Quantum device and evaluation apparatus

Abstract

This quantum device comprises: a quantum material that includes a color center having an electron spin; a stage that has an installation surface; and a microwave resonator that irradiates the quantum material with microwaves. The quantum material has a first surface and a second surface which is a counter-surface of the first surface. The quantum material is disposed on the stage so that the first surface opposes the installation surface. The stage has an optical waveguide through which pass excitation light, which is radiated onto the quantum material, and fluorescence, which is generated by the quantum material. The microwave resonator radiates microwaves so that a first intensity, which is the intensity of the microwave on the first surface, and a second intensity, which is the intensity of the microwave on the second surface, are at least 0.5 times a third intensity, which is the maximum value of the intensity of the microwave.

Description

Quantum devices and evaluation equipment

[0001] The present disclosure relates to a quantum device and an evaluation apparatus. This application claims priority to Japanese Patent Application No. 2024-032150, filed on March 4, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] For example, Japanese Patent Laid-Open No. 2022-186414 (Patent Document 1) describes a detection device that detects an external field by irradiating a quantum material such as diamond containing an NV center with a laser and an electromagnetic wave and detecting fluorescence generated in the quantum material.

[0003] Japanese Patent Application Laid-Open No. 2022-186414

[0004] The quantum device of the present disclosure includes a quantum material including a color center having electron spin, a stage having a mounting surface, and a microwave resonator that irradiates microwaves onto the quantum material. The quantum material has a first surface and a second surface opposite the first surface, and is placed on the stage so that the first surface faces the mounting surface. The stage has an optical waveguide through which excitation light irradiated onto the quantum material and fluorescence generated by the quantum material pass. The microwave resonator irradiates microwaves so that a first intensity, which is the intensity of the microwaves on the first surface, and a second intensity, which is the intensity of the microwaves on the second surface, are 0.5 times or more a third intensity, which is the maximum intensity of the microwaves.

[0005] FIG. 1 is a cross-sectional view of a quantum device 100. FIG. 2 is a schematic diagram of the magnetic field of microwaves MW generated by microwave resonator 30. FIG. 3 is an explanatory diagram of the space above microwave resonator 30. FIG. 4A is a first explanatory diagram illustrating energy levels in quantum material 20. FIG. 4B is a second explanatory diagram illustrating energy levels in quantum material 20. FIG. 5 is a schematic diagram illustrating pulse waveforms of microwaves MW used in various measurement methods. FIG. 6 is a cross-sectional view of quantum device 100 according to Modification 1. FIG. 7 is a schematic diagram of the magnetic field of microwaves MW generated by microwave resonator 30 in quantum device 100 according to Modification 1. FIG. 8 is a cross-sectional view of quantum device 100 according to Modification 2. FIG. 9 shows the results of CW-ODMR spectrum measurement in the first measurement example. FIG. 10 is a partially enlarged view of FIG. 9. FIG. 11 shows the results of Rabi oscillation measurement in the first measurement example. FIG. 12 shows the results of pulsed ODMR spectrum measurement in the first measurement example. Fig. 13 is a partially enlarged view of Fig. 12. Fig. 14 shows the results of Ramsey method measurement in the first measurement example. Fig. 15 shows the results of Hahn-Echo method measurement in the first measurement example. Fig. 16 shows the results of Rabi vibration measurement in the second measurement example.

[0006] In the detection device described in Patent Document 1, electromagnetic waves are irradiated from one side of the quantum material, so the intensity of the electromagnetic waves varies depending on the location, and the phase of the electron transition also varies depending on the location. As a result, even if an external field is detected or the transverse relaxation time is measured using, for example, Rabi oscillation measurement, Ramsey method, or Hahn-Echo method, the above-mentioned phase change cannot be ignored.

[0007] In order to suppress the effect of different electromagnetic wave intensities at different locations, it is conceivable to use a confocal microscope to limit the volume of the quantum material where fluorescence is detected, thereby treating that portion as if it were irradiated with a pseudo-uniform electromagnetic wave. However, in this case, the volume where fluorescence is detected is small, so the amount of fluorescence is small and the S / N ratio is low.

[0008] The present disclosure has been made in view of the above-mentioned problems of the conventional technology. More specifically, the present disclosure provides a quantum device with an improved S / N ratio in fluorescence detection.

[0009] [Advantages of the Present Disclosure] The quantum device of the present disclosure can improve the S / N ratio in fluorescence detection.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (1) A quantum device according to one embodiment includes a quantum material including a color center having electron spin, a stage having a mounting surface, and a microwave resonator for irradiating microwaves onto the quantum material. The quantum material has a first surface and a second surface opposite the first surface, and is disposed on the stage such that the first surface faces the mounting surface. The stage has an optical waveguide through which excitation light irradiated onto the quantum material and fluorescence generated by the quantum material pass. The microwave resonator irradiates microwaves such that a first intensity, which is the intensity of the microwaves on the first surface, and a second intensity, which is the intensity of the microwaves on the second surface, are at least 0.5 times a third intensity, which is the maximum intensity of the microwaves. The quantum device according to (1) above can improve the signal-to-noise ratio in fluorescence detection.

[0012] (2) In the quantum device of (1) above, when the direction normal to the installation surface is defined as the first direction, the microwave resonator may irradiate microwaves so that the width in the first direction of an irradiation area in which the microwave intensity is within a range of 0.5 times or more of the third intensity is 100 μm or more.

[0013] (3) In the quantum device of (1) or (2) above, if the direction of the normal to the installation surface is defined as a first direction, and the central positions of the microwave resonator and the quantum material in the first direction are defined as a first central position and a second central position, respectively, the microwave resonator may be arranged so that the distance in the first direction between the first central position and the second central position is 0.5 times or less the thickness of the quantum material.

[0014] (4) In the quantum devices of (1) to (3) above, when the direction of the normal to the installation surface is defined as a first direction, the direction perpendicular to the first direction is defined as a second direction, and the center position of the installation surface in the second direction is defined as a third center position, the angle formed with the normal passing through the third center position is 45° or less and the distance from the third center position in the second direction is equal to or less than the minimum width of the installation surface in the second direction may be open above the microwave resonator. The quantum device of (4) above makes it easy to operate the quantum material.

[0015] (5) In the quantum devices of (1) to (4) above, the ends of the optical waveguides from which the excitation light is emitted and to which the fluorescence is incident may be disposed on an installation surface. The quantum device of (5) above facilitates manipulation of the quantum material.

[0016] (6) In the quantum devices of (1) to (5) above, the microwave resonator may be a λ / 4 stub having two linear conductors. According to the quantum device of (6) above, microwaves can be uniformly irradiated onto the quantum material while the microwave resonator is disposed near the quantum material. Furthermore, according to the quantum device of (6) above, strong microwaves can be applied to the quantum material, and quantum operations can be completed within a coherent time with low power.

[0017] (7) In the quantum devices of (1) to (5) above, the microwave resonator may be a λ / 4 stub having four linear conductors. According to the quantum device of (7) above, microwaves can be uniformly irradiated onto the quantum material while the microwave resonator is disposed near the quantum material. Furthermore, according to the quantum device of (7) above, strong microwaves can be applied to the quantum material, and quantum operations can be completed within a coherent time with low power.

[0018] (8) In the quantum devices of (1) to (5), the microwave resonator may be a conductor wound in a coil shape. According to the quantum device of (8), microwaves can be uniformly irradiated onto the quantum material.

[0019] (9) The quantum devices of (1) to (8) above may perform quantum operations based on Rabi oscillations, the Ramsey method, or the Hahn-Echo method.

[0020] (10) The quantum device of (1) to (9) above may further include a photodetector that receives fluorescence emitted from the optical waveguide and a microcontroller connected to the photodetector. The microcontroller may have an analog-to-digital converter that converts an analog signal output from the photodetector into a digital signal. The dimensions of the microcontroller may be 6 cm x 12 cm or less when viewed from the direction in which its area is maximized. The quantum device of (10) above can be made into a portable device that can be used in a variety of environments.

[0021] (11) In the quantum device of (10) above, the microcontroller may automatically measure the transverse relaxation time of the quantum material.

[0022] (12) In the quantum devices of (1) to (11) above, the quantum material may be continuously irradiated with excitation light. The quantum material may be pulsed with microwaves. In the quantum device of (12) above, it is possible to lower the required precision of the optical system and to make the device highly environmentally resistant.

[0023] (13) In the quantum devices of (1) to (12) above, the quantum material may be diamond, silicon carbide, or boron nitride.

[0024] (14) In the quantum devices of (1) to (13), the color center may be any of an NV center in diamond, a SiV center in diamond, a GeV center in diamond, a SnV center in diamond, a PbV center in diamond, a SiV center in silicon carbide, and a VB center in boron nitride. The quantum device may measure electron spin.

[0025] (15) The quantum device according to any one of (1) to (14) above may further include a housing and a connection cable connected to the microwave resonator. The housing may be formed of a metal or an electromagnetic wave absorber. The microwave may be irradiated only when the stage is sealed in the housing or when the stage, the microwave resonator, and the connection cable are sealed in the housing.

[0026] (16) Another embodiment of a measurement device is an apparatus for evaluating a quantum material including a color center having quantum spin and having a first surface and a second surface opposite the first surface. The measurement device includes: a stage having a mounting surface on which the quantum material is placed so that the mounting surface faces the first surface; and a microwave resonator that irradiates microwaves onto the quantum material. The stage has an optical waveguide through which excitation light irradiated onto the quantum material and fluorescence generated by the quantum material pass. The microwave resonator irradiates microwaves so that a first intensity, which is the intensity of the microwaves on the first surface, and a second intensity, which is the intensity of the microwaves on the second surface, are 0.5 times or more the third intensity, which is the maximum intensity of the microwaves. The measurement device described above in (16) makes it possible to improve the S / N ratio in fluorescence detection.

[0027] (17) The measuring device of (17) may further include a housing and a connection cable connected to the microwave resonator. The housing may be formed of a metal or an electromagnetic wave absorber. The microwave may be irradiated only when the stage is sealed in the housing or when the stage, the microwave resonator, and the connection cable are sealed in the housing.

[0028] [Details of the embodiment of the present disclosure] The details of the embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated. A quantum device according to the embodiment is referred to as a quantum device 100.

[0029] (Configuration of the Quantum Device 100) The configuration of the quantum device 100 will be described below.

[0030] 1 is a cross-sectional view of a quantum device 100. As shown in FIG. 1, the quantum device 100 includes a stage 10, a quantum material 20, and a microwave resonator 30.

[0031] The stage 10 has a mounting surface 10a. The mounting surface 10a is a surface on which the quantum material 20 is placed. The direction normal to the mounting surface 10a is defined as a first direction DR1. The direction perpendicular to the first direction DR1 is defined as a second direction DR2. The direction perpendicular to both the first direction DR1 and the second direction DR2 is defined as a third direction DR3. In FIG. 1, the first direction DR1 corresponds to the up-down direction in the figure, and the second direction DR2 corresponds to the left-right direction in the figure. In FIG. 1, the third direction DR3 corresponds to the direction perpendicular to the plane of the page in the figure.

[0032] The stage 10 has a first surface 10b and a second surface 10c in the thickness direction of the stage 10, i.e., in the first direction DR1. The second surface 10c is the surface opposite to the first surface 10b. A recess 10d is formed in the first surface 10b. The recess 10d is recessed toward the second surface 10c.

[0033] A through hole 10e is formed in the stage 10. The through hole 10e extends along the first direction DR1. The through hole 10e is open to the bottom surface (the installation surface 10a) of the recess 10d and the second surface 10c.

[0034] The stage 10 has an optical waveguide 11 and a ferrule 12. The ferrule 12 is disposed in the through-hole 10e. The ferrule 12 and the bottom surface of the recess 10d form the installation surface 10a. The ferrule 12 is made of, for example, zirconia (ZrO ２ ) is formed.

[0035] The optical waveguide 11 is inserted into the ferrule 12. One end of the optical waveguide 11 is disposed on the installation surface 10a. The optical waveguide 11 is, for example, an optical fiber. The optical fiber used in the optical waveguide 11 may be a multimode optical fiber or a single-mode optical fiber. The core diameter of the optical fiber can be selected appropriately, and may be, for example, 10 μm or more, 100 μm or more, or 400 μm or more. Instead of an optical fiber, the optical waveguide 11 may be made of silicon oxide (SiO ２ A waveguide made of aluminum or resin may also be used.

[0036] Quantum material 20 has a first surface 20a and a second surface 20b. Second surface 20b is the surface opposite to first surface 20a. First surface 20a and second surface 20b are end surfaces in the thickness direction of quantum material 20. Quantum material 20 is placed on stage 10 so that first surface 20a faces installation surface 10a. In other words, quantum material 20 is placed so that its thickness direction is along first direction DR1.

[0037] The quantum material 20 is, for example, any one of diamond, silicon carbide (SiC), and boron nitride (BN). The quantum material 20 is not limited to these materials. The quantum material 20 is, for example, a single crystal. The quantum material 20 includes a color center. The color center is a lattice defect in the quantum material 20 that exhibits color when irradiated with light.

[0038] A color center is composed of an element (a constituent element or an impurity element of quantum material 20) at one position in the crystal lattice of quantum material 20 and a vacancy at another position in the crystal lattice adjacent to the one position. The color center has an electron spin.

[0039] The color center in diamond is, for example, an NV center, a SiV center, a GeV center, a SnV center, or a PbV center. The color center in silicon carbide is, for example, an SiV center. The color center in boron nitride is, for example, a VB center. Here, the V in the notation of the color center means a vacancy, and for example, the NV center in diamond is composed of nitrogen (N) as an impurity at one position of the diamond crystal lattice and a vacancy (V) adjacent to that position.

[0040] FIG. 2 is a schematic diagram of the magnetic field of microwaves MW generated by microwave resonator 30. As shown in FIG. 2, microwave resonator 30 generates microwaves MW and irradiates the generated microwaves MW to quantum material 20. In the example shown in FIG. 2, the direction of the magnetic field of the microwaves MW is along a first direction DR1. Note that microwaves MW refer to electromagnetic waves with a wavelength of 1 mm or more and 1 m or less. Microwave resonator 30, for example, pulses (intermittently irradiates) microwaves MW to quantum material 20. Microwave resonator 30 may also continuously irradiate microwaves MW to quantum material 20.

[0041] The quantum material 20 is arranged, for example, so that the direction of the magnetic field of the microwave MW and the direction of the color center (the direction in which the constituent elements (or impurity elements) and vacancies of the quantum material 20 are aligned) are not parallel. If the quantum material 20 is diamond and the color center is an NV center, the direction of the color center is the <111> direction. If the first surface 20a (second surface 20b) is a (100) or (110) plane, the direction of the color center and the direction of the magnetic field of the microwave MW are not parallel. In this case, the direction of the color center has a component of the second direction DR2. If the first surface 20a of the quantum material 20 is a (110) plane, the direction of the magnetic field of the microwave MW is perpendicular to the direction of the color center, allowing for the most efficient driving of electron spins. Although not shown, a permanent magnet, for example, is arranged outside the microwave resonator 30 as a magnetic field generator, and a bias magnetic field is applied to the quantum material 20. The bias magnetic field is preferably applied in a direction parallel to the direction of the color center. The bias magnetic field may be applied in a direction perpendicular to the direction of the color center. In this case, the deviation of the bias magnetic field from the direction perpendicular to the direction of the color center is preferably 1° or less.

[0042] The microwave resonator 30 is, for example, a λ / 4 stub made up of two linear conductors. That is, the microwave resonator 30 has a linear conductor 31 and a linear conductor 32. When a current flows through the linear conductor 31 and the linear conductor 32, microwaves MW are generated.

[0043] The linear conductors 31 and 32 extend along a third direction DR3. The length of the linear conductors 31 and 32 in the third direction DR3 is 0.25 (1 / 4) times the wavelength of the microwave MW. For example, when microwaves MW having a frequency of about 2.87 GHz (wavelength of about 100 mm) are generated to drive NV centers in diamond, the length of the linear conductors 31 and 32 in the third direction DR3 is about 25 mm.

[0044] The linear conductors 31 and 32 are arranged to face each other with a gap in the second direction DR2. The gap between the linear conductors 31 and 32 in the second direction DR2 is, for example, 0.5 mm or more and 4.0 mm or less. The recess 10d (installation surface 10a, quantum material 20) is located between the linear conductors 31 and 32 in the second direction DR2. The linear conductors 31 and 32 are arranged on, for example, the first surface 10b.

[0045] The center position of the microwave resonator 30 in the first direction DR1 is defined as a center position CP1. The intensity of the microwave MW varies along the first direction DR1, becoming weaker as it moves away from the center position CP1 along the first direction DR1. The intensity of the microwave MW at the first surface 20a is defined as a first intensity, and the intensity of the microwave MW at the second surface 20b is defined as a second intensity. The maximum value of the intensity of the microwave MW is defined as a third intensity.

[0046] The microwaves MW exhibit a third intensity at the center position CP1. The microwave resonator 30 irradiates the quantum material 20 with the microwaves MW such that the first intensity and the second intensity are 0.5 times or more the third intensity. Alternatively, the microwave resonator 30 may irradiate the quantum material 20 with the microwaves MW such that the first intensity and the second intensity are 0.7 times or more or 0.9 times or more the third intensity.

[0047] The center position of quantum material 20 in first direction DR1 is defined as center position CP2. The distance in first direction DR1 between center position CP1 and center position CP2 is, for example, 0.5 times or less, 0.25 times or less, or 0.125 times or less the thickness of quantum material 20 (the distance between first surface 20a and second surface 20b).

[0048] A region where the intensity of microwaves MW is 0.5 times or more the third intensity is defined as a uniform region. When quantum material 20 is placed on stage 10 so that center position CP2 coincides with center position CP1, the relationship that the first intensity and the second intensity are 0.5 times or more the third intensity is satisfied for quantum material 20 having a thickness equal to the width of the uniform region in first direction DR1. The width of the uniform region in first direction DR1 is, for example, 100 μm or more. The width of the uniform region in first direction DR1 may be 300 μm or more or 500 μm or more.

[0049] 2, the quantum device 100 may further include a housing 70. The housing 70 is made of metal or an electromagnetic wave absorber. The microwaves MW may be irradiated only when the stage 10 is sealed within the housing 70. Furthermore, the microwaves MW may be irradiated only when the stage 10, the microwave resonator 30, and the cables connected to the microwave resonator 30 are sealed within the housing 70.

[0050] FIG. 3 is an explanatory diagram of the space above the microwave resonator 30. As shown in FIG. 3, the center position of the installation surface 10a in the second direction DR2 is defined as a center position CP3. A normal line to the installation surface 10a that passes through the center position CP3 is defined as a normal line NL. Lines LI1 and LI2 are defined as lines that pass through the center position CP3 and form an angle θ with the normal line NL. Lines LI3 and LI4 are defined as lines that are parallel to the normal line NL and whose distance from the normal line NL in the second direction DR2 (distance DIS) is the shortest distance between the normal line NL and the microwave resonator 30. The angle θ is 45° or more, 30° or more, or 15° or more. The distance DIS is equal to or greater than the width W, 0.75 times the width W, or 0.5 times the width W.

[0051] The space defined by the lines LI1, LI2, LI3, and LI4 and located above the microwave resonator 30 is defined as the space above the microwave resonator 30. The space above the microwave resonator 30 is, for example, open. That is, no solid object is disposed in the space above the microwave resonator 30.

[0052] As shown in FIG. 1, the quantum device 100 further includes a light source 40 , a light receiving element 50 , and a microcontroller 60 .

[0053] The light source 40 generates excitation light L1. The excitation light L1 is, for example, laser light. The wavelength of the laser light is selected appropriately. When the quantum material 20 is diamond containing an NV center as a color center, the wavelength of the laser light is, for example, 532 nm.

[0054] The excitation light L1 enters the other end of the optical waveguide 11, exits from one end of the optical waveguide 11 (i.e., the installation surface 10a), and is irradiated onto the quantum material 20. The intensity of the excitation light L1 at one end of the optical waveguide 11 is, for example, 10 mW. The energy density P of the excitation light L1 at one end of the optical waveguide 11 is, for example, 80 mW / mm ２ Below, 10mW / mm ２ Below, 1mW / mm ２ or less than 0.1 mW / mm ２ The excitation light L1 is continuously irradiated onto the quantum material 20, for example.

[0055] By irradiating the quantum material 20 with excitation light L1, an irradiation region 20c is formed in the quantum material 20. The length of the irradiation region 20c in the first direction DR1 is, for example, 100 μm or more. The length of the irradiation region 20c in the first direction DR1 may be 300 μm or more or 500 μm or more. When microwaves MW are irradiated onto the quantum material 20 while it is being irradiated with excitation light L1, fluorescence L2 is generated from the irradiation region 20c. The fluorescence L2 enters one end of the optical waveguide 11 and exits the other end of the optical waveguide 11. When the quantum material 20 is a diamond containing an NV center as a color center, fluorescence L2 having a wavelength of 637 nm and distributed on the long wavelength side due to phonon scattering is generated from the irradiation region 20c.

[0056] The fluorescence L2 emitted from the other end of the optical waveguide 11 is incident on the light receiving element 50 after the excitation light L1 is cut off by a low-pass filter (not shown). The light receiving element 50 is, for example, a photodiode. The light receiving element 50 outputs an analog signal corresponding to the incident fluorescence L2.

[0057] The microcontroller 60 is connected to the light-receiving element 50. The microcontroller 60 may be, for example, ArduinoDue (registered trademark), RasberryPi (registered trademark), or the like. The dimensions of the microcontroller 60, when viewed from the direction in which its area is maximized, are, for example, 6 cm × 12 cm or less, 4 cm × 7 cm or less, or 3 cm × 5 cm or less. The analog signal output from the light-receiving element 50 is converted to a digital signal by an analog-to-digital converter in the microcontroller 60 and processed in the microcontroller 60. The microcontroller 60 may measure the intensity of the excitation light L1 using a light-receiving element (not shown) and normalize the intensity of the fluorescence L2 based on the measured intensity of the excitation light L1. The microcontroller 60 is also connected to the microwave resonator 30 along with a pulse pattern generator, a microwave oscillator, a microwave switch, etc., and performs pulse control of the magnetic field of the microwave MW. Furthermore, the microcontroller 60 may transmit processed data to a PC (personal computer) (not shown).

[0058] FIG. 4A is a first explanatory diagram illustrating the energy levels in the quantum material 20. FIG. 4B is a second explanatory diagram illustrating the energy levels in the quantum material 20. As shown in FIGS. 4A and 4B, the ground state ( １ A) and excited state ( ３ E) is m depending on the state of the electron spin Ｓ = 0, m Ｓ = +1, m Ｓ It has three energy levels: m = -1. Ｓ = +1 and m Ｓ The energy level of ≡-1 is degenerate when no external field is applied, but splits when an external field such as a magnetic field is applied.

[0059] Ground state １ A's m Ｓ When the excitation light L1 is irradiated onto an electron at the level of 0, the electron enters an excited state ３ E's m Ｓ= 0 level, and then returns to the original level while emitting red fluorescence L2. １ A's m Ｓ = +1 level or m Ｓ = -1 level is irradiated with excitation light L1, and the electron is excited ３ E's m Ｓ = +1 or m Ｓ Even if the electron transitions to the level of ≈-1, it cannot emit fluorescence L2 when it returns to its original state. １ E and ground states １ A １ ' via the ground state １ A's m Ｓ By continuing this process, the ground state １ A's m Ｓ = 0, m Ｓ = +1 and m Ｓ = -1, the electrons are in the ground state １ A's m Ｓ = 0. This is called initialization.

[0060] After initialization, the ground state １ A's m Ｓ = 0 level electrons in the ground state １ A's m Ｓ =0 level and ground state １ A's m Ｓ When microwaves MW corresponding to the energy difference between the level of ≈±1 are applied, the electron １ A's m Ｓ =±1 also has a probability of existence, and although the fluorescence L2 would normally be generated when irradiated with the excitation light L1, the fluorescence L2 is no longer generated.

[0061] m Ｓ The levels of m = ±1 are split by the Zeeman effect and the Stark effect. Ｓ The level of L = 0 varies with temperature. Therefore, by measuring the frequency of the microwave MW and the intensity of the fluorescence L2, the quantum device 100 can detect various external fields (magnetic field, electric field, temperature).

[0062] The detection of the external field is performed based on a pulsed microwave supply sequence such as Rabi oscillation measurement, Ramsey method measurement, Hahn-Echo method measurement, or XY8-N method. The quantum device 100 may measure the transverse relaxation time (T2, T2*) of the quantum material 20 based on the detected fluorescence L2. The transverse relaxation time may be automatically measured by the microcontroller 60. In the following, the Rabi oscillation measurement and other operations are referred to as m Ｓ =0 level and m Ｓ The explanation is given using the relationship between the level of m = +1 as an example. Ｓ =0 level and m Ｓ The same is true for the level of =-1.

[0063] Fig. 5 is a schematic diagram showing the pulse waveform of microwave MW used in various measurement methods. As shown in Fig. 5, in the Rabi vibration measurement, the pulse width of microwave MW is changed while m Ｓ =0 level and m Ｓ This is a method of measuring the periodic oscillations that transition between the levels of 0 and 1.

[0064] The Ramsey method applies a microwave MW having a predetermined pulse width and intensity called a π / 2 pulse, Ｓ =0 level and m Ｓ A superposition state is formed with the level of +1. After that, the electron spin is affected by the external field for a predetermined time (τ), and a phase shift called transverse relaxation occurs. After that, when a π / 2 pulse microwave MW is applied again, m Ｓ =0 level and m Ｓ Since the probability of existence of the level ranking of =+1 is determined, the Ramsey method is a microwave supply sequence that can detect an external field with higher sensitivity.

[0065] In this case, m Ｓ =0 level and m Ｓ The superposition state with the level of =+1 loses coherence due to crystal defects in the quantum material 20, and so the coherence time (free induction decay time, T2*) in transverse relaxation can be measured by measuring how much the signal of the Ramsey method decays during τ.

[0066] The Hahn-Echo method applies a π / 2 pulse microwave MW to Ｓ =0 level and m Ｓ = +1 level. After that, the electron spin is transversely relaxed by the external field for τ / 2, and then the phase is inverted by applying a π-pulse microwave MW. During the subsequent τ / 2 period, the influence of the DC component of the external field on the electron spin and phase fluctuations due to crystal defects are canceled out, and information about the amount of change in the external field remains as the phase of the electron spin. If a π / 2-pulse microwave MW is applied again after that, m Ｓ =0 level and m Ｓ The Hahn-Echo method is a microwave supply sequence that can detect external fields with high sensitivity because the probability of existence of the level of = +1 is determined. This method is suitable for measuring external fields of alternating current.

[0067] Even in the Hahn-Echo method, coherence is lost due to the quality of quantum material 20, such as crystal defects, so the coherence time (T2) in transverse relaxation can be measured by measuring how much the Hahn-Echo method signal decays during τ. Furthermore, although FIG. 5 illustrates a pulse waveform for the XY8-N method, the quantum operation performed by quantum device 100 (the operation of applying pulsed microwaves MW possessed by the color centers of quantum material 20 to transition electron spins between ground state levels) is not limited to Rabi oscillation measurement, Ramsey method, Hahn-Echo method, or XY8-N method, and may be other microwave supply sequences, such as the Ramsey method, Hahn-Echo method, CMPG method, or XY4-N method, in which the microwave phase is changed. The interval T (seconds) between the start time of one set of pulse microwave supply sequences, such as the π / 2 pulse-π / 2 pulse of the Ramsey method, and the start time of the next sequence is determined by the energy density P (W / mm ２ ) satisfies the equation T≧0.00001 / P. This ensures sufficient initialization of the electron spin, enabling accurate measurement of the external field and transverse relaxation times (T2, T2*). The interval T desirably satisfies the relationship T≧0.0001 / P, for example, T≦0.01 / P.

[0068] (Modification 1) Fig. 6 is a cross-sectional view of a quantum device 100 according to Modification 1. As shown in Fig. 6, the microwave resonator 30 may be a λ / 4 stub having four linear conductors. These four linear conductors are designated as linear conductor 33, linear conductor 34, linear conductor 35, and linear conductor 36, respectively.

[0069] The linear conductors 33, 34, 35, and 36 extend along the third direction DR3. The linear conductors 33 and 34 are arranged opposite each other with a gap in the second direction DR2, and the linear conductors 35 and 36 are arranged opposite each other in the second direction DR2. The linear conductors 33 and 35 are arranged opposite each other with a gap in the first direction DR1, and the linear conductors 34 and 36 are arranged opposite each other with a gap in the first direction DR1. The quantum material 20 is located between the linear conductors 33 and 34 (between the linear conductors 35 and 36) in the second direction DR2, and between the linear conductors 33 and 35 (between the linear conductors 34 and 36) in the first direction DR1.

[0070] The distance between the linear conductors 33 and 34 in the second direction DR2 and the distance between the linear conductors 35 and 36 in the second direction DR2 are, for example, 0.5 mm or more and 4.0 mm or less. The distance between the linear conductors 33 and 35 in the first direction DR1 and the distance between the linear conductors 34 and 36 in the first direction DR1 are, for example, 0.5 mm or more and 4.0 mm or less. Note that the center position CP1 in this example is the center position between the linear conductors 33 and 35 (between the linear conductors 34 and 36).

[0071] 7 is a schematic diagram of the magnetic field of microwaves MW generated by microwave resonator 30 in quantum device 100 according to Modification 1. As shown in FIG. 7, microwaves MW are generated by current flowing through linear conductors 33, 34, 35, and 36. However, in this example, the direction of the magnetic field of microwaves MW is along second direction DR2. Since quantum material 20 is arranged so that the direction of the color center and the direction of the magnetic field of microwaves MW are not parallel, in this example, if quantum material 20 is diamond containing an NV center as a color center, first face 20a and second face 20b are, for example, (111) planes.

[0072] (Modification 2) Fig. 8 is a cross-sectional view of quantum device 100 according to Modification 2. As shown in Fig. 8, microwave resonator 30 is composed of conductor 37 wound in a coil shape. Conductor 37 extends along first direction DR1 while being wound spirally around a coil axis along first direction DR1. In this example, stage 10 and quantum material 20 are disposed inside conductor 37 wound in a coil shape, and the coil axis of conductor 37 passes through center position CP3, for example.

[0073] (Variation 3) Quantum material 20 may be replaceable. By measuring fluorescence L2 after replacing quantum material 20, quantum device 100 can measure the material properties of different quantum materials 20. That is, in this case, quantum device 100 functions as an evaluation device for quantum material 20.

[0074] (Effects of the Quantum Device 100) The effects of the quantum device 100 will be described below.

[0075] In quantum device 100, microwave resonator 30 irradiates quantum material 20 with microwaves MW such that the first intensity and second intensity are 0.5 times or more (0.7 times or more, 0.9 times or more) the third intensity. Therefore, even if irradiation region 20c has a large length in first direction DR1, microwaves MW are uniformly irradiated to irradiation region 20c, thereby reducing the phase shift at each location in irradiation region 20c. For example, if the first intensity and second intensity are 0.9 times or more the third intensity, when irradiating center position CP2 with microwaves MW that form a π / 2 pulse, the phase shift at first surface 20a and second surface 20b is limited to approximately 9° (= 90° × 0.1 = 9°). Therefore, quantum device 100 allows for accurate measurement of the external field and the transverse relaxation time of quantum material 20.

[0076] As described above, quantum device 100 can increase the length of irradiation region 20c in first direction DR1 while suppressing phase shift, thereby increasing the volume for generating fluorescence L2. Therefore, quantum device 100 can improve the S / N ratio when detecting fluorescence L2 while suppressing phase shift.

[0077] In quantum device 100, the space above microwave resonator 30 defined by lines LI1, LI2, LI3, and LI4 is open, allowing for a high degree of freedom in the placement of quantum material 20. Furthermore, because the space above microwave resonator 30 is open, quantum material 20 can be easily replaced by transporting it along first direction DR1 using, for example, a robot arm. Furthermore, because excitation light L1 is irradiated from installation surface 10a, optical waveguide 11 for supplying excitation light L1 does not interfere with the replacement of quantum material 20.

[0078] In the quantum device 100, since the pump light L1 is continuously irradiated even while the microwave MW pulse is being irradiated, an optical element (such as an acousto-optical element) for pulsing the pump light L1 is not required, and the required precision of the optical system can be reduced. As a result, it is possible to create a device with high environmental resistance (for example, vibration resistance and temperature stability).

[0079] When microwave resonator 30 is a λ / 4 stub, it is possible to uniformly irradiate quantum material 20 with strong microwaves MW while placing microwave resonator 30 near quantum material 20, and quantum operation can be completed within the coherence time with low input power to microwave resonator 30. When microwave resonator 30 is a conductor 37 wound in a coil shape, it is possible to uniformly irradiate quantum material 20 with microwaves MW.

[0080] (Examples and Comparative Examples) The first measurement example is an example, and the second measurement example is a comparative example. In the first and second measurement examples, diamond containing an NV center as a color center was used as the quantum material 20. The planar dimensions of the quantum material 20 were 1 mm x 1 mm, and the thickness of the quantum material 20 was 0.5 mm (500 μm). A λ / 4 stub having a linear conductor 31 and a linear conductor 32 was used as the microwave resonator 30.

[0081] In the first and second measurement examples, a magnetic field of 2 mT was applied as a bias magnetic field by a permanent magnet along the second direction DR2. In the first and second measurement examples, an ArduinoDue was used as the microcontroller 60, and pulse control of the microwave MW, measurement of the fluorescence L2 by the light receiving element 50, and transmission of data to a PC were performed.

[0082] In the first measurement example, the distance in the first direction DR1 between the center position CP1 and the installation surface 10a was 250 μm. Therefore, in the first measurement example, the distance in the first direction DR1 between the center position CP1 and the center position CP2 was within 0.025 times the thickness of the quantum material 20. In the second measurement example, the distance in the first direction DR1 between the center position CP1 and the center position CP2 was 0.6 times the thickness of the quantum material 20, and the distance in the first direction DR1 between the center position CP1 and the center position CP2 was not within 0.5 times the thickness of the quantum material 20.

[0083] <Examples> FIG. 9 shows the results of CW-ODMR spectrum measurement in the first measurement example. FIG. 10 is a partially enlarged view of FIG. 9. In FIGS. 9 and 10, the vertical axis represents the intensity of the fluorescence L2, and the horizontal axis represents the frequency of the microwave MW. As shown in FIGS. 9 and 10, in the first measurement example, a minimum resonance frequency of 2816.5 MHz was obtained. FIG. 11 shows the results of Rabi oscillation measurement in the first measurement example. As shown in FIG. 11, in the first measurement example, the microwave MW frequency was set to 2816.5 MHz, and the microwave MW intensity was set to 0 dBm, and Rabi oscillation measurement was performed, resulting in a π pulse width of 800 ns.

[0084] Fig. 12 shows the results of pulsed ODMR spectrum measurement in the first measurement example. Fig. 13 is a partially enlarged view of Fig. 12. In Figs. 12 and 13, the vertical axis represents the intensity of fluorescence L2, and the horizontal axis represents the frequency of the microwave MW. As shown in Figs. 12 and 13, in the first measurement example, pulsed ODMR spectrum measurement was performed with a microwave MW pulse width of 800 nsec. Compared to Figs. 9 and 10, the half-width of each peak was smaller, and the minimum resonance frequency of 2816.6 MHz could be precisely read.

[0085] Fig. 14 shows the results of Ramsey method measurement in Measurement Example 1. In Measurement Example 1, the Ramsey method measurement was performed with a π / 2 pulse width of 400 ns and a microwave MW resonance frequency of 2816.6 MHz, and the data shown in Fig. 14 was sent from the microcontroller 60 to a PC and fitted using Igor (registered trademark), resulting in the calculation of a transverse relaxation time (T2*) of 535 ns.

[0086] 15 shows the results of the Hahn-Echo measurement in the first measurement example. １２ Because C-enriched diamond is an example, １３The waveform is smooth and free from vibrations due to C nuclear spin. In the first measurement example, the Hahn-Echo measurement was performed with a π / 2 pulse width of 400 ns, a π pulse width of 800 ns, and a microwave MW resonance frequency of 2816.6 MHz. The data shown in Fig. 15 was sent from the microcontroller 60 to a PC and fitted using Igor, resulting in a transverse relaxation time (T2) of 13 µs.

[0087] Comparative Example: Figure 16 shows the Rabi oscillation measurement results for the second measurement example. As shown in Figure 16, in the second measurement example, the first minimum value of the fluorescence L2 was detected at 800 ns. However, compared to Figure 11, the change in the fluorescence L2 after the second minimum was small and unclear. This is because the first surface 20a was irradiated with a strong microwave MW, which increased the spin rotation speed of the NV center, while the second surface 20b was irradiated with a weak microwave MW of 0.4 times the third intensity, which decreased the spin rotation speed of the NV center. As a result, Rabi oscillations with different periods overlapped, shortening the effective coherence time. As such, measurement methods using long pulse sequences, such as the Hahn-Echo method and the XY8-N method, exhibited significant attenuation of quantum data, making measurement virtually impossible.

[0088] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0089] CP1 center position, CP2 center position, CP3 center position, DIS distance, DR1 first direction, DR2 second direction, DR3 third direction, L1 excitation light, L2 fluorescence, LI1, LI2, LI3, LI4 straight line, MW microwave, NL normal, W width, 100 quantum device, 10 stage, 10a installation surface, 10b first surface, 10c second surface, 10d recess, 10e through hole, 11 optical waveguide, 12 ferrule, 20 quantum material, 20a first surface, 20b second surface, 20c irradiation area, 30 microwave resonator, 31, 32, 33, 34, 35, 36 linear conductor, 37 conductor, 40 light source, 50 light receiving element, 60 microcontroller, 70 housing.

Claims

1. A quantum device comprising: a quantum material including a color center having electron spin; a stage having a mounting surface; and a microwave resonator that irradiates microwaves onto the quantum material, wherein the quantum material has a first surface and a second surface opposite to the first surface, and is placed on the stage so that the first surface faces the mounting surface; the stage has an optical waveguide through which excitation light irradiated onto the quantum material and fluorescence generated by the quantum material pass; and the microwave resonator irradiates the microwaves so that a first intensity that is the intensity of the microwaves on the first surface and a second intensity that is the intensity of the microwaves on the second surface are 0.5 times or more a third intensity that is the maximum intensity of the microwaves.

2. The quantum device of claim 1, wherein the microwave resonator irradiates the microwaves such that the width in the first direction of an irradiation region where the microwave intensity is within a range of 0.5 times or more the third intensity is 100 μm or more, when the direction normal to the installation surface is defined as a first direction.

3. A quantum device as described in claim 1 or claim 2, wherein, when the direction of the normal to the installation surface is defined as a first direction and the central positions of the microwave resonator and the quantum material in the first direction are defined as a first central position and a second central position, respectively, the microwave resonator is positioned such that the distance in the first direction between the first central position and the second central position is 0.5 times or less the thickness of the quantum material.

4. A quantum device as described in any one of claims 1 to 3, wherein, when the direction of the normal to the installation surface is defined as a first direction, the direction perpendicular to the first direction is defined as a second direction, and the center position of the installation surface in the second direction is defined as a third center position, the angle formed with the normal passing through the third center position is 45° or less and the distance from the third center position in the second direction is less than the minimum width of the installation surface in the second direction, the space above the microwave resonator is open.

5. A quantum device according to any one of claims 1 to 4, wherein the end of the optical waveguide from which the excitation light is emitted and to which the fluorescence is incident is disposed on the installation surface.

6. A quantum device according to any one of claims 1 to 5, wherein the microwave resonator is a λ / 4 stub having two linear conductors.

7. A quantum device according to any one of claims 1 to 5, wherein the microwave resonator is a λ / 4 stub having four linear conductors.

8. A quantum device according to any one of claims 1 to 5, wherein the microwave resonator is a conductor wound in a coil shape.

9. The quantum device according to any one of claims 1 to 8, wherein the quantum device performs quantum operations based on Rabi oscillations, Ramsey method, or Hahn-Echo method.

10. A quantum device according to any one of claims 1 to 9, further comprising: a photodetector that receives the fluorescence emitted from the optical waveguide; and a microcontroller connected to the photodetector, wherein the microcontroller has an analog-to-digital converter that converts an analog signal output from the photodetector into a digital signal, and the size of the microcontroller is 6 cm x 12 cm or less when viewed from the direction in which its area is greatest.

11. The quantum device of claim 10, wherein the microcontroller automatically measures the transverse relaxation time of the quantum material.

12. A quantum device according to any one of claims 1 to 11, wherein the excitation light is continuously irradiated onto the quantum material, and the microwave is pulsed onto the quantum material.

13. A quantum device according to any one of claims 1 to 12, wherein the quantum material is diamond, silicon carbide or boron nitride.

14. A quantum device according to any one of claims 1 to 13, wherein the color center is any one of an NV center in diamond, a SiV center in diamond, a GeV center in diamond, a SnV center in diamond, a PbV center in diamond, a SiV center in silicon carbide, and a VB center in boron nitride, and the quantum device measures the electron spin.

15. A quantum device as described in any one of claims 1 to 14, further comprising a housing and a connection cable connected to the microwave resonator, the housing being formed of a metal or an electromagnetic wave absorber, and the microwaves being irradiated only when the stage is sealed within the housing or when the stage, the microwave resonator, and the connection cable are sealed within the housing.

16. An evaluation device for a quantum material including a color center having quantum spin and having a first surface and a second surface opposite the first surface, comprising: a stage having a mounting surface on which the quantum material is placed so that the mounting surface faces the first surface; and a microwave resonator that irradiates microwaves onto the quantum material, the stage having an optical waveguide through which excitation light irradiated onto the quantum material and fluorescence generated by the quantum material pass, and the microwave resonator irradiates the microwaves so that a first intensity that is the intensity of the microwaves at the first surface and a second intensity that is the intensity of the microwaves at the second surface are 0.5 times or more a third intensity that is the maximum intensity of the microwaves.

17. The evaluation device according to claim 16, further comprising: a housing; and a connection cable connected to the microwave resonator, wherein the housing is formed of a metal or an electromagnetic wave absorber, and the microwaves are irradiated only when the stage is sealed within the housing or when the stage, the microwave resonator, and the connection cable are sealed within the housing.

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