Solid-state spin sensing structure based on polarization excitation and quantum magnetometer

Abstract

The invention relates to the technical field of quantum precision measurement, in particular to a solid spinning sensing structure based on polarization excitation, which comprises a diamond block, a first optical fiber and a microwave radiator, the first optical fiber is a polarization-maintaining single-mode optical fiber, the output end face of the first optical fiber is fixedly connected with the diamond block, and the output end face of the first optical fiber is fixedly connected with the microwave radiator. An included angle between a transmission main shaft and the NV axial direction of the [111] crystal orientation is 80-90 degrees; according to the scheme, the optical waveguide for transmitting the linear polarization excitation light in the specific direction is connected with the diamond block containing the NV color center, and the transmission direction of the linear polarization excitation light and the NV axial direction are controlled to form a specific angle, so that efficient excitation in the specified NV axial direction is realized, and the measurement accuracy of the magnetic component in the specified axial direction is further improved; the structure is simple and stable, the size is small, and the practicability is high.

Description

Technical Field

[0001] This invention relates to the field of quantum precision measurement technology, specifically to a solid-state spin sensing structure based on polarization excitation and a quantum magnetometer. Background Technology

[0002] In recent years, research on solid-state spin color center systems in the field of quantum precision has developed rapidly, especially in the research on magnetic field detection. The detection method based on optically detected magnetic resonance (ODMR) has been developed. By studying the linear relationship between the magnetic resonance frequency and the external magnetic field, the sensing, measurement and quantification of the external magnetic field can be realized.

[0003] However, current diamond NV center sensing structures based on ODMR technology suffer from inaccurate spin resonance frequency positioning due to low NV center excitation efficiency. The spin resonance frequency corresponding to each NV axis can be used to calculate the magnetic component of the external magnetic field along that NV axis. If the spin resonance frequency positioning is inaccurate, the accuracy of magnetic field measurement will be reduced. There are existing technologies that use linearly polarized light to improve the NV center excitation efficiency, but these mainly achieve polarization excitation by adjusting the spatial light irradiation of the NV center. Such probes have complex structures, low stability and practicality, and are generally large in size, making them difficult to apply in practice. Summary of the Invention

[0004] This invention proposes a solid-state spin sensing structure and quantum magnetometer based on polarization excitation. By connecting an optical waveguide that transmits linearly polarized excitation light in a specific direction to a diamond block containing NV color centers, and controlling the transmission direction of the linearly polarized excitation light to be at a specific angle with the NV axis, efficient excitation of a specified NV axis can be achieved. This structure is simple, stable, compact, and highly practical.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A solid-state spin sensing structure based on polarization excitation, comprising: - A diamond block containing an ensemble NV color center and having four NV axes, one of which is the

[111] crystal orientation, and the other three NV axes are collectively referred to as non-critical axes; - The first optical fiber is a polarization-maintaining single-mode optical fiber. The output end face of the first optical fiber is fixed to the diamond block and is configured such that the angle between its transmission main axis and the NV axis of the

[111] crystal direction is 80°-90°. - A microwave radiator used to load external microwave signals and radiate them onto the diamond block.

[0006] In a preferred design of the solid-state spin sensing structure described above, the diamond block includes a first surface, the parallelism deviation between the normal of the first surface and the NV axis of the

[111] crystal orientation is ≤2°.

[0007] In a preferred design of the solid-state spin sensing structure described above, the output end face of the first optical fiber is fixed to the first surface, and the parallelism deviation between the light transmission direction of the first optical fiber and the normal of the first surface is ≤2°.

[0008] In a preferred design of the solid-state spin sensing structure described above, the transmission axis of the first optical fiber is configured such that the angle between it and any two of the non-critical NV axes is ≥45°.

[0009] In a preferred design of the solid-state spin sensing structure described above, it further includes at least two second optical fibers, both of which are polarization-maintaining single-mode fibers. The second optical fibers are both fixed to the first surface, and at least two of the non-critical NV axes are at an angle of 80°-90° with the transmission principal axis of the second optical fibers.

[0010] In a preferred design of the solid-state spin sensing structure described above, an optical fiber splitter is included, with its multi-head output end aligned with each polarization-maintaining single-mode fiber and its single-head input end aligned with an externally loaded linearly polarized excitation light.

[0011] In a preferred design of the solid-state spin sensing structure described above, the transmission spindle is the fast axis of a polarization-maintaining single-mode fiber.

[0012] In a preferred design of the solid-state spin sensing structure described above, a photodetector module is also included, which is located near the diamond block and is used to collect the photoluminescence generated by the diamond block through a spatial light transmission mode.

[0013] In a preferred design of the solid-state spin sensing structure described above, the diamond block has a first-form cured adhesive on its surface facing the photodetector module, which is used to concentrate photoluminescence.

[0014] Another aspect of this application also introduces a different solid-state spin sensing structure, wherein the polarization-maintaining single-mode fiber is replaced with a polarization fiber.

[0015] Another aspect of this application also describes a quantum magnetometer that performs vector magnetic field measurements based on the ODMR method, comprising: It has at least one solid-state spin sensing structure as described in the previous item; A bias magnetic source is used to provide a bias magnetic field with magnetic field components in all four NV axes of the diamond block.

[0016] Compared with the prior art, the beneficial effects of the present invention are: by connecting the optical waveguide transmitting linearly polarized excitation light in a specific direction to a diamond block containing NV color centers, and controlling the transmission direction of the linearly polarized excitation light to be at a specific angle with the NV axis, efficient excitation of the specified NV axis is achieved, thereby improving the measurement accuracy of the magnetic component in the specified axis. This structure is simple and stable, compact in size, and highly practical. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the solid-state spin sensing structure in Example 1; Figure 2 This is a four-axis schematic diagram of the ensemble NV color center; Figure 3 This is a schematic diagram of the installation of a single polarization-maintaining single-mode optical fiber and a diamond block in Example 1. Figure 4 This is a diagram showing the relationship between the four axes in the ensemble NV color center and the projection plane. Figure 5 for Figure 4 A top-down view; Figure 6 This is a schematic diagram of the sensing structure with a photoelectric detection module in Example 1; Figure 7 This is a schematic diagram of the installation of three polarization-maintaining single-mode optical fibers and a diamond block in Example 2. Figure 8 This is a schematic diagram of the sensing structure with a one-to-many fiber optic switch in Embodiment 2; Figure 9 This is a system block diagram of the quantum magnetometer in Example 4; Figure 10 To produce an ODMR spectrum with four pairs of peaks. Detailed Implementation

[0019] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, one or more embodiments are now described with reference to the accompanying drawings, wherein similar reference numerals are used throughout the text to refer to similar components. In the following description, numerous specific details are set forth for purposes of explanation in order to provide a more thorough understanding of one or more embodiments. However, it will be apparent that one or more embodiments may be practiced in various circumstances without these specific details, and the various embodiments may be combined with and referenced to each other without contradiction.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] A diamond NV center (nitrogen-vacancy center) is an atomic-level defect in the diamond lattice, formed by a nitrogen atom (N) replacing a carbon atom and combining with its adjacent vacancy (V). It is one of the most studied solid-state spin center systems due to its superior quantum properties at room temperature, making it a core platform for quantum sensing, quantum computing, and quantum communication.

[0023] The core principle of ODMR (Optically Probemed Magnetic Resonance) is to initialize the spin state of the NV center to the m_s=0 ground state using a green laser, while simultaneously applying a tunable microwave. When the microwave frequency precisely matches the energy level difference between the m_s=0 and m_s=±1 states, the microwave frequency becomes the central resonance frequency. The NV center undergoes a resonant transition, flipping part of its spin to the m_s=±1 state. Since the red fluorescence intensity emitted by the NV center in the m_s=0 state is significantly stronger than that in the m_s=±1 state, the fluorescence intensity detected at the resonance frequency will decrease. By scanning the microwave frequency and monitoring this decrease in fluorescence intensity (i.e., the "resonance valley"), the magnitude of the resonance frequency can be determined. At this point, under the influence of a magnetic field, the m_s=±1 state will also split into the m_s=+1 and m_s=-1 states. This will generate two sets of resonance frequencies symmetrical about the central resonance frequency, and the difference between these two sets of frequencies is positively correlated with the external magnetic field. Obtaining the corresponding resonance frequencies allows for accurate calculation of the magnitude of the external magnetic field. Example 1

[0024] See appendix Figure 1 As a basic scheme, this example proposes a solid-state spin sensing structure based on polarization excitation, including a diamond block 1, a first optical fiber 2, and a microwave radiator 3.

[0025] In this example, diamond block 1 contains an ensemble of NV color centers (meaning a large number of NV color centers) and has four NV axes. Based on the characteristics of the diamond lattice, the included angles between each NV axis are equal, and their spatial relationships are shown in the attached figure. Figure 2 As shown, one of the NV axes is the

[111] crystal orientation, and the other three NV axes are collectively referred to as non-critical axes. Here, the term "non-critical axis" is merely a synonym for the other three NV axes. Regarding the structure of the diamond block 1, this example does not impose specific limitations, but in the exemplary scheme, the diamond block 1 is preferably a cube or cuboid. Regarding the size of the diamond block 1, since it needs to be connected to the optical fiber and ensure sufficient laser excitation, its size is generally on the order of micrometers. Figure 1 In this illustration, the size relationship between the diamond block 1 and the first optical fiber 2 is only for ease of demonstration. In fact, based on the basic scheme of Embodiment 1, the diamond block 1 is at most slightly larger than the end face diameter of the first optical fiber 2. More preferably, the size of the diamond block 1 is smaller than the end face diameter of the first optical fiber 2, such as close to the diameter of the fiber core.

[0026] In this example, the first optical fiber 2 is a polarization-maintaining single-mode fiber. The output end face of the first optical fiber 2 is fixed to the diamond block 1, and its transmission principal axis is configured to have an angle of 80°-90° with the NV axis of the

[111] crystal direction. Regarding the polarization-maintaining single-mode fiber, it mainly achieves polarization maintenance function based on the principle of stress birefringence. It can be panda fiber, bowtie fiber, elliptical cladding fiber, etc. The reason for choosing single-mode fiber is that its mode is singular, which can avoid the optical field changes caused by fiber jitter and ensure the reliability of sensing data. The fixing of the first optical fiber 2 to the diamond block 1 can be done by optical adhesive. The end face of the existing polarization-maintaining single-mode fiber is marked with the direction of the transmission principal axis, which is generally marked as the slow axis. In this scheme, both the fast axis and the slow axis can be used as the transmission principal axis of the polarization-maintaining fiber.

[0027] We know that the polarization direction of the excitation light has a very important influence on the spin excitation efficiency of diamond nitrogen-vacancy centers. For excitation light with a linear polarization direction, the excitation efficiency P of nitrogen-vacancy centers satisfies: P = P 0* [sin 2 (α) + 1 / 9*cos 2 (α)] In the formula, α is the laser polarization angle, and P0 is the total excitation efficiency when the nitrogen-vacancy color center is aligned with the laser polarization direction. It can be observed that when α = 90°, i.e., the laser polarization direction is perpendicular to the axis of the nitrogen-vacancy color center, the excitation efficiency P of the nitrogen-vacancy color center is the highest. However, when φ = 0°, the excitation efficiency P of the nitrogen-vacancy color center is only 1 / 9 of that in the vertical direction, and the laser excitation efficiency reaches its lowest point.

[0028] Based on the above reasons, this case sets the angle between the transmission main axis of the first optical fiber 2 and the NV axis of the

[111] crystal direction to 80°-90°, that is, a vertical or nearly vertical state, of course, the vertical state is preferred, so as to achieve efficient excitation of the NV color center.

[0029] To facilitate understanding of how to achieve the perpendicularity between the transmission main axis and the

[111] crystal direction, in one example scheme, we select the fast axis as the transmission main axis. The normal of one face of the diamond block 1 is as parallel as possible to one of the NV axes (e.g., parallel deviation ≤ 2°), such as the NV axis of the

[111] crystal direction. During connection, this face is contacted with a relatively smooth base surface. Through the fiber fixing device, the slow axis mark is made perpendicular to the base surface. At this time, the slow axis is basically parallel to the NV axis of the

[111] crystal direction. Then, the connection and fixation of the two are achieved by optical adhesive. During operation, we align the external linearly polarized excitation light into the first fiber 2. The polarization-maintaining linearly polarized excitation light is approximately perpendicular to the NV axis of the

[111] crystal direction, achieving the purpose of efficient excitation.

[0030] We know that the diamond block 1 containing the ensemble NV color center has four NV axes, and the external magnetic field has components in each NV axis. This polarization angle design can achieve efficient excitation of a specific NV axis, and thus, in this NV axis, the spin resonance change caused by the magnetic field can be obtained more accurately. In other words, the measurement accuracy of the magnetic component in this NV axis is higher. This design is particularly suitable for magnetic field measurement with a defined direction. When detecting a solid spin sensing structure with this design, the magnetic field direction can be made parallel to the

[111] crystal direction. At this time, the NV color center of this crystal direction can fully sense the external magnetic field. Combined with the ODMR measurement method, we know that in this case, the corresponding peak has a higher bandwidth. Tracking its resonance frequency will improve the measurement accuracy.

[0031] In this example, microwave radiator 3 is used to load external microwave signals and radiate them to the diamond block 1. There are various structures and types of microwave radiators 3, such as helical antennas, microstrip antennas, and planar waveguides. In this exemplary solution, we use a planar radiating device such as a microstrip antenna. Its advantages include not only providing a more stable microwave signal but also serving as a backing plate for mounting the diamond block 1 and the first optical fiber 2, as shown in the attached diagram. Figure 1The structure shown can fix the diamond block to the antenna surface with optical adhesive, or fix the front end of the first optical fiber 2 to the antenna to improve structural stability.

[0032] Based on the foregoing description, alignment is crucial when connecting the first optical fiber 2 to the diamond block 1. However, the NV axis orientation of a conventional diamond block 1 is difficult to determine and typically does not point to a reference plane. This necessitates reliance on optical detection for alignment (e.g., adjusting the angle of the linearly polarized excitation light and monitoring fluorescence intensity in real time to determine if the optimal excitation angle has been reached). This method is complex and time-consuming. To address this issue, in a preferred example, such as... Figure 3 As shown, the diamond block 1 includes a first surface 100. The parallelism deviation between the normal of the first surface 100 and the NV axis of the

[111] crystal direction is ≤2°. Thus, the NV axis of the diamond block has a corresponding reference plane. It is relatively easy to make the horizontal axis mark on the polarization-maintaining fiber perpendicular to the normal of this reference plane. For example, the first surface 100 is brought into contact with a relatively smooth base surface. By using an optical fiber fixing device, the slow axis mark is made perpendicular to the base surface. At this time, the fast axis is basically perpendicular to the NV axis of the

[111] crystal direction. Then, the connection and fixation of the two are achieved by optical adhesive, which can ensure that the NV axis is perpendicular or nearly perpendicular to the fast axis. This design of the diamond block can greatly simplify the connection difficulty with the polarization-maintaining fiber. It should be understood that the first surface 100 includes all parallel surfaces on the diamond block 1 that meet the conditions. For example, in a cube-shaped diamond block 1, the top and bottom opposing surfaces are both the first surface 100.

[0033] Based on the special design of the aforementioned diamond block 1, while the slow axis marking can quickly achieve a design where the transmission main axis is perpendicular to the NV axis of the

[111] crystal direction, on the other hand, the aforementioned first surface 100 is perpendicular or approximately perpendicular to the NV axis of the

[111] crystal direction. Considering that the transmission direction and polarization direction of the linearly polarized excitation light are also perpendicular, and the transmission direction of the linearly polarized excitation light (parallel to the extension direction of the fiber core) can be perpendicular to the fiber end face, we can connect the fiber end face to the first surface 100 or a surface parallel to it. At this time, the polarization direction will necessarily be perpendicular to the NV axis of the

[111] crystal direction, and the angle setting can be achieved without relying on the transmission main axis marking. Based on this, in a preferred embodiment, as shown in the attached... Figure 3 As shown, the output end face 200 of the first optical fiber 2 is fixedly connected to the first surface 100 (the two are not connected in the figure for ease of display), and the parallel deviation between the light transmission direction of the first optical fiber 2 and the normal of the first surface 100 is ≤2°; it should be known that the output end face 200 should be perpendicular to the fiber core extension direction and have a smooth and flat surface.

[0034] Based on the aforementioned connection design of the output end face 200, we have ensured that the polarization direction of the excitation light is aligned with the NV axis of the

[111] crystal direction. In this scheme, the NV axis of the

[111] crystal direction achieves the most efficient excitation, and the magnetic field measurement accuracy of this axis is extremely high, making it very suitable for non-vector magnetic measurement scenarios. However, in vector magnetic field measurement, we know that at least three magnetic field component data along the NV axis are required (the magnetic field vector measurement technology and algorithm of diamond NV color center are existing technologies and will not be elaborated here). In order to achieve accurate vector measurement, the magnetic measurement accuracy along other NV axes should not be too poor. Based on this consideration of vector magnetic field measurement, in a preferred design, we require that the transmission main axis of the first optical fiber 1 be configured such that the angle between it and any two NV axes in the non-critical axes is ≥45°. Combined with the aforementioned excitation efficiency P calculation formula, the excitation efficiency of the NV axis participating in the vector magnetic field calculation is not less than 5 / 9*P0.

[0035] Based on the foregoing, this section provides supplementary information on how to achieve angle adjustment between the polarization direction and any two NV axes among the non-critical axes; please refer to the appendix. Figure 4 This is a schematic diagram of the spatial distribution of the four NV axes, where NV1 represents the NV axis of the

[111] crystal orientation. Perpendicular to NV1, we draw a projection plane (virtual). Based on the special properties of the diamond block lattice, we know that the projection lines of NV2, NV3, and NV4 on the projection plane have equal angles, that is, the angle between them is 120°. The direction of NV1 is parallel to the transmission direction of the excitation light, and the polarization direction of the excitation light is parallel to the projection plane. By rotating the first fiber 1, the polarization direction of the excitation light can be arbitrarily adjusted on the projection plane. Based on this principle, we know that as long as the first fiber 1 is rotated, the angle adjustment of the polarization direction with other axes can be achieved. During adjustment, the excitation efficiency of the corresponding NV axis can be quantitatively judged based on the fluorescence detection results. In one example, as shown in the attached figure... Figure 5 As shown, we adjust the polarization direction to be parallel to NV4. At this point, the angle between the polarization direction and NV2 and NV3 is 60°. Calculations show that the excitation efficiency of NV2 and NV3 can reach 7 / 9*P0. By obtaining the magnetic field component data along these two NV axes and the magnetic field component data along the NV1 direction, we can obtain the vector magnetic field data through the NV color center vector calculation method. In practice, we can use fluorescence measurement. When the fluorescence intensity along any NV axis reaches its minimum (this NV axis is NV4 in the diagram), it indicates that the polarization direction is parallel to that NV axis. Naturally, based on geometric angle relationships, the polarization direction is at 60° to the other two NV axes. It should be noted that the magnetic component data of NV4 can also be used as a calibration quantity in the vector calculation.

[0036] Regarding polarization-maintaining fiber, we know that it has a fast axis and a slow axis. The fast axis has a low refractive index, propagates light quickly, and is less sensitive to disturbances; the slow axis has a high refractive index, propagates light slowly, has a significant phase delay, but is easily affected by interference. Considering the characteristics of this scheme, the fiber transmission process is prone to disturbances. Therefore, as a preferred option, we choose the fast axis of polarization-maintaining single-mode fiber as the transmission main axis.

[0037] In the various schemes described in Embodiment 1, the method of collecting photofluorescence generated by the NV color center is not limited. We can collect it by reverse transmission of photofluorescence through the first optical fiber 2. For example, a dichroic filter can be placed between the laser source and the first optical fiber 2. The excitation light can pass through the dichroic filter, and the photofluorescence is reflected by the dichroic filter and then received by the photodetector. In this design, the photodetector can be designed at the far end (i.e., close to the data processing side). In another design, we consider improving the integration of the solid-state spin sensing structure and choose to place the photodetector module near the diamond block 1 to collect the photofluorescence generated by the diamond block 1 through spatial light transmission mode, as shown in the attached figure. Figure 6 As shown, the photodetector module 4 is positioned above the top surface of the diamond block 1. The photodetector module 4 includes a filter device (not shown in the figure) to filter stray light in the photoluminescence.

[0038] Furthermore, to improve the collection efficiency of photofluorescence, see Appendix Figure 6We have a first-form curing adhesive 1001 on the surface of the diamond block 1 facing the photodetector module 4. This first-form curing adhesive 1001 is used to focus photoluminescence. As its functional description indicates, the first-form curing adhesive 1001 is mainly used to focus photoluminescence. Theoretically, any structural form that achieves this function is included in the so-called first form, such as a hemispherical or near-hemispherical curing adhesive. During fabrication, liquid optical adhesive is dropped onto this surface and inverted, and the curing time is controlled to form the first-form curing adhesive (it can also be fabricated using a nanoimprinting method). The design of the first-form curing adhesive 1001 not only improves the optical density of photoluminescence, but also, as we know, the NV color center is located within the diamond block 1, which means that the photoluminescence... The light is generated inside the diamond block and needs to pass through the diamond block-air interface before it can be sensed by the photodetector module 4. However, the refractive index of the diamond block is much greater than that of air, so the photoluminescence will be reflected by total internal reflection at the interface, which will affect the collection of the photoluminescence. In this example, a curing adhesive is used instead of air as the interface that contacts the diamond block 1. Since the refractive index of the curing adhesive is much higher than that of air, this significantly reduces the loss of fluorescence by total internal reflection, so more photoluminescence will pass through the diamond interface, thereby improving the fluorescence collection efficiency. Based on this purpose, in a further design, the refractive index of the first-form curing adhesive 1001 is required to be no less than 1.5, preferably a curing adhesive with a refractive index of about 1.7. The solid-state spin sensing structure formed by the above structure is characterized by the use of a curing adhesive with light-gathering function, which can focus the photoluminescence generated by the diamond block. The increase in fluorescence density will significantly improve the measurement bandwidth and response speed in ODMR measurement technology. The bandwidth can improve the measurement accuracy, while the increase in response speed represents the increase in sampling rate. Compared with existing fluorescence focusing lenses, the curing adhesive has lower manufacturing cost and difficulty, is easier to mass-produce, and has a smaller size, making it suitable for small-volume integration with other devices in a confined space. Example 2

[0039] In Embodiment 1, a polarization-maintaining single-mode fiber was used to connect to the diamond block. During vector measurement, angle adjustments were necessary to effectively excite multiple NV axes. However, this method ultimately had low excitation efficiency for non-critical axes, affecting the accuracy of magnetic field measurement along these axes. To improve the accuracy of vector magnetic field measurement, it was necessary to increase the laser's excitation efficiency for non-critical axes. Based on the requirements of vector measurement, at least three sets of magnetic component data were needed. Therefore, in Embodiment 2, combined with the aforementioned design of the first surface 100, as shown in the attached diagram... Figure 7As shown, the solid-state spin sensing structure in this example also includes at least two second optical fibers 5, which are both polarization-maintaining single-mode fibers. The second optical fibers 5 are both fixed to the first surface 100, and the angle between at least two of the non-critical NV axes and the transmission principal axis of the second optical fiber 5 is 80°-90°. In short, the purpose is to achieve three linearly polarized light paths by adding two polarization-maintaining fibers, and to achieve efficient excitation of at least three NV axes by adjusting the angle. When performing vector measurements, we can obtain more accurate magnetic components, thereby greatly improving the accuracy of vector magnetic measurements.

[0040] In this example, the size of the diamond block 1 used is larger than that in Example 1, but only slightly larger than the outer diameter of the three polarization-maintaining single-mode fibers. During installation, the three polarization-maintaining single-mode fibers are kept as close as possible. To improve excitation efficiency, from a top-down view, a cuboid diamond with an aspect ratio greater than 1.5:1 can be selected as the diamond block 1 used in this example. The three polarization-maintaining fibers are bonded to the narrower face of the cuboid diamond, so that the excitation light has a longer movement path inside the diamond block 1, thereby achieving the excitation of more NV color centers. Furthermore, reflective materials can be added to some surfaces of the diamond block 1 to achieve multiple reflections of the excitation light inside the diamond block, further improving the photoconversion effect.

[0041] In the above example, the optical access of the three polarization-maintaining single-mode fibers can be achieved by using three sets of laser source modules to align and provide linearly polarized excitation light. The advantage is that it ensures that the three excitation lights can be simultaneously aligned with the input of the three polarization-maintaining single-mode fibers. The disadvantage is that the design cost of three sets of laser source modules is relatively high. Therefore, in another preferred design, as shown in the attached... Figure 8 As shown, the solid-state spin sensing structure includes a fiber optic splitter 6 (in the figure, it is a 1-to-3 fiber optic splitter). Its multi-head output end is aligned with each polarization-maintaining single-mode fiber, and its single-head input end is aligned with the externally loaded linearly polarized excitation light. In this design, the multi-head output end is required to be aligned with each polarization-maintaining single-mode fiber, which means that linearly polarized light in a single direction can generate linearly polarized light in three directions after passing through the fiber optic splitter 6. Of course, multiple polarization controllers or waveplate arrays can be added to the output end of the fiber optic splitter 6 to split the input polarized light and generate three different directions of linearly polarized light by independently adjusting the polarization device of each branch. However, this solution still makes the solid-state spin sensing structure relatively complex. To solve this problem, in a preferred example, the polarization direction of the excitation light can also be changed by slightly rotating the fiber optic connector at the output end of the fiber optic switch. Example 3

[0042] In both Embodiment 1 and Embodiment 2, polarization-maintaining fiber (PM fiber) is used to input linearly polarized excitation light. While this approach is effective, using polarization-maintaining fiber requires precise positioning and adjustment of the fiber connections and splices to ensure stable polarization, a complex process. As an alternative, Embodiment 3 proposes replacing the polarization-maintaining single-mode fiber in the aforementioned solutions with polarization-inducing fiber (PZ fiber). Polarization fiber is a special type of fiber in which only one polarization state of light can propagate, similar to a polarization polarizer. When light with other polarization directions propagates within it, it experiences high optical loss and cannot continue propagating. PZ fiber uses a special design structure (such as a bowtie shape) to generate a high birefringence effect. This birefringence effect allows light with a specific polarization direction to propagate along the fiber, while light with other polarization directions experiences high optical loss and attenuates rapidly.

[0043] When connecting an external laser source to an optical fiber, the connection and alignment process of polarized fiber (PZ fiber) is significantly simpler than that of polarization-maintaining fiber (PM fiber). The core difference lies in the difficulty of controlling the polarization direction.

[0044] PM fiber optic connections to lasers present the following challenges: Polarization axis pre-calibration: A dedicated device (such as a polarization controller) is required to adjust the laser output polarization state to match the slow axis direction of the PM fiber. If a polarization-maintaining jumper is used, ensure that the jumper key direction is consistent with the laser polarization direction (manual rotation is difficult to control due to errors).

[0045] Dynamic stability challenge: Temperature / vibration can easily cause the aligned polarization axis to shift (requiring repeated calibration).

[0046] Verification is complex: insertion loss (IL) and polarization extinction ratio (PER≥25dB) must be tested simultaneously, and the equipment cost is high (such as polarization analyzer).

[0047] Advantages of PZ fiber optic laser connection: Polarization-free matching: Laser can be directly incident without adjusting the polarization direction (e.g., Optiphase PZ1 achieves phase modulation by stretching optical fiber with piezoelectric ceramics, which is independent of polarization).

[0048] Simplified process: Operation is similar to that of ordinary single-mode fiber: Focus laser → Inject into fiber core → Optimize coupling efficiency (only power meter monitoring required).

[0049] Strong anti-interference capability: The multi-layer winding structure reduces the impact of environmental disturbances and eliminates the need for continuous polarization state calibration.

[0050] In summary, using PZ fiber can eliminate the polarization matching step during the connection process with an external laser source, and the docking process is no different from that of ordinary fiber, while improving efficiency by 3-5 times. Example 4

[0051] This embodiment also introduces a quantum magnetometer, which performs vector magnetic field measurements based on the ODMR method, as shown in the attached figure. Figure 9 As shown, it has at least one solid-state spin sensing structure as described above and a bias magnetic source, wherein the bias magnetic source is used to provide a bias magnetic field with magnetic field components in all four NV axes of the diamond block; when the magnetic field has magnetic field components in all four NV axes, the spectrum of fluorescence voltage signal and microwave frequency obtained by ODMR method is shown in the attached figure. Figure 10 As shown, it contains four pairs of peaks, representing NV1-NV4 respectively. By obtaining the frequency difference between each pair of peaks, each magnetic component can be calculated. At least three sets of magnetic component data can be obtained, and then vector magnetic field information can be obtained through vector algorithm.

[0052] An exemplary solution is shown in the appendix. Figure 9 As shown, the quantum magnetometer is equipped with a laser unit, a microwave unit, and a data processing unit. The laser unit provides the required linearly polarized excitation light to the solid-state spin sensing structure, the microwave unit provides the required microwave signal to the solid-state spin sensing structure, and the solid-state spin sensing structure transmits the photocurrent signal (the electrical signal converted from photofluorescence) to the data processing unit for processing and calculation.

[0053] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0054] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A solid-state spin sensing structure based on polarization excitation, characterized in that, include: - A diamond block containing an ensemble NV color center and having four NV axes, one of which is the [111] crystal orientation, and the other three NV axes are collectively referred to as non-critical axes; - The first optical fiber is a polarization-maintaining single-mode optical fiber. The output end face of the first optical fiber is fixed to the diamond block and is configured such that the angle between its transmission main axis and the NV axis of the [111] crystal direction is 80°-90°. - A microwave radiator used to load external microwave signals and radiate them onto the diamond block.

2. The solid-state spin sensing structure according to claim 1, characterized in that, The diamond block includes a first surface, the parallelism deviation of the normal of the first surface from the NV axis of the [111] crystal orientation is ≤2°.

3. The solid-state spin sensing structure according to claim 2, characterized in that, The output end face of the first optical fiber is fixed to the first surface, and the parallelism deviation between the optical transmission direction of the first optical fiber and the normal of the first surface is ≤2°.

4. The solid-state spin sensing structure according to claim 3, characterized in that, The transmission spindle of the first optical fiber is configured such that the angle between it and any two NV axes in the non-critical axes is ≥45°.

5. The solid-state spin sensing structure according to claim 3, characterized in that, It also includes at least two second optical fibers, both of which are polarization-maintaining single-mode fibers. The second optical fibers are fixed to the first surface, and at least two of the non-critical NV axes are at an angle of 80°-90° with the transmission principal axis of the second optical fiber.

6. The solid-state spin sensing structure according to claim 5, characterized in that, It includes a fiber optic splitter, with its multi-head output end aligned with each polarization-maintaining single-mode fiber, and its single-head input end aligned with the external linearly polarized excitation light.

7. The solid-state spin sensing structure according to claim 1, characterized in that, The transmission spindle is the fast axis of a polarization-maintaining single-mode fiber.

8. The solid-state spin sensing structure according to claim 1, characterized in that, It also includes a photoelectric detection module located near the diamond block, used to collect the photoluminescence generated by the diamond block through a spatial light transmission mode.

9. The solid-state spin sensing structure according to claim 8, characterized in that, The diamond block has a first-form cured adhesive on its surface facing the photoelectric detection module, which is used to concentrate photoluminescence.

10. The solid-state spin sensing structure according to claim 1, characterized in that, The polarization-maintaining single-mode fiber was replaced with a polarization fiber.

11. A quantum magnetometer, which measures vector magnetic fields based on the ODMR method, characterized in that, Include: It has at least one solid-state spin sensing structure as described in any one of claims 1-10; A bias magnetic source is used to provide a bias magnetic field with magnetic field components in all four NV axes of the diamond block.

Images