micro-nano structure is large and the single photon is not easy to obtain in the prior art are solved.

First, a single photon source based on quantum dots provided by the embodiment of the invention is described below.

As shown in fig. 1, fig. 1 is a single photon source based on quantum dots, according to an embodiment of the present invention, where the single photon source includes: the device comprises a substrate 1, quantum dots 2, a metal micro-nano structure 3 and a gain medium layer 4;

as shown in fig. 1, a quantum dot 2 and a metal micro-nano structure 3 are respectively arranged on a substrate 1;

the metal micro-nano structure 3 comprises: the quantum dot structure comprises two same semi-ellipsoids which are split in half along a long axis, wherein the planes of the semi-ellipsoids are attached to a substrate 1, and quantum dots 2 are positioned between the two semi-ellipsoids and respectively have intervals with the two semi-ellipsoids;

In the single-photon source, the material of the substrate may be silicon dioxide SiO₂The material may be silicon Si, etc., and the embodiment of the present invention is not limited herein. In practical applications, the energy levels of the quantum dots are split, and the quantum dots in the embodiments of the present invention are exemplified by two-level quantum dots, that is, quantum dots with only two energy levels.

An optional implementation manner in the embodiment of the present invention is as follows: in the single photon source, the substrate material may be set to SiO₂The substrate was set to 500nm in length, width and height and to have a dielectric constant of ε_s2.25. Disposing a two-level quantum dot with radius of 1.7nm and dielectric constant of ε on the substrate at the center of the substrate plane_dExpression takes the form Lorentz ∈_d(ω)＝∈_∞-

Wherein e is_∞4.84 is the dielectric constant of the two-level quantum dot at high frequency, f 0.1 is the converted oscillator strength, and ω is_dIs the center frequency, gamma, of the two-level quantum dot_d2meV is the line width and ω is the incident frequency of the planar lightwave. Arranging a metal micro-nano structure consisting of two same semiellipsoids which are split in half along the major axis on a substrate, wherein the major axis and the minor axis of the two semiellipsoids are respectively 50nm and 10nm, the plane of the semiellipsoid is attached to the substrate, the centers of the two semiellipsoids are respectively positioned at the positions of the left side and the right side of the center of the quantum dot at an interval of 52nm in the horizontal direction, the two semiellipsoids are made of gold, and the dielectric constant of the two semiellipsoids is epsilon_mThe expression takes the form of DrudeWherein e is_∞9.5 is the dielectric constant of gold at high frequencies, ω_pThe plasma frequency is 8.56eV, i is an imaginary unit, and Γ is 69meV is the damping constant. Covering a gain medium layer on the substrate, and wrapping the quantum dots and the metal micro-nano structure in the gain medium layer, wherein the dielectric constant expression of the gain medium layer is (n-ik)²Where n ═ 1.5 is a refractive index, k is a gain coefficient, and the height of the gain medium layer is set to 20nm and the length and width are set to 500 nm. And finally, exciting the quantum dot-gain-assisted metal micro-nano structure of the single photon source by adopting a planar light wave 5, and working the single photon source to generate a single photon.

For the gain medium layer, an optional implementation manner of the embodiment of the present invention is that the gain medium layer is made of silicon dioxide SiO₂Doped with rare earth element ions.

Specifically, the gain medium layer may be: in SiO₂Rare earth element ions are doped as a gain medium, the rare earth element ions can be erbium, thulium or ytterbium and the like, and in practical application, the rare earth element ions can be in SiO₂One or more rare earth element ions are doped as a gain medium.

The gain medium layer is covered on the substrate by depositionAbove. The following steps can be also included: will be in SiO₂The gain medium doped with rare earth element ions covers the substrate, the two-level quantum dots and the metal micro-nano structure layer by layer. In the embodiment of the present invention, a specific implementation manner of covering the gain medium layer on the substrate is not limited.

Aiming at the single photon source based on the quantum dots provided by the embodiment of the invention, the gain medium layer of the single photon source is made of SiO₂Doped with rare earth element ions. The embodiment of the invention also provides a method for determining the gain coefficient of the gain medium layer.

As shown in fig. 2, fig. 2 is a method for determining a gain factor of a gain medium layer according to an embodiment of the present invention, where the method includes:

s201, determining a structural object to be calculated, wherein the structural object to be calculated comprises: a target structure object.

In this embodiment of the present invention, the determined structural object to be calculated may include: a target structure object. The determined structural object to be calculated may further include: a first structural object and a second structural object, wherein the first structural object is: a metal nanoparticle structure covered with a gain medium layer or a gain auxiliary metal micro-nano structure; the second structural object is: a two-level quantum dot; the target structure objects are: quantum dot-gain auxiliary metal micro-nano structure.

In the embodiment of the invention, the LSPs near the metal micro-nano structure can limit the incident light field of the planar light wave near the two-level quantum dots, namely, the electric field of free electrons near the metal micro-nano structure is localized in a smaller size, a surface plasma field is formed near the metal micro-nano structure, and the LSPs and the two-level quantum dots resonate simultaneously, so that when the surface plasma field and the eigenfrequency of the two-level quantum dots are the same, the interaction between the light field and the two-level quantum dots can be greatly enhanced, and the generation of single photons is facilitated.

S202, values are taken from the gain coefficients in a preset range according to a preset rule, and the gain coefficients with different values are sequentially selected to serve as candidate gain coefficients.

In practical application, the gain coefficient of the gain medium layer can be preset. In the embodiment of the present invention, the manner of taking the value of the gain coefficient according to the preset rule in the preset range may be: and carrying out value taking at a preset certain interval within a preset gain coefficient parameter range to obtain a series of gain coefficient values with different values as candidate gain coefficients. It can also be: in a preset gain coefficient parameter range, the parameter range is divided into different parameter areas, for example, the parameter range can be divided into 3 areas, and then values are taken at different intervals in the different areas to obtain a series of gain coefficient values with different values as candidate gain coefficients. The parameter range is divided into 3 regions, and then values are taken at different intervals in different regions, which may be: and carrying out value taking in the first area and the third area at a first parameter interval, carrying out value taking in the second area at a second parameter interval and the like, wherein the first parameter interval is different from the second parameter interval. The specific division and value-taking modes are not limited herein in the embodiments of the present invention.

For example, an optional implementation manner in the embodiment of the present invention may be: setting the parameter range of the gain coefficient to be 0-0.18, and carrying out value taking on the parameters in the parameter range at the interval of 0.01 within the preset parameter range, and then taking the gain coefficients with different values selected in sequence as candidate gain coefficients. Namely, the candidate gain factors are: and within the preset gain coefficient parameter range of 0-0.18, taking values at intervals of 0.01 to obtain a series of parameters.

Of course, the embodiment of the present invention is only described as an example of the implementation manner of taking the value of the gain coefficient according to the preset rule in the preset range, and the implementation manner of taking the value of the gain coefficient according to the preset rule in the preset range in practical application is not limited to this.

And S203, determining basic parameters of the target structure object corresponding to the candidate gain coefficient under the candidate gain coefficient.

In the embodiment of the invention, after the structural object to be calculated is determined, different candidate gain coefficients are sequentially selected for the determined structural object to be calculated. And establishing a model corresponding to each structural object to be calculated under the selected candidate gain coefficient, calculating the absorption cross section of each structural object to be calculated aiming at the model corresponding to each structural object to be calculated, and further determining the basic parameters of the target structural object corresponding to the candidate gain coefficient based on the calculated absorption cross section of each structural object to be calculated. Specifically, the relevant content of establishing the model corresponding to each structural object to be calculated is described in detail below.

S204, determining a target structure object model based on the basic parameters, and calculating a coherence function of the target structure object model.

And determining basic parameters of the target structure object corresponding to the candidate gain coefficients, namely determining the established model corresponding to the target structure object, and further calculating to obtain a coherence function of the target structure object model based on the model of the target structure object. Specifically, the relevant content of the model corresponding to the target structure object is described in detail below.

And S205, if the coherent functions of the target structure object models corresponding to the candidate gain coefficients of all the selected values are obtained through calculation, determining the candidate gain coefficients corresponding to the coherent functions meeting the preset judgment conditions as the target gain coefficients.

When all candidate gain coefficients selected according to a preset rule in a preset range have been calculated to obtain the correlation functions of the target structure object models corresponding to all different candidate gain coefficients, the candidate gain coefficients corresponding to the correlation functions meeting the preset judgment conditions are determined as target gain coefficients, that is, the gain coefficients of the gain medium layer are determined.

In the embodiment of the invention, after the structural object to be calculated is determined, different candidate gain coefficients are sequentially selected according to the determined structural object to be calculated. And then, under the selected candidate gain coefficient, further determining the basic parameters of the target structure object corresponding to the selected candidate gain coefficient, determining a model of the target structure object, and calculating to obtain a coherence function of the model of the target structure object. And finally, calculating to obtain the coherent functions of the target structure object models corresponding to all the different candidate gain coefficients aiming at all the selected candidate gain coefficients, and determining the gain coefficient corresponding to the coherent function meeting the preset judgment condition as the target gain coefficient. The gain medium layer is applied to a single photon source based on quantum dots, so that in the single photon source, a substrate is covered with the gain medium layer, and the quantum dots and a metal micro-nano structure are wrapped in the gain medium layer, the metal micro-nano structure can limit an incident light field of planar light waves near the quantum dots to enhance the interaction between light and substances, and the gain medium layer wraps the quantum dots and the metal micro-nano structure therein, so that the attenuation of LSPs near the metal micro-nano structure can be limited, single photons can be better obtained, and the problems that in the prior art, the loss of the quantum dots-metal micro-nano structure is large, and the single photons are not easy to obtain are solved.

Based on the embodiment shown in fig. 2, as shown in fig. 3, fig. 3 is an implementation manner of determining basic parameters of the target structure object in the embodiment shown in fig. 2, and the implementation manner may include:

s301, establishing a frequency domain model corresponding to each structural object to be calculated by using a finite element method according to the determined structural object to be calculated, and calculating a first absorption intercept direction of each structural object to be calculated under the candidate gain coefficient.

In the embodiment of the invention, after the structural object to be calculated is determined, different candidate gain coefficients are sequentially selected according to the determined structural object to be calculated. And then, under the selected candidate gain coefficient, establishing a frequency domain model corresponding to each structural object to be calculated by using a finite element method aiming at the determined structural object to be calculated, and calculating a first absorption cross section of each structural object to be calculated under the selected candidate gain coefficient.

Specifically, the step of establishing a frequency domain model corresponding to each structural object to be calculated by using a finite element method for the determined structural object to be calculated, and calculating the first absorption cross section of each structural object to be calculated under the candidate gain coefficient may include:

wherein, the calculation formula of the first absorption cross section is as follows:

σ_abs1(ω)＝Q_rh(ω)/S₀

wherein σ_abs1(ω) is a first absorption cross section at an incident frequency ω of the planar lightwave 5, Q_rh(omega) is the heat loss, S, corresponding to the frequency omega of the incident planar lightwave 5₀The energy density of the planar lightwave 5.

In the embodiment of the present invention, an optional implementation manner may be: and aiming at the determined structural objects to be calculated, establishing a frequency domain model corresponding to each structural object to be calculated by using a finite element method. The physical model corresponding to each structural object to be calculated can refer to the description attached to fig. 1, the physical model of the target structural object can directly refer to the description attached to fig. 1, and the physical model of the first structural object and the physical model of the second structural object can refer to part of the structure in the description attached to fig. 1. The specific implementation manner of establishing the frequency domain model corresponding to each structural object to be calculated may be as follows: based on the finite element method, the frequency domain model is built in the calculation software according to the designed specific parameters, such as the size, dielectric constant and the like of each part in the model, wherein the relevant introduction of the size and dielectric constant of each part in the model is as described above.

And then, exciting each structural object to be calculated by adopting the planar light waves. In the embodiment of the present invention, a planar light wave is perpendicularly incident to each structural object to be calculated for excitation, and the embodiment of the present invention is not limited herein with respect to the incident mode of the planar light wave. In practical application, the incident frequency of the planar lightwave can be selected from frequency values in any interval, and in the embodiment of the invention, the incident frequency of the planar lightwave is 3 × 10¹⁴Hz～6×10¹⁴Between Hz and power of 10⁶W is an example.

And after the planar light wave excites each structural object to be calculated, calculating the first absorption cross section of each structural object to be calculated under the selected candidate gain coefficient by using a calculation formula of the first absorption cross section.

In the formula for calculating the first absorption cross section, Q_rhAnd (omega) is the corresponding heat loss when the incident frequency of the planar light wave is omega, the heat loss value can be obtained by integrating and calculating ewfd. Qrh in the metal structure through calculation software, and the ewfd. Qrh is a calculation variable carried by the calculation software and represents the ohmic loss of the space. S₀The energy density of the planar lightwave indicates the magnitude of the incident power P of the planar lightwave per unit area.

In the embodiment of the present invention, after the frequency domain model corresponding to each structural object to be calculated is established by using the finite element method for each determined structural object to be calculated, the first absorption cross section of each structural object to be calculated under the selected candidate gain coefficient may be calculated by using the calculation formula of the first absorption cross section, and the curve diagram of the first absorption cross section of each structural object to be calculated is drawn according to the calculation result.

S302, establishing a steady-state model corresponding to each structural object to be calculated aiming at the determined structural object to be calculated based on the cavity quantum electrodynamics CQED, and calculating a second absorption cross section of each structural object to be calculated under the condition of a candidate gain coefficient under a steady-state condition.

In the embodiment of the invention, after the structural object to be calculated is determined, different candidate gain coefficients are sequentially selected for the determined structural object to be calculated. Then, under the selected candidate gain coefficient, based on Cavity-quantum electrodynamics (CQED), establishing a steady-state model corresponding to each structural object to be calculated for the determined structural object to be calculated, and calculating a second absorption cross section of each structural object to be calculated under the candidate gain coefficient selected under the steady-state condition.

Specifically, based on the CQED, the step of establishing a steady-state model corresponding to each structural object to be calculated for the determined structural object to be calculated, and calculating a second absorption cross section of each structural object to be calculated under the steady-state condition candidate gain coefficient may include:

σ_abs2(ω)＝(ω/2)Im[μ_ωE₀ ^*]/S₀

μ_ω＝〈μ|ρ>

wherein σ_abs2(ω) is the second absorption cross section at the incident frequency ω of the planar lightwave 5, ω is the incident frequency μ of the planar lightwave 5_ωThe dipole moment of the planar light wave 5 at the incident frequency ω represents the expected value of μ found in ρ, μ is the total dipole operator, ρ is the density matrix of the object model of the structure to be calculated, E₀ ^*For a planar light wave 5 excitation intensity E₀Conjugation of (1).

In the embodiment of the present invention, an optional implementation manner may be: and (3) equivalent the surface plasma field near the metal micro-nano structure into a cavity, so that the quantum dot-surface plasma field can be regarded as a two-energy-level quantum dot-microcavity coupling system, and the system can be represented by using a JC model in CQED. In the embodiment of the invention, aiming at the determined structural objects to be calculated, based on the CQED, a JC model corresponding to each structural object to be calculated is established, and specifically, the JC model is expressed by using a hamilton quantity and a quantum principal equation.

In each structural object to be calculated, the hamilton corresponding to the target structural object may be represented as:

wherein,

for the two-level system up/down operator,for photon generation/annihilation operators of surface plasmon fields, omega_cAnd omega_aRespectively the eigenfrequency of the surface plasma field and the two-level quantum dot, g is the coupling strength of the two-level quantum dot and the surface plasma field, E₀Excitation intensity of planar light wave, omega_lMu is the total dipole operator for the planar lightwave incident frequency.

The total dipole operator μ can be expressed as:

wherein d is_aAnd d_cDipole moments of the two-level quantum dots and the surface plasmon, respectively.

In each structural object to be calculated, the quantum principal equation corresponding to the target structural object can be expressed as:

wherein i is an imaginary unit,

the rate of change of the density matrix ρ for the target structure object model.

The incoherent term is:

where κ is the dissipation rate of the surface plasmon field, γ₁Spontaneous emissivity of two-level quantum dots, gamma₂Is pure dephasing.

For the first structure object and the second structure, the representing modes of the hamiltonian and the quantum principal equation thereof may refer to the hamiltonian and the quantum principal equation corresponding to the target structure object, and set the parameters not involved therein to 0, so as to obtain the hamiltonian and the quantum principal equation corresponding to the first structure object and the second structure.

And after the planar light waves excite each structural object to be calculated, calculating a second absorption cross section of each structural object to be calculated under the selected candidate gain coefficient by using a calculation formula of the second absorption cross section.

In the embodiment of the invention, for each determined structural object to be calculated, based on the CQED, after the JC model corresponding to each structural object to be calculated is established, the hamilton quantities and quantum principal equations corresponding to each structural object to be calculated can be obtained. Wherein, the Hamiltonian and quantum master corresponding to each structural object to be calculatedParametric surface plasmon field eigenfrequency ω involved in the equation_cQuantum dot eigenfrequency omega_aPoint-cavity coupling strength g, quantum point dipole moment d_aSurface plasma dipole moment d_cCavity mode dissipation rate kappa and quantum dot spontaneous emissivity gamma₁And pure dephasing gamma₂Are unknown and all need to be solved computationally to be able to obtain.

For the above parameters to be solved, the method adopted in the embodiment of the present invention may be: first, a set of initial values is set to be assigned to the parameters. And then, calculating to obtain a second absorption cross section of each structural object to be calculated under the selected candidate gain coefficient by using a calculation formula of the second absorption cross section, and drawing a curve schematic diagram of the second absorption cross section of each structural object to be calculated according to the calculation result. And finally, determining each parameter needing to be calculated and solved by fitting each curve of the first absorption cross section and the second absorption cross section obtained through calculation.

And S303, fitting each first absorption cross section and each second absorption cross section obtained by calculation, and determining basic parameters of the target structure object corresponding to the candidate gain coefficients.

And establishing a model corresponding to each structural object to be calculated by respectively using a finite element method and based on CQED for the determined structural object to be calculated, and further determining basic parameters of a target structural object corresponding to the candidate gain coefficient by drawing a first absorption section curve and a second absorption section curve corresponding to each structural object to be calculated after calculating a first absorption section and a second absorption section corresponding to each structural object to be calculated under the condition that the selected candidate gain coefficient is obtained.

Wherein the basic parameters of the target structure object may include:

In the embodiment of the invention, the basic parameters of the target structure object required to be determined are the above-mentioned constructionEstablishing the corresponding Hamiltonian quantity of the target structure object and the parameter omega involved in the quantum principal equation_c、ω_a、g、d_a、d_c、κ、γ₁And gamma₂。

On the basis of the embodiment shown in fig. 3, as shown in fig. 4, fig. 4 is an implementation manner of step S303 in the embodiment shown in fig. 3, and the implementation manner may include:

s401, fitting the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the first structural object.

In the embodiment of the invention, aiming at the determined first structural object, a model corresponding to the first structural object is established by using a finite element method, and then a first absorption cross section corresponding to the first structural object under the selected candidate gain coefficient is obtained through calculation; and establishing a model corresponding to the first structural object based on the CQED, and then calculating to obtain a second absorption cross section corresponding to the first structural object under the selected candidate gain coefficient. And drawing a frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the first structural object.

The first structural object is a gain auxiliary metal micro-nano structure, and parameters related to a Hamilton quantity and a quantum principal equation corresponding to the first structural object are established based on CQED: surface plasma field eigenfrequency omega_cAnd the cavity mode dissipation rate (i.e., the dissipation rate of the surface plasmon field) κ is unknown at ω_cAnd after assigning initial values to kappa, calculating a second absorption cross section corresponding to the first structural object, and drawing a steady-state frequency domain curve of the second absorption cross section corresponding to the first structural object.

Then, drawing the frequency domain curve of the first absorption cross section corresponding to the first structural object and the steady-state frequency domain curve of the second absorption cross section in the same coordinate system, and continuously adjusting the parameter omega_cAnd a value of κ, fitting the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the first structure object such that the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the first structure objectThe steady-state frequency domain curves of the absorption cross sections are overlapped to obtain omega corresponding to the curve overlapping_cAnd k, completing the fitting process of the frequency domain curve of the first absorption cross section corresponding to the first structural object and the steady-state frequency domain curve of the second absorption cross section.

S402, fitting the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the second structural object.

In the embodiment of the invention, a finite element method is used for establishing a model corresponding to the second structural object aiming at the determined second structural object, and then a first absorption cross section corresponding to the second structural object under the selected candidate gain coefficient is obtained through calculation; and establishing a model corresponding to the second structural object based on the CQED, and then calculating to obtain a second absorption cross section corresponding to the second structural object under the selected candidate gain coefficient. And drawing a frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the second structural object.

The second structural object is a two-energy-level quantum dot, and parameters related to a Hamiltonian quantity and a quantum principal equation corresponding to the second structural object are established based on CQED: quantum dot eigenfrequency omega_aAnd pure dephasing gamma₂Is unknown at given ω_aAnd gamma₂And after an initial value is given, calculating a second absorption cross section corresponding to the second structural object, and drawing a steady-state frequency domain curve of the second absorption cross section corresponding to the second structural object.

Then, drawing the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the second structural object under the same coordinate system, and continuously adjusting the parameter omega_aAnd gamma₂Fitting the frequency domain curve of the first absorption cross section corresponding to the second structural object and the steady-state frequency domain curve of the second absorption cross section to ensure that the frequency domain curve of the first absorption cross section corresponding to the second structural object and the steady-state frequency domain curve of the second absorption cross section are overlapped to obtain corresponding omega when the curves are overlapped_aAnd gamma₂To complete the frequency domain curve of the first absorption cross section corresponding to the second structure objectFitting process of the line and the steady state frequency domain curve of the second absorption cross section.

And S403, fitting the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the target structure object.

In the embodiment of the invention, aiming at the determined target structure object, a model corresponding to the target structure object is established by using a finite element method, and then a first absorption cross section corresponding to the target structure object under the selected candidate gain coefficient is obtained through calculation; and establishing a model corresponding to the target structure object based on the CQED, and then calculating to obtain a second absorption cross section corresponding to the target structure object under the selected candidate gain coefficient. And drawing a frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the target structure object.

The target structure object is a quantum dot-gain auxiliary metal micro-nano structure, and the Hamilton quantity and the parameters related to a quantum principal equation corresponding to the target structure object are established based on CQED: dipole moment d of quantum dots_aSurface plasma dipole moment d_cG point-cavity coupling strength (i.e. coupling strength of two-energy-level quantum point and surface plasma field) and gamma spontaneous emissivity of quantum point₁Is unknown at given d_a、d_cG and gamma₁And after an initial value is given, calculating a second absorption cross section corresponding to the target structure object, and drawing a steady-state frequency domain curve of the second absorption cross section corresponding to the target structure object.

Then, drawing the frequency domain curve of the first absorption cross section and the steady-state frequency domain curve of the second absorption cross section corresponding to the target structure object under the same coordinate system, and continuously adjusting the parameter d_a、d_cG and gamma₁Fitting the frequency domain curve of the first absorption cross section and the steady state frequency domain curve of the second absorption cross section corresponding to the target structure object, so that the frequency domain curve of the first absorption cross section and the steady state frequency domain curve of the second absorption cross section corresponding to the target structure object are overlapped, and obtaining the corresponding d when the curves are overlapped_a、d_cG and gamma₁To complete the target junctionAnd fitting the frequency domain curve of the first absorption cross section corresponding to the structural object and the steady-state frequency domain curve of the second absorption cross section.

S404, based on the fitting of the frequency domain curves of all the first absorption cross sections and the steady-state frequency domain curve of the second absorption cross section, determining the basic parameters of the target structure object corresponding to the candidate gain coefficients.

Based on the fitting result obtained by fitting the frequency domain curves of all the first absorption cross sections corresponding to the structural objects to be calculated with the steady-state frequency domain curve of the second absorption cross section, the basic parameters of the target structural object corresponding to the selected candidate gain coefficient can be further determined.

Referring to fig. 5a and 5b, fig. 5a is a schematic diagram of a frequency domain curve of a first absorption cross section and a steady-state frequency domain curve of a second absorption cross section corresponding to a first structural object according to an embodiment of the present invention; fig. 5b is a schematic diagram of another steady-state frequency domain curve of the first absorption cross section and the second absorption cross section corresponding to the first structural object according to another embodiment of the present invention. Fig. 5a and 5b show the results of steady-state frequency domain curve fitting of the frequency domain curve of the first absorption cross section and the frequency domain curve fitting of the second absorption cross section corresponding to the first structural object under the candidate gain coefficients of 0.05 and 0.086, respectively. In fig. 5a and 5b, the abscissa represents the incident energy of the planar light wave, the ordinate represents the value corresponding to the absorption cross section, the dots represent the first absorption cross section, and the curve represents the second absorption cross section.

From the results of the steady-state frequency domain curve fitting of the first absorption cross section and the second absorption cross section corresponding to the first structural object shown in fig. 5a and 5b, it can be obtained that when the candidate gain coefficient is 0.05, the corresponding ω is obtained_c1.3078eV, κ 33 meV; when the candidate gain coefficient is 0.086, the corresponding omega is obtained_c1.3078eV, κ is 3.8 meV.

Referring to fig. 6a and fig. 6b, fig. 6a is a schematic diagram of a frequency domain curve of a first absorption cross section and a steady-state frequency domain curve of a second absorption cross section corresponding to a fitting second structure object according to an embodiment of the present invention; fig. 6b is a schematic diagram of another frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the second structural object according to the embodiment of the present invention. Fig. 6a and 6b are steady-state frequency domain curve fitting results of the frequency domain curve of the first absorption cross section and the second absorption cross section corresponding to the second structure object under the candidate gain coefficients, which are plotted when the candidate gain coefficients are 0.05 and 0.086, respectively. In fig. 6a and 6b, the abscissa represents the incident energy of the planar light wave, the ordinate represents the value corresponding to the absorption cross section, the dots represent the first absorption cross section, and the curve represents the second absorption cross section.

From the results of the fitting of the frequency domain curves of the first absorption cross section and the steady-state frequency domain curves of the second absorption cross section corresponding to the second structural object shown in fig. 6a and 6b, when the candidate gain coefficient is 0.05, the corresponding ω is obtained_a1.3078eV, γ₂Is 0.5 meV; when the candidate gain coefficient is 0.086, the corresponding omega is obtained_a1.3078eV, γ₂It was 0.4 meV.

Referring to fig. 7a and 7b, fig. 7a is a schematic diagram of a frequency domain curve of a first absorption cross section and a steady-state frequency domain curve of a second absorption cross section corresponding to a fitting target structure object according to an embodiment of the present invention; fig. 7b is a schematic diagram of another frequency domain curve of the first absorption cross section and a steady-state frequency domain curve of the second absorption cross section corresponding to the fitting target structure object in the embodiment of the present invention. Fig. 7a and 7b are steady-state frequency domain curve fitting results of the frequency domain curve of the first absorption cross section and the second absorption cross section corresponding to the target structure object under the candidate gain coefficients, which are plotted when the candidate gain coefficients are 0.05 and 0.086, respectively. In fig. 7a and 7b, the abscissa represents the incident energy of the planar light wave, the ordinate represents the value corresponding to the absorption cross section, the dots represent the first absorption cross section, and the curve represents the second absorption cross section.

From the results of the steady-state frequency domain curve fitting of the first absorption cross section and the second absorption cross section corresponding to the target structure object shown in fig. 7a and 7b, it can be obtained that when the candidate gain coefficient is 0.05, the corresponding d is obtained_aIs 102D, D_c800D, g 7.6meV, calculated as gamma₁25.5 neV; when the candidate gain factor is 0.0At 86, get the corresponding d_aIs 430D, D_c1780D, g 7.6meV, calculated as γ₁Was 35.4 neV. Wherein, γ₁Is obtained by the formula

Calculated in the formula

Is the approximate Planck constant, and c is the speed of light in vacuum.

Based on the embodiment shown in fig. 2, as shown in fig. 8, fig. 8 is an implementation manner of determining the coherence function in the embodiment shown in fig. 2, and the implementation manner may include:

s801, applying the basic parameters to a Hamiltonian quantity and a quantum principal equation of the target structure object to determine a target structure object model.

In the embodiment of the present invention, after determining the basic parameters of the target structure object corresponding to the selected candidate gain coefficient under the selected candidate gain coefficient, the determined basic parameters of the target structure object are substituted into the hamiltonian and the quantum principal equation of the target structure object, so as to determine the accurate model of the target structure object (i.e., the hamiltonian and the quantum principal equation of the target structure object after determining the basic parameters). The basic parameters of the target structure object corresponding to the selected candidate gain coefficient are determined by the first absorption cross section and the second absorption cross section obtained by fitting calculation: surface plasma field eigenfrequency omega_cQuantum dot eigenfrequency omega_aPoint-cavity coupling strength g, quantum point dipole moment d_aSurface plasma dipole moment d_cCavity mode dissipation rate kappa and quantum dot spontaneous emissivity gamma₁And pure dephasing gamma₂。

S802, calculating a coherent function of the target structure object model by using a calculation formula of the coherent function.

In the embodiment of the invention, after the accurate model of the target structure object is determined under the selected candidate gain coefficient, further calculation can be carried out by applying a quantum optical calculation toolbox to obtain the density matrix rho of the target structure object model, and then, a calculation formula of a coherence function is used to calculate and obtain the coherence function of the target structure object model.

Wherein, the calculation formula of the coherent function is as follows:

in the calculation formula, g²(0) Is a coherent function of the object of the target structure,

an operator is generated/annihilated for photons of the surface plasmon field,

is operator

The result of the desired value in p,

is that

The expected value is obtained in ρ.

Based on the embodiment shown in fig. 2, as shown in fig. 9, fig. 9 is an implementation manner of determining the target gain factor in the embodiment shown in fig. 2, and the implementation manner may include:

s901, obtaining the minimum value of each coherent function as the minimum value of the coherent function.

In the embodiment of the invention, when all candidate gain coefficients selected according to a preset rule in a preset range are calculated to obtain the coherence functions of the target structure object model corresponding to all different candidate gain coefficients, the minimum value of each coherence function in all the obtained coherence functions is obtained, and the minimum value corresponding to each coherence function is taken as the minimum value of the coherence function.

And S902, judging whether the minimum value of each coherent function meets a preset judgment condition, and determining the coherent function meeting the preset judgment condition as a candidate coherent function.

Under the condition that all candidate gain coefficients selected according to a preset rule in a preset range are obtained and each coherence function minimum value is obtained, whether each obtained coherence function minimum value meets a preset judgment condition or not is judged, and then the coherence function meeting the preset judgment condition is determined to be a candidate coherence function.

An optional implementation manner in the embodiment of the present invention is as follows: and setting a preset judgment condition to judge whether the minimum value of each coherent function is less than 1, and when the minimum value of the coherent function is less than 1, indicating that the target structure object model corresponding to the coherent function can generate a single photon. And determining the coherent function meeting the preset judgment condition as a candidate coherent function, namely determining a target structure object model corresponding to the coherent function meeting the preset judgment condition as a candidate target structure object model, and determining a candidate gain coefficient corresponding to the candidate target structure object model as a target candidate gain coefficient.

And S903, comparing all the candidate coherence function minimum values, and determining a candidate gain coefficient corresponding to the candidate coherence function corresponding to the minimum value in the candidate coherence function minimum values as a target gain coefficient.

After the candidate coherent functions are determined, all the candidate coherent function minimum values are values smaller than 1, all the candidate coherent function minimum values are compared, then the candidate coherent function corresponding to the minimum value in the candidate coherent function minimum values is determined as a target coherent function, a candidate target structure object model corresponding to the target coherent function is determined as a final target structure object model, and a candidate gain coefficient corresponding to the final target structure object model is determined as a target gain coefficient.

Referring to fig. 10a and 10b, fig. 10a is a schematic diagram of a coherence function curve of an object model of a target structure according to an embodiment of the present invention; fig. 10b is a schematic diagram of a coherence function curve of another object model of the target structure according to an embodiment of the present invention. Fig. 10a and 10b are respectively a coherence function curve of the target structure object model under the candidate gain factor when the candidate gain factor is 0.05 and 0.086. In fig. 10a and 10b, the abscissa represents the incident energy of the planar light wave, and the ordinate is the value of the coherence function corresponding to the target structure object model under the candidate gain coefficient.

According to the coherence function curve of the target structure object model under the candidate gain coefficient shown in fig. 10a and 10b, when the candidate gain coefficient is 0.05, the minimal value of the coherence function of the corresponding target structure object model is 0.98; and when the candidate gain coefficient is 0.086, obtaining the minimum value of the coherence function of the corresponding target structure object model to be 0.35.

In practical application, when the minimum value of the coherence function corresponding to the target structure object model is smaller than 1, the gain coefficient corresponding to the target structure object model should be in the single photon source based on the quantum dots, and then a single photon can be generated. When the minimum value of the coherent function corresponding to the target structure object model is smaller than 1 and relatively smaller, the gain coefficient corresponding to the target structure object model should be in the single photon source based on the quantum dots, and the performance of generating single photons is better.

In the embodiment of the invention, after the structural object to be calculated is determined, different candidate gain coefficients are sequentially selected according to the determined structural object to be calculated. And then, under the selected candidate gain coefficient, further determining the basic parameters of the target structure object corresponding to the selected candidate gain coefficient, determining a model of the target structure object, and calculating to obtain a coherence function of the model of the target structure object. And finally, calculating to obtain the coherent functions of the target structure object models corresponding to all the different candidate gain coefficients aiming at all the selected candidate gain coefficients, and determining the candidate gain coefficients corresponding to the coherent functions meeting the preset judgment conditions as the target gain coefficients. The gain medium layer is applied to a single photon source based on quantum dots, so that in the single photon source, a substrate is covered with the gain medium layer, and the quantum dots and a metal micro-nano structure are wrapped in the gain medium layer, the metal micro-nano structure can limit an incident light field of planar light waves near the quantum dots to enhance the interaction between light and substances, and the gain medium layer wraps the quantum dots and the metal micro-nano structure therein, so that the attenuation of LSPs near the metal micro-nano structure can be limited, single photons can be better obtained, and the problems that in the prior art, the loss of the quantum dots-metal micro-nano structure is large, and the single photons are not easy to obtain are solved.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term "comprising", without further limitation, means that the element so defined is not excluded from the group consisting of additional identical elements in the process, method, article, or apparatus that comprises the element.

All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. A single photon source based on quantum dots, comprising: the device comprises a substrate (1), quantum dots (2), a metal micro-nano structure (3) and a gain medium layer (4);

the quantum dots (2) and the metal micro-nano structures (3) are respectively arranged on the substrate (1);

the metal micro-nano structure (3) comprises: the quantum dot structure comprises two identical semiellipsoids which are cut along the long axis in half, the planes of the semiellipsoids are attached to the substrate (1), and the quantum dots (2) are positioned between the two semiellipsoids and respectively have intervals with the two semiellipsoids;

the gain medium layer (4) covers the substrate (2) and wraps the quantum dots (2) and the metal micro-nano structure (3);

the gain medium layer is made of silicon dioxide SiO₂Doped with rare earth element ions.

2. A method for determining the gain factor of a gain medium layer, the method being used for the gain medium layer in the single photon source of claim 1, comprising:

3. The method of claim 2, wherein the structural object to be computed further comprises: a first structural object and a second structural object; under the candidate gain coefficient, determining the basic parameters of the target structure object corresponding to the candidate gain coefficient, including:

4. The method of claim 3, wherein the structural object to be computed further comprises: a first structural object and a second structural object; the step of establishing a frequency domain model corresponding to each structural object to be calculated by using a finite element method aiming at the determined structural object to be calculated, and calculating a first absorption cross section of each structural object to be calculated under a candidate gain coefficient comprises the following steps:

exciting each structural object to be calculated by adopting a planar light wave (5);

σ_abs1(ω)＝Q_rh(ω)/S₀

wherein σ_abs1(omega) is a first absorption cross section when the incident frequency of the planar lightwave (5) is omega, Q_rh(omega) is the corresponding heat loss when the incident frequency of the planar lightwave (5) is omega, S₀Is the energy density of the planar lightwave (5).

5. The method of claim 3, wherein the structural object to be computed further comprises: a first structural object and a second structural object; the method comprises the following steps of establishing a steady-state model corresponding to each structural object to be calculated aiming at the determined structural object to be calculated based on the cavity quantum electrodynamics CQED, and calculating a second absorption cross section of each structural object to be calculated under a steady-state condition candidate gain coefficient, wherein the step comprises the following steps of:

σ_abs2(ω)＝(ω/2)Im[μ_ωE₀ ^*]/S₀

μ_ω＝<μ|ρ>

wherein σ_abs2(ω) is a second absorption cross-section at an incident frequency of said planar lightwave (5) ω, ω being an incident frequency of said planar lightwave (5) μ_ωRepresents an expected value of mu obtained in rho for a dipole moment when the incident frequency of the planar lightwave (5) is omega, mu is a total dipole operator, rho is a density matrix corresponding to the incident frequency of the planar lightwave (5), E₀ ^*For the excitation intensity E of the planar light wave (5)₀Conjugation of (1).

6. The method of claim 3, wherein the structural object to be computed further comprises: a first structural object and a second structural object; the step of fitting each of the first absorption cross sections and the second absorption cross sections obtained by calculation and determining the basic parameters of the target structure object corresponding to the candidate gain coefficients includes:

7. The method of claim 2, wherein the basic parameters of the target structure object comprise:

8. The method of claim 2, wherein the step of determining a target structure object model based on the base parameters and calculating a coherence function of the target structure object model comprises:

wherein, the calculation formula of the coherence function is as follows:

wherein, g²(0) Is a stand forA coherence function of the object of the target structure,

an operator is generated/annihilated for photons of the surface plasmon field.

9. The method according to claim 2, wherein the step of determining the gain coefficient corresponding to the coherence function that satisfies the predetermined determination condition as the target gain coefficient comprises: