阅读说明：本技术 一种包含磁通聚集器的金刚石nv色心磁力仪 (Diamond NV color center magnetometer containing magnetic flux collector ) 是由 张效源 孙芝茵 李立毅 邹志龙 陈乐朋 李运召 于 2021-09-18 设计创作，主要内容包括：本发明涉及磁场测量技术领域,尤其涉及一种包含磁通聚集器的金刚石NV色心磁力仪,包括：金刚石NV色心薄片样品和至少一个磁通聚集器；磁通聚集器具有两个平行相对的底面,磁通聚集器的底面与金刚石NV色心薄片样品的底面平行设置,磁通聚集器的底面所聚集的磁通线穿过金刚石NV色心薄片样品。本发明将环境磁场放大,可以实现更高灵敏度、更大范围的磁场探测。(The invention relates to the technical field of magnetic field measurement, in particular to a diamond NV color center magnetometer with a magnetic flux collector, which comprises: a diamond NV colour centre flake sample and at least one magnetic flux concentrator; the magnetic flux collector is provided with two parallel opposite bottom surfaces, the bottom surface of the magnetic flux collector is arranged in parallel with the bottom surface of the diamond NV color center thin sheet sample, and magnetic flux lines collected by the bottom surface of the magnetic flux collector penetrate through the diamond NV color center thin sheet sample. The invention amplifies the environmental magnetic field and can realize magnetic field detection with higher sensitivity and wider range.)

1. A diamond NV colour centre magnetometer comprising a magnetic flux concentrator, comprising:

a diamond NV colour centre flake sample and at least one magnetic flux concentrator;

the magnetic flux collector is provided with two parallel opposite bottom surfaces, the bottom surface of the magnetic flux collector is arranged in parallel with the bottom surface of the diamond NV color center thin sheet sample, and magnetic flux lines collected by the bottom surface of the magnetic flux collector penetrate through the diamond NV color center thin sheet sample.

2. The diamond NV colour heart magnetometer of claim 1, wherein: the two floors of the flux concentrator are of unequal area, with the smaller floor being adjacent to the diamond NV colour centre chip sample.

3. The diamond NV colour heart magnetometer of claim 1, wherein: the magnetic flux collector is made of high-permeability materials, and the relative permeability is larger than 1000.

4. The diamond NV colour heart magnetometer of claim 1, wherein: comprises two of the magnetic flux concentrators;

the two magnetic flux collectors are coaxially and oppositely arranged at intervals, and the diamond NV color center thin sheet sample is arranged between the two magnetic flux collectors.

5. The diamond NV colour heart magnetometer of claim 1 or 4, wherein: the geometry of the individual flux concentrators may be long rod-like, conical, triangular, T-shaped rod-like or angular.

6. A diamond NV colour centre magnetometric system comprising a magnetic flux concentrator, characterized in that: comprising a diamond NV colour centre magnetometer according to any one of claims 1 to 5.

7. The diamond NV colour centre magnetic force measurement system of claim 6, wherein: the microwave optical system also comprises an optical path subsystem and a microwave subsystem;

the optical path subsystem is used for providing green pumping laser to be incident to the diamond NV color center slice sample and collecting red fluorescence emitted by the diamond NV color center slice sample; the microwave subsystem is used for providing a microwave magnetic field for the diamond NV color center thin slice sample in a microwave radiation area.

8. A magnetic measurement method for NV color center of diamond is characterized in that,

the method is realized by adopting the diamond NV color center magnetic force measuring system of any one of the claims 6 or 7, and comprises the following steps:

s1, acquiring a magnetic field amplification factor E of the magnetic flux collector;

s2, obtaining red fluorescence emitted by a diamond NV color center sheet sample in a microwave radiation area under different microwave frequencies;

s3, drawing a relation graph of microwave frequency and red fluorescence light intensity, determining a microwave frequency value corresponding to the lowest light intensity, and further determining the energy level interval between the diamond NV color center excited states I +/-1 >;

s4, according to excited state | + -1>Between energy levels Δ ═ 2 γ B_zCalculating the magnetic field amplitude B in the NV color center region of the diamond_zWherein γ is the NV gyromagnetic ratio;

s5 based on magnetic field amplitude B in NV color center area of diamond_zAnd the magnetic field magnification factor E is obtained, the background magnetic field is calculated, and the background magnetic field B is B_z/∈。

9. A magnetometer, comprising: a magnetic sensor and at least one magnetic flux concentrator;

the magnetic flux collector has two parallel opposite bottom surfaces, and the magnetic flux lines collected by the bottom surfaces pass through the magnetic sensor and are used for amplifying the magnetic field and restraining the magnetic sensor.

10. A magnetic flux concentrator for use in a magnetometer, the magnetic flux concentrator comprising: for collecting the magnetic flux and confining it to the magnetic sensor in the magnetometer.

Technical Field

The invention relates to the technical field of magnetic field measurement, in particular to a diamond NV color center magnetometer comprising a magnetic flux collector, a measuring system, a diamond NV color center magnetic force measuring method, a diamond NV color center magnetic force magnetometer and a magnetic sensor used in the diamond NV color center magnetic force magnetometer.

Background

The magnetometer can detect the magnetic induction intensity of the magnetic field of the environment at the position and provide magnetic field information of the surrounding space environment or the target object. The basic principle of the magnetometer is simply described as follows: the change of the basic property of the object caused by the magnetic field is reflected as other basic physical quantities and measured, and the magnitude of the magnetic field is reversely deduced through the linear relation of the physical quantities and the magnetic field. Magnetometers based on the principle include giant magnetoresistance magnetometers, atomic magnetometers, superconducting quantum interferometers, diamond NV color center magnetometers and the like.

With social development and technological progress, scientific research and technical application in various fields under extreme environments have provided the requirements for zero magnetic field calibration, that is, higher requirements are provided for the detection range, measurement sensitivity, spatial resolution and the like of a magnetometer. At present, the detection range and the sensitivity of the magnetometer in the prior art are limited, and the magnetometer is easily interfered by background noise. Compared with giant magnetoresistance magnetometers, atomic magnetometers, superconducting quantum interferometers and the like, the diamond NV color center magnetometer has great potential because of small size and high sensitivity and can realize zero magnetic field detection under higher spatial resolution. However, on one hand, because the diamond NV color center magnetometer considers the hyperfine structure and the nuclear spin factor, a measurement blind zone exists in a magnetic field below 80uT, and on the other hand, the diamond NV color center magnetometer is also limited by background noise interference.

Disclosure of Invention

The invention aims to overcome at least part of defects and provide a magnetometer with a larger detectable range and higher measurement sensitivity.

To achieve the above object, the present invention provides a diamond NV colour centre magnetometer comprising a magnetic flux concentrator, comprising:

a diamond NV colour centre flake sample and at least one magnetic flux concentrator;

the magnetic flux collector is provided with two parallel opposite bottom surfaces, the bottom surface of the magnetic flux collector is arranged in parallel with the bottom surface of the diamond NV color center thin sheet sample, and magnetic flux lines collected by the bottom surface of the magnetic flux collector penetrate through the diamond NV color center thin sheet sample.

Optionally, the two bottom surfaces of the flux concentrator are of unequal area, and the bottom surface of smaller area is adjacent to the diamond NV colour center chip sample.

Optionally, the magnetic flux concentrator is made of a high permeability material, and the relative permeability is greater than 1000.

Optionally, the diamond NV colour centre magnetometer comprises two of the magnetic flux concentrators;

the two magnetic flux collectors are coaxially and oppositely arranged at intervals, and the diamond NV color center thin sheet sample is arranged between the two magnetic flux collectors.

Optionally, the geometry of a single said flux concentrator is long rod, conical, triangular, T-shaped rod or angular.

The invention also provides a diamond NV color center magnetometry system comprising a magnetic flux concentrator, which comprises the diamond NV color center magnetometer defined in any one of the above items.

Optionally, the diamond NV color center magnetic force measuring system further comprises a light path subsystem and a microwave subsystem;

the optical path subsystem is used for providing green pumping laser to be incident to the diamond NV color center slice sample and collecting red fluorescence emitted by the diamond NV color center slice sample; the microwave subsystem is used for providing a microwave magnetic field for the diamond NV color center thin slice sample in a microwave radiation area.

The invention also provides a diamond NV color center magnetic measurement method which is realized by adopting the diamond NV color center magnetic measurement system of any one of the above steps, and comprises the following steps:

s1, acquiring a magnetic field amplification factor E of the magnetic flux collector;

s2, obtaining red fluorescence emitted by a diamond NV color center sheet sample in a microwave radiation area under different microwave frequencies;

s3, drawing a relation graph of microwave frequency and red fluorescence light intensity, determining a microwave frequency value corresponding to the lowest light intensity, and further determining the energy level interval between the diamond NV color center excited states I +/-1 >;

s4, according to excited state | + -1>Between energy levels Δ ═ 2 γ B_zCalculating the magnetic field amplitude B in the NV color center region of the diamond_zWherein γ is the NV gyromagnetic ratio;

s5 based on magnetic field amplitude B in NV color center area of diamond_zAnd the magnetic field magnification factor E is obtained, the background magnetic field is calculated, and the background magnetic field B is B_z/∈。

The present invention also provides a magnetometer comprising: a magnetic sensor and at least one magnetic flux concentrator;

the magnetic flux collector has two parallel opposite bottom surfaces, and the magnetic flux lines collected by the bottom surfaces pass through the magnetic sensor and are used for amplifying the magnetic field and restraining the magnetic sensor.

The invention also provides a magnetic flux concentrator for use in a magnetometer to concentrate magnetic flux and to constrain a magnetic sensor in the magnetometer.

The technical scheme of the invention has the following advantages: the invention provides a diamond NV color center magnetometer comprising a magnetic flux collector, a measuring system, a diamond NV color center magnetometric method, a magnetometer and the magnetic flux collector used in the magnetometer.

Drawings

FIG. 1(a) shows a model of an embodiment of the invention using a long rod-like flux concentrator;

FIG. 1(b) shows a model using two long rod-like flux concentrators in an embodiment of the invention;

FIG. 2(a) shows a model of an embodiment of the invention employing a conical flux concentrator;

FIG. 2(b) shows a model using two conical flux concentrators in an embodiment of the invention;

FIG. 2(c) is a schematic diagram showing the magnetic field distribution calculated by finite element analysis software for the two conical flux concentrators (permalloy) shown in FIG. 2 (b);

FIG. 3(a) shows a model employing a triangular flux concentrator in an embodiment of the invention;

FIG. 3(b) shows a model employing two triangular-shaped flux concentrators in an embodiment of the present invention;

FIG. 4(a) shows a model using a T-bar shaped flux concentrator in an embodiment of the present invention;

FIG. 4(b) shows a model using two T-bar shaped flux concentrators in an embodiment of the present invention;

FIG. 5(a) illustrates a model employing a horn flux concentrator in an embodiment of the present invention;

FIG. 5(b) illustrates a model employing two horn flux concentrators in an embodiment of the present invention;

FIG. 6(a) shows a partial design of the optical path subsystem for the case where two flux concentrators are employed in an embodiment of the invention;

FIG. 6(b) shows another partial design of the optical path subsystem for the case where two flux concentrators are employed in an embodiment of the present invention;

FIG. 6(c) shows a partial design of the optical path subsystem for the case where one flux concentrator is employed in an embodiment of the present invention;

FIG. 7 shows a schematic structural diagram of a magnetic measurement system for NV color centers of diamond in an embodiment of the present invention.

In the figure: 1: a laser; 2: an optical filter; 3: a first convex lens; 4: an acousto-optic modulator; 5: a beam splitter; 6: a photodetector; 7: a dichroic mirror; 8: an objective lens; 9: a magnetic flux concentrator; 10: diamond NV colour centre flake samples; 11: a data acquisition card; 12: an upper computer; 13: a microwave generator; 14: a power amplifier; 15: a microwave antenna; 16: a third convex lens; 17: a second convex lens.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

As mentioned above, the magnetometer can detect the magnetic induction intensity of the magnetic field of the environment at the position, and provide the magnetic field information of the surrounding space environment or the target object. The basic principle of the diamond NV color center magnetometer is as follows: in the tetrahedral structure of diamond, the carbon atom at the center is replaced by a nitrogen atom (N), and one of the four carbon atoms bonded thereto is removed to form a Vacancy (Vacancy), which is a natural charge state defect NV⁰While being firmly bonded to absorb an electron from the surrounding environment to form a negative charge state defect NV^-The negative charge defect has a higher sensitivity to various physical quantities and is therefore more widely studied, the negative charge defect NV^-Generally denoted NV for simplicity. The diamond NV defect structure exists in a triplet spin quantum state, its |0 state at room temperature>State and | + -1>Zero field splitting energy D between states_gsBased on the Zeeman effect, its | +1>State and | -1>The states degenerate and merge under the action of environmental magnetic field, | +/-1>Energy level differences between states, i.e. | +1>State and | -1>State spacing Δ ═ 2 γ B_zGamma is the gyromagnetic ratio of NV, B_zIs the projection size of the environment magnetic field on NV symmetry axis, i.e. | + -. 1>The energy level difference between the states is linear with the projection of the ambient magnetic field along the NV symmetry axis, B_zAnd can also be used to represent the magnitude of the magnetic field in the NV colour centre region of the diamond.

Transitions between NV quantum states can be manipulated by applying an ac microwave magnetic field to the diamond NV defect in a plane perpendicular to the NV symmetry axis. The magneto-sensitive microwave transition of the diamond NV defect can be detected by an Optical Detection Magnetic Resonance (ODMR) technique, which relies on the attenuation change in light intensity caused by the magnetic resonance transition during the optically pumped diamond NV defect. The ODMR technique polarizes NV defects to an excited state |0> by optical pumping, scans the frequency of the microwave magnetic field to the resonance frequency, so that the NV quantum state transits from the |0> state to the excited state | ± 1> state, and the excited state | ± 1> state spontaneously attenuates to the metastable singlet state through a radiationless attenuation path, and thus the singlet state transits back to the ground states |0> and | ± 1> almost with equal probability, which leads to the decrease of the background light intensity generated by the pump cycle due to non-optical radiation in the process.

The diamond NV color center magnetometer can realize the detection of a zero magnetic field under higher spatial resolution due to small size and high sensitivity, so the diamond NV color center magnetometer has great potential in the field of magnetic field imaging. On one hand, because the factors of a hyperfine structure and nuclear spin are considered, the magneto-sensitive microwave transition of the NV defect is overlapped below about 0.08mT and is completely separated above 0.08mT, and because the transition of the overlapped part takes the nuclear spin state into consideration, the magnetic field information cannot be correctly reflected, the factor causes the magnetic field of the NV color center magnetometer of diamond to have a measurement blind area below 80uT, so that the NV color center magnetometer of diamond has defects in the aspect of magnetic field detection; on the other hand, the background noise of the diamond NV color-center magnetometer is considered, the noise mainly comprises laser intensity noise, photon shot noise, electronic background noise and environmental noise which are emitted by a used laser generating device, wherein the photon shot noise spectrum is similar to a white noise spectrum, the magnetometer cannot distinguish magnetic field amplitude values near the noise spectrum, a measurement result is covered by the noise, the measurement result is large and has no reference, and therefore the measurement sensitivity of the diamond NV color-center magnetometer is limited by the background noise of the magnetometer to a large extent.

In view of the above, the invention provides a method for amplifying a magnetic field to be measured by adding a magnetic flux collector so as to solve the problem that the sensitivity and the measurement range are limited due to the overlapping of magnetic sensitive transition and the background noise of the diamond NV color center magnetometer.

The embodiment of the invention provides a diamond NV color center magnetometer containing a magnetic flux concentrator, which comprises: a diamond NV colour centre flake sample and at least one magnetic flux concentrator; the magnetic flux collector is provided with two parallel opposite bottom surfaces for collecting magnetic flux, the bottom surface of the magnetic flux collector is arranged in parallel with the bottom surface of the diamond NV color center thin sheet sample, and magnetic flux lines collected by the bottom surface of the magnetic flux collector penetrate through the diamond NV color center thin sheet sample. The bottom surface of the diamond NV colour centre chip sample, i.e. the surface of the chip structure which has the largest area. Preferably, to ensure the effect of concentrating the magnetic flux, one of the bottom surfaces of the flux concentrator may be closely adjacent to the bottom surface of the sample diamond NV colour centre wafer, or spaced no more than 1mm apart.

In the invention, the diamond NV color center magnetometer comprises a magnetic flux collector and a magnetic sensor (namely a diamond NV color center thin sheet sample), the magnetic flux collector is designed in such a way that the magnetic field noise introduced in the working process is lower than the shot noise of the diamond NV color center magnetometer, namely, the magnetic field gain of the magnetic flux collector is required to be within a measurable range and above a background noise, and the magnetic field noise introduced by the magnetic flux collector is required to be as low as possible so as not to cover the amplitude of a magnetic field to be measured. In use, the flux concentrator will cause an amplification of the amplitude of the magnetic field to be measured, the amplification being related to the geometry and relative permeability of the flux concentrator. Based on the optimized design of the magnetic flux collector, the weak magnetic field exceeding the magnetic field sensitivity of the diamond NV color center magnetometer can be detected on the basis of keeping a certain spatial resolution, and the magnetic measurement with high sensitivity and wide measurement range is realized.

Preferably, in order to better collect the magnetic flux, the magnetic flux collector may adopt a structure with one end larger and the other end smaller, and the smaller end is closer to the diamond NV color center thin sheet sample, that is, the two bottom surfaces of the magnetic flux collector have different areas, and the bottom surface of the end with the smaller area is close to the diamond NV color center thin sheet sample to serve as a magnetic flux releasing end, and the end with the larger area is relatively far away from the diamond NV color center thin sheet sample to serve as a magnetic flux receiving end.

Considering that the magnetic field gain of the flux concentrator should be sufficiently large, the flux concentrator is preferably made of a highly permeable material with a relative permeability of more than 1000. Furthermore, the material of the magnetic flux collector can be ferrite or permalloy.

In some preferred embodiments, the diamond NV color center magnetometer comprises two magnetic flux collectors, the two magnetic flux collectors are coaxially arranged oppositely at intervals, and the diamond NV color center thin sheet sample is arranged between the two magnetic flux collectors, namely the two magnetic flux collectors are respectively arranged on two sides of two bottom surfaces of the diamond NV color center thin sheet sample. By arranging two opposite magnetic flux collectors at intervals and arranging the diamond NV color center thin sheet sample in the interval (or called gap) between the two magnetic flux collectors, a better magnetic field gain effect can be obtained. When the diamond NV color center magnetometer comprises two oppositely arranged magnetic flux concentrators, the amplification factor is related to the size of the interval between the magnetic flux concentrators besides the geometric shape and the relative permeability of materials of a single magnetic flux concentrator, the smaller the interval is, the larger the magnetic field amplification factor is, the better the uniformity is, and if necessary, the magnetic field gain factor can be adjusted by increasing the interval between the two magnetic flux concentrators.

In some preferred embodiments, the geometry of the individual flux concentrators may be long rod-like, conical, triangular, T-shaped rod-like or angular. The T-shaped bar shape can be regarded as being formed by combining two vertically placed long bars with the same width and the same height and different lengths, and the angle shape can be similar to a cone shape, and the difference is that the curvature radius of the contour of the angle shape at different axial length positions in the direction of the symmetry axis is different, and the curvature radius of the contour is very large and does not change greatly along with the axial position from the top end of the cone to the bottom in the axial direction; and as the end approaches, the radius of curvature of the profile decreases rapidly and decreases in a non-linear (quadratic) relationship with axial position. In addition to the long rod-shaped flux concentrator, the conical, triangular, T-shaped rod-shaped or horn-shaped flux concentrator has two bottom surfaces of unequal areas, i.e., one end is larger and the other end is smaller. When the diamond NV color center magnetometer comprises two magnetic flux concentrators, the two magnetic flux concentrators with the same geometric shape are preferably adopted, and the symmetry axes of the bottom surfaces of the two magnetic flux concentrators are collinear, so that a better amplification effect can be obtained.

Fig. 1(a) and 1(b) show a long rod-shaped flux concentrator, fig. 1(a) shows a model using one long rod-shaped flux concentrator, and fig. 1(b) shows a model using two long rod-shaped flux concentrators. In fig. 1(a), the length, width and height of a single long rod-shaped magnetic flux collector are h 3-5 mm, L6-0.1 mm and L5-0.5 mm, respectively, in fig. 1(b), two long rod-shaped magnetic flux collectors are oppositely arranged, the symmetry axes are collinear, the distance between two bottom surfaces is 0.1mm, namely, the distance (or referred to as a gap) is d-0.1 mm, and a diamond NV color center thin sheet sample is vertically placed between the two bottom surfaces. It was calculated that the gain of a pair of ferrite long rod shaped flux concentrators at the spaced center position was about 36 and the gain of a pair of permalloy long rod shaped flux concentrators at the spaced center position was about 37; the gain of a ferrite long rod-shaped flux concentrator at the center of the bottom surface was about 8.5, and the gain of a permalloy long rod-shaped flux concentrator at the center of the bottom surface was about 8.7.

Fig. 2(a) and 2(b) show a conical flux concentrator, fig. 2(a) shows a model using one conical flux concentrator, and fig. 2(b) shows a model using two conical flux concentrators. As shown in fig. 2(b), a pair of conical magnetic flux collectors are placed opposite to each other with a small area bottom surface directed inward as a magnetic flux releasing end and a gap left therebetween, and a diamond NV color center sheet sample is placed vertically between the bottom surfaces of the two conical magnetic flux collectors, as shown in fig. 2(a), the case of using one conical magnetic flux collector is relatively simpler, and the diamond NV color center sheet sample is located at the same position as in the case of using two conical magnetic flux collectors. In fig. 2(a), the length h1 of the conical magnetic flux concentrator is 6mm, the diameters of the smaller and larger bottom surfaces are respectively L1 mm 0.2mm and L2 mm 6mm, and in fig. 2(b), the distance d between the two conical magnetic flux concentrators is 0.1mm, and the symmetry axes are collinear. It was calculated that the magnetic field gain of a pair of ferrite cone-shaped magnetic flux concentrators at the spaced center position was about 68.05, as shown in fig. 2(c), and the magnetic field gain of a pair of permalloy cone-shaped magnetic flux concentrators at the spaced center position was about 68.3; the gain of a single ferrite cone shaped flux concentrator and a single permalloy cone shaped flux concentrator at the center of the flux discharging end is about 12. Because the shape has stronger magnetic gathering capacity and the magnetic material is not saturated, the gains of the ferrite conical magnetic flux collector and the permalloy conical magnetic flux collector are similar under a low-magnetic environment.

Fig. 3(a) and 3(b) show a triangular-shaped flux concentrator, fig. 3(a) shows a model using one triangular-shaped flux concentrator, and fig. 3(b) shows a model using two triangular-shaped conical-shaped flux concentrators. As shown in fig. 3(a), the triangular magnetic flux collectors are obtained by increasing the height t1 to 0.5mm in the normal direction of the plane from a plane triangle having an upper base length L3 of 0.1mm, a lower base length L4 of 1.5mm, and a height h2 of 5mm (the upper base surface is a magnetic flux releasing end), and as shown in fig. 3(b), a pair of the magnetic flux collectors are horizontally placed, the symmetry axes of the upper base surfaces are collinear, and the distance d between the upper base surfaces of the two magnetic flux collectors is 0.1mm, and are used for placing a sample of a diamond NV color center sheet. The calculated gain of a pair of ferrite delta shaped flux concentrators at the spaced center position is approximately 47.9 and the gain of a pair of permalloy delta shaped flux concentrators at the spaced center position is approximately 48.3; the gain of a ferrite delta and a permalloy delta in the center of the top and bottom surfaces is approximately 10.

Fig. 4(a) and 4(b) show a T-bar shaped flux concentrator, fig. 4(a) shows a model using one T-bar shaped flux concentrator, and fig. 4(b) shows a model using two T-bar shaped flux concentrators. The T-bar shaped magnetic flux collector model can be regarded as being formed by combining two vertically placed long bar shaped magnetic flux collectors having the same width and height but different lengths, as shown in fig. 4(a) and fig. 1(a), the advantage of the longer bar shaped magnetic flux collector of the T-bar shaped magnetic flux collector is that the upper half of the T-shape (i.e. the end of the magnetic flux collector far away from the diamond NV color center thin sheet sample) has a larger area as a magnetic flux receiving end, and can collect more magnetic flux, and compared with the long bar shaped magnetic flux collector, the T-bar shaped magnetic flux collector can release from a rectangular bottom surface (i.e. a magnetic flux releasing end) with the same area, and can obtain better gain effect. Taking a background magnetic field of 1uT as an example (where T represents the magnetic induction tesla), a T-shaped bar-shaped flux concentrator having a dimension of width L9 of 0.1mm, height L10 of 0.5mm, T-shaped transverse length L11 of 1.5mm, and T-shaped longitudinal length h4 of 5mm has a gain of about 12.5 at the center of a bottom surface (i.e., flux releasing end) having a small area, and the gain of the flux concentrator is slightly different but very small for ferrite and permalloy materials. As shown in fig. 4(b), a pair of T-bar shaped magnetic flux concentrators are placed opposite to each other with a bottom surface at a distance d of 0.1mm, and used to place a sample of a diamond NV color center chip. It was calculated that the gain of a pair of ferrite T-bar flux concentrators at the spaced center position was about 42 and the gain of a pair of permalloy material T-bar flux concentrators at the spaced center position was about 44.

Fig. 5(a) and 5(b) show angular flux concentrators, fig. 5(a) shows a model employing one angular flux concentrator, and fig. 5(b) shows a model employing two angular flux concentrators. In the angular flux concentrator shown in fig. 5(a), the diameter of the upper bottom surface (i.e., the flux releasing end) is L7 equal to 0.1mm, the diameter of the lower bottom surface (i.e., the flux receiving end) is L8 equal to 1.5mm, and the axial length h5 equal to 5 mm. Compared with a long rod-shaped magnetic flux concentrator, the magnetic flux concentrator with the shape can also concentrate more magnetic flux by increasing the surface area of the magnetic flux receiving end, a larger magnetic field gain can be obtained at the magnetic flux releasing end with the same area, for a 1uT background magnetic field, the magnetic field gain of a permalloy horn-shaped magnetic flux concentrator at the center position of the upper bottom surface is 17, and the magnetic field gain of a ferrite horn-shaped magnetic flux concentrator at the center position of the upper bottom surface is 16. As shown in fig. 5(b), a pair of horn-shaped magnetic flux collectors have upper bottom surfaces directed inward, the symmetry axes of the upper bottom surfaces are collinear, and the distance d between the two upper bottom surfaces is 0.1 mm. It was calculated that the magnetic field gain of a pair of permalloy horn shaped flux concentrators at the center of the gap was about 58 and the magnetic field gain of a pair of ferrite horn shaped flux concentrators at the center of the gap was about 55.

The magnetic flux collectors with different geometric shapes have different gains under different materials, obviously, the magnetic field gain of the magnetic flux collector based on the permalloy material is generally larger than that of the ferrite material, and relatively speaking, the magnetic field noise of the magnetic flux collector based on the permalloy material becomes a short plate and the magnetic flux collector based on the ferrite material becomes a preferable scheme in consideration of the background noise of the diamond NV color center magnetometer. The magnetic material of the magnetic flux collector can be flexibly selected according to different experimental conditions and experimental environments, and the noise level of the magnetic flux collector with the existing volume and different materials can be evaluated according to finite element analysis software.

The invention also provides an evaluation mode: an imaginary excitation coil is established in the center of the gap between the two flux concentrators, the coil being located as a source of the magnetic field noise, i.e. an estimated location of the flux concentrators producing magnetic noise, the coil being assumed to have a magnetic dipole with an area a, a number of turns N, and a current I. Calculating, based on finite element analysis software, a power loss P (f) of the flux concentrator due to the imaginary excitation coil at the center of the gap, the power lossThe loss is composed of two parts, one is hysteresis loss generated by magnetization and magnetic domain rotation friction of material, and P is used_hystAnother aspect is the eddy current loss due to eddy currents induced in the material by the AC magnetic field, expressed as P_eddyIs represented by the formula P (f) ═ P_eddy+P_hystTwo losses are calculated by the following formula:

where σ is the electrical conductivity of the material, μ "is the imaginary part of the relative permeability μ ═ μ' -i μ" of the material, ω represents the angular frequency, and the integration is over the volume V of the material of the oscillating electric and magnetic fields with amplitudes E and H, respectively, resulting from the fictive current. According to the fluctuation loss theorem, the magnetic field noise generated at this place by the magnetic noise source can be estimated from the power loss of the magnetic noise source:

where δ b (f) is expressed as magnetic field noise, k is the boltzmann constant, the system is in thermal equilibrium at temperature T, a represents the area, N represents the number of turns, and I represents the current. It is noted that the power in the above equation is quadratic to the driving dipole in the linear response range, and therefore the calculation of this equation is independent of the size of the hypothetical coil and the driving current.

Taking the model of a conical magnetic flux concentrator shown in FIG. 2(a) as an example, the noise generated at the center of a sample of a diamond NV color center thin sheet is about that of permalloy, which is the material of the conical magnetic flux concentrator under 1HzWhen ferrite is selected, the noise is aboutUnder the condition of 100Hz, when permalloy and ferrite are selected,noise is respectivelyAndit can be seen that, for a conical magnetic flux concentrator as shown in fig. 2(a), the magnetic flux concentrator with ferrite for the high frequency band is preferred to limit the magnetic field noise introduced by the magnetic flux concentrator, and the magnetic flux concentrator with permalloy for the low frequency band in the allowable noise range can obtain higher measurement sensitivity.

The invention also provides a diamond NV color center magnetometer system comprising the magnetic flux concentrator, and the diamond NV color center magnetometer comprises the magnetic flux concentrator.

Preferably, the diamond NV color center magnetic force measuring system further comprises an optical path subsystem and a microwave subsystem; the optical path subsystem is used for providing green pumping laser to be incident to the diamond NV color center slice sample and collecting red fluorescence emitted by the diamond NV color center slice sample; the microwave subsystem is used for providing a microwave magnetic field for the diamond NV color center thin slice sample in a microwave radiation area.

The energy level structure of diamond NV color center in a laboratory coordinate system comprises a ground state |0>And | + -1>Excited state |0>And | + -1>And singlet | e>，|±1>Interval between energy levels is 2 gamma B_zGamma is the gyromagnetic ratio of NV, B_zIs the projected component of the ambient magnetic field about the NV axis of symmetry after amplification by the flux concentrator.

Selecting a central position area in a diamond NV color center slice sample, focusing 532nm green pumping laser, initializing the polarization state of the NV color center, and polarizing the spin state of the NV color center into an excited state |0>, wherein the NV color center of the spin state is subjected to self-luminescence transition to a ground state to radiate a red fluorescence signal.

The microwave magnetic field acts on a diamond NV color center slice sample, when the frequency of the microwave magnetic field is proper, the microwave magnetic field transfers NV color center quantum state population to an excited state I +/-1 >, and the NV color center of the quantum state population is spontaneously attenuated to a singlet state | e > without radiation and is attenuated to ground states |0> and | +/-1 > without radiation from the singlet state | e >.

Further, if the diamond NV color center magnetometer only comprises a magnetic flux collector, the green pumping laser provided by the optical path subsystem is incident along the direction vertical to the bottom surface or the side surface of the diamond NV color center slice sample; if the diamond NV color center magnetometer comprises two magnetic flux concentrators, the green pumping laser provided by the optical path subsystem is incident along the direction vertical to the side surface of the diamond NV color center thin slice sample. When the optical path subsystem collects the red fluorescence, the same path (but the propagation direction is opposite, the green pump laser is incident, and the red fluorescence is emitted) as that for providing the green pump laser can be adopted, and the green pump laser and the red fluorescence are separated through the optical splitter, or a path irrelevant to the incident path for providing the green pump laser can also be adopted.

Referring to fig. 6(a) to 6(c), fig. 6(a) shows a partial design of an optical path subsystem for the case of using two magnetic flux collectors, where a diamond NV color center magnetometer includes two magnetic flux collectors, green pump laser (green laser for short) provided by the optical path subsystem is incident along a direction perpendicular to a side surface of a diamond NV color center thin sheet sample (diamond thin sheet for short), and a path same as that provided by the green pump laser is adopted when collecting red fluorescence, because the magnetic flux collectors are disposed on two sides of two bottom surfaces of the diamond NV color center thin sheet sample, the green pump laser and the red fluorescence are propagated through the same path (the same side surface of the diamond NV color center thin sheet sample is used), and are mixed in the optical path, and a beam splitter is required to be subsequently used to separate the red fluorescence, which has the advantage of saving the space occupied by the optical path, the volume is reduced; FIG. 6(b) shows another partial design of the optical subsystem for the case of two flux concentrators, where a path unrelated to the incident path for providing the green pump laser is used for collecting the red fluorescence, such as the incident green pump laser and the collecting red fluorescence from two opposite sides of the diamond NV color center thin slice sample, which has the advantage that the red fluorescence and the green pump laser are completely separated, and the quality of the red fluorescence can be improved; fig. 6(c) shows a partial design of the optical path subsystem for the case of using a magnetic flux concentrator, when the diamond NV color center magnetometer only includes a magnetic flux concentrator, the green pump laser and the collected red fluorescence can be incident on the same side or two opposite sides of the diamond NV color center thin sheet sample in a similar manner to fig. 6(a) or fig. 6(b), or the green pump laser can be incident in a direction perpendicular to the bottom of the diamond NV color center thin sheet sample by using the bottom of the diamond NV color center thin sheet sample as shown in fig. 6(c), in which case, considering the space occupied by the magnetic flux concentrator, the same path as that of the green pump laser is preferably used when the red fluorescence is collected.

Preferably, in order to improve the light intensity contrast of the red fluorescence, a concave reflecting surface is added on each surface of the diamond NV color center flake sample so as to gather the red fluorescence emitted by the rest surfaces at the selected surface for collecting the red fluorescence.

Further, as shown in fig. 7, in a magnetic measurement system for NV color center of diamond, the optical subsystem preferably includes: the device comprises a laser 1, an optical filter 2, an acousto-optic modulator 4, a beam splitter 5, a dichroic mirror 7, an objective lens 8, a third convex lens 16, two second convex lenses 17, two first convex lenses 3 and two photoelectric detectors 6; wherein, specifically:

the laser 1 is used for generating green pumping laser with the wavelength of 532 nm; the optical filter 2 is used for filtering stray light in the green pumping laser emitted by the laser 1;

the acousto-optic modulator 4 is used for controlling and modulating the intensity of the green pumping laser emitted by the optical filter 2; the two first convex lenses 3 are respectively arranged at two sides of the acousto-optic modulator 4, the first convex lens 3 close to the laser 1 is used for focusing the green pumping laser input into the acousto-optic modulator 4, and the other first convex lens 3 is used for straightening the green pumping laser output from the acousto-optic modulator 4;

the beam splitter 5 is used for collecting a part of the straightened green pumping laser, and the PID algorithm control is carried out through the acousto-optic modulator 4 after the green pumping laser passes through the photoelectric detector 6; after beam splitting by the beam splitter 5, the remaining straightened green pump laser is incident into a dichroic mirror 7;

the dichroic mirror 7 is used for reflecting the green pumping laser and transmitting the red fluorescence, namely a light splitter, and is arranged at the intersection of the green light and the red light between the output side of the acousto-optic modulator 4 and the input end of the photoelectric detector for the red fluorescence;

the objective lens 8 is arranged on one side of the diamond NV color center slice sample and is used for providing green pumping laser to be incident to the diamond NV color center slice sample and collecting red fluorescence emitted by the diamond NV color center slice sample;

a pair of second convex lenses 17 is disposed between the dichroic mirror 7 and the objective lens 8 for straightening the green pump laser light and the red fluorescence light.

In this embodiment, when the optical path subsystem collects the red fluorescence, the same path as that for providing the green pump laser is adopted, when the red fluorescence is collected, the red fluorescence emitted by the diamond NV color center sheet sample enters the optical path subsystem through the objective lens 8, is straightened by the pair of second convex lenses 17, transmits the dichroic mirror 7, and enters the photoelectric detector through the third convex lens 16, the third convex lens 16 is used for focusing the red fluorescence so that the photoelectric detector receives the red fluorescence (the photoelectric detector can be matched with the lock-in amplifier or the photomultiplier to collect the red fluorescence and convert the red fluorescence into an electric signal), and the photoelectric detector for receiving the red fluorescence is in signal connection with the data acquisition card 11 and is used for realizing the signal conversion and processing of the red fluorescence.

The microwave subsystem preferably comprises a microwave generator 13, a power amplifier 14, a microwave antenna 15 and an upper computer 12; wherein, specifically:

the upper computer 12 is connected with the optical path subsystem (namely, connected with the data acquisition card 11 by signals) and also connected with the microwave generator 13, the microwave generator 13 is connected with the power amplifier 14, the microwave generator 13 is used for outputting alternating current signals with specific frequency required by a user, the power amplifier 14 is used for converting the alternating current signals output by the microwave generator 13 into current signals to drive the rear-stage microwave antenna 15, and the microwave antenna 15 is connected with the power amplifier 14 and is used for applying a microwave magnetic field NV to the diamond color center thin slice sample.

Further, the microwave antenna 15 preferably has two sets of connection schemes, one of which is a short-circuit scheme, in which a wire is connected to the inner core and the outer core of the coaxial cable (connected to the power amplifier 14) to form a short-circuit loop, and the loop surrounding area is a radiation surface; the second scheme is an open circuit scheme, the inner core of the coaxial cable is externally connected with a radio frequency resistor of 50ohm, and the surrounding area of the wires is a radiation surface. In use, a sample of diamond NV colour centre flakes is fixed to the radiation surface.

As shown in fig. 7, in the diamond NV color center magnetometer, the magnetic flux collector 9 amplifies the ambient magnetic field, so as to improve the measurement sensitivity of the diamond NV color center magnetometer, the diamond NV color center thin sheet sample 10 induces the ambient magnetic field amplified by the magnetic flux collector 9, and performs transition conversion under the irradiation of green pump laser, so as to emit red fluorescence related to the amplitude of the converted magnetic field, which is collected by the optical path subsystem.

Particularly, the invention further provides a diamond NV color center magnetic measurement method, which is realized by adopting the diamond NV color center magnetic measurement system comprising the magnetic flux collector according to any one of the embodiments, and specifically comprises the following steps:

s1, acquiring a magnetic field amplification factor E of the magnetic flux collector;

s2, obtaining red fluorescence emitted by a diamond NV color center sheet sample in a microwave radiation area under different microwave frequencies;

preferably, step S2 includes: injecting green pumping laser to a diamond NV color center sheet sample by using a diamond NV color center magnetic measurement system, collecting red fluorescence emitted by the diamond NV color center sheet sample, converting the red fluorescence into a red fluorescence signal and storing the red fluorescence signal;

setting a frequency scanning step length according to the expected frequency spectral line resolution, and sequentially acquiring red fluorescent signals of microwave radiation areas at different microwave frequencies from low to high in a preset frequency range;

s3, drawing a relation graph of microwave frequency and red fluorescence light intensity, determining the microwave frequency value corresponding to the lowest light intensity, and further determining the diamond NV color center excited state | + -1>The energy level interval therebetween; obtaining two microwave frequency values f capable of causing background light intensity difference₊And f_-The difference between the two is the excited state | + -1>The energy level separation Δ;

s4, according to excited state | + -1>Between energy levels Δ ═ 2 γ B_zCalculating the magnetic field amplitude B in the NV color center region of the diamond_zWherein γ is the NV gyromagnetic ratio;

s5 based on magnetic field amplitude B in NV color center area of diamond_zAnd the magnetic field magnification factor E is obtained, the background magnetic field is calculated, and the background magnetic field B is B_z/∈。

E.g. the magnetic field amplification e of the flux concentrator is 160, which means that the sensitivity is The diamond NV color center magnetic instrument can detectThe magnetic field of (1).

The invention also provides a magnetometer, which comprises a magnetic sensor and at least one magnetic flux collector; the magnetic flux collector has two parallel opposite bottom surfaces for collecting magnetic flux, and lines of the magnetic flux collected by the bottom surfaces of the magnetic flux collector pass through the magnetic sensor for amplifying the magnetic field and are constrained to the magnetic sensor so as to detect a weak magnetic field beyond the sensitivity of the original magnetic sensor.

Preferably, the two bottom surfaces of the flux concentrator are unequal in area, and the bottom surface of smaller area is close to the magnetic sensor.

Preferably, the flux concentrator is made of a highly permeable material with a relative permeability greater than 1000.

Preferably, the magnetometer comprises two magnetic flux concentrators; the two magnetic flux collectors are coaxially opposite and respectively arranged at two sides of two bottom surfaces of the magnetic sensor.

Preferably, the geometry of the individual flux concentrators is long rod-like, conical, triangular, T-shaped rod-like or angular.

The invention adopts the magnetic flux collector to provide gain for measuring the magnetic field, and provides various magnetic flux collector designs, which can effectively improve the sensitivity and the measuring range of the magnetometer.

The invention also provides a magnetic flux collector used in the magnetometer, which is used for collecting the magnetic flux and restraining the magnetic sensor in the magnetometer so as to amplify the magnetic field of the magnetic sensor.

Preferably, the two bottom surfaces of the flux concentrator are unequal in area, and the bottom surface of smaller area is close to the magnetic sensor.

Preferably, the flux concentrator is made of a highly permeable material with a relative permeability greater than 1000.

Preferably, the two magnetic flux collectors are coaxially opposite to each other and are respectively arranged on two sides of two bottom surfaces of the magnetic sensor.

Preferably, the geometry of the individual flux concentrators is long rod-like, conical, triangular, T-shaped rod-like or angular.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.