Quantum diamond with long drying time and preparation method and application thereof

Abstract

The invention relates to the technical field of diamond preparation, in particular to quantum diamond with long drying time and a preparation method and application thereof. As the NV-color center density is increased, the distance between the NV-color centers is reduced, and the interaction is enhanced, so that the de-coherence process is accelerated, and the coherence time is shortened. Therefore, the characteristic of long drying time only exists in the quantum diamond with the low-density NV-color center at present; quantum diamonds with high NV-color center density and long drying time superposition characteristics do not appear in the field. The quantum diamond with high NV-color center density and long drying time superposition characteristics is successfully prepared by adopting electron irradiation and high-temperature annealing modes.

Description

Technical Field

[0001] The present invention relates to the technical field of diamond preparation, and more particularly to a quantum diamond with a long coherence time and a preparation method and application thereof. Background Art

[0002] Quantum diamond is a diamond with quantum properties that is doped with nitrogen, vacancies and other defects. Quantum diamond is a diamond with special properties. Quantum diamond can stabilize quantum states at room temperature and interact with light, which makes it have important application prospects in high-tech fields such as quantum computing. - Color-centered diamond is a type of quantum diamond.

[0003] The coherence of quantum diamond refers to the ability of its quantum state to maintain phase consistency in time or space. The coherence of quantum diamond is a key property in applications such as quantum computing and quantum sensing. - The color center of diamond is mainly reflected in the nitrogen-vacancy (NV - ) center's spin-state coherence.

[0004] With NV - Color-centered diamond NV - The central electron's spin state is a triplet in its ground state, with three energy levels. These spin states can be manipulated using microwave pulses, with coherence determining the precision and duration of manipulation. Coherence time is a key parameter measuring the coherence of a quantum system. Long coherence times facilitate the implementation of more complex quantum algorithms.

[0005] With NV - NV of color-centered diamond - There is a coupling relationship between the color center density and its coherence time. - When the density of color centers is low, the distance between the color centers is relatively far and the interaction is weak, which can reduce the decoherence phenomenon caused by the coupling between the color centers and thus prolong the coherence time. - As the density of color centers increases, the distance between color centers decreases and the interaction increases, thereby accelerating the decoherence process and shortening the coherence time.

[0006] For the sensitivity of quantum sensors, high NV - Color center density and long coherence time are required; however, high NV - The appearance of color center density will greatly reduce the coherence time. - Color center density and long coherence time in quantum diamond. Summary of the Invention

[0007] In order to solve the existing high NV- The technical problem of short coherence time of quantum diamond with high color center density is solved by the present invention, which provides a high density (high NV) with long coherence time. - Color center density) quantum diamond and its preparation method and application.

[0008] NV - Color center (Nitrogen-Vacancy Center) is a point defect in diamond crystal formed by nitrogen atoms (N) replacing carbon atoms and combining with adjacent vacancies (V). Its density refers to the NV per unit volume. - The number of color centers, usually expressed in "ppm". High-density quantum diamond refers to NV - Quantum diamonds with a color center density greater than or equal to 10ppm.

[0009] Since NV - The increase in color center density, NV - The distance between the color centers decreases, the interaction increases, and the decoherence process is accelerated, resulting in a shorter coherence time. Therefore, the long coherence time characteristic currently only exists in low-density NV. - Quantum diamond with color centers; high NV has not yet appeared in this field - The present invention successfully prepared high NV by electron irradiation and high temperature annealing. - Quantum diamond with color center density and long coherence time superposition characteristics.

[0010] One of the objects of the present invention is to provide a quantum diamond with a long coherence time.

[0011] The T2 of the quantum diamond is 1.5-3.5μs, T2 * is 100-400ns; T2 is the time for the quantum bit to maintain phase coherence, T2 * Refers to the overall decoherence time of the quantum bit. - The color center density is greater than or equal to 10ppm.

[0012] T2 and T2 * are two different time constants that describe the quantum properties of quantum diamond, which are related to the NV of quantum diamond. - It is related to the spin state decoherence of the color center.

[0013] T2 (quantum coherence time) usually refers to the quantum bit (such as NV -T2 is the time during which the electron spins of the qubit (electron spins at the color center) remain phase-coherent, that is, the time during which a qubit can maintain its quantum superposition state before decoherence occurs. T2 measures how long an electron spin can maintain its quantum state despite being affected by external factors (such as temperature, magnetic field fluctuations, and nuclear spin). T2 is a key parameter in quantum computing and quantum information processing because it limits the time window within which quantum operations can be performed.

[0014] T2 * (decoherence time) refers to the overall decoherence time of the qubit, which includes all effects that cause qubit decoherence, including the loss of quantum coherence time described by T2, and rapid dephasing due to external magnetic field inhomogeneities. * It is usually shorter than T2 because it includes not only the decoherence caused by the interaction between the qubit and the environment, but also the dephasing caused by the inhomogeneity of the local magnetic field. * The measurement of NV usually involves - The decay time of the color center fluorescence signal is observed, which reflects the overall decoherence of the spin state.

[0015] In summary, T2 * Is a measure of NV - The ability of the color center electron spin to maintain a quantum coherent state, while T2 is a more comprehensive parameter that describes the NV - The actual time scale of decoherence of color center spin states. In practical applications, such as quantum sensing and quantum information processing, it is usually desirable to have T2 * and T2 as long as possible to enable more complex quantum operations and more precise measurements.

[0016] T2, T2 * NV was detected using Hahn echo sequence and standard free induction decay (FID). - The spin coherence of the color center is quantified.

[0017] The quantum diamond can be - Under the condition that the color center density is greater than or equal to 10ppm, T2 is 1.5-3.5μs and T2 * Therefore, the quantum diamond provided by the present invention has high NV - The superposition characteristics of color center density and long coherence time have broken through the technical difficulty that existing high-density quantum diamonds cannot have both long coherence time and high density.

[0018] A second object of the present invention is to provide a method for preparing quantum diamond with a long coherence time as described in one of the objects of the invention.

[0019] The preparation method comprises sequentially irradiating and annealing the diamond;

[0020] The diamond is nitrogen-containing diamond, and its nitrogen content is 30-800ppm, preferably 30-300ppm;

[0021] The irradiation dose was 0.5×10 19 cm -2 ~20×10 19 cm -2 , preferably 1×10 19 cm -2 ~6×10 19 cm -2 ;

[0022] The annealing temperature is greater than or equal to 1300°C, for example, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, preferably 1300-1800°C, more preferably 1300-1500°C.

[0023] Compared with the existing preparation method of quantum diamond, the present invention only requires one annealing, greatly increases the irradiation dose, and greatly increases the annealing temperature; thereby increasing the coherence time of the prepared high-density quantum diamond.

[0024] The annealing pressure can be 0-15GPa. Compared with vacuum annealing (0GPa), when the annealing pressure is 5-7GPa, the NV of the prepared quantum diamond is - Therefore, as a preferred solution, high pressure annealing is adopted: the annealing pressure is 5-7 GPa, preferably 5.0.

[0025] The annealing time can be a conventional annealing time in the art. As a solution, the annealing time is 0.1-20 hours, preferably 0.5-6 hours.

[0026] The irradiation energy may be conventional irradiation energy in the art, for example, 0.2-10 MeV. The irradiation energy is selected according to the thickness of the diamond: preferably 1-5 MeV for a thickness of 1 mm, and preferably 5-10 MeV for a thickness of 2 mm.

[0027] The irradiation current can be conventional in the art, for example, 1-10 mA. The irradiation current and irradiation time are selected based on the diamond's nitrogen content: when the diamond nitrogen content is 30-100 ppm, the irradiation current is preferably 1-5 mA; when the diamond nitrogen content is 100-800 ppm, the irradiation current is preferably 5-10 mA. The irradiation time is calculated and determined based on the irradiation dose and equipment parameters.

[0028] The irradiation temperature can be conventional in the art, such as room temperature (20°C). However, when the irradiation temperature is raised to 190-1050°C, the resulting high-density quantum diamond exhibits not only a long coherence time but also high transparency. Therefore, as a preferred embodiment, the irradiation temperature is greater than or equal to 20°C, for example, 20-1050°C. More preferably, a high-temperature irradiation method is employed: the irradiation temperature is 190-1050°C. The irradiation temperature refers to the temperature at which the diamond is heated during irradiation; the temperature at which the diamond is heated is the irradiation temperature.

[0029] In the preparation of NV-containing - During the process of producing diamonds with color centers (quantum diamonds), the diamonds are irradiated without further treatment, and the angle between the irradiating electron beam and the diamond can be any angle. The magnetic resonance contrast of the quantum diamonds produced is generally low. Studies have found that along the {111} crystal plane of the diamond, when the angle between the irradiating electron beam and the cut diamond surface is greater than or equal to 70° during irradiation, the magnetic resonance contrast of the produced quantum diamonds is high. The magnetic resonance contrast parameter C of the diamonds reaches 4.2%. Therefore, as a more preferred embodiment, the angle between the irradiating electron beam and the cut diamond surface is greater than or equal to 70°, and more preferably, it is between 70° and 90°.

[0030] When NV - When the electron spin state of the color center interacts with the external magnetic field, its energy level will split, resulting in different intensities of the fluorescence signal under different magnetic fields. - When the color center is measured by magnetic resonance, the degree of signal intensity change, that is, under different magnetic field conditions, NV - The relative change in the intensity of the fluorescence signal generated by the color center. This magnetic resonance contrast is a measure of the NV - The amount of change in the intensity of the optical signal (usually fluorescence) caused by the change in the electron spin state of the color center under a change in the magnetic field.

[0031] In the magnetic resonance research of quantum diamond, the parameter C usually refers to a quantitative index of magnetic resonance contrast, which describes the NV caused by the change of external magnetic field in the magnetic resonance experiment. - The degree of change in the fluorescence signal intensity of the color center. The higher the value of parameter C, the higher the magnetic resonance contrast.

[0032] The nitrogen-containing diamond with a nitrogen content of 30-800 ppm can be prepared by any existing method; for example, by chemical vapor deposition or high temperature and high pressure. As an alternative, the nitrogen-containing diamond with a nitrogen content of 30-800 ppm is prepared by the following method:

[0033] Type Ib diamond was selected as the seed, high-purity graphite powder (purity 99.9 wt%) as the carbon source, and Fe-Ni alloy as the catalyst for diamond growth; nitride (NaN3 / Ba(N3)2) was used as the nitrogen source to control the nitrogen content in the growth medium, and aluminum powder or titanium powder was used as the nitrogen absorber; the temperature was kept at high temperature and high pressure for 60 h; the Fe-Ni alloy was preferably Fe 70 Ni 30 The nitride is preferably NaN3 / Ba(N3)2, and the high temperature and high pressure are 1500°C and 20 GPa. Theoretically, any mass ratio of type Ib diamond, high-purity graphite powder, Fe-Ni alloy, nitride, and nitrogen absorber can be used. However, in practice, the ratio can be selected based on different nitrogen concentrations.

[0034] The third object of the present invention is to provide a quantum diamond with a long coherence time as described in the first object of the invention or a quantum diamond with a long coherence time prepared by the preparation method as described in the second object of the invention for use in the field of quantum sensing.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] High-density quantum diamonds contain paramagnetic defects, resulting in extremely low coherence times. The quantum diamonds provided by the present invention achieve high density while significantly improving their coherence times, solving the problem of poor coherence properties of quantum diamonds at high densities. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a graph of fluorescence intensity versus quantum state evolution time for the quantum diamond prepared in Example 12; the abscissa is the quantum state evolution time (μs), and the ordinate is the normalized fluorescence intensity;

[0038] Figure 2 This is a graph of fluorescence intensity versus quantum state free evolution time of the quantum diamond prepared in Example 12; the abscissa is the quantum free state evolution time (ns), and the ordinate is the normalized fluorescence intensity;

[0039] Figure 3 This is a graph of fluorescence intensity-quantum state evolution time of the quantum diamond prepared in Comparative Example 1; the abscissa is the quantum state evolution time (μs) and the ordinate is the normalized fluorescence intensity;

[0040] Figure 4 This is a fluorescence intensity-quantum state free evolution time diagram of the quantum diamond prepared in Comparative Example 1; the abscissa is the quantum free state evolution time (ns) and the ordinate is the normalized fluorescence intensity. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below with reference to specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0042] The reagents used in the examples and comparative examples are all commercially available products.

[0043] Example 1

[0044] (1) Preparation of nitrogen-containing diamond using high temperature and high pressure method:

[0045] Type Ib diamond with a particle size of 0.4 mm was selected as the seed crystal, high-purity graphite powder (purity 99.9 wt%) was selected as the carbon source, and Fe-Ni (Fe 70 Ni 30 ) alloy as a catalyst for diamond growth. Nitrides (NaN3 / Ba(N3)2) were used as nitrogen sources to control the nitrogen content in the growth medium, with aluminum powder or titanium powder acting as nitrogen absorbers. Diamonds with nitrogen contents of 30 ppm, 100 ppm, 200 ppm, 300 ppm, and 800 ppm were synthesized under high temperature and high pressure (20 GPa, 1500°C) for 60 hours.

[0046] (2) Preparation of ultra-high NV - Color center density in quantum diamond:

[0047] The diamond prepared in step (1) with a particle size of 3 mm and a nitrogen content of 30 ppm was selected and prepared into a sample with a thickness of 1 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 1 MeV, an irradiation current of 1 mA, and an irradiation dose of 1 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1300°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0048] Example 2

[0049] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 10 19 cm -2During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1300°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0050] Example 3

[0051] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1400°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0052] Example 4

[0053] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1500°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0054] Example 5

[0055] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1600°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0056] Example 6

[0057] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 1019 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1700°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0058] Example 7

[0059] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1800°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0060] Example 8

[0061] Diamond with a nitrogen content of 300 ppm and a particle size of 3 mm prepared in Example 1 was selected and prepared into a sample with a thickness of 2 mm. The sample was wrapped with aluminum foil. The sample was irradiated at room temperature with an irradiation energy of 10 MeV, an irradiation current of 16 mA, and an irradiation dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1800°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0062] Example 9

[0063] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm, prepared in Example 1, was selected and prepared into a 2 mm thick sample. The sample was placed on top of a thermally insulating boron nitride layer and wrapped with aluminum foil. The sample was irradiated at a temperature of 190°C, an energy of 10 MeV, a current of 16 mA, and a dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1500°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0064] Example 10

[0065] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm, prepared in Example 1, was selected and prepared into a 2 mm thick sample. The sample was placed on top of a thermally insulating boron nitride layer and wrapped with aluminum foil. The sample was irradiated at a temperature of 1050°C, an energy of 10 MeV, a current of 16 mA, and a dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond surface was 60°. The irradiated diamond was annealed at 1500°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamond.

[0066] Example 11

[0067] Diamond with a nitrogen content of 200 ppm and a particle size of 3 mm, prepared in Example 1, was selected and 2 mm thick along the {111} diamond crystal plane. The sample was placed on top of a thermally insulating boron nitride layer and wrapped with aluminum foil. The sample was irradiated at a temperature of 1050°C, an energy of 10 MeV, a current of 16 mA, and a dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam exit and the diamond cut surface was 70°. The irradiated diamond was annealed at a temperature of 1500°C, a pressure of 5 GPa, and a time of 0.1 h to obtain quantum diamond.

[0068] Example 12

[0069] Diamond with a nitrogen content of 100 ppm and a particle size of 3 mm, prepared in Example 1, was selected and cut along the {111} diamond plane to obtain a 2 mm thick sample. The sample was placed on top of a thermally insulating boron nitride layer and wrapped with aluminum foil. The sample was irradiated at a temperature of 1050°C, an energy of 10 MeV, a current of 16 mA, and a dose of 6 × 10 19 cm -2 During irradiation, the angle between the electron beam outlet and the diamond cut surface was 90°. The irradiated diamond was annealed at a temperature of 1500°C, a pressure of 7 GPa, and a time of 0.1 h to obtain quantum diamond.

[0070] The fluorescence intensity-quantum state evolution time diagram of the quantum diamond prepared in this embodiment is shown in FIG. Figure 1 shown. Figure 1 In the equation, Data represents the measured data, Fitting Curve represents the fitted curve obtained based on the measured data, and the symbol in the upper right corner indicates the sequence method used for the test (well known in the art). y0, y1, and T2 are fitted parameters, n is a free parameter, t is the quantum state evolution time, and T2 is the coherence time T2. Figure 1 It was found that the T2 of the quantum diamond prepared in Example 12 was 3.5±0.2μs.

[0071] The fluorescence intensity-quantum state free evolution time diagram of the quantum diamond prepared in this embodiment is shown in FIG. Figure 2 shown. Figure 2 In the equation, Data represents the measured data, Fitting Curve represents the fitted curve obtained based on the measured data, and the symbol in the upper right corner indicates the sequence method used for the test (well known in the art). f i correspond 14 The energy level shift of the N nuclear spin (known), T2 is the fitted parameter, n is a free parameter, t is the free evolution time of the quantum state; T2 is the coherence time T2 * .Depend on Figure 2 It is found that the T2 of the quantum diamond prepared in Example 12 is * It is 301±4ns.

[0072] Comparative Example 1

[0073] Diamonds prepared in Example 1 with a particle size of 3 mm and a nitrogen content of 30 ppm were selected and prepared into 1 mm thick samples. The samples were wrapped in aluminum foil. The samples were irradiated at room temperature with an energy of 1 MeV, an irradiation current of 1 mA, and an irradiation time of 1 hour. During irradiation, the angle between the electron beam exit and the diamond surface was 60°. The irradiated diamonds were annealed at 650°C, atmospheric pressure, and for 0.1 hour to obtain quantum diamonds.

[0074] The fluorescence intensity-quantum state evolution time diagram of the quantum diamond prepared in this comparative example is shown in FIG. Figure 3 shown. Figure 3 In the equation, data represents the measured data, Fitting Curve represents the fitted curve obtained based on the measured data, and the symbol in the upper right corner indicates the sequence method used for the test (well known in the art). y0, y1, and T2 are fitted parameters, n is a free parameter, t is the quantum state evolution time, and T2 is the coherence time T2. Figure 3 It was found that the T2 of the quantum diamond prepared in Comparative Example 1 was 1.2±0.2 μs.

[0075] The fluorescence intensity-quantum state free evolution time diagram of the quantum diamond prepared in this embodiment is shown in FIG. Figure 4 shown. Figure 4In the equation, data represents the measured data, Fitting Curve represents the fitted curve obtained based on the measured data, and the symbol in the upper right corner indicates the sequence method used for the test (well known in the art). f i correspond 14 The energy level shift of the N nuclear spin (known), T2 is the fitted parameter, n is a free parameter, t is the free evolution time of the quantum state; T2 is the coherence time T2 * .Depend on Figure 4 It is found that the T2 of the quantum diamond prepared in Comparative Example 1 is * It is 60±2ns.

[0076] Performance Testing

[0077] The quantum diamonds prepared in Examples 1-12 and Comparative Example 1 were tested.

[0078] NV was obtained by quantitative analysis of nitrogen vacancy concentration - Color center density. The quantitative analysis process of nitrogen vacancy concentration is as follows: Under the same experimental conditions (laser power 7mW), the fluorescence count rate of the sample to be tested is compared with that of the standard sample to complete the calibration. The validity of the standard sample is verified by a single NV - Fluorescence count rate measurement verification of color centers under the same experimental conditions. All fluorescence count rate data are calibrated based on the dead time correction factor of the single photon counting module.

[0079] The transparency of quantum diamonds is typically characterized by spectral transmittance. Transparency can be assessed by measuring the transmittance of diamond at different wavelengths. Transmittance is tested using ultraviolet-visible (UV-Vis) absorption spectroscopy. UV-Vis absorption spectra are measured in transmission mode at room temperature using a custom system equipped with a xenon lamp light source, a 10x objective lens, an adjustable sample holder, and a fiber optic spectrometer (FX2000) with a detection range of 400-800 nm.

[0080] Coherence time test method: The spin coherence time of NV- color center (coherence time T2, coherence time T2) is measured by standard free induction decay (FID) and Hahn echo sequence. * ) was quantified. In the experiment, an external magnetic field of 80 Gauss was applied to eliminate the degeneracy of the |m_S=±1> state and the NV - The energy level mixing caused by the four crystal directions of the color center. T2 is a quantum bit (such as NV - The time that the electron spin of the color center remains phase coherent, and T2* refers to the overall decoherence time of the quantum bit.

[0081] The calculation method of magnetic resonance contrast (C) is: C = Imax-Imin / Imax+Imin. Where Imax is the value of NV when there is no microwave excitation. - The maximum intensity of the color center fluorescence signal; Imin is the microwave frequency and NV - The minimum intensity of the fluorescence signal when the color center spin resonance frequency matches. Imax and Imin are obtained through detection.

[0082] The test results of the above tests are shown in Table 1.

[0083] Table 1

[0084]

[0085] The data in Table 1 show that the coherence time T2 (ms) of the quantum diamonds prepared in Examples 1-12 is above 2.1, T2 * (ns) is greater than 100; the coherence time T2 (ms) of comparative example 1 is 1.2 μs, T2 * The coherence time T2 (ms) and T2 (ms) of the quantum diamonds prepared in Examples 1-12 were significantly improved compared to Comparative Example 1. Comparative Example 1 was annealed at a conventional annealing temperature (650°C), while Examples 1-12 were annealed at a high temperature (1300-1800°C). This indicates that high-temperature annealing (1300-1800°C) can significantly extend the coherence time of high-quantum diamonds compared to conventional annealing.

[0086] Examples 1-8 used room-temperature irradiation, without heating the diamond during the irradiation process. Examples 9-12 all heated the diamond to above 190°C during the irradiation process. Compared to Examples 1-8, the transmittance of Examples 9-12 was significantly improved. This indicates that, compared to room-temperature annealing, heating the diamond to above 190°C during irradiation can significantly improve the transparency of the prepared quantum diamond.

[0087] Examples 9-10 were annealed at atmospheric pressure, while Examples 11-12 were annealed at 5-7 GPa. Compared with Examples 9-10, the NV of the quantum diamonds prepared in Examples 11-12 was - The color center density is further improved. Compared with the normal pressure vacuum annealing, high pressure annealing can further improve the NV of quantum diamond. - Color center density.

[0088] Compared to Examples 1-10, Examples 11-12 focused on the diamond {111} crystal plane at the irradiation front; during irradiation, the angles between the electron beam exit and the diamond cut surface were 70° and 90°. Compared to Examples 1-10, the magnetic resonance contrast of Examples 11-12 was significantly improved. This indicates that focusing on the diamond {111} crystal plane and limiting the angle between the irradiating electron beam and the cut surface to 70° or greater can further enhance the magnetic resonance contrast of quantum diamond.

Claims

1. A quantum diamond with a long coherence time, characterized in that The T2 of the quantum diamond is 1.5-3.5μs, T2 * is 100-400ns; T2 is the time for the quantum bit to maintain phase coherence, T2 * It refers to the overall decoherence time of the quantum bit.

2. The quantum diamond with long coherence time as claimed in claim 1, characterized in that Its NV - The color center density is greater than or equal to 10ppm.

3. A method for preparing quantum diamond according to claim 1 or 2, characterized in that: The preparation method comprises sequentially irradiating and annealing the diamond; The diamond is nitrogen-containing diamond, and its nitrogen content is 30-800ppm, preferably 30-300ppm; The irradiation dose was 0.5×10 19 cm -2 ~20×10 19 cm -2 , preferably 1×10 19 cm -2 ~6×10 19 cm -2 ; The annealing temperature is greater than or equal to 1300°C, preferably 1300-1800°C.

4. The method for preparing quantum diamond according to claim 3, wherein: The annealing pressure is 0-15 GPa, preferably 5-7 GPa.

5. The method for preparing quantum diamond according to claim 3, wherein: The annealing time is 0.1-20 hours, preferably 0.5-6 hours.

6. The method for preparing quantum diamond according to claim 3, wherein: Irradiation energy is 0.2-10 MeV; or / and, The irradiation current is 1-10mA.

7. The method for preparing quantum diamond according to claim 3, wherein: The irradiation temperature is 20-1050℃.

8. The method for preparing quantum diamond according to claim 3, wherein: Before irradiation, the diamond is cut along the {111} crystal plane; during the irradiation process, the angle between the irradiating electron beam and the diamond cutting surface is greater than or equal to 70 degrees.

9. The method for preparing quantum diamond according to claim 3, wherein: The diamond is prepared by a chemical vapor deposition method or a high temperature and high pressure method.

10. Use of the quantum diamond according to claim 1 or 2, or the quantum diamond prepared by the preparation method according to any one of claims 3 to 9, in the field of quantum sensing.

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