Method for accurately measuring plasmon nanocavity-single molecule exciton strong coupling energy level Rabi cleavage

Abstract

The invention provides a method for accurately measuring plasmon nanocavity-single molecule exciton strong coupling energy level Rabi splitting. The method is used for solving the problem that spectrum splitting measured through experiments is not equivalent to coupling system energy level Rabi splitting. The preparation method comprises the following steps: embedding a single dye molecule into a single CB [7] molecule to prepare a CB [7] at single dye molecule; coupling the CB [7] at single dye molecule with two gold nanospheres to obtain a gold nanosphere dimer (Au ND) / CB [7] at single dye molecule coupling system; the coupling system is transferred to a Si / SiO2 photonic substrate, and the photon mode frequency and line width are regulated and controlled by regulating the thickness of a SiO2 layer, so that the gold nanosphere dimer plasmon resonance line width is effectively regulated and controlled, and the gold nanosphere dimer plasmon resonance line width is matched with the exciton line width. According to the invention, the relative error between the spectral splitting obtained based on the spectral measurement of the single-molecule strong coupling system and the energy level Rabi splitting of the coupling system is reduced to-1.3% from the original-27.3%, so that the measurement error of the energy level Rabi splitting of the single-molecule strong coupling system is greatly reduced, and accurate measurement is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum precise measurement of light-matter strong coupling interaction, focuses on precise measurement of plasmonic nanocavity-single molecule room temperature strong coupling system energy level Rabi splitting, and particularly relates to a method for precisely measuring plasmonic nanocavity-single molecule exciton strong coupling energy level Rabi splitting, and specifically relates to preparation of a hybrid system composed of a gold nanosphere dimer plasmonic nanocavity with precisely positioned single molecule emitters and a photonic substrate (Si / SiO2) and precise measurement of plasmonic-single molecule strong coupling energy level Rabi splitting. BACKGROUND

[0002] Precise control of new optical fields and their interaction with single-exciton emitters (atoms, molecules, excitons) is not only a basic problem in quantum optics, but also an important basis for the study of light-matter interaction. Its research content is of great significance and value not only from the perspective of the basic theory of nanophotonics and optoelectronics, but also from the perspective of the development of new quantum optoelectronic devices and quantum technology. At present, related research results have been widely applied in many research fields such as quantum computing, quantum devices and quantum communication. Therefore, in recent years, new optical control and its interaction with single-exciton emitters have gradually developed into an international frontier and hotspot research field.

[0003] The realization of precise measurement of plasmonic nanocavity-single molecule room temperature strong coupling system energy level Rabi splitting provides a new scheme for studying light-matter interaction under extreme light fields. We know that the key to maintaining the quantum superposition state of the system lies in suppressing the quantum decoherence effect of the system, and the photon-emitter strong coupling is one of the important means to prepare the quantum superposition state. At this time, the coupling rate of the system is greater than its decay rate, and it enters the strong coupling region, and the quantum decoherence effect of the system is greatly suppressed. Under strong coupling, the quantum system and the light field are strongly coupled together, and the energy exchange between the two subsystems is superfast and reversible. The energy exchange rate is much faster than the decay rate of the system, which is manifested in the mode hybridization of photons and quantum emitters and the vacuum Rabi splitting from the frequency domain. This strong coupling can greatly suppress the quantum decoherence of the system, and maximize the system coherence state, which is an important prerequisite and foundation for quantum computing, quantum communication, quantum network and other quantum information processing.

[0004] However, due to the rapid decay of plasmons accompanied by huge loss, a large number of radiation sub- particles are usually needed to participate in the coupling process to improve the coupling rate, overcome the plasmon loss and achieve strong coupling effect, which is not conducive to the precise manipulation of single quantum state and the construction of corresponding quantum optical devices. Therefore, it is a great challenge to achieve strong coupling between plasmons and single radiation sub-particle at room temperature. To solve this problem, many research groups around the world have competed to carry out research. Recently, we take methylene blue (MB) dye molecule radiation sub-particle as an example, and successfully prepare a gold nanosphere dimer plasmonic nanocavity and single MB molecule coupling system-Au ND / CB[7]@single MB by comprehensively using “host-guest chemistry” method and CB[7] molecule assisted active self-assembly technology. In the study, we precisely control the nanocavity length (dimer gap) to sub-nanometer level (~0.9 nm), construct a super-small mode volume (~53 nm 3 ) high local plasmonic optical field, and successfully position a single MB molecule radiation sub-particle at the center of the nanocavity with the strongest electric field. In this process, based on the CB[7] molecule cavity control, the perfect alignment of the excitation transition dipole moment and the direction of the plasmonic electric field is realized. Finally, the deterministic single molecule excitation and plasmonic nanocavity are strongly coupled at room temperature and normal pressure, and the spectral Rabi splitting of ~115.9±2.27 meV is measured on a pure SiO2 substrate (without the design of a photonic substrate), and then the energy level Rabi splitting of ~91 meV is calculated, and the relative difference between them is as high as ~27.3±2.5%.

[0005] Due to the serious mismatch between the resonance linewidth (Γ d ) of the plasmonic nanocavity and the linewidth (Γ c ) of the molecular radiation sub-particle, the observed spectral splitting of the plasmonic-radiation sub-particle strong coupling system is not equal to the energy level Rabi splitting; in 2024, Zhong Jie et al. reported that the relative difference between the spectral splitting and the intrinsic energy level splitting in the strong coupling system composed of transition metal dichalcogenides and plasmons was as high as 100.6%. In addition, especially in the plasmonic nanocavity-single molecule strong coupling system, due to the huge difference between the decay linewidth of the single molecule radiation sub-particle and the plasmonic nanocavity, and the small coupling rate, the coupling system may not even have energy level splitting, but clear spectral splitting can be seen in the spectral measurement, resulting in the phenomenon of “pseudo strong coupling”, which makes it very difficult to accurately measure the energy level Rabi splitting of the strong coupling system by spectrum. At present, people mostly equate the experimentally measured spectral splitting to the energy level Rabi splitting of the coupling system, and it is a difficult problem to know under what quantitative conditions this equivalence holds and how to accurately measure the energy level Rabi splitting of the strong coupling system by spectrum. SUMMARY

[0006] In view of the technical problem that it is difficult to accurately measure the Rabi splitting of the energy level of a coupling system by using the prior art, the present application provides a method for accurately measuring the Rabi splitting of the energy level of a plasmonic nanocavity-single-molecule exciton strong coupling system, which adopts cucurbituril [7] (CB[7]) molecule assisted active self-assembly technology to couple two gold nanospheres of uniform size and smooth surface to form a dimer plasmonic nanocavity, and accurately position a single dye molecule at the position of the maximum electric field in the dimer plasmonic nanocavity (the center of the dimer gap), while realizing perfect alignment of the molecular radiation transition dipole moment and the direction of the plasmonic electric field; in combination with a photonic substrate design, the resonance linewidth (Γ d ) of the gold nanosphere dimer plasmonic nanocavity on the Si / SiO2 substrate is effectively compressed to match the linewidth (Γ c ) of the dye molecule (Γ d ≈Γ c ), and thus the spectral accurate measurement of the Rabi splitting of the energy level of the plasmonic nanocavity-single-molecule strong coupling system at room temperature is realized, which provides a solution for quantum precision measurement of the light-matter strong coupling under extreme light field.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows: a method for accurately measuring the Rabi splitting of the energy level of a plasmonic nanocavity-single-molecule exciton strong coupling system, comprising the following steps:

[0008] Preparation of CB[7]@single dye molecule by embedding a single dye molecule into a single CB[7] molecule by host-guest chemistry method;

[0009] Coupling of CB[7]@single dye molecule with two gold nanospheres to form a gold nanosphere dimer (Au ND) / CB[7]@single dye molecule coupling system, to obtain Au ND / CB[7]@single dye molecule;

[0010] Transfer of the Au ND / CB[7]@single dye molecule coupling system to a Si / SiO2 photonic substrate to form a hybrid system, and regulation of the thickness of the SiO2 layer to regulate the frequency and linewidth of the photonic mode, so as to effectively regulate the resonance linewidth Γ d of the gold nanosphere dimer plasmonic nanocavity, and match the resonance linewidth Γ d with the exciton linewidth Γ c .

[0011] Preferably, the gap width between the two gold nanospheres is equal to the thickness of a single connected CB[7] molecule; the AuND / CB[7]@single dye molecule is precisely positioned at the center of the gold nanosphere dimer plasmon nanocavity, and the dipole moment direction of the AuND / CB[7]@single dye molecule is controlled in the direction of the plasmon electric field through the CB[7] molecular cage.

[0012] Preferably, the method for preparing the gold nanospheres is:

[0013] Step 1: Prepare ultra-high purity gold nanorods using a hydrothermal chemical seed growth method;

[0014] Step 2: Using Au 3+ The gold nanorods were etched into ultra-round gold nanospheres with controllable diameters by oxidation etching.

[0015] Preferably, the method for preparing ultra-high purity gold nanorods by the hydrothermal chemical seed growth method is:

[0016] Synthesis of gold seeds: Add 75-150 μL of 0.01 mol / L HAuCl4 to 15 mL of CTAB and stir evenly for 30 min. Then, inject 0.5-1 mL of 0.1 mol / L ice-cold NaBH4 and stir evenly for 5 min to obtain a seed solution. Store in a 25°C water bath for 2 h before use.

[0017] Preparation of growth solution: Add 1-2.5 mL of 0.1 mol / L HAuCl4 to 150 mL of 0.1 mol / L CTAB solution and stir rapidly for 20 minutes to obtain the growth solution;

[0018] Preparation of gold nanorods: 0.1 mol / L, 150 μL of AgNO3, 100 μL of seed solution, and 0.1 mol / L, 600 μL of ascorbic acid were quickly added to the growth solution and stirred for 3 min. The gold nanorod solution was obtained after standing for 12 h.

[0019] Purification of gold nanorods: The resulting gold nanorod solution was centrifuged twice to remove unreacted ions. The gold nanorods were redispersed in CTAB after centrifugation and 4 mL of NaCl was added and allowed to stand for 24 hours. The gold nanoparticles with larger surface areas adhered to the bottom of the vessel. The supernatant was centrifuged to remove the solvent to obtain high-purity gold nanorods.

[0020] High-purity gold nanorods in Au 3+ Gold nanospheres with a diameter of r~35-45nm and an ultra-smooth surface were prepared under ion oxidation etching.

[0021] Preferably, the preparation method of the gold nanospheres is:

[0022] First etching: add 5-15 mM, 10-50 μL of HAuCl4 to 2 mL, 0.05 mol / L of CTAB gold nanorod solution, stir well, and then place in a 28°C water bath for 4-5 h. Centrifuge the obtained ~2 mL gold nanorod solution at 12000 rpm / 12 min for 3 times to terminate the reaction and remove CTAB and excess reagents in the solution. The obtained precipitate is washed and diluted with cetylpyridinium chloride until the concentration is 1;

[0023] Regrowth: add 350-700 μL of HAuCl4 to 20 mL of CPC and stir for 3 min. Then quickly add 4.5-9 mL of AA and 6 mL of the solution after the first etching in sequence. Stir gently in a water bath at 26°C for 15 min. Then centrifuge the solution twice to remove unreacted ions, resuspend the precipitate in CTAB, and adjust the concentration to 1.

[0024] Second etching: add a certain amount of HAuCl4 to the gold nanosphere solution after regrowth, centrifuge the solution at 12000 rpm / 12 min after a certain reaction time, and remove the excess solution to obtain super-smooth gold nanospheres.

[0025] Preferably, in the second etching process of gold nanosphere preparation, the size of the gold nanosphere is controlled by changing the amount of HAuCl4 added; at the same time, the super-circular gold nanosphere is ensured by accurately controlling the etching time.

[0026] The dye molecule is an MB dye molecule;

[0027] The method for preparing CB[7]@single MB by embedding a single MB molecule into CB[7] molecules using host-guest chemistry is as follows: add an MB solution dissolved in water to a CB[7] aqueous solution, the molar ratio of MB to CB[7] is 1:2, and mix well using ultrasonic waves for 10 min.

[0028] Preferably, the preparation method of the Au ND / CB[7]@single dye molecule is as follows:

[0029] Add CB[7]@single dye molecules to a gold nanosphere solution dispersed in deionized water. The CB[7] molecule cage actively binds to the surface of the gold nanosphere particles through the carbonyl group on one side. When another gold nanosphere approaches, the carbonyl group on the other side of the CB[7] molecule cage grabs the sidewall of the second gold nanosphere, forming a gold nanosphere dimer (Au ND) / CB[7]@single dye molecule.

[0030] The single dye molecule exciton transition dipole moment is perfectly restricted in the direction perpendicular to the CB[7] molecule ring plane, and in the direction parallel to the plasmonic field in the nanocavity gap.

[0031] Preferably, the preparation method of the hybrid system is: 4-10 μL of Au ND / CB[7]@single dye molecule solution is dropped on the surface of Si / SiO2 photonic substrate, respectively, after 5 min, the droplet is removed, and the surface of the substrate is washed with deionized water for 1-2 times, then the surface of the substrate is blown dry with nitrogen, and Au ND / CB[7]@single dye molecule is scattered on the surface of Si / SiO2 substrate.

[0032] Preferably, the photonic substrate composed of Si / SiO2 double-layer dielectric layer is prepared by inductively coupled plasma chemical vapor deposition method, the thickness of the SiO2 layer is controlled to be 2500-2650 nm by changing the deposition time, the Au ND / CB[7]@single dye molecule coupling system is placed on the Si / SiO2 photonic substrate, and the large decay linewidth Γ d ≈140-170 meV of the gold nanosphere dimer plasmon resonance can be greatly compressed to 80-100 meV.

[0033] Preferably, the eigenenergy of the single-exciton and plasmon coupling system is represented as:

[0034]

[0035] The energy level splitting of the coupling system is where δ=ε d -ε c is the detuning between the two coupling components; when the resonance δ=0, the energy level splitting is: and where g EP =|Γ d -Γ c | / 4 is the critical coupling strength of the system at the singular point;

[0036] For the single-exciton and plasmon coupling system, the absorption spectrum signal is mainly dominated by the plasmonic channel, which is given by:

[0037] where i represents the imaginary unit, and are the resonance energies of the plasmon and the exciton, respectively, ω c , ω d represent the reduced Planck constant, the exciton transition frequency, and the plasmon resonance frequency, respectively, Γ d and Γ c are the decay linewidths of the plasmon and the exciton, respectively, and g is the coupling strength between the exciton and the plasmon;

[0038] Absorption Rabi splitting at resonance and the critical condition is:

[0039]

[0040] If

[0041]

[0042] The spectral splitting observed in the spectroscopic measurement depends on the degree of matching between the plasmonic linewidth Γ d and the excitonic linewidth Γ c ; only when the ratio of the plasmonic linewidth Γ d to the excitonic linewidth Γ c is close to 1, the absorption spectrum intersects with the energy level Rabi splitting spectrum, and the plasmonic linewidth Γ d is equal to the excitonic linewidth Γ c at this time.

[0043] Compared with the prior art, the present application has the beneficial effects that: the super-smooth gold nanospheres prepared by etching gold nanorods with Au 3+ oxide are used, a CB[7]@single dye molecule radiation subsystem is prepared by embedding a single dye molecule (taking a methylene blue molecule as an example, Methylene blue, MB) into a single cyclic cucurbituril [7] (CB[7]) molecular cage by using a host-body chemical method, a CB[7]@single dye molecule radiation subsystem and two gold nanospheres with uniform size and smooth surface are coupled by using a cucurbituril [7] (CB[7]) molecule assisted active self-assembly technology to form a gold nanosphere dimer / CB[7]@single dye molecule coupling system (Au ND / CB[7]@single dye molecule), namely a dimer plasmonic nanocavity, the gap width of the two gold nanospheres is accurately controlled at about 0.9 nm (equal to the thickness of the connected CB[7] molecules), the Au ND / CB[7]@single dye molecule is accurately positioned at the center position of the dimer plasmonic nanocavity (that is, the position with the strongest electric field), and the direction of the dipole moment of the Au ND / CB[7]@single dye molecule is controlled in the direction of the plasmonic electric field through the CB[7] molecular cage; the single dye molecule radiation subsystem can be accurately positioned and the direction of the dipole moment can be accurately controlled in the plasmonic nanocavity at the same time. Then, the prepared Au ND / CB[7]@single dye molecule is transferred to the surface of a Si / SiO2 photonic substrate to form a hybrid system, the thickness of the SiO2 in the photonic substrate Si / SiO2 is designed to regulate the frequency and the linewidth of the photonic mode, the resonance linewidth (Γ d ) of the gold nanosphere dimer plasmonic nanocavity is effectively regulated to match the exciton linewidth (Γ c ) (Γ d ≈Γ c), thereby greatly reducing the spectral measurement error of the plasmon-monomer strong coupling system energy level Rabi splitting (-1.3+ / -0.86%) to meet the requirement of accurate measurement. The hybrid system helps to deeply understand the light-matter interaction in quantum mechanics on a nanoscale, and is expected to provide technical support in quantum information processing, single photon source, optical nonlinearity, low threshold laser and other applications. Experimental results show that the relative error between the spectral splitting obtained based on the spectral measurement of the monomer strong coupling system and the energy level Rabi splitting of the coupling system is reduced to -1.3%; compared with the large error (-27.3%) between the two when the plasmonic cavity-monomer coupling system is measured on a pure SiO2 substrate (without the design of the photonic substrate), the spectral measurement method based on the ingenious design of the photonic substrate greatly reduces the measurement error of the monomer strong coupling system energy level Rabi splitting, and achieves accurate measurement. The accurate measurement of the energy level Rabi splitting of the plasmon-monomer strong coupling system realized by the application will provide technical support for quantum information processing and quantum device application research.

[0044] By using the application, (1) a single dye molecule can be precisely positioned at the maximum electric field position (the center of the gap between the gold nanosphere dimers) in the gold nanosphere dimer nanocavity, and the direction of the transition dipole moment of the dye molecule is perfectly aligned with the direction of the plasmonic electric field, so that the plasmonic nanocavity-monomer strong coupling effect is realized, and the theoretical value of the energy level Rabi splitting of the plasmon-monomer strong coupling system can be accurately predicted; (2) the prepared plasmon-monomer strong coupling system is combined with the Si / SiO2 substrate by using the photonic substrate design, the thickness of the SiO2 layer is adjusted, the plasmonic nanocavity resonance linewidth is perfectly adjusted and matched with the exciton linewidth, so that the relative error between the observed spectral splitting in the spectral measurement and the energy level Rabi splitting of the strong coupling system is greatly reduced, and accurate measurement is realized.

[0045] The application constructs a plasmon-monomer strong coupling-photonic substrate hybrid system, matches the plasmonic linewidth with the exciton linewidth, greatly reduces the relative error between the observed spectral splitting in the spectral measurement and the energy level Rabi splitting of the strong coupling system, and realizes accurate measurement. 3+The gold nanospheres with the diameter precisely controlled and the super-smooth surface are prepared under the ion oxidation etching, and a single dye molecule is precisely encapsulated in the CB[7] molecular cage by using the host-guest chemical method, so that a single molecule radiation subsystem-CB[7]@single dye molecule is successfully prepared. d ≈140-170meV) can be greatly compressed to 80meV-100meV, which is matched with the radiation subsystem line width of the dye molecule (for example, the methylene blue molecule, Methylene blue, MB), and when the two are coupled, the relative error of the spectrum splitting and the coupling system energy level Rabi splitting measured can be controlled to about 1.3%, so that the precise measurement of the energy level Rabi splitting of the plasmonic nanocavity-single molecule strong coupling system can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0047] Figure 1 It is a schematic diagram of the principle of the present application and the plasmonic resonance line width control experiment, wherein a is the schematic diagram of the present application, and b is the plasmonic resonance line width regulated by the Si / SiO2 photonic substrate.

[0048] Figure 2 It is a TEM diagram of the high-purity gold nanorods prepared in the embodiment of the present application.

[0049] Figure 3 It is a flowchart of the preparation of the gold nanosphere dimer in the embodiment of the present application.

[0050] Figure 4 It is an absorption spectrum diagram of the methylene blue (MB) molecule and the CB[7] aqueous solution in the embodiment of the present application with and without CB[7].

[0051] Figure 5 It is a TEM diagram of the gold nanosphere dimer prepared in the embodiment of the present application.

[0052] Figure 6Graphs of Au NDs on SiO2 substrates at different wavelengths in an example of the present invention (Comsol simulation), where a is the mode volume and b is the normalized scattering.

[0053] Figure 7 : These are curves of Au NDs on Si / SiO2 substrates at different wavelengths in an example of the present invention (Comsol simulation), where a is the mode volume and b is the normalized scattering.

[0054] Figure 8 Graph showing the normalized scattering curves of Au NDs experimentally measured on SiO2 and Si / SiO2 substrates in an example of the present invention.

[0055] Figure 9 This is the normalized scattering curve of the strong coupling of Au ND single excitons located on SiO2 and Si / SiO2 substrates in the examples of the present invention.

[0056] Figure 10 2 is a comparison diagram of the energy level splitting and Rabi splitting of the strong coupling of Au ND single excitons located on SiO2 and Si / SiO2 substrates in the examples of the present invention. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0058] A method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels mainly includes the following steps:

[0059] Step 1: Prepare ultra-high purity gold nanorods using a hydrothermal chemical seed growth method.

[0060] Before the experiment, all glassware was washed with aqua regia (V 盐酸 :V 硝酸 =3:1) soaking and cleaning, then rinsing with deionized water several times and drying before use to remove organic pollutants, metal ions and other impurities on the glassware, which is conducive to the preparation of high-quality gold nanorods.

[0061] Step 1: Synthesize Gold Seeds

[0062] Add 75-150 μL (0.01 mol / L) of HAuCl4 (tetrachloroauric acid) to 15 mL of CTAB (hexadecyltrimethylammonium bromide), stir evenly for 30 min, then inject 0.5-1 mL (0.1 mol / L) of freshly prepared frozen NaBH4 (sodium borohydride), stir evenly for 5 min to obtain a seed solution, and store it in a 25°C water bath for 2 h before use.

[0063] Step 2: Preparation of growth medium

[0064] 1-2.5 mL (0.1 mol / L) HAuCl4 was added to 150 mL (0.1 mol / L) CTAB solution and rapidly stirred for 20 min to obtain a growth solution.

[0065] Step 3: Preparation of gold nanorods

[0066] AgNO3 (0.1 mol / L, 150 μL), seed solution (100 μL) and ascorbic acid (AA) (0.1 mol / L, 600 μL) were quickly added to the growth solution and stirred for 3 min. After standing for 12 h, a gold nanorod solution was obtained.

[0067] Purification of gold nanorods

[0068] A purification method based on the surface area differences of metal nanoparticles can be used to separate uniform nanostructures from a mixture of nanoparticles of unequal mass and volume. Irregularly shaped gold nanoparticles can be removed from a gold nanorod solution. This method can be used to obtain high-purity gold nanorods, such as Figure 2 The specific operation is as follows: the gold nanorod solution obtained above is centrifuged twice (6000 rpm, 15 minutes) to remove unreacted ions. The gold nanorods after centrifugation are redispersed in CTAB (0.05M), 4 mL of NaCl (2.0M) is added, and the mixture is allowed to stand for 24 hours. The gold nanoparticles with larger surface areas first adhere to the bottom of the vessel. The supernatant is transferred to a clean beaker to obtain a uniformly dispersed, high-purity gold nanorod solution. The non-gold nanorod gold nanoparticles at the bottom of the vessel are removed. The supernatant (containing the high-purity gold nanorods) is then centrifuged (8000 rpm, 10 minutes) to remove the solvent to obtain the high-purity gold nanorods.

[0069] Step 2: Using Au 3+ The gold nanorods were etched into ultra-round and ultra-smooth gold nanospheres with controllable diameter by oxidation etching.

[0070] Step 1: First Etch

[0071] First, the gold nanorods were prepared by a slow, controllable, and selective etching process on the surface atoms with the lowest metal coordination number in a self-limited manner. The reaction selectively occurs at the tips of the gold nanorods, rather than on the surface, and the edge structure will change. Oxidative dissolution selectively occurs at the unsaturated coordination of the nanoparticles, without significantly affecting the rest of the structure. Au 3+ Oxidation was used to etch Au atoms, and the tips of the prepared Au NRs (gold nanorods) were smoothed to obtain gold nanospheres, Figure 3 The flowchart for preparing gold nanosphere dimers is shown. The specific operation is as follows: a certain amount of HAuCl4 is added to the gold nanorod solution dissolved in 2 mL of CTAB (0.05 mol / L), and after being fully stirred and uniformly mixed, it is placed in a 28°C water bath for 4-5 hours, at which time the gold nanosphere extinction value is about 525 nm. The concentration of HAuCl4 is 5-15 mM, and the optimal concentration is 10 mM, and the volume added is about 10-50 μL. Finally, the ~2 mL gold nanorod solution obtained is centrifuged at 12000 rpm / 12 min for 3 times to terminate the reaction and remove the CTAB and excess reagents in the solution, and the obtained precipitate is washed and diluted with CPC (cetylpyridinium chloride) (10 mM) until the concentration is 1, and is placed aside for standby.

[0072] Second step: regrowth

[0073] 350-700 μL of HAuCl4 (10 mM) is added to 20 mL of CPC (10 mM) and stirred for 3 min, and then 4.5-9 mL of AA (100 mM) and 6 mL of the above solution after the first etching with a concentration of 1 are quickly added in sequence, and the solution is gently stirred at 26°C in a water bath for 15 min. Then the solution is centrifuged twice (12000 rpm, 15 min) to remove unreacted ions, and the precipitate is resuspended in CTAB (50 mM) to a concentration of 1.

[0074] Third step: second etching

[0075] The process of the second etching is similar to that of the first etching. Briefly, a certain amount of HAuCl4 (10 mM) is added to the regrown gold nanosphere solution, and after a certain period of reaction, the solution is centrifuged at 12000 rpm / 12 min and the excess solution is removed to obtain super-smooth gold nanospheres. In the process of the second etching, the size of the gold nanospheres can be effectively controlled by changing the amount of HAuCl4 added; at the same time, by accurately controlling the etching time, super-circular gold nanospheres can be obtained.

[0076] Step 3: CB[7]@single dye molecule was prepared by embedding single dye molecule into single macrocyclic cucurbituril [7] (CB[7]) molecule.

[0077] High purity gold nanorods in Au 3+ Under ion-oxidation etching, gold nanospheres with precisely controlled diameter (r ~ 35-45 nm) and super-smooth surface were prepared, and single dye molecule was precisely encapsulated in CB[7] molecular cage by host-guest chemistry method, and a single-molecule radiation subsystem—CB[7]@single dye molecule was successfully prepared.

[0078] Pumpkin-shaped CB[7] molecules with hollow and hydrophobic internal volume are water-soluble, and only one MB (methylene blue) dye molecule can be accommodated in one CB[7] molecule. The absorption spectrum of MB dimer (gray dotted line) shows a small shoulder peak at 615 nm, which almost disappears after mixing MB with CB[7], as shown in Figure 4 , which indicates that MB mainly exists in the form of single molecule (blue dotted line) at this concentration (1.0×10 -7 M), which is conducive to the formation of single-molecule radiation subsystem—CB[7]@single dye molecule. CB[7]@single MB was prepared by embedding single MB molecule into CB[7] molecule using host-guest chemistry method. The specific operation is as follows: the MB (1.0×10 -7 M) solution dissolved in water was added to the CB[7] (1.0×10 -7 M) aqueous solution, and ultrasonic mixing was used for 10 min (the molar ratio of MB to CB[7] was 1:2).

[0079] Step 4: CB[7]@single dye molecule was coupled with two gold nanospheres to form gold nanosphere dimer / CB[7]@single dye molecule coupling system, and Au ND / CB[7]@single dye molecule was obtained. The gap width of the two gold nanospheres was precisely controlled at ~ 0.9 nm (equal to the thickness of the connected CB[7] molecule), and Au ND / CB[7]@single dye molecule was precisely located at the center position of the gold nanosphere dimer plasmonic nanocavity (i.e. the position with the strongest electric field), and the direction of the dipole moment of Au ND / CB[7]@single dye molecule was controlled in the direction of the plasmonic electric field through the CB[7] molecular cage.

[0080] The gold nanosphere dimer-single MB molecule (CB[7]@single MB) coupling gold nanosphere is used to add a certain amount of CB[7]@single MB to the gold nanosphere solution dispersed in deionized water after the secondary etching in step 2 above, and gold nanosphere dimer can be obtained after standing for a period of time. The specific process is that the CB[7]@single MB molecule is added to the gold nanosphere solution dispersed in deionized water, and the CB[7] molecule cage can actively bind to the surface of the gold nanosphere particle through the carbonyl group on one side. When the other gold nanosphere approaches, the carbonyl group on the other side of the CB[7] molecule cage can grab the sidewall of the second gold nanosphere, forming a gold nanosphere dimer Au ND / CB[7]@single MB, Figure 5 The TEM morphology thereof is shown, from which it can be seen that two gold nanospheres with smooth surfaces and a radius of ~39 nm form a gold nanosphere dimer nanocavity under the action of the CB[7] molecule cage, and the gap between the two gold nanospheres is exactly equal to the thickness of the connecting molecule CB[7] (~0.9 nm). At this time, the MB molecule exciton transition dipole moment (in the longitudinal direction of the MB molecule) can be perfectly restricted in the direction perpendicular to the CB[7] ring plane, i.e. parallel to the direction of the plasmonic electric field in the nanocavity gap. Based on this technology, a single dye molecule can not only be precisely positioned at the center position of the gold nanosphere dimer nanocavity gap with the maximum electric field strength (i.e. the position of the maximum plasmonic electric field), but also the dye molecule exciton transition dipole moment is precisely controlled and perfectly aligned with the direction of the electric field of the gap plasmonic mode, thereby preparing an Au ND / CB[7]@single dye molecule coupling system.

[0081] Step 5: The Au ND / CB[7]@single dye molecule coupling system is transferred to the surface of a Si / SiO2 photonic substrate to form a hybrid system, the thickness of the SiO2 layer is adjusted to control the frequency and linewidth of the photonic mode, and the effective regulation of the plasmonic nanocavity resonance linewidth (Γ d ) of the gold nanosphere dimer is realized to match the exciton linewidth (Γ c ) (Γ d ≈Γ c ), so as to greatly reduce the spectral measurement error of the Rabi splitting of the plasmonic-single molecule strong coupling system and achieve accurate measurement.

[0082] 4-10 μL of the above Au ND / CB[7]@single MB solution is dropped on the surface of the Si / SiO2 photonic substrate, the droplet is removed after 5 min, and the substrate surface is washed with deionized water for 1-2 times, and then the substrate surface is blown dry with nitrogen. At this time, the Au ND / CB[7]@single MB is scattered on the surface of the Si / SiO2 substrate, and then dark field optical measurement is performed.

[0083] The photonic substrate composed of Si / SiO2 double-layer dielectric layer was prepared by inductively coupled plasma chemical vapor deposition. The thickness of SiO2 layer was adjusted to 2500-2650nm by changing the deposition time (visible Figure 8 The experimental results of the left illustration) are shown. The Au ND / CB[7]@single dye molecule coupling system is placed on the surface of the photonic substrate. At this time, the large attenuation line width (Γ d The optical field interference (≈140-170 meV) of a Si / SiO2 film can be significantly compressed to 80-100 meV. This is due to the optical field interference between the Si / SiO2 film and the low-refractive-index dielectric film. The optical field interference between the films causes a redistribution of the electromagnetic environment on the substrate surface, forming an optical channel with a certain linewidth. This reshapes the scattering of the metal nanoparticles within the channel, thereby compressing the linewidth of the plasmon resonance mode, reducing the plasmon radiation loss and matching it with the exciton linewidth of dye molecules (such as methylene blue, MB). When the two are coupled, the system energy level Rabi splitting is increased while reducing system losses. The relative error between the measured spectral splitting and the coupled system energy level Rabi splitting is controlled to approximately 1%, thus achieving accurate measurement of the energy level Rabi splitting of the plasmon nanocavity-single molecule strong coupling system.

[0084] This method provides a new strategy for the precise spectral measurement of the energy level Rabi splitting of strong coupling between plasmons and single quantum radiators (atoms, molecules, excitons, etc.) at room temperature, which will provide technical support for quantum information processing, quantum device research, etc.

[0085] Generally, for the intrinsic energy level of the coupled system of a single exciton and a plasmon It can be expressed as:

[0086]

[0087] Among them, Ω LS , i represent the energy level splitting and imaginary unit of the coupled system respectively.

[0088] The energy level splitting (LS) is given by

[0089]

[0090] Where δ = ω d -ε c is the detuning between the two coupled components. At resonance δ = 0, the expression for the energy level Rabi splitting is:

[0091]

[0092] Among them, gEP =|Γ d -Γ c | / 4 is the critical coupling strength of the system at the singular point (EP).

[0093] For the coupled system of a single exciton and a plasmon, the absorption spectrum signal is mainly dominated by the plasma channel and is given by the following formula:

[0094] in, and are the resonance energies of plasmons and excitons, ω c 、ω d , σ d (ω) represents the reduced Planck constant, exciton transition frequency, plasmon resonance frequency and absorption spectrum of plasmon-exciton strong coupling system, Γ d and Γ c are the decay linewidths of plasmons and excitons, respectively, and g is the coupling strength between excitons and plasmons. According to formula (4), the absorption Rabi splitting at resonance Its critical condition is given by the following formula:

[0095]

[0096] if

[0097]

[0098] From equations (2) and (5), it can be seen that the spectrum splitting observed by spectral measurement is not directly equal to the energy level splitting, but depends on the plasmon resonance linewidth Γ d and exciton linewidth Γ c The degree of matching between them; using equations (2) and (5) to draw Figure 1 It can be seen more intuitively that for the common plasmon-radion coupling system (Γ d >Γ c , Γ d and Γ c The spectral splitting observed by spectral measurement is not equivalent to its energy level Rabi splitting, and there may be a big difference between the two. d and the exciton linewidth Γ c When the ratio is close to 1, the absorption spectrum and the energy level Rabi splitting spectrum intersect, and the two are equal at this time. In addition, it can be found from equation (3) that if the plasmon line width Γ d can be sufficiently compressed to match the exciton linewidth Γ c , then the critical coupling strength g EPThe energy level splitting Ω will be significantly reduced, even to zero LS , and the corresponding increase to 2g.This shows that effective inhibition of plasmonic damping and matching with exciton damping (Γ d ≈Γ c ) not only can easily achieve single-exciton-plasmon strong coupling, but also can greatly reduce the relative error between the observed spectral splitting and the energy level Rabi splitting of the strong coupling system, and achieve its accurate measurement.

[0099] Therefore, if the effective compression of the plasmon resonance linewidth (Γ d ) and the matching with the exciton radiation sub-linewidth (Γ c ) can be achieved (see Figure 1 b), the coupling system loss can be reduced, and the critical coupling strength of the coupling system singularity (i.e. the singularity of the non-Hermite coupling system in the Hilbert space, where the system eigenenergy and eigenstate are simultaneously degenerate) can be regulated, thereby increasing the energy level Rabi splitting width, significantly reducing the difficulty of realizing plasmon-single radiation sub-room temperature strong coupling, and greatly improving its success rate; and the relative error between the observed spectral splitting and the energy level Rabi splitting of the strong coupling system can be greatly reduced, so that the splitting widths are consistent, see Figure 1 the intersection of the spectral splitting and the energy level splitting in a of , which is expected to solve the problem of accurately measuring the energy level Rabi splitting of the strong coupling system using spectrum.

[0100] The Au ND / CB[7]@single MB system prepared in the present application is the only one reported so far that can simultaneously locate a single dye molecule (the present application takes methylene blue molecule as an example, Methylene blue, MB) MB molecule in the maximum electric field position of the gold nanosphere dimer plasmonic nanocavity and perfectly align its transition dipole moment with the direction of the plasmonic electric field. In addition, the present application combines the plasmonic metal nanostructure with the carefully designed photon substrate (Si / SiO2) to form a plasmonic-photon hybrid system, which can greatly enhance the metal nanostructure cavity field to produce a local hot spot, so as to have super-high photon localization ability. At the same time, the photon mode in the photon substrate and the plasmonic resonance are coupled to produce a hybrid mode with high Q factor, which provides an ideal platform for light-matter coupling regulation. In the present application, the nanocavity length (dimer gap) is accurately controlled to sub-nanometer level (~0.9nm), and a high-localization plasmonic optical field with ultra-small mode volume (~53nm 3 ) is constructed, such as Figure 6 and Figure 7The mode volume and normalized scattering spectrum of two 39 nm radius gold nanospheres dimer nanocavity on SiO2 substrate and designed Si / SiO2 photonic substrate are calculated respectively using COMSOL simulation, from which it can be seen that the mode volume of gold nanospheres dimer nanocavity is 53-54 nm when resonating with exciton (MB molecule) (~ 659 nm) 3 Meanwhile, the above preparation method can successfully locate a single MB dye molecule at the strongest electric field in the center of the nanocavity, and combine it with SiO2 substrate and Si / SiO2 substrate respectively to form two different hybrid systems, and the line width of the plasmonic nanocavity on the Si / SiO2 substrate is obviously compressed, as shown in Figure 8 The spectrum splitting of the two systems is measured using dark field scattering, as shown in Figure 9 The obvious spectral Rabi splitting The room temperature single exciton strong coupling effect is achieved (as it meets the strong coupling criterion, The coupling constant g dc (see the following calculation and analysis), which indicates that the energy level of the coupling system is split. The energy level Rabi splitting and absorption spectrum Rabi splitting of the two hybrid systems are calculated using equations (2) and (5). For the pure SiO2 substrate hybrid system, the parameters Γ d = 170 meV, Γ c = 70 meV are extracted, and the coupling constant g = 52 meV is obtained by equation (5), and the energy level splitting The spectral Rabi splitting On the Si / SiO2 photonic substrate, the resonance line width of the plasmonic nanocavity can be compressed to Γ d = 90 meV (see Figure 1 b), which is well matched with the exciton line width Γ c = 70 meV. The coupling constant g dc = 51.8 meV is calculated using equation (5), and the energy level Rabi splitting is The spectral Rabi splitting As shown in Figure 10 , the relative deviation η = (Ω ab - Ω LS ) / Ω LS is calculated to be ~ 27.3 ± 2.5% and ~ 1.3 ± 0.86% respectively at resonance. The coupling constant g dc is calculated by equation (6):

[0101]

[0102] Where, it is calculated that the effective mode volume of plasmonic nanocavity on SiO2 and Si / SiO2 substrate is and ( Figure 6 and Figure 7 ), mu c = 0.09e nm is the MB molecule exciton transition dipole moment, f d = E d (r) / |E d (r)| max is the normalized electric field (EF) intensity at position r, and epsilon0 represents the vacuum permittivity. Compared with being placed on a pure SiO2 substrate, the resonance linewidth of the plasmonic nanocavity is effectively compressed d ( Figure 8 ) and matched with the exciton linewidth Gamma c , and finally the spectral accurate measurement of the energy level plasmonic nanocavity and single molecule exciton room temperature strong coupling system level Rabi splitting (error is reduced to the order of ~1%) can be realized.

[0103] Figure 1 b is the scattering spectrum of the gold nanosphere dimer plasmonic nanocavity placed on SiO2 and Si / SiO2 substrates, respectively, from which it can be seen that the plasmonic resonance linewidth Gamma d = 170meV is compressed to 90meV on the Si / SiO2 substrate, which demonstrates the complete design of Si / SiO2 photon to manipulate the plasmonic resonance linewidth.

[0104] The high-performance plasmonic metal-photon substrate hybrid system constructed by the application successfully realizes effective suppression of plasmonic resonance loss, and further realizes accurate measurement of plasmonic nanocavity-single molecule room temperature strong coupling and its energy level Rabi splitting. The successful verification in experiments provides inspiration for people to deeply understand the role of the low-loss electromagnetic environment of the optical microcavity in suppressing the plasmonic resonance loss, and provides new ideas and important data reference for promoting the research of room temperature solid-state quantum information processing and quantum optical devices.

[0105] The application utilizes Au 3+Ultra-smooth gold nanospheres are prepared by oxidative etching of gold nanorods. A single dye molecule (this patent takes methylene blue molecule as an example, Methylene blue, MB) MB molecular radiator is embedded into a ring-shaped cucurbituril [7] (CB [7]) molecule to form a single molecule radiator system. Cucurbituril [7] (CB [7]) molecule-assisted active self-assembly technology is used to couple two gold nanospheres with uniform size and smooth surface to form a dimer plasmon nanocavity. The single dye molecule is precisely positioned at the maximum electric field position (the center of the dimer gap) in the gold nanosphere dimer nanocavity. At the same time, the molecular radiator transition dipole moment is perfectly aligned with the plasmon electric field direction. The precisely controlled nanocavity length (dimer gap) reaches the sub-nanometer level (~0.9nm), and a nanostructured ... 3 ) of highly localized plasmon light field; secondly, the prepared plasmon nanocavity-single exciton system was combined with a carefully designed Si / SiO2 photonic substrate to form a hybrid system, achieving the plasmon nanocavity resonant attenuation linewidth (Γ d ) compression, and the MB molecular radiation sub-line width (Γ c ) matches (Γ d ≈Γ c ), and successfully reduced the experimentally measured spectral splitting and coupled system energy level Rabi splitting error from ~27.3% (pure SiO2 substrate) to ~1.3% (Si / SiO2 photonic substrate), demonstrating a new strategy for precise spectral measurement of the energy level Rabi splitting of a plasmonic nanocavity-single-molecule room-temperature strong coupling system. This invention will further promote the development of single-quantum strong-coupling room-temperature quantum devices.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for accurately measuring the Rabi splitting of the strong coupling energy level of plasmon nanocavity-single molecule exciton, characterized in that: The steps are as follows: A single dye molecule was embedded into a single CB[7] molecule using a host-body chemistry approach to prepare CB[7]@single dye molecule; The CB[7]@ single dye molecule was coupled with two gold nanospheres to form a gold nanosphere dimer (Au ND) / CB[7]@ single dye molecule coupling system, obtaining Au ND / CB[7]@ single dye molecule; The Au ND / CB[7]@single dye molecule coupling system was transferred to the Si / SiO2 photonic substrate to form a hybrid system. The photon mode frequency and line width were controlled by adjusting the thickness of the SiO2 layer to achieve the resonance line width Γ of the gold nanosphere dimer plasmon nanocavity. d The effective control of the resonance line width Γ d and the exciton linewidth Γ c Match.

2. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 1, characterized in that: The gap width between the two gold nanospheres is equal to the thickness of a single connected CB[7] molecule; the AuND / CB[7]@single dye molecule is precisely positioned at the center of the gold nanosphere dimer plasmon nanocavity, and the dipole moment direction of the AuND / CB[7]@single dye molecule is controlled in the direction of the plasmon electric field through the CB[7] molecular cage.

3. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 1 or 2, characterized in that: The preparation method of the gold nanospheres is as follows: Step 1: Prepare ultra-high purity gold nanorods using a hydrothermal chemical seed growth method; Step 2: Using Au 3+ The gold nanorods were etched into ultra-circular gold nanospheres with controllable diameter by oxidation etching.

4. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 3, characterized in that: The method for preparing ultra-high purity gold nanorods by using the hydrothermal chemical seed growth method is as follows: Synthesis of gold seeds: Add 75-150 μL of 0.01 mol / L HAuCl4 to 15 mL of CTAB and stir evenly for 30 min. Then, inject 0.5-1 mL of 0.1 mol / L ice-cold NaBH4 and stir evenly for 5 min to obtain a seed solution. Store in a 25°C water bath for 2 h before use. Preparation of growth solution: Add 1-2.5 mL of 0.1 mol / L HAuCl4 to 150 mL of 0.1 mol / L CTAB solution and stir rapidly for 20 minutes to obtain the growth solution. Preparation of gold nanorods: 0.1 mol / L, 150 μL of AgNO3, 100 μL of seed solution, and 0.1 mol / L, 600 μL of ascorbic acid were quickly added to the growth solution and stirred for 3 min. The gold nanorod solution was obtained after standing for 12 h. Purification of gold nanorods: The resulting gold nanorod solution was centrifuged twice to remove unreacted ions. The gold nanorods were redispersed in CTAB after centrifugation and 4 mL of NaCl was added and allowed to stand for 24 hours. The gold nanoparticles with larger surface areas adhered to the bottom of the vessel. The supernatant was centrifuged to remove the solvent to obtain high-purity gold nanorods. High-purity gold nanorods in Au 3+ Gold nanospheres with a diameter of r~35-45nm and an ultra-smooth surface were prepared under ion oxidation etching.

5. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 4, characterized in that: The preparation method of the gold nanospheres is: First etching: Add HAuCl4 with a concentration of 5-15 mM and a volume of 10-50 μL to a solution of gold nanorods dissolved in 2 mL of 0.05 mol / L CTAB. Stir thoroughly and let it stand in a 28°C water bath for 4-5 hours. The resulting 2 mL of gold nanorod solution was centrifuged and washed three times at 12000 rpm / 12 min to terminate the reaction and remove the CTAB and excess reagents in the solution. The resulting precipitate was washed and diluted with cetylpyridinium chloride until the concentration was 1; Regrowth: Add 350-700 μL of HAuCl4 to 20 mL of CPC and stir for 3 minutes. Then quickly add 4.5-9 mL of AA and 6 mL of the solution with a concentration of 1 after the first etching. Stir gently in a water bath at 26°C for 15 minutes. Then centrifuge the solution twice to remove unreacted ions, and resuspend the precipitate in CTAB and adjust the concentration to 1. Secondary etching: A certain amount of HAuCl4 was added to the regrown gold nanosphere solution. After a period of reaction, the solution was centrifuged at 12000 rpm / 12 min and the excess solution was removed to obtain ultra-smooth gold nanospheres.

6. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 1 or 5, characterized in that: During the secondary etching process of gold nanosphere preparation, the size of the gold nanospheres was controlled by varying the amount of HAuCl4 added; at the same time, the etching time was precisely controlled to ensure that ultra-round gold nanospheres were obtained. The dye molecule is an MB dye molecule; CB[7]@single MB was prepared by embedding a single MB molecule into a CB[7] molecule using the host-guest chemistry method. The method is as follows: MB solution dissolved in water is added to the CB[7] aqueous solution with a molar ratio of MB to CB[7] of 1:2, and ultrasonic mixing is used for 10 minutes.

7. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 6, characterized in that: The preparation method of the Au ND / CB[7]@ single dye molecule is as follows: When CB[7]@single dye molecules are added to a solution of gold nanospheres dispersed in deionized water, the CB[7] molecular cage actively binds to the surface of the gold nanosphere particles through the carbonyl group on one side. When another gold nanosphere approaches, the carbonyl group on the other side of the CB[7] molecular cage grabs the sidewall of the second gold nanosphere, forming a gold nanosphere dimer (Au ND) / CB[7]@single dye molecule. The exciton transition dipole moment of a single dye molecule is perfectly confined in a direction perpendicular to the CB[7] molecule ring plane and parallel to the direction of the isotropic exciton electric field in the nanocavity gap.

8. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 7, characterized in that: The preparation method of the hybrid system is as follows: 4 to 10 μL of Au ND / CB[7]@ single dye molecule solution is dropped on the surface of Si / SiO2 photonic substrate respectively, the small droplets are removed after 5 minutes, and the substrate surface is rinsed with deionized water 1 to 2 times, and then the substrate surface is blown dry with nitrogen gas, and the Au ND / CB[7]@ single dye molecules are scattered on the surface of Si / SiO2 substrate.

9. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to claim 8, characterized in that: The photonic substrate composed of Si / SiO2 double-layer dielectric layer was prepared by inductively coupled plasma chemical vapor deposition. The thickness of SiO2 layer was adjusted to 2500-2650nm by changing the deposition time. The Au ND / CB[7]@single dye molecule coupling system was placed on the Si / SiO2 photonic substrate. The attenuation linewidth Γ of the gold nanosphere dimer plasmon resonance was large. d ≈140-170meV, which can be greatly compressed to 80-100meV.

10. The method for accurately measuring Rabi splitting of plasmon nanocavity-single molecule exciton strong coupling energy levels according to any one of claims 1 and 7 to 9, characterized in that: For the intrinsic energy level of the coupled system of single exciton and plasmon Expressed as: The energy level splitting of the coupled system is Where δ = ε d -ε c is the detuning between the two coupled components; at resonance δ = 0, the energy level splitting is: and Among them, g EP =|Γ d -Γ c | / 4 is the critical coupling strength of the system at the singular point; For the coupled system of a single exciton and a plasmon, the absorption spectrum signal is mainly dominated by the plasma channel and is given by the following formula: Where i represents the imaginary unit, and are the resonance energies of plasmons and excitons, ω c 、ω d denote the reduced Planck constant, exciton transition frequency, and plasmon resonance frequency, respectively. d and Γ c are the decay linewidths of plasmons and excitons, respectively, and g is the coupling strength between excitons and plasmons; Absorption Rabi splitting at resonance And its critical conditions are: if The spectral splitting observed by spectroscopic measurements depends on the plasmon resonance linewidth Γ d and exciton linewidth Γ c The degree of matching between them; only when the plasmon line width Γ d and the exciton linewidth Γ c When the ratio is close to 1, the absorption spectrum and the energy level Rabi splitting spectrum intersect, and the plasmon line width Γ d and the exciton linewidth Γ c Equal at this time.

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