Physical quantity detection device, control method for physical quantity detection device, and computer program for physical quantity detection device

Abstract

To provide a physical quantity detection device capable of improving detection sensitivity. [Solution] The physical quantity detection device comprises a sensor element including a light-emitting center, an excitation light pulse generation unit that generates excitation light and irradiates the sensor element, a high-frequency pulse generation unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element, and a photodetection unit that detects the light emission from the light-emitting center. The light-emitting center has two different spin qubits. The two spin qubits are equivalent to each other but consist of different energy levels. The high-frequency pulse generation unit generates a high-frequency pulse with two different frequencies superimposed and irradiates the sensor element to simultaneously manipulate the two spin qubits.

Description

Technical Field

[0001] This specification relates to a physical quantity detection device, a control method for the physical quantity detection device, and a computer program for the physical quantity detection device.

Background Art

[0002] Conventionally, a physical quantity detection device has been proposed that uses a sensor element having spin defects (luminescent centers) in a solid to detect physical quantities such as magnetic fields, temperatures, and electric fields. In such a physical quantity detection device, the luminescence intensity of the luminescent center is utilized, which changes depending on the physical quantity. Specifically, excitation energy and resonance electromagnetic waves are applied to the sensor element, and the change in luminescence intensity during resonance of the ground state or excited state of the luminescent center is detected. Related techniques are disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There are known luminescent centers that contain two different spin qubits (having four or more magnetic quantum numbers). For example, silicon vacancies in silicon carbide, which is a spin 3 / 2 system. However, compared to NV centers (nitrogen-vacancy centers) in diamond, which are similar qubits, the signal intensity (contrast) is small, which is a problem.

Means for Solving the Problems

[0005] The physical quantity detection device disclosed herein comprises a sensor element including a light-emitting center; an excitation light pulse generation unit that generates excitation light and irradiates the sensor element with it; a high-frequency pulse generation unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with it; and a photodetection unit that detects the light emission from the light-emitting center. The light-emitting center has two distinct spin qubits. The two spin qubits are equivalent to each other but consist of different energy levels. The high-frequency pulse generation unit generates high-frequency pulses with two different frequencies superimposed and irradiates the sensor element with them, thereby simultaneously manipulating the two spin qubits.

[0006] When a high-frequency pulse with only one frequency is irradiated onto a light-emitting center having two spin qubits, only one spin qubit can be manipulated. The other spin qubit, which is not being manipulated, does not contribute to the detection signal, so a detection signal can only be obtained from one of the two spin qubits. With the above structure, by irradiating with a high-frequency pulse in which two different frequencies are superimposed, both spin qubits can be manipulated simultaneously. As a result, detection signals can be obtained from both spin qubits. This can increase the detection intensity (contrast), making it possible to improve the detection sensitivity of the physical quantity detection device. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of the physical quantity detection device 1. [Figure 2] This is an energy level diagram of silicon vacancies. [Figure 3] This figure shows the change in the energy levels of spin. [Figure 4] This is a flowchart of the detection sequence for a physical quantity. [Figure 5] This is a timing chart for applying the excitation light pulse EP and the high-frequency pulse HP. [Figure 6] This is a diagram that represents quantum states using a Bloch sphere. [Figure 7]This is a flowchart for calibrating a pulse width of π / 2. [Figure 8] This figure shows an example of a continuous wave ODMR spectrum. [Figure 9] This figure shows an example of Rabi oscillation. [Figure 10] This diagram illustrates the detection principle in the comparative example. [Figure 11] This diagram illustrates the detection principle in this embodiment. [Figure 12] This figure shows the quantum state in Example 2. [Figure 13] This is a timing chart for the application of the excitation light pulse EP and the high-frequency pulse HP in Example 3. [Figure 14] This figure shows an example of the results obtained when a sensor is operated by applying an AC magnetic field AF. [Modes for carrying out the invention] [Examples]

[0008] (Overview of Physical Quantity Detection Device 1) Figure 1 is a schematic diagram showing the general configuration of a physical quantity detection device 1 according to one embodiment. The physical quantity detection device 1 mainly comprises a sensor element 10, an excitation light pulse generation unit 20, a high-frequency pulse generation unit 30, a photodetection unit 40, a static magnetic field application unit 50, and a control unit 60.

[0009] The sensor element 10 is made of a material that includes a light-emitting center. The light-emitting center has two distinct spin qubits. The two spin qubits are equivalent to each other but consist of different energy levels. In this embodiment, the light-emitting center has a spin 3 / 2 that is detectable by photodetection and magnetic resonance in silicon carbide (SiC). Specifically, the material of the sensor element 10 is 4H-SiC, and the light-emitting center is a silicon vacancy. The sensor element 10 may be attached to the tip of a sensor probe (not shown).

[0010] The static magnetic field application unit 50 is located near the sensor element 10 and applies a known static magnetic field to the sensor element 10. The static magnetic field application unit 50 is located near the sensor element 10. The static magnetic field application unit 50 may be, for example, a permanent magnet or an electromagnet. The light detection unit 40 is the part that detects the light emission from the light emission center. The light detection unit 40 may include a photodetector such as a photodiode, a filter, a mirror, a lens, etc.

[0011] The excitation light pulse generation unit 20 is the part that generates excitation light pulses EP and irradiates the sensor element 10. The excitation light pulse generation unit 20 may include a light source such as a light-emitting diode, a filter, a mirror, a lens, etc. Furthermore, since the excitation light pulses EP are irradiated as digital pulses, the excitation light pulse generation unit 20 may include an acousto-optic modulator for digital modulation as needed. Alternatively, the light source itself may be configured to be digitally modulated.

[0012] The high-frequency pulse generation unit 30 is the part that generates high-frequency pulses HP for manipulating the spin qubit at the light-emitting center and irradiates the sensor element 10 with them. The high-frequency pulse generation unit 30 in this embodiment is characterized by generating a high-frequency signal in which two different frequencies are superimposed as synchronized high-frequency pulses HP. As a result, as will be described later, it is possible to manipulate two spin qubits simultaneously.

[0013] The high-frequency pulse generation unit 30 mainly comprises a first high-frequency signal source 31, a second high-frequency signal source 32, a combining unit 33, a high-frequency switch 34, and an amplifier 35. The first high-frequency signal source 31 has a first resonant frequency f + This is the part that generates the high-frequency signal. The second high-frequency signal source 32 has a second resonance frequency f - This is the part that generates the high-frequency signal. As will be described later, the first resonance frequency f + These are the resonance frequencies for magnetic quantum numbers +1 / 2 and +3 / 2. Also, the second resonance frequency f -These are the resonance frequencies for magnetic quantum numbers -1 / 2 and -3 / 2. The combining unit 33 is the part that combines the output of the first high-frequency signal source 31 and the output of the second high-frequency signal source 32. The high-frequency switch 34 receives a timing signal TS from the control unit 60. The high-frequency switch 34 pulses the high-frequency signal based on the timing signal TS. The amplifier 35 is the part that outputs the amplified high-frequency pulse HP. If necessary, the high-frequency pulse generation unit 30 may also include high-frequency circuit elements (e.g., antenna, waveguide, etc.) for pulse irradiation of the sensor probe.

[0014] The control unit 60 is configured to control the operation of the excitation light pulse generation unit 20, the high-frequency pulse generation unit 30, the photodetection unit 40, and other components. Various information terminal devices, such as a known general-purpose computer, can be used for the control unit 60. The control unit 60 mainly comprises a memory and an arithmetic circuit (not shown). The memory mainly stores a physical quantity detection program. The arithmetic circuit is composed of a microprocessor equipped with an NPU or GPU. The arithmetic circuit executes the physical quantity detection sequence (Figure 4), which will be described later, by executing the physical quantity detection program stored in the memory.

[0015] (Operating principle) The operating principle is explained below. Figure 2 shows the energy level diagram of a silicon vacancy. The main (optical) energy levels consist of a ground state and an excited state. By irradiating with light above this energy difference, emission (photoluminescence, fluorescence) from the silicon vacancy is observed. The typical excitation light wavelength is around 780-830 nm. The emission spectrum is around 900-1000 nm at room temperature. Looking at the energy structure of the ground and excited states in more detail, there are levels that originate from electron spin. The silicon vacancy is a spin 3 / 2 system and consists of four levels with magnetic quantum numbers m = +3 / 2, +1 / 2, -1 / 2, and -3 / 2. In the absence of an external magnetic field, +3 / 2, -3 / 2 and +1 / 2, -1 / 2 each have the same energy (degenerate). Therefore, in Figure 2, they are grouped together as ±3 / 2, ±1 / 2.

[0016] In the case of silicon vacancies, there is a process that transitions from the excited state to the ground state via a non-luminescent state. When the transition passes through the non-luminescent state, no luminescence occurs in the 900-1000 nm range. The probability of this non-luminescent process occurring is spin-state dependent, and is higher when m=±1 / 2 than when m=±3 / 2. Therefore, by continuing photoexcitation for a certain period of time and repeating the excitation-relaxation process, a state in which the magnetic quantum number is biased towards m=±1 / 2 can be formed ((1) Spin polarization by light).

[0017] Furthermore, the difference in the transition probability to the non-luminescent state reveals that "when the spin is at m=±3 / 2, the luminescence intensity increases compared to when it is at m=±1 / 2" ((2) Reading out the spin state by light).

[0018] The energy of a spin is affected by external fields such as magnetic and electric fields, as well as lattice strain, but the response to a magnetic field is the most pronounced, so we will explain using a magnetic field as an example. Figure 3 shows the change in the energy levels of the spin when a magnetic field parallel to the c-axis is applied to a 4H-SiC crystal. The degeneracy at zero magnetic field is lifted, and four different energies appear. Here, the first resonance frequency f + This is the resonance frequency equal to the energy difference between m = +3 / 2 and +1 / 2. Also, the second resonance frequency f - This is the resonance frequency equal to the energy difference between m = -3 / 2 and -1 / 2. And the first resonance frequency f + and the second resonance frequency f - By applying a high frequency having the properties of (3) magnetic resonance, the occupancy probability between states can be changed ((3) manipulation of spin states by magnetic resonance).

[0019] By using the above-described methods—(1) optical spin polarization (initialization), (3) manipulation of the spin state by magnetic resonance, and (2) optical reading of the spin state—to detect minute changes in energy levels, minute physical quantities (such as magnetic fields) can be detected. The specific sequence is described below.

[0020] (Sequence for detecting physical quantities) FIG. 4 shows a flowchart of a detection sequence of a physical quantity. In this embodiment, the case of detecting a physical quantity that does not change with time (DC magnetic field) will be described. FIG. 5 shows an application timing chart of an excitation light pulse EP and a high-frequency pulse HP. FIG. 6 shows a diagram representing a quantum state by a Bloch sphere. The upper part of FIG. 6 shows the quantum state of the + qubit QB1, and the lower part shows the quantum state of the - qubit QB2. FIGS. 6(a)-(c) show the quantum states at each stage described later.

[0021] In step S0, calibration of the π / 2 pulse width is performed. A specific calibration method will be described later.

[0022] In step S1, the first excitation light irradiation is performed. Specifically, an excitation light pulse EP is irradiated to the sensor element 10 by the excitation light pulse generation unit 20 (see FIG. 5, times t1 - t2). Thereby, the electron spin is initialized to the state of m = ±1 / 2. As shown in FIG. 6(a), the initialized electron spins SP1 are aligned in the direction along the z-axis (quantization axis).

[0023] In step S2, the first π / 2 pulse irradiation is performed. Specifically, a high-frequency pulse HP of a π / 2 pulse is irradiated to the sensor element 10 by the high-frequency pulse generation unit 30 (see FIG. 5, times t3 - t4). The π / 2 pulse applies a high frequency in a pulse shape for a certain length. Since the π / 2 pulse is well-known, detailed description thereof will be omitted.

[0024] Here, the feature of the present invention is that the π / 2 pulse of the first resonance frequency f + and the π / 2 pulse of the second resonance frequency f - are applied simultaneously. That is, the feature is that operations can be performed simultaneously on two sets of the + qubit QB1 and the - qubit QB2. Thereby, it is possible to generate a superposition state in which each of m = +1 / 2, +3 / 2, and m = -1 / 2, -3 / 2 is occupied with a probability of half.

[0025] Furthermore, the phase of the first π / 2 pulse irradiation is set to +x. Therefore, as shown in the quantum state by the Bloch sphere in Figure 6(a), it is possible to rotate the quantum state by 90 degrees in the positive rotation direction around the x-axis. By doing so, the electron spin SP1 along the quantization axis (z-axis) is tilted to the xy-plane perpendicular to the quantization axis, becoming the electron spin SP2 (see arrow A1).

[0026] In step S3, a predetermined time is waited for after the first π / 2 pulse irradiation (see Figure 5, time t4-t5). This allows information about the physical quantity (magnetic field) to be accumulated in the phase difference of the quantum state. In the quantum state representation in Figure 6(b), the electron spin SP2, tilted to the xy plane, acquires a phase through interaction with the magnetic field of the measurement target during the predetermined time, becoming the electron spin SP3. In this case, when the measurement target is a magnetic field (Example 1, Figure 6), the sign of the phase φ is the same between the +qubit QB1 and the -qubit QB2. Therefore, the electron spin SP3 rotates in the same direction (see Figure 6(b), arrow A2; shown counterclockwise here).

[0027] In step S4, a second π / 2 pulse irradiation is performed. Specifically, the high-frequency pulse generator 30 irradiates the sensor element 10 with a π / 2 pulse high-frequency pulse HP (see Figure 5, time t5-t6). This allows the operation to convert the phase difference into the occupation probability for the two sets of +qubit QB1 and -qubit QB2.

[0028] Specifically, the phase of the second π / 2 pulse irradiation is set to +y. That is, the first resonance frequency f + The phase of the π / 2 pulse and the second resonance frequency f - The phases of the π / 2 pulses are assumed to be identical (+y). This allows the rotation direction of the quantum states of the positive qubit QB1 and the negative qubit QB2 to be the same. Thus, as shown in Figure 6(c), the quantum states of the positive qubit QB1 and the negative qubit QB2 can be rotated 90 degrees in the positive rotation direction around the y-axis. As a result, electron spin SP4 is obtained (see arrow A3).

[0029] As shown in Figure 6(c), in the positive qubit QB1, the emission intensity is high in the +z-axis direction and low in the -z-axis direction. On the other hand, in the negative qubit QB2, the emission intensity is high in the -z-axis direction and low in the +z-axis direction. Furthermore, in the positive qubit QB1, by rotating the quantum state by 90 degrees in the positive direction of the y-axis rotation, the z-axis component of the electron spin SP4 becomes positive (emission intensity increases). Similarly, in the negative qubit QB2, by rotating the quantum state by 90 degrees in the positive direction of the y-axis rotation, the z-axis component of the electron spin SP4 becomes negative (emission intensity increases). In other words, since the emission intensity can be increased in both the positive qubit QB1 and the negative qubit QB2, it becomes possible to improve the sensor sensitivity as will be described later.

[0030] In step S5, a second excitation light irradiation is performed. Specifically, the excitation light pulse EP is irradiated onto the sensor element 10 by the excitation light pulse generator 20 (see Figure 5, time t7-t8). As a result, the electron spin is projected onto the z axis (quantization axis), becoming the electron spin SP5 along the z axis (see arrow A4).

[0031] In step S6, phase information is read out. Specifically, with the excitation light pulse EP applied, the photodetector 40 detects the emission state of the emission center.

[0032] In step S7, the strength of the magnetic field being measured is calculated. Specifically, the phase information of the electron spin SP5 state detected by the photodetector 40 corresponds to the state of the DC magnetic field being measured. By appropriately processing this phase information, the strength of the DC magnetic field can be calculated.

[0033] In this embodiment, the phase is set to x during the first π / 2 pulse irradiation (step S2) (i.e., rotated 90 degrees around the x-axis). On the other hand, the phase is set to y during the second π / 2 pulse irradiation (step S4) (i.e., rotated 90 degrees around the y-axis). The reason is as follows: When the phase is set to x during the second π / 2 pulse irradiation, the phase information readout signal (z-coordinate of electron spin SP5) becomes a cosine function. On the other hand, when the phase is set to y during the second π / 2 pulse irradiation, the phase information readout signal becomes a sine function. Here, since the change in phase φ is small, the sine function can have a larger rate of change (derivative) than the cosine function. Therefore, by setting the phase to y during the second π / 2 pulse irradiation (step S4), it is possible to increase the detection sensitivity of minute signals.

[0034] (Calibration sequence with π / 2 pulse width) Using the flowchart in Figure 7, the calibration of the π / 2 pulse width performed in step S0 of Figure 4 will be explained. In step S20, a static magnetic field is applied to the sensor element 10 by the static magnetic field application unit 50. The static magnetic field may be one that is generally known.

[0035] In step S22, the first resonant frequency f + and the second resonance frequency f - This is determined. This determination can be made using a continuous-wave ODMR spectrum. Figure 8 shows an example of a continuous-wave ODMR spectrum. The horizontal axis is the frequency of the high-frequency signal. The vertical axis is the ODMR contrast (rate of change in emission intensity). A continuous-wave ODMR spectrum can be obtained by applying excitation light and high-frequency signal as a continuous wave and measuring the change in emission intensity when the frequency of the high-frequency signal is changed. First resonance frequency f + and the second resonance frequency f - Peaks PK1 and PK2 appear in each of these parts. This results in the first resonance frequency f + and the second resonance frequency f - It is possible to make a decision.

[0036] In step S24, the required value (target value) for the π / 2 pulse width is set. If the π / 2 pulse width is an approximately constant value determined by the device configuration of the physical quantity detection device 1, that constant value may be used.

[0037] In steps S30-S36, the first resonant frequency f + Only is the π / 2 pulse width calibration performed. This will be explained in detail. In step S30, the first resonance frequency f + Rabi oscillations are measured at arbitrary amplitudes. Rabi oscillations are oscillations at a constant frequency that can be observed when the emission intensity (occupancy probability of a quantum state) is plotted as a function of pulse length.

[0038] Figure 9 shows an example of Rabi oscillation. The horizontal axis represents the pulse width of the high-frequency pulse (HP). The vertical axis represents the rate of change in ODMR contrast (luminescence intensity). In Figure 9, the first resonance frequency f + The plot when only is used is shown by a triangle. The second resonance frequency f - The plot using only is shown by the square. The first resonance frequency f + and the second resonance frequency f - The plot when both are used simultaneously is shown by the circles. Also, the first resonance frequency f + In the case of only, and the second resonance frequency f - The graph of the Rabi oscillation in the case of only is shown as Rabi oscillation RO0. The first resonance frequency f + and the second resonance frequency f - The graph of Rabi oscillation when both are used simultaneously is shown as Rabi oscillation RO1.

[0039] In this example, the first resonance frequency f + Because only is used, the Rabi vibration RO0 is measured in step S30.

[0040] In step S32, the π / 2 pulse width is calculated. This will be explained in detail. The Rabi frequency is calculated from the Rabi oscillation measured in step S30. For this calculation, for example, fitting (e.g., fitting using the least squares method) or FFT can be used. Then, 1 / 4 of the period of the calculated Rabi oscillation becomes the π / 2 pulse width. In the example in Figure 9, 1 / 4 period PR is the π / 2 pulse width.

[0041] In step S34, it is determined whether the calculated π / 2 pulse width is within the tolerance range. The tolerance may be predetermined. If the determination is negative (S34: NO), the process proceeds to step S36, where the π / 2 pulse width is feedback-adjusted. This will be explained in detail. When the power (amplitude) of the first high-frequency signal source 31 increases, the first resonant frequency f + The π / 2 pulse width is reduced. Therefore, if the calculated π / 2 pulse width is large, the power of the first high-frequency signal source 31 should be increased. On the other hand, if the calculated π / 2 pulse width is small, the power of the first high-frequency signal source 31 should be decreased. Then the process returns to step S30, and the calculation of the π / 2 pulse width is performed again.

[0042] On the other hand, in step S34, if the calculated π / 2 pulse width is within the tolerance range (S34: YES), the first resonance frequency f + The calibration of the π / 2 pulse width using only is completed. Therefore, proceed to step S40.

[0043] In steps S40-S46, the second resonance frequency f - Only is the π / 2 pulse width calibration performed. The contents of each of steps S40-S46 are the same as those of steps S30-S36 described above, so a detailed explanation is omitted.

[0044] 2nd resonance frequency f - Once the calibration of the π / 2 pulse width using only is complete, proceed to step S50. In step S50, the first resonance frequency f + and the second resonance frequency f -The Rabi vibration is measured by simultaneously applying the following. The procedure in step S50 is the same as in step S30 described above. As a result, the Rabi vibration RO1 is measured, as shown in the example in Figure 9.

[0045] In step S52, the π / 2 pulse width is calculated. The processing in step S52 is the same as in step S32 described above. In step S54, it is determined whether the calculated π / 2 pulse width is within the tolerance range. If the judgment is negative (S54: NO), the process returns to step S22 and the calibration is restarted from the beginning. On the other hand, if the judgment is positive (S54: YES), the first resonance frequency f + and the second resonance frequency f - In this case, it can be confirmed that the same π / 2 pulse width is achieved. Therefore, the calibration process is complete.

[0046] The effect of calibration with a pulse width of π / 2 will be explained. In the technique of this embodiment, the first resonance frequency f + π / 2 pulse and second resonance frequency f - It features the simultaneous application of a π / 2 pulse. Therefore, the first resonance frequency f + The pulse width of π / 2 and the second resonance frequency f - It is important that the π / 2 pulse widths are the same. However, the π / 2 pulse width may fluctuate due to changes in the device environment. Furthermore, the π / 2 pulse width depends on the power (amplitude) of the first high-frequency signal source 31 and the second high-frequency signal source 32. That is, the higher the power of the high-frequency signal source, the smaller the π / 2 pulse width. Therefore, the π / 2 pulse width can be calibrated by feedback control of the power of the high-frequency signal source based on the calculation result of the π / 2 pulse width. This makes it possible to perform operations on two sets of qubits, +qubit QB1 and -qubit QB2, simultaneously.

[0047] (Effects and their principles) In Figure 9, the first resonance frequency f + In the case of only, and the second resonance frequency f -In the case of only, the Rabi oscillation RO0 has an amplitude AM0. On the other hand, the first resonance frequency f + and the second resonance frequency f - When both are applied simultaneously, the Rabi vibration RO1 has an amplitude AM1. Furthermore, the amplitude AM1 is approximately twice as large as the amplitude AM0. This results in the first resonance frequency f + When only is applied, or the second resonance frequency f - Compared to when the first resonance frequency f is applied, + and the second resonance frequency f - It can be seen that applying both simultaneously can increase the detection sensitivity (magnetic sensitivity) of the physical quantity detection device 1 by approximately twofold.

[0048] The principle by which detection sensitivity can be increased is explained using Figures 10 and 11. Figure 10 shows a comparative example (first resonance frequency f + This is an embodiment (using only). Figure 11 shows this embodiment (first resonance frequency f + and the second resonance frequency f - (Used simultaneously). Figures 10 and 11 schematically illustrate the three states: (1) initialization, (2) spin state manipulation, and (3) readout.

[0049] The comparative example in Figure 10 is explained below. (1) An excitation light pulse is applied for initialization (see step S1). This initializes the silicon vacancies to a state where m = +1 / 2 and -1 / 2 are occupied with equal probability.

[0050] Next, (2) in spin state manipulation, the first resonance frequency f + Only the π / 2 pulse is applied (see step S2). As a result, the +qubit QB1 (m=+1 / 2,+3 / 2) is generated into a superposition state by resonance (see arrow A11). On the other hand, the -qubit QB2 (m=-1 / 2,-3 / 2) does not resonate and remains in its initialized state (see region R11).

[0051] (3) During readout (see step S6), a change in emission intensity is detected in the positive qubit QB1, and a sensor signal can be obtained. On the other hand, the negative qubit QB2 does not change in emission intensity and only emits background light, so it does not contribute to the sensor signal. In other words, the negative qubit QB2 becomes a source of background noise.

[0052] This embodiment shown in Figure 11 will be described. (1) Initialization is the same as in the comparative example. (2) In spin state manipulation, the first resonance frequency f + π / 2 pulse and second resonance frequency f - A π / 2 pulse is applied simultaneously. This allows the equivalent +qubit QB1 and -qubit QB2 to be manipulated simultaneously. Thus, a superposition state is generated in both the +qubit QB1 and -qubit QB2 (see arrows A21 and A22). Consequently, (3) during readout, the light emission intensity changes in both the +qubit QB1 and -qubit QB2, allowing sensor signals to be obtained from both qubits. As a result, in this embodiment, it is possible to obtain up to twice the sensor sensitivity compared to the comparative example. [Examples]

[0053] Example 2 describes the case where the physical quantity detected by the physical quantity detection device 1 is temperature or electric field. The following description will only include details specific to Example 2.

[0054] (Sequence for detecting physical quantities) Figure 12 shows the quantum state in Example 2. Figure 12, like Figure 6 described above, is a diagram that represents the quantum state using a Bloch sphere. The contents of steps S0 to S2 in Figure 4 are common to both Examples 1 and 2. Therefore, the state in Figure 12(a) in Example 2 is identical to the state in Figure 6(a) in Example 1.

[0055] In step S3, information about a physical quantity (temperature or electric field) is stored in the phase difference of the quantum states. When the object of measurement is a magnetic field (Example 1, Figure 6), the sign of the phase φ is the same between the +qubit QB1 and the -qubit QB2. Therefore, the electron spin SP3 rotates counterclockwise in both (see Figure 6(b), arrow A2). In contrast, when the object of measurement is temperature or an electric field (Example 2, Figure 12), the signs of the phase φ are opposite between the +qubit QB1 and the -qubit QB2. Therefore, the electron spin SP3 rotates counterclockwise in the +qubit QB1 (see arrow A2a). On the other hand, it rotates clockwise in the -qubit QB2 (see arrow A2b).

[0056] In step S4, a second π / 2 pulse irradiation is performed. At this time, the first resonance frequency f + The phase of the π / 2 pulse and the second resonance frequency f - The phases of the π / 2 pulses are set to be opposite to each other. This allows the rotation direction of the quantum state around the y-axis to be opposite to that of the +qubit QB1 and the -qubit QB2. Specifically, in the +qubit QB1, rotating the quantum state by 90 degrees in the positive direction of rotation around the y-axis makes the z-axis component of the electron spin SP4 positive (increases emission intensity) (see Figure 12(c), arrow A3a). On the other hand, in the -qubit QB2, rotating the quantum state by 90 degrees in the negative direction of rotation around the y-axis makes the z-axis component of the electron spin SP4 negative (increases emission intensity) (see Figure 12(c), arrow A3b).

[0057] In other words, when the measurement target is temperature or electric field, if the quantum states of both the +qubit QB1 and the -qubit QB2 are rotated 90 degrees in the positive direction of rotation around the y-axis, the z-axis component of the electron spin SP4 of the -qubit QB2 becomes positive (the emission intensity decreases). As a result, the detection signals cancel each other out. Therefore, in the technique described herein, the rotation directions of the quantum states around the y-axis of the +qubit QB1 and the -qubit QB2 are set to opposite directions (i.e., the first resonance frequency f +(The phase of the π / 2 pulse and the phase of the π / 2 pulse at the second resonance frequency f- are reversed.) This allows the emission intensity to be increased in both the positive qubit QB1 and the negative qubit QB2, making it possible to improve the sensor sensitivity as described later.

[0058] (Reason why the sign of the phase φ is reversed) As described above, when the measurement target is a magnetic field (Example 1, Figure 6), the sign of the phase φ is the same between the positive qubit QB1 and the negative qubit QB2 (see Figure 6(b), arrow A2). On the other hand, when the measurement target is temperature or an electric field (Example 2, Figure 12), the signs of the phase φ are opposite between the positive qubit QB1 and the negative qubit QB2 (see Figure 12(b), arrows A2a and A2b). The reason for this will be explained.

[0059] When the object being measured is a magnetic field, the sign of the phase φ is the same for the positive qubit QB1 and the negative qubit QB2, as shown in equation (1) below.

number

number

[0060] In equations (2) and (3) above, B Z The first term, which includes this, means that the electron spin functions as a magnetic field sensor. The sign of the first term is the same for the +qubit QB1 and the -qubit QB2. Therefore, when the object being measured is a magnetic field, the sign of the phase φ is the same (see Figure 6(b), arrow A2).

[0061] On the other hand, when the object being measured is temperature or electric field, the energy level difference of the qubit is expressed by equations (4) and (5) below.

number

[0062] The second term, represented as "2D(T)", indicates that the electron spin functions as a temperature sensor. The sign of the second term is reversed between equations (4) and (5) above. Therefore, the phase φ obtained by integrating these small shifts also has opposite signs (see Figure 12(b), arrows A2a and A2b).

[0063] Also, "2dE Z The third term, expressed as , means that the electron spin functions as an electric field sensor. The sign of the third term is reversed between equations (4) and (5) above. Therefore, the phase φ obtained by integrating these small shifts also has opposite signs (see Figure 12(b), arrows A2a and A2b). [Examples]

[0064] Example 3 describes the case where the physical quantity detected by the physical quantity detection device 1 is a time-varying physical quantity (AC magnetic field AF). The following description will only include details specific to Example 3.

[0065] Figure 13 shows the timing chart for the application of the excitation light pulse EP and the high-frequency pulse HP in Example 3. Example 3 is an example that uses the spin echo method (also called the Hahn echo method) in magnetic resonance. The timing chart of Example 3 (Figure 13) differs from the timing chart of Example 1 (Figure 5) in that a π pulse (times t4a-t4b) has been added. Since the spin echo method is well known, a detailed explanation will be omitted.

[0066] At times t3-t4, the first π / 2 pulse irradiation is performed. After a predetermined time TT1 has elapsed, a π pulse irradiation is performed (see times t4a-t4b). The π pulse is a high-frequency pulse with twice the length (or twice the amplitude) of the π / 2 pulse. By irradiating with the π pulse, it is possible to reverse the electron spin that has accumulated phase due to interaction with the object being measured (rotate it 180 degrees around the x-axis) in a plane. Then, after a predetermined time TT2 has elapsed since the π pulse irradiation, the second π / 2 pulse irradiation is performed (see times t5-t6). The predetermined times TT1 and TT2 correspond to the half-period of the AC magnetic field AF of the object being measured.

[0067] The spin echo method provides the effect of canceling out the influence of static disturbances acting on the quantum state. Here, static disturbances refer to influences such as DC current or external fields that evolve sufficiently slowly compared to the length of this sequence. To explain in detail: During a predetermined time TT1, a phase φ accumulation occurs due to static disturbances (the tip position of the electron spin rotates by a phase φ in the xy plane). Then, after the predetermined time TT1 has elapsed, inversion occurs due to a π pulse. During the subsequent predetermined time TT2, a phase φ accumulation occurs due to static disturbances, but because of the inversion, the phases cancel each other out. In other words, regardless of the magnitude of the disturbance (i.e., the magnitude of the phase φ), the disturbance component (static magnetic field component) is canceled out, so the disturbance has no effect on the quantum state.

[0068] On the other hand, in the AC magnetic field AF synchronized with the pulse train, the sign of the phase accumulation changes to -φ after inversion by the π pulse. As a result, in the AC magnetic field AF, the tip position of the electron spin in the xy plane is rotated by a phase of 2φ. Therefore, the magnitude of the AC magnetic field AF is not canceled out and can be read out.

[0069] (Example of measurement results for AC magnetic field AF) Figure 14 shows an example of the results obtained when an AC magnetic field AF is applied to the sensor. The horizontal axis represents the amplitude of the AC magnetic field. The vertical axis represents the rate of change of the spin echo signal. In Figure 14, the first resonance frequency f + The plot when only is used is shown by a triangle. The second resonance frequency f - The plot using only is shown by the square. The first resonance frequency f + and the second resonance frequency f - The plot when both are used simultaneously is shown by the circles. Also, the first resonance frequency f + In the case of only, and the second resonance frequency f - The graph for the case with only this is shown in graph G0. The first resonance frequency f + and the second resonance frequency f - Graph G1 shows the result when both methods are used simultaneously.

[0070] If the amplitude of the alternating magnetic field is b, the phase accumulation 2φ is expressed by the following equation (6).

number

[0071] The information read out is the occupation probability of the quantum state (the z-coordinate of the electron spin SP5 in Figure 6(c)). Therefore, the shapes of graphs G1 and G2 are as shown in equation (7) below.

number

[0072] In Figure 14, the first resonance frequency f + In the case of only, and the second resonance frequency f -In the case of only this, graph G0 has an amplitude AM0a. On the other hand, the first resonance frequency f + and the second resonance frequency f - When both are applied simultaneously, graph G1 has an amplitude AM1a. Furthermore, amplitude AM1a is approximately twice as large as amplitude AM0a. This results in the first resonance frequency f + When only is applied, or the second resonance frequency f - Compared to when the first resonance frequency f is applied, + and the second resonance frequency f - It can be seen that applying both simultaneously can increase the detection sensitivity (AC magnetic field AF sensitivity) of the physical quantity detection device 1 by approximately twofold.

[0073] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. Furthermore, the technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness.

[0074] (modified version) In this embodiment, the case in which silicon vacancies of 4H-SiC are used as the light-emitting center has been described, but the embodiment is not limited to this form, and various light-emitting centers can be used. For example, Frenkel defects of 6H-SiC may be used as the light-emitting center. In this case, the dependence of the second term (D(T)) in equations (4) and (5) described above on T can be increased. This makes it possible to increase the sensitivity of the temperature sensor.

[0075] In this embodiment, SiC was used as the material with the light-emitting center, but the embodiment is not limited to this. Various materials with color centers, such as diamond, SiC, and hBN, can be used.

[0076] The configuration of the high-frequency pulse generation unit 30 is not limited to the configuration shown in Figure 1, and may vary. For example, an arbitrary waveform generator can be used to generate the first resonance frequency f + and the second resonance frequency f - Alternatively, the configuration may directly generate high-frequency pulses (HP) having two frequencies. Alternatively, the desired frequency may be obtained by performing frequency conversion using a high-frequency mixer.

[0077] In the calibration sequence with a pulse width of π / 2 (Figure 7), the order of each step can be rearranged or any step can be skipped as desired. For example, the order of the calibration processes S30-S36 and S40-S46 can be swapped. Also, the first resonance frequency f + and the second resonance frequency f - If this is already known, step S22 may be omitted.

[0078] The following are embodiments of this technology. [Aspect 1] A sensor element including a light-emitting center, An excitation light pulse generation unit generates excitation light and irradiates the sensor element with it, A high-frequency pulse generating unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with them, A light detection unit for detecting the light emission from the light emission center, Equipped with, The light-emitting center has two different spin qubits (four or more magnetic quantum numbers), The two spin qubits are equivalent to each other but have different energy levels. The high-frequency pulse generation unit generates the high-frequency pulse in which two different frequencies are superimposed and irradiates the sensor element to simultaneously operate the two spin qubits. A physical quantity detection device. [Aspect 2] The physical quantity detection device according to embodiment 1, wherein the light-emitting center has a spin 3 / 2 that can be detected by photodetection and magnetic resonance in silicon carbide. [Aspect 3] The physical quantity detection device according to embodiment 2, wherein the two spin qubits are a set of magnetic quantum numbers {+3 / 2, +1 / 2} and a set of magnetic quantum numbers {-3 / 2, -1 / 2}. [Aspect 4] The physical quantity detection device according to embodiment 3, wherein the two frequencies are a first resonance frequency which is the resonance frequency of magnetic quantum numbers +1 / 2 and +3 / 2, and a second resonance frequency which is the resonance frequency of magnetic quantum numbers -1 / 2 and -3 / 2. [Aspect 5] The aforementioned high-frequency pulse generating unit is A first high-frequency signal source that generates a high-frequency signal of the first resonant frequency, A second high-frequency signal source that generates a high-frequency signal of the second resonant frequency, A combining unit that generates the high-frequency pulse by combining the output of the first high-frequency signal source and the output of the second high-frequency signal source, A physical quantity detection device according to any one of embodiments 1 to 4, comprising the above. [Aspect 6] The physical quantity detection device further includes a control unit configured to control the operation of the excitation light pulse generation unit, the high-frequency pulse generation unit, and the photodetection unit. The control unit, The excitation light pulse generation unit is instructed to perform the first excitation light irradiation, which irradiates the sensor element with an excitation light pulse. The high-frequency pulse generating unit is instructed to perform a first π / 2 pulse irradiation, which irradiates the sensor element with the high-frequency pulses of π / 2 pulses. After a predetermined time has elapsed since the first π / 2 pulse irradiation, the high-frequency pulse generation unit is instructed to perform a second π / 2 pulse irradiation, which irradiates the sensor element with the π / 2 pulse high-frequency pulse. After the execution of the second π / 2 pulse irradiation, the excitation light pulse generation unit is instructed to perform a second excitation light irradiation, irradiating the sensor element with the excitation light pulse. A physical quantity detection device according to any one of embodiments 1 to 5, wherein the photodetector is made to detect the emission state of the emission center due to the second excitation light irradiation. [Aspect 7] The two spin qubits are a pair with magnetic quantum numbers {+3 / 2, +1 / 2} and a pair with magnetic quantum numbers {-3 / 2, -1 / 2}. The two frequencies are the first resonance frequency, which is the resonance frequency for magnetic quantum numbers +1 / 2 and +3 / 2, and the second resonance frequency, which is the resonance frequency for magnetic quantum numbers -1 / 2 and -3 / 2. The physical quantity detection device according to embodiment 6, wherein, with respect to the pulse phase of the first resonance frequency and the pulse phase of the second resonance frequency included in the high-frequency pulse used in the second π / 2 pulse irradiation, either the pulse phase of the first resonance frequency or the pulse phase of the second resonance frequency included in the high-frequency pulse used in the first π / 2 pulse irradiation is inverted. [Aspect 8] The physical quantity detection device according to embodiment 6 or 7, wherein the physical quantity detected by the physical quantity detection device is temperature or electric field. [Aspect 9] A sensor element including a light-emitting center, An excitation light pulse generation unit generates excitation light and irradiates the sensor element with it, A high-frequency pulse generating unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with them, A light detection unit for detecting the light emission from the light emission center, A control method for a physical quantity detection device comprising: The light-emitting center has two different spin qubits, The two spin qubits are equivalent to each other but consist of different energy levels. The high-frequency pulse generation unit generates a high-frequency pulse in which two different frequencies are superimposed and irradiates the sensor element to simultaneously operate the two spin qubits. A control method for a physical quantity detection device. [Aspect 10] A sensor element including a light-emitting center, An excitation light pulse generation unit generates excitation light and irradiates the sensor element with it, A high-frequency pulse generating unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with them, A light detection unit for detecting the light emission from the light emission center, Memory and Calculation circuit and, A computer program for a physical quantity detection device comprising, The light-emitting center has two different spin qubits, The two spin qubits are equivalent to each other but consist of different energy levels. The aforementioned high-frequency pulse generation unit generates a high-frequency pulse in which two different frequencies are superimposed and irradiates the sensor element, thereby enabling the calculation circuit to function as an irradiation unit that simultaneously manipulates the two spin qubits. Computer program. [Explanation of Symbols]

[0079] 1: Physical quantity detection device 10: Sensor element 20: Excitation light pulse generation unit 30: High-frequency pulse generation unit 40: Photodetector HP: High-frequency pulse f + :1st resonance frequency f - :2nd resonance frequency

Claims

1. A sensor element including a light-emitting center, An excitation light pulse generation unit generates excitation light and irradiates the sensor element with it, A high-frequency pulse generating unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with them, A light detection unit for detecting the light emission from the light emission center, Equipped with, The light-emitting center has two different spin qubits, The two spin qubits are equivalent to each other but have different energy levels. The high-frequency pulse generation unit generates a high-frequency pulse in which two different frequencies are superimposed and irradiates the sensor element to simultaneously operate the two spin qubits. A physical quantity detection device.

2. The physical quantity detection device according to claim 1, wherein the light-emitting center has a spin 3 / 2 that can be detected by photodetection and magnetic resonance in silicon carbide.

3. The physical quantity detection device according to claim 2, wherein the two spin qubits are a set of magnetic quantum numbers {+3 / 2, +1 / 2} and a set of magnetic quantum numbers {-3 / 2, -1 / 2}.

4. The physical quantity detection device according to claim 3, wherein the two frequencies are a first resonance frequency which is the resonance frequency of magnetic quantum numbers +1 / 2 and +3 / 2, and a second resonance frequency which is the resonance frequency of magnetic quantum numbers -1 / 2 and -3 / 2.

5. The aforementioned high-frequency pulse generating unit is A first high-frequency signal source that generates a high-frequency signal of the first resonance frequency, A second high-frequency signal source that generates a high-frequency signal of the second resonant frequency, A combining unit that generates the high-frequency pulse by combining the output of the first high-frequency signal source and the output of the second high-frequency signal source, A physical quantity detection device according to claim 4, comprising:

6. The physical quantity detection device further includes a control unit configured to control the operation of the excitation light pulse generation unit, the high-frequency pulse generation unit, and the photodetection unit. The control unit, The excitation light pulse generation unit is instructed to perform the first excitation light irradiation, which irradiates the sensor element with an excitation light pulse. The high-frequency pulse generating unit is instructed to perform the first π / 2 pulse irradiation, which irradiates the sensor element with the high-frequency pulses of π / 2 pulses. After a predetermined time has elapsed since the first π / 2 pulse irradiation, the high-frequency pulse generation unit is instructed to perform a second π / 2 pulse irradiation, which irradiates the sensor element with the π / 2 pulse high-frequency pulse. After the execution of the second π / 2 pulse irradiation, the excitation light pulse generation unit is instructed to perform a second excitation light irradiation, irradiating the sensor element with the excitation light pulse. A physical quantity detection device according to any one of claims 1 to 5, wherein the photodetector is made to detect the emission state of the emission center due to the second excitation light irradiation.

7. The two spin qubits are a set of magnetic quantum numbers {+3 / 2, +1 / 2} and a set of {-3 / 2, -1 / 2}. The two frequencies are the first resonance frequency, which is the resonance frequency for magnetic quantum numbers +1 / 2 and +3 / 2, and the second resonance frequency, which is the resonance frequency for magnetic quantum numbers -1 / 2 and -3 / 2. The physical quantity detection device according to claim 6, wherein with respect to the pulse phase of the first resonance frequency and the pulse phase of the second resonance frequency included in the high-frequency pulse used in the second π / 2 pulse irradiation, either the pulse phase of the first resonance frequency or the pulse phase of the second resonance frequency included in the high-frequency pulse used in the first π / 2 pulse irradiation is inverted.

8. The physical quantity detection device according to claim 7, wherein the physical quantity detected by the physical quantity detection device is temperature or electric field.

9. A sensor element including a light-emitting center, An excitation light pulse generation unit generates excitation light and irradiates the sensor element with it, A high-frequency pulse generating unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with them, A light detection unit for detecting the light emission from the light emission center, A control method for a physical quantity detection device comprising: The light-emitting center has two different spin qubits, The two spin qubits are equivalent to each other but have different energy levels. The high-frequency pulse generation unit generates a high-frequency pulse in which two different frequencies are superimposed and irradiates the sensor element to simultaneously operate the two spin qubits. A control method for a physical quantity detection device.

10. A sensor element including a light-emitting center, An excitation light pulse generation unit generates excitation light and irradiates the sensor element with it, A high-frequency pulse generating unit that generates high-frequency pulses for manipulating the spin qubit of the light-emitting center and irradiates the sensor element with them, A light detection unit for detecting the light emission from the light emission center, Memory and Calculation circuit and, A computer program for a physical quantity detection device comprising, The light-emitting center has two different spin qubits, The two spin qubits are equivalent to each other but consist of different energy levels. The aforementioned high-frequency pulse generation unit generates a high-frequency pulse in which two different frequencies are superimposed and irradiates the sensor element, thereby enabling the calculation circuit to function as an irradiation unit that simultaneously manipulates the two spin qubits. Computer program.

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