A method for preparing a single photon source using hexagonal boron nitride

Abstract

The present invention discloses a method for preparing a single-photon source using hexagonal boron nitride, which successively includes the following steps: cleaning a substrate wafer; transferring hBN material onto the substrate wafer by mechanical exfoliation; treating with an ultraviolet ozone machine; processing the hBN material with femtosecond laser pulses; treating with an ultraviolet ozone machine; and annealing treatment. The method for preparing a single-photon source using hexagonal boron nitride according to the present invention realizes the fabrication of a highly efficient spatially position-controllable single-photon source based on a femtosecond laser pulse process. The fabricated single-photon source has the characteristics of high brightness, high purity, and room-temperature operation, and does not require high production costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum communication, and particularly relates to a method for preparing a single-photon source by using hexagonal boron nitride. Background Art

[0002] Quantum information technology has broad application prospects in the fields of sensing and measurement, communication, simulation, high-performance computing, etc. People urgently need a quantum state carrier that can realize quantum technology. Photons, with excellent quantum properties, are natural carriers for realizing the quantum states of quantum computing and quantum communication, and play an important role in quantum information technology. In 1977, Kimble et al. first observed the photon antibunching effect in experiments, opening the door to the exploration of quantum optics. With the in-depth study of photons, single photons have shown important application values in several fields. For example, in quantum key distribution of quantum secure communication, single photons are crucial for securely transmitting information using the quantum key distribution protocol. Only in the case of single-photon communication can the quantum key distribution protocol ensure that information is not eavesdropped. In terms of quantum computing, photon qubits can be encoded by manipulating degrees of freedom such as the polarization and phase of photons. Therefore, a controllable, stable and repeatedly emitable single-photon source is crucial for the development of quantum information.

[0003] Through continuous development, various quantum light sources have been prepared in different physical systems to meet different experimental and application requirements, mainly including single atoms, single molecules, diamond color centers, and self-assembled quantum dots, etc. The single photons generated in these different systems have different characteristics. For example, the single photons generated by the single-atom system have good coherence and a long lifetime, but the preparation of the single-photon source is complex; the preparation of the single-photon source in the single-molecule system is relatively simple, but high-quality single photons can only be generated at extremely low temperatures. The diamond color center has the advantage of simple preparation, but the quantum efficiency at room temperature is not high, and the photon extraction rate is relatively low, which is the limitation of three-dimensional materials themselves. Self-assembled quantum dots can form a two-level structure similar to natural atoms and can provide the highest-quality single-photon source so far, but they require expensive equipment and technical support.

[0004] It has been found that defect luminescence can be achieved at room temperature in hexagonal boron nitride (hBN), which is the only single-photon source among two-dimensional materials that can achieve room-temperature emission. In addition, the single-photon source in hBN has high stability and high brightness at room temperature, making it the most promising two-dimensional single-photon source for practical applications. During the experimental preparation of hBN, intrinsic vacancies and doping of impurity elements will be generated, but these defects are randomly generated and usually have a relatively low density, which is not conducive to the analysis of their types and internal mechanisms by people. Therefore, researchers have continuously tried various treatments on hBN to obtain a reliable method for generating single photons. For example, high-temperature annealing of the material in different gas atmospheres results in an increase in the defect density with the continuous increase of the annealing temperature, but the defect positions are randomly generated and difficult to control; using the chemical etching method of peroxymonosulfuric acid (H2O2 + H2SO4), the results show that the single-photon source density has increased by 6 times, reaching 0.54 per square micrometer, but most of these defects are concentrated on the edge of the material; using electron beam irradiation, ion irradiation, and neutron irradiation to treat hBN materials can randomly generate single-photon sources on the entire piece of material. Although defects can be fabricated at fixed points using templates or focused ion beams, expensive micro-nano processing equipment is required, the process is complex and costly, and additional ion contamination may occur to the hBN material; in addition, single-photon sources are also induced by stress on structures such as wrinkles or bubbles. Although these methods can improve the defect yield to a certain extent, they have high technical requirements and most defect positions are generated at the edge of the material. Therefore, it is necessary to explore a simple and effective method for generating single-photon sources with controllable positions and types. Summary of the Invention

[0005] Aiming at the technical problems of the uncontrollable position of the single-photon source and how to generate high-quality single-photon sources in the process of preparing the single-photon source in the above-mentioned existing technologies, the purpose of the present invention is to provide a method for preparing high-quality single-photon sources using hexagonal boron nitride.

[0006] To achieve the above object, the present invention provides a method for preparing a single-photon source using hexagonal boron nitride, comprising the following steps:

[0007] (1) Placing the substrate wafer with hBN material into an ultraviolet ozone machine for treatment;

[0008] (2) Irradiating the hBN material processed in step (1) with femtosecond laser pulses, adjusting the processing speed by simultaneously adjusting the laser repetition rate and the moving speed of the two-dimensional moving platform, and moving the two-dimensional moving platform to fabricate defects or array batch single-photon sources at fixed points;

[0009] (3) Placing the hBN material irradiated with laser pulses in step (2) into an ultraviolet ozone machine for treatment;

[0010] (4) Put the hBN material processed in step (3) into an annealing furnace for annealing treatment.

[0011] The function of the ultraviolet ozone machine treatment in step (1) is to remove the residual glue in the hBN material, and the function of the ultraviolet ozone machine treatment in step (3) is to remove the impurities that may be introduced during the production process, thereby improving the luminescence quality of the single-photon source.

[0012] The present invention uses a femtosecond laser pulse process to induce the generation of a color center single-photon source at a specified position in a thin-layer hBN material, combines the femtosecond laser pulse process and the annealing process to activate a high-quality color center single-photon source in the hBN material, and realizes the rapid large-scale array processing of the color center single-photons in the hBN material by adjusting the laser repetition rate and the two-dimensional moving platform in the system.

[0013] Further, before step (1), the following steps are also included: cleaning the substrate wafer; transferring the hBN material to the substrate wafer by mechanical exfoliation method.

[0014] Further, the substrate wafer is a quartz substrate wafer.

[0015] Further, in step (2), different emission characteristics of the single-photon source are obtained by adjusting the laser parameters, the laser parameters include laser power and irradiation pulse number, the irradiation pulse number is 1-5 pulses, and the laser repetition rate is less than 1000 Hz.

[0016] The single-photon sources with different emission characteristics refer to the different brightness, emission wavelength, single-photon purity, and polarization state of the single photons.

[0017] Further, the treatment time of the ultraviolet ozone machine in step (1) and step (3) is both 5-30 min, and the annealing treatment time in step (4) is 30-60 min.

[0018] Further, the two-dimensional moving platform is used to carry and move the hBN material, and the spatial distance between each single-photon source is adjusted by adjusting the moving step length of the two-dimensional moving platform.

[0019] Further, the temperature of the annealing furnace is 700-1000 °C, and the rising and falling rates of the temperature of the annealing furnace are 10-30 °C / min.

[0020] The single-photon source is contained in the hBN material, and the annealing temperature is 700-1000 °C, reaching an equilibrium point, so that neither the hBN material nor the single-photon source is damaged during the processing.

[0021] Further, the operation process of cleaning the substrate wafer is as follows: ultrasonically clean the substrate wafer with acetone, alcohol, and distilled water respectively, dry it with nitrogen, and bake it on a hot plate for 1 - 1.5 min, where the temperature of the hot plate is 100 - 120 °C.

[0022] Further, the operation process of transferring the hBN material onto the substrate wafer is as follows: place the hBN material on the tape, stick it repeatedly 3 - 5 times to peel off the bulk hBN material to obtain the layered hBN material, transfer the layered hBN material onto the cleaned substrate wafer, and after standing for 1 - 20 min, peel off the tape so that the layered hBN material remains on the substrate wafer.

[0023] Further, the thickness of the layered hBN material is 15 - 120 nm.

[0024] Compared with the prior art, the technical effects of the present invention are as follows: The method for preparing a single - photon source using hexagonal boron nitride according to the present invention is based on a femtosecond laser pulse process to achieve the fabrication of a high - quality single - photon source with high efficiency and controllable spatial position. The fabricated single - photon source has the characteristics of high brightness, high purity, and room - temperature operation, and does not require high production costs. Description of the Drawings

[0025] The above - mentioned and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0026] Figure 1 is a flow chart of the preparation method of the present invention;

[0027] Figure 2 is an external view of the light - emitting part of the hBN single - photon source prepared by the present invention;

[0028] Figure 3 is a fluorescence spectrum diagram of the hBN single - photon source emitted by the present invention;

[0029] Figure 4 is the test result of the second - order correlation characteristics of the hBN single - photon source emitted by the present invention;

[0030] Figure 5 is a schematic diagram of the femtosecond laser processing system of the present invention. Detailed Embodiments

[0031] The embodiments of the present invention are described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] The following describes a method for preparing a single photon source using hexagonal boron nitride according to an embodiment of the present invention with reference to the accompanying drawings.

[0033] The single crystal hBN material used was BN2A1 purchased from HQ Graphene, and the tape was Scotch tape.

[0034] like Figure 1 As shown, the method for preparing a single photon source using hexagonal boron nitride comprises the following steps:

[0035] (1) Cleaning the substrate;

[0036] (2) Transferring the hBN material to the substrate sheet by mechanical exfoliation;

[0037] (3) UV ozone treatment;

[0038] (4) Femtosecond laser pulse processing of hBN materials;

[0039] (5) UV ozone treatment;

[0040] (6) Annealing treatment.

[0041] The specific operation process of cleaning the substrate in step (1) is: ultrasonically cleaning the substrate with acetone, alcohol and distilled water respectively, the substrate is a quartz substrate, blowing it dry with nitrogen, wherein the purity of the nitrogen is 99.9%, and baking it on a hot plate for 1-1.5 minutes, and the temperature of the hot plate is 100-120°C.

[0042] The specific operation process of transferring the hBN material to the substrate sheet by mechanical stripping in step (2) is as follows: placing the purchased single crystal hBN material on Scotch tape, repeatedly sticking it 3-5 times to strip the block hBN material to obtain a layered hBN material, wherein the thickness of the layered hBN material is 15-120nm, transferring the layered hBN material to the cleaned substrate sheet, standing for 1-20 minutes, and then stripping the tape so that the layered hBN material remains on the substrate sheet.

[0043] In step (3), the UV ozone treatment is to place the quartz substrate with the hBN material into the UV ozone machine for treatment for 5-30 minutes to remove the residual glue in the hBN material.

[0044] In step (4), the hBN material processed in step (3) is irradiated with femtosecond laser pulses, and the processing speed is adjusted by adjusting the laser repetition rate and the moving speed of the two-dimensional moving platform at the same time, and the two-dimensional moving platform is moved to produce defects or array single photon sources at fixed points. Figure 5As shown in the figure, the femtosecond laser processing system includes a lens, a mirror, a half-wave plate, a polarizer, a spatial light modulator, a femtosecond laser, and a two-dimensional moving platform. The two-dimensional moving platform is used to carry and move the hBN material. The spatial distance between each single photon is adjusted by adjusting the moving step of the two-dimensional moving platform. The batch preparation of single photon sources is achieved by moving the two-dimensional moving platform. Specifically, the position of the two-dimensional moving platform is stepwise, with a moving accuracy of 0.01 um each time, a maximum speed of 3 mm / s, and a maximum moving distance of 20 mm. The two-dimensional moving platform is controlled by a motion controller. Irradiating the hBN material with femtosecond laser pulses, one or several pulses can generate a defect. By adjusting the laser power, the two-dimensional moving platform can be moved to make defects at a fixed point or make a high-density array of single photon sources, obtaining the defects as shown in Figure 2 From the figure, it can be seen that the present invention can achieve the fabrication of array defects on the hBN material. The spatial distance between defects is adjusted by adjusting the moving step of the two-dimensional moving platform, and the processing speed is adjusted by adjusting the laser repetition rate. The product of the number of movements per second and the laser repetition rate is 1. For example, under the condition of a laser repetition rate of 1 KHz, it moves one thousand times per second, and the processing speed can be one thousand defects per second. Different laser parameters result in different emission characteristics of the single photon source. Different single photon emission characteristics refer to different single photon brightness, emission wavelength, single photon purity, and polarization state. Laser parameters include the single pulse energy of the laser and the number of irradiation pulses. The single pulse power of the femtosecond laser is adjusted by rotating the half-wave plate and the polarizer. The single pulse energy is 15 nJ - 80 nJ, the laser repetition rate is less than 1000 Hz, and the pulse width of the femtosecond pulse laser used in the present invention is < 500 femtoseconds.

[0045] In step (5), the treatment with an ultraviolet ozone machine is to put the hBN material irradiated by laser pulses in step (4) into the ultraviolet ozone machine for 5 - 30 minutes to remove impurities that may be introduced during the manufacturing process, thereby improving the luminescence quality of the single photon source.

[0046] In step (6), the annealing treatment is to put the hBN material processed in step (5) into an annealing furnace for annealing. The temperature of the annealing furnace is 700 - 1000 °C, the annealing time is 30 - 60 min, and the rate of temperature rise and fall of the annealing furnace is 10 - 30 °C / min. The single - photon source is contained in the hBN material. During the processing, it is neither desired to damage the hBN material nor the single - photon source. Therefore, it is necessary to make the annealing temperature reach the temperature balance point through the processing technology. If the annealing temperature is low and the time is short, it cannot repair the defects well and cannot activate the defects that can emit light. If the annealing temperature is high and the time is long, it will damage the material, possibly damaging the single - photon defects or generating a large noise background. If the rate of temperature rise and fall of the annealing furnace is fast, the stress in the material cannot be released sufficiently, which will damage the formation of the single - photon source. Therefore, in the present invention, the annealing temperature is controlled at 700 - 1000 °C, the annealing time is controlled at 30 - 60 min, and the rate of temperature rise and fall of the annealing furnace is controlled at 10 - 30 °C / min.

[0047] Figure 3 This is the fluorescence spectrum emitted by the hBN single - photon source prepared by this method. It can be seen from the figure that the light - emitting position of the single - photon source is near 553 nm. In the visible light band, the signal - to - noise ratio of the emission is relatively high, and the noise intensity is about 0.15% of the emission intensity. Figure 4 This is the test result of the second - order correlation characteristics of the hBN single - photon source prepared by this method. It can be seen from the fact that the second - order correlation at the position where the time is zero is less than 0.5 that the fabricated one is a single - photon source, and the minimum obtained g 2 (0)=0.06, indicating a relatively high single - photon purity.

[0048] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above - mentioned terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0049] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0050] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a single photon source using hexagonal boron nitride, characterized in that, The following steps are involved: (1) Place the substrate sheet with hBN material into a UV ozone machine for treatment; (2) irradiating the hBN material processed in step (1) with a femtosecond laser pulse, adjusting the processing speed by simultaneously adjusting the laser repetition rate and the moving speed of the two-dimensional moving platform, moving the two-dimensional moving platform to produce defects or array batch single-photon sources at fixed points, and obtaining the single-photon sources with different emission characteristics by adjusting the laser parameters in step (2), wherein the laser parameters include the laser single pulse energy and the number of irradiation pulses, the number of irradiation pulses is 1-5 pulses, and the laser repetition rate is less than 1000 Hz; (3) placing the hBN material irradiated by the laser pulse in step (2) into an ultraviolet ozone machine for treatment; (4) placing the hBN material processed in step (3) into an annealing furnace for annealing, wherein the temperature of the annealing furnace is 700-1000° C., and the rate of temperature increase and decrease of the annealing furnace is 10-30° C. / min.

2. The method according to claim 1, wherein Prior to step (1), the method further includes the following steps: The substrate sheet is cleaned; and the hBN material is transferred to the substrate sheet by a mechanical peeling method.

3. The method according to claim 1 or 2, characterized in that, The substrate is a quartz substrate.

4. The method according to claim 1, characterized in that The time for the ultraviolet ozone treatment in step (1) and step (3) is 5-30 minutes, and the time for the annealing treatment in step (4) is 30-60 minutes.

5. The method according to claim 1, wherein The two-dimensional mobile platform is used to carry and move the hBN material, and the spatial distance between each single photon is adjusted by adjusting the moving step length of the two-dimensional mobile platform.

6. The method according to claim 2, wherein The operation process of cleaning the substrate sheet is: ultrasonically cleaning the substrate sheet with acetone, alcohol, and distilled water respectively, blowing it dry with nitrogen, and baking it on a hot plate for 1-1.5 minutes, and the temperature of the hot plate is 100-120°C.

7. The method according to claim 2, wherein The operation process of transferring the hBN material to the substrate sheet is as follows: placing the hBN material on a tape, repeatedly sticking it 3-5 times to peel off the blocky hBN material to obtain a layered hBN material, transferring the layered hBN material to the cleaned substrate sheet, standing for 1-20 minutes, and then peeling off the tape so that the layered hBN material remains on the substrate sheet.

8. The method according to claim 7, wherein The thickness of the layered hBN material is 15-120 nm.

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