A single-beam SERF atomic magnetometer device and method based on perfect vortex weak light measurement

Abstract

This invention discloses a single-beam SERF atomic magnetometer device and method based on weak measurement using perfect vortex light. The device includes a light source unit, a perfect vortex light preparation unit, a polarization modulation unit, a gas cell coil unit, a polarization calibration unit, a weak measurement unit, and a detection unit arranged sequentially along the optical path. This invention is the first to combine perfect vortex light with weak measurement, and is applicable to any gas-filled or coated atomic gas cell. It proposes a quantitative relationship between topological charge and signal amplification, and the amplified weak magnetic field signal can be directly controlled by utilizing the orbital angular momentum of the perfect vortex light.

Description

Technical Field

[0001] This invention belongs to the field of weak magnetic field detection technology, and specifically relates to a single-beam SERF atomic magnetometer device and method based on perfect vortex optical weak measurement. Background Technology

[0002] Weak magnetic detection techniques based on atomic gas cells and ordinary Gaussian light sources are already quite mature. However, since its inception, the theory of weak measurement has demonstrated its ability to significantly improve the measurement sensitivity of minute physical quantities. In recent years, numerous experimental studies have employed the weak measurement principle to amplify signals of minute physical quantities. This method effectively suppresses various experimental noise interferences, thereby improving the signal-to-noise ratio. Typical applications include phase estimation, angular rotation measurement, refractive index detection, and magnetic field detection. Recent research has further explored schemes for coupling the magneto-optical rotation effect with weak measurement techniques: for example, integrating magneto-optical rotation into the geometrical spin Hall effect system of light and employing a dual-channel scheme with a single-photon detector successfully suppressed noise introduced by elliptic polarization, thus improving the sensitivity of weak magnetic detection.

[0003] In recent years, the development of vortex light fields (represented by Laguerre-Gaussian beams and Bessel-Gaussian beams) has provided new methods for magnetic field detection, including using vortex light to detect the direction and intensity of magnetic fields, and even achieving dead-zone-free magnetic field measurement through hybrid Poincaré beams (HPB). From the perspective of the geometric spin Hall effect of light, vortex beams carrying orbital angular momentum generally produce a larger geometric spin Hall shift than Gaussian beams because this effect is jointly modulated by the total angular momentum of light (including spin and orbital angular momentum).

[0004] Current magnetic weak detection techniques lack a solution that combines a perfect vortex beam with the principle of weak magnetic field measurement, and utilizes the larger geometrical spin Hall shift of the vortex beam to improve the amplification of the magneto-optical rotation signal. Vortex beams significantly improve the sensitivity of magnetic weak detection compared to traditional Gaussian beams, with sensitivity positively correlated with the topological charge of the vortex beam. Generally, as the topological charge increases, the spot size of a conventional vortex beam acting on the gas cell also increases, and the topological charge is limited by the size of the gas cell and cannot be increased too much. However, perfect vortex beams can ensure that the spot size acting on the atomic gas cell remains constant, thus significantly increasing the topological charge and consequently improving the sensitivity of magnetic weak measurements. This is the significance of this invention. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a single-beam SERF atomic magnetometer device and method based on perfect vortex light weak measurement, which solves the problems that the prior art has not yet combined a perfect vortex light field with the weak measurement principle, and lacks the technical problem of using the larger geometric spin Hall displacement of the vortex light field to improve the amplification of the magneto-optical rotation signal.

[0006] The technical solution adopted in this invention is: I. A single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement: It includes a light source unit, a perfect vortex light preparation unit, a polarization modulation unit, a gas cell coil unit, a polarization calibration unit, a weak measurement unit, and a detection unit arranged sequentially along the optical path; the gas cell coil unit includes an atomic gas cell and a coil system surrounding the atomic gas cell.

[0007] The Gaussian beam emitted by the light source unit enters the polarization modulation unit after passing through the perfect vortex light preparation unit, and then enters the gas cell coil unit. The magnetic field to be measured acts on the atomic gas cell in the gas cell coil unit. The coil system compensates for the magnetic field. The beam passes through the atomic gas cell, polarization calibration unit and weak measurement unit in sequence before entering the detection unit. The detection unit calculates and outputs the corresponding magnetic field magnitude.

[0008] The atomic gas chamber is filled with alkali metal atomic vapor in a spinless exchange relaxation state. The coil system is used to provide a compensating magnetic field to establish a near-zero magnetic field environment in the atomic gas chamber. The magnetic field to be measured acts on the atomic gas chamber and causes a magneto-optical rotation signal.

[0009] The light source unit emits a Gaussian beam for detection; the perfect vortex beam preparation unit converts the Gaussian beam emitted by the light source unit into a perfect vortex beam; the polarization modulation unit modulates the perfect vortex beam prepared by the perfect vortex beam preparation unit into an elliptical polarization state; the gas cell coil unit includes an atomic gas cell and a coil system surrounding the atomic gas cell, the atomic gas cell is filled with alkali metal atomic vapor in a spin-free exchange relaxation state, the coil system is used to provide a compensation magnetic field to establish a near-zero magnetic field environment at the atomic gas cell, the magnetic field to be measured acts on the atomic gas cell and induces a magneto-optical rotation signal; the polarization calibration unit compensates for the magnetic field generated by the atomic gas cell. The residual elliptic polarization component introduced by the atomic gas cell and optical path in the emitted beam after use restores the beam to a linear polarization state carrying only magneto-optical rotation angle information; the weak measurement unit performs a post-selection operation on the beam emitted by the polarization calibration unit to amplify the magneto-optical rotation signal caused by the magnetic field to be measured. The weak measurement unit includes a converging lens, a reflecting element, a collimating lens, and a polarizer arranged sequentially along the optical path. The transmission axis of the polarizer is approximately orthogonal to the polarization direction of the emitted beam after passing through the polarization calibration unit; the detection unit receives the magneto-optical rotation signal amplified by the weak measurement unit and converts it into an electrical signal to calculate the magnetic field information to be measured.

[0010] The light source unit includes a laser, the frequency of which is tuned to the near-resonance frequency of alkali metal atom transitions within the atomic chamber.

[0011] The perfect vortex beam preparation unit includes a spatial light modulator and a Fourier transform lens arranged in sequence. The spatial light modulator converts the incident probe beam into a Bessel-Gaussian beam, which is then subjected to Fourier transform by the Fourier transform lens to generate a perfect vortex beam.

[0012] The polarization modulation unit includes a half-wave plate and a quarter-wave plate. By adjusting the relative angle between the half-wave plate and the quarter-wave plate, the incident perfect vortex beam is modulated into an elliptically polarized state.

[0013] The atomic chamber is filled with one of rubidium atoms, cesium atoms, potassium atoms, sodium atoms or lithium atoms and a buffer gas; the coil system is a triaxial orthogonal Helmholtz coil group, used to generate a compensating magnetic field along three orthogonal directions to counteract the ambient magnetic field.

[0014] The polarization calibration unit includes a quarter-wave plate for compensating for the residual elliptic polarization component introduced by the atomic gas cell, restoring the beam to a linear polarization state.

[0015] The reflecting element is a dielectric mirror or a lens coated with a highly reflective medium. The refractive index of the reflecting element is greater than 1, and it is used to introduce a geometric spin Hall displacement when the beam is reflected.

[0016] The detection unit includes a photodetector and a signal processing module. The photodetector is used to convert light intensity signals into electrical signals. The signal processing module calculates the intensity distribution or centroid displacement of the light spot based on the electrical signals, and calculates the intensity of the magnetic field to be measured by combining the topological charge of the perfect vortex beam and the known amplification parameters of the weak measurement unit.

[0017] II. A measurement method for a single-beam SERF atomic magnetometer: S1. Construct the single-beam SERF atomic magnetometer device.

[0018] S2. Start the light source unit and tune the frequency to the near-resonance frequency of alkali metal atom transition in the atomic gas chamber.

[0019] S3. Heat the atomic gas chamber and control its temperature so that the alkali metal atom vapor inside reaches a spinless exchange relaxation state.

[0020] S4. The control coil system generates a compensation magnetic field, which cancels the background magnetic field in the region where the atomic gas chamber is located to near zero.

[0021] S5. Set the target topological charge in the perfect vortex beam preparation unit to generate the corresponding perfect vortex beam.

[0022] S6. Modulate the perfect vortex beam into an elliptically polarized state using a polarization modulation unit.

[0023] S7. The modulated elliptic polarized perfect vortex beam is passed sequentially through the atomic gas cell, polarization calibration unit, and weak measurement unit, which are in a near-zero magnetic field environment.

[0024] S8. When a magnetic field to be measured acts on the atomic gas cell, the detection unit detects the change in the optical signal after it has been amplified by the weak measurement unit, and the intensity information of the magnetic field to be measured is obtained after processing.

[0025] The beneficial effects of this invention are: 1. This invention is the first to combine perfect vortex light with weak measurement, and is applicable to any gas-filled or coated atomic gas cell. It proposes a quantitative relationship between topological charge and signal amplification, and the amplified weak magnetic field signal can be directly controlled by utilizing the orbital angular momentum of the perfect vortex light.

[0026] 2. The device of the present invention uses only a single laser, and the device structure is simple, eliminating the traditional operation process that requires auxiliary equipment such as photodetectors and lock-in amplifiers to amplify small signals.

[0027] 3. The device of this invention uses only one beam of elliptically polarized light to interact with atoms. The device has a simple structure, which simplifies the traditional dual-beam optical path construction process that uses one beam of circularly polarized light for pumping and one beam of linearly polarized vortex light for detection, making the device more highly integrated.

[0028] 4. This invention demonstrates a weak measurement amplification process using geometric spin Hall displacement as the coupling method, allowing the amplification factor of the magneto-optical rotation angle to be simultaneously controlled by both geometric spin Hall displacement and topological charge. Attached Figure Description

[0029] Figure 1 This is a diagram of the apparatus of the present invention.

[0030] Figure 2 The perfect vortex light measured by the device of this invention ( l =20) and ordinary light ( l =0) Comparison of weak measurement amplified signals in magneto-optical rotation.

[0031] In the figure: Light source unit 1, perfect vortex light preparation unit 2, polarization modulation unit 3, gas cell coil unit 4, polarization calibration unit 5, weak measurement unit 6, detection unit 7, converging lens 8, reflecting element 9, collimating lens 10, polarizer 11. Detailed Implementation

[0032] The present invention will now be described in more detail with reference to the accompanying drawings and embodiments. However, the present invention is not limited thereto. For those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

[0033] Example 1: like Figure 1 As shown, the single-beam SERF atomic magnetometer device of this embodiment includes: The light source unit 1, perfect vortex light preparation unit 2, polarization modulation unit 3, gas cell coil unit 4, polarization calibration unit 5, weak measurement unit 6, and detection unit 7 are arranged sequentially along the optical path. The gas cell coil unit 4 includes an atomic gas cell and a coil system surrounding the atomic gas cell. The atomic gas cell is filled with alkali metal atomic vapor in a spinless exchange relaxation state. The coil system is used to provide a compensation magnetic field to establish a near-zero magnetic field environment at the atomic gas cell. The magnetic field to be measured acts on the atomic gas cell and causes a magneto-optical rotation signal. The Gaussian beam emitted by the light source unit 1 enters the polarization modulation unit 3 after passing through the perfect vortex light preparation unit 2, and then enters the gas cell coil unit 4. The magnetic field to be measured acts on the atomic gas cell in the gas cell coil unit 4. The beam passes through the atomic gas cell, polarization calibration unit 5 and weak measurement unit 6 in sequence before entering the detection unit 7. The detection unit 7 calculates and outputs the corresponding magnetic field magnitude.

[0034] Specifically, the Gaussian beam emitted by the light source unit 1 is converted into a perfect vortex beam by the perfect vortex beam preparation unit 2. The perfect vortex beam is modulated into an elliptic polarization state by the polarization modulation unit 3. The elliptic polarization beam is emitted from the atomic gas cell of the gas cell coil unit 4 under the action of the magnetic field to be measured. The emitted beam is restored to a linear polarization state carrying only magneto-optical rotation angle information by the polarization calibration unit 5. The linear polarization beam is then subjected to a post-selection operation by the weak measurement unit 6, and finally received by the detection unit 7 to calculate the magnetic field information to be measured.

[0035] Furthermore, specifically: The light source unit 1 emits a Gaussian beam for detection; the light source unit 1 includes a laser, and the frequency of the Gaussian beam emitted by the laser is pre-tuned to the near-resonance frequency of the transition of alkali metal atoms in the atomic gas chamber.

[0036] Near-resonance frequency refers to the detuning of the probe beam frequency relative to the center frequency of a specific electronic transition line in alkali metal atoms, such as the D2 line of rubidium atoms, within the range of -20 GHz to +5 GHz, preferably a negative detuning within the range of -1 GHz to -10 GHz. At this frequency, the probe beam can interact sufficiently with the atoms to produce a significant magneto-optical rotation effect, while avoiding excessive light absorption and frequency shift.

[0037] The perfect vortex beam preparation unit 2 converts the Gaussian beam reflected from the light source unit 1 into a perfect vortex beam carrying a linearly polarized state with a specific topological charge.

[0038] The perfect vortex beam preparation unit 2 includes a spatial light modulator and a Fourier transform lens. The spatial light modulator is used to load a phase diagram corresponding to the target topological charge number to convert the incident probe beam into a Bessel-Gaussian beam. Then, the Fourier transform lens performs a Fourier transform to generate a perfect vortex beam with a linearly polarized state whose spot size does not change with the topological charge number.

[0039] A perfect vortex beam is a light field in which the intensity distribution forms a ring on a cross-section perpendicular to the propagation direction, and the radius of this ring, i.e., the size of the spot, does not change with the topological charge or orbital angular momentum quantum number it carries. A Bessel-Gaussian beam is generated by applying a spiral phase to a Gaussian beam using a spatial light modulator, and then transformed by a Fourier lens to obtain a perfect vortex beam with a constant ring radius at the back focal plane. This radius is determined only by the lens focal length and the incident beam parameters, and does not change with the topological charge, thus overcoming the limitation that the radius of ordinary vortex beams increases with the topological charge. Therefore, with the atomic gas cell size remaining constant, a higher topological charge can be used to proportionally enhance the weak measurement amplification effect and improve the sensitivity of the magnetometer.

[0040] The polarization modulation unit 3 modulates the perfect vortex beam prepared by the perfect vortex beam preparation unit 2 into an elliptic polarization state.

[0041] The polarization modulation unit 3 includes a half-wave plate and a quarter-wave plate. By adjusting the relative angle between the half-wave plate and the quarter-wave plate, the incident linearly polarized perfect vortex beam is modulated into an elliptically polarized state.

[0042] The modulation principle is as follows: rotating the half-wave plate changes the polarization direction of linearly polarized light; this linearly polarized light is then incident on a quarter-wave plate. By adjusting the angle between the optical axis of the quarter-wave plate and the incident polarization direction, elliptically polarized light with different ellipticities can be obtained. When the optical axis of the quarter-wave plate is precisely at a 45° angle to the incident polarization direction, the outgoing light is circularly polarized. By jointly adjusting the half-wave plate and the quarter-wave plate, the azimuth angle and ellipticity of the elliptically polarized state can be independently controlled. This elliptically polarized state, as a pre-selected state in the weak measurement process, is the physical basis for subsequently introducing a geometric spin Hall displacement through a reflecting medium, followed by post-selection via polarizer 11, ultimately achieving amplification of the tiny magneto-optical rotation angle signal.

[0043] The gas cell coil unit 4 includes an atomic gas cell and a coil system surrounding the atomic gas cell. The atomic gas cell is filled with alkali metal atomic vapor in a spinless exchange relaxation state. The coil system provides a compensation magnetic field to establish a near-zero magnetic field environment at the atomic gas cell. The magnetic field to be measured acts on the atomic gas cell and causes a magneto-optical rotation signal.

[0044] The atomic gas chamber is filled with one of rubidium, cesium, potassium, sodium, or lithium atoms, and a buffer gas. The coil system is a triaxial orthogonal Helmholtz coil assembly used to generate compensating magnetic fields along three orthogonal directions to counteract the ambient magnetic field.

[0045] Three sets of orthogonal Helmholtz coils are independently powered by current sources to generate magnetic fields along the X, Y, and Z directions. The residual magnetic field is monitored by a triaxial magnetometer placed near the atomic gas cell, and the current in each coil is adjusted through a feedback control system until the background magnetic field in the region where the atomic gas cell is located is compensated to a level below 1 nT, thereby establishing a near-zero magnetic field environment necessary to achieve a spin-free exchange relaxation state.

[0046] In this embodiment, the atomic gas chamber is located at the center of the Helmholtz coil group. The atomic gas chamber is filled with alkali metal atoms and buffer gas. The outer wall of the atomic gas chamber is wound with non-magnetic twisted pair wires for heating, which causes the alkali metal atoms to exhibit a spin-free exchange relaxation state or a high atomic number density state. The Helmholtz coil group generates a compensating magnetic field to cancel the excess magnetic field around the atomic gas chamber, so that the magnetic field around the atomic gas chamber is zero.

[0047] The polarization calibration unit 5 is used to compensate for the residual elliptic polarization component introduced by the atomic gas cell and the optical path in the outgoing beam after the action of the atomic gas cell, and restore the beam to a linear polarization state that only carries magneto-optical rotation angle information.

[0048] The polarization calibration unit 5 includes a quarter-wave plate to compensate for the residual elliptic polarization component introduced by the atomic gas cell, restoring the beam to a linear polarization state.

[0049] Without applying the magnetic field to be measured, the light intensity signal of the detector unit 7 after the weak measurement unit 6 is monitored simultaneously by rotating the quarter-wave plate in the polarization calibration unit 5. When the light intensity signal reaches its minimum value, it indicates that the residual elliptical polarization caused by non-reciprocal birefringence and other effects introduced by the atomic gas cell and other parts of the optical path has been compensated, and the outgoing beam has been restored to a pure linear polarization state. This calibration step ensures that the beam entering the weak measurement unit 6 has a definite initial polarization direction, which is the basis for the repeatability and accuracy of the weak measurement amplification process.

[0050] The weak measurement unit 6 performs a post-selection operation on the beam emitted from the polarization calibration unit 5 to amplify the magneto-optical rotation signal caused by the magnetic field to be measured. The weak measurement unit 6 includes a converging lens 8, a reflecting element 9, a collimating lens 10, and a polarizer 11 arranged sequentially along the optical path. The transmission axis of the polarizer 11 is approximately orthogonal to the polarization direction of the beam emitted from the polarization calibration unit 5. Specifically, the converging lens 8 focuses the beam emitted from the polarization calibration unit 5 into a minimum spot at its focal length, and reflects it after it hits the surface of the reflecting element 9. The beam is then collimated at the focal length of the collimating lens 10, passes through the polarizer 11, and enters the detection unit 7. The reflecting element 9 can be a lens, a mirror, etc. The higher the refractive index of the medium, the more significant the geometric spin Hall effect it produces. The polarization direction of the polarizer 11 must be almost orthogonal to the polarization direction of the beam emitted from the perfect vortex light preparation unit 2.

[0051] In this embodiment, the reflective element 9 is a dielectric mirror or a lens coated with a highly reflective medium. The refractive index of the reflective element 9 is greater than 1, which is used to introduce geometric spin Hall displacement when the beam is reflected.

[0052] When a beam carrying both spin angular momentum and orbital angular momentum is reflected at an interface between media with different refractive indices, such as the medium from air to reflector element 9, the left-hand and right-hand circularly polarized components will exhibit a transverse displacement perpendicular to the incident plane due to the optical path difference; this is known as the geometric spin Hall displacement. This displacement is related to the topological charge of the beam, the angle of incidence, the refractive index of the reflecting medium, and the wavefront curvature of the beam. In the weak measurement unit 6, this displacement, as a coupling term of the weak interaction, amplifies the minute magneto-optical rotation angle as a change in polarization state, resulting in an observable shift in the spatial position of the light spot or a change in intensity distribution. Generally, the greater the refractive index of the reflecting medium, the more significant the displacement.

[0053] An approximate orthogonal relationship means that the angle between the two is between 85° and 95°, preferably between 89° and 91°. This setting enables the polarizer 11 to have an extremely high suppression ratio for light beams without magnetic field, so that when a small magneto-optical rotation angle occurs, a high-magnification weak measurement amplification of the rotation angle signal can be achieved by significantly changing the light intensity passing through the polarizer 11.

[0054] The detection unit 7 receives the magneto-optical rotation signal amplified by the weak measurement unit 6 and converts it into an electrical signal to calculate the information of the magnetic field to be measured. The detection unit 7 includes a photodetector and a signal processing module. The photodetector converts the light intensity signal into an electrical signal, and the signal processing module calculates the intensity distribution or centroid displacement of the light spot based on the electrical signal. Combining this with the topological charge of the perfect vortex beam and the known amplification parameters of the weak measurement unit 6, the intensity of the magnetic field to be measured is calculated. Specifically, the photodetector is a silicon photodiode. The signal processing module records the reference value of the light intensity distribution or the centroid of the light spot under zero magnetic field conditions; when the magnetic field to be measured is applied, this distribution or centroid shifts. The shift is proportional to the magneto-optical rotation angle, which is determined by the axial component of the magnetic field to be measured, the cell length, and the Welder constant. By combining the weak measurement amplification factor, which depends on the topological charge of the perfect vortex beam, the geometric spin Hall displacement, and the post-selection angle, the intensity of the magnetic field to be measured can be inferred.

[0055] Specifically, from the perspective of the vector properties of light: The light source unit 1 emits Gaussian linearly polarized light, the perfect vortex light preparation unit 2 emits horizontally linearly polarized vortex light with orbital angular momentum, the polarization modulation unit 3 emits ellipticly polarized vortex light with orbital angular momentum, and the polarization calibration unit 5 emits horizontally linearly polarized vortex light with orbital angular momentum.

[0056] This embodiment is implemented according to the following steps of the single-beam SERF atomic magnetometer measurement method: S1. Construct a single-beam SERF atomic magnetometer device.

[0057] S2. Start the light source unit 1 and tune the frequency to the near-resonance frequency of alkali metal atom transition in the atomic gas chamber.

[0058] S3. Heat the atomic gas chamber and control its temperature so that the alkali metal atom vapor inside reaches a spinless exchange relaxation state.

[0059] S4. The control coil system generates a compensation magnetic field, which cancels the background magnetic field in the region where the atomic gas chamber is located to near zero.

[0060] S5. Set the target topological charge in the perfect vortex beam preparation unit 2 to generate the corresponding perfect vortex beam.

[0061] S6. Use polarization modulation unit 3 to modulate the perfect vortex beam into an elliptically polarized state.

[0062] S7. The modulated elliptic polarized perfect vortex beam is passed sequentially through the atomic gas cell, polarization calibration unit 5, and weak measurement unit 6, which are in a near-zero magnetic field environment.

[0063] S8. When a magnetic field to be measured acts on the atomic gas cell, the detection unit 7 detects the change in the light signal after weak measurement amplification, and obtains the intensity information of the magnetic field to be measured after processing.

[0064] The core principles of this invention are twofold: one is the magneto-optical rotation principle, and the other is the vortex light weak measurement principle.

[0065] Magneto-optical rotation principle: When linearly polarized probe light passes through an atomic gas cell placed in a magnetic field, the left-handed and right-handed circularly polarized light produce a phase difference due to the different refractive indices and absorption coefficients caused by the magneto-optical birefringence effect of the atomic medium. This results in a rotation of the polarization direction of the outgoing light, and the magneto-optical rotation angle is [not specified]. It is proportional to the magnetic field strength. This phenomenon is called magneto-optical rotation, and it is particularly pronounced when the atom is in a spinless exchange relaxation state. The final relationship between the magnetic field and the rotation angle is given by the following equation, using the D2 line of rubidium-87 atoms as an example: in, This is the magneto-optical rotation angle, which is the rotation angle of the polarization direction of the linearly polarized probe light after it passes through the atomic gas cell. This is the electron gyromagnetic ratio, which is the ratio of the electron's spin magnetic moment to its angular momentum; here, it is a constant. Optical pump rate is the rate at which pump light transports an atom to a specific spin state. It is related to factors such as pump light intensity and atomic energy level structure. The relaxation rate is the total rate of atomic spin relaxation, including depolarization processes caused by non-optical pumping such as spin-breaking collisions and wall relaxation. The length of the air chamber. For the classical electron radius, At the speed of light, It is the atomic number density. The saturation parameter of the probe light is the ratio of the probe light intensity to the transition saturation intensity. Let be the component of the magnetic field in the y-direction. It is the intensity of the oscillation. It detects the frequency of light. It is the D2 line transition frequency of the rubidium-87 atom. It is the pressure broadening of atoms.

[0066] Principle of vortex weak light measurement: Weak measurement is a technique that amplifies minute physical quantities by carefully designing "pre-selected states" and "post-selected states." Its core steps are as follows: 1. Preparation of preselected states: Photons are prepared as a superposition of left-handed and right-handed circularly polarized states, i.e., linearly polarized states, and endowed with the momentum component of vortex light: in, To detect the initial state of light, It is a left-handed circularly polarized state. It is a right-handed circularly polarized state. This represents the Bessel-Gaussian photon momentum distribution.

[0067] 2. Effect of the magnetic field to be measured: When elliptically polarized light passes through an atomic gas cell surrounded by a magnetic field, the polarization state of its linearly polarized component evolves as follows: in, To detect the polarization state evolution of the linearly polarized component of light, and These are small quantities, representing differences in phase and amplitude.

[0068] 3. Geometric spin Hall displacement coupling: After light exits the atomic gas cell, it undergoes a geometric spin Hall shift through the reflecting medium, the magnitude of which is related to the spin and orbital angular momentum of the vortex light. in, For the evolution operator of geometric spin Hall shift, Let be the radial wave function in the y-direction of momentum space. This represents the spin Hall shift of horizontally linearly polarized light. Let be the topological charge of the vortex beam. Let z be the z-component of the Pauli matrix.

[0069] 4. Subsequent selection: Through a polarization state that is almost orthogonal to the initial state The polarizer 11 is used for filtering, at which point the tiny magneto-optical rotation angle is observed. The intensity shift signal was significantly amplified into an observable signal. in, To detect the final state of light.

[0070] After final selection, the efficiency of light intensity detection is determined. The expression is: in, , , For the Kummer convergent hypergeometric function, This is the spin Hall displacement. The beam waist.

[0071] This invention, based on the principle of weak measurement, combines the magneto-optical rotation of atoms with the geometrical spin Hall effect of perfect vortex light to achieve weak measurement amplification of the magneto-optical rotation angle. The improvement in the topological charge of ordinary vortex beams is limited by the size of the gas cell, but perfect vortex light ensures that the spot size acting on the atomic gas cell remains constant, significantly increasing the topological charge and thus improving the sensitivity of weak magnetic field measurements. This invention utilizes an elliptical polarized perfect vortex beam for detection, demonstrating that after the probe light passes through atoms in a spin-free exchange-relaxed state, it is amplified by the weak measurement unit 6. The amplified magneto-optical rotation signal is then converted into an electrical signal by the photodetector of the detection unit 7, and the signal processing module calculates and outputs the magnetic field value.

[0072] Example 2: When measuring the atomic magnetic field of rubidium-87 atoms in an atomic gas chamber filled with a buffer gas at 1 atmosphere, the following procedures are performed: Step 1: Set up the laser source device: tune the laser frequency of the laser in the light source unit 1 to the near-resonance frequency of the transition of alkali metal atoms in the gas chamber coil unit.

[0073] Specifically, the wavelength of the laser is locked to the D2 line of rubidium 87 atoms. , At the negatively detuned transition energy level; among which, , Represents a specific energy level in the ground state of an atom. 5 represents a specific energy level of an excited state of an atom, and 5 represents the principal quantum number. n =5, the 1 / 2 in the lower right corner represents the total angular momentum of the electron. J =1 / 2, the 2 in the top left corner represents 2 J +1, F It is the ordinal number of the ground state energy level of an atom. It is the energy level number of the excited state of an atom.

[0074] The laser is activated, and the beam emitted by the laser passes sequentially through the perfect vortex light preparation unit 2, polarization modulation unit 3, gas cell coil unit 4, polarization calibration unit 5, and weak measurement unit 6 before being received by the detection unit 7.

[0075] Step 2: Turn on the heating: Apply alternating current with a frequency of 500kHz or higher and a power of 7W or higher to the non-magnetic twisted pair heating wire to heat the atomic gas cell to 150 degrees Celsius, so that the atoms reach a state of spin-free exchange relaxation. At this time, the atoms have a high sensitivity to the magnetic field.

[0076] Step 3: Activate residual magnetic field compensation: Apply DC current to three sets of orthogonal Helmholtz coils to generate compensation magnetic fields along the X, Y, and Z axes respectively, thereby canceling the magnetic field around the atomic gas chamber to a near-zero field below 1nT.

[0077] Step 4: Adjust the light intensity in the photodetector in the detection unit to the minimum or maximum under the condition of no magnetic field.

[0078] Step 5: Apply the magnetic field to be measured around the atomic gas cell so that the atomic gas cell can feel the magnetic field. The light passing through the atomic gas cell enters the photodetector, is converted into an electrical signal and is collected. The signal processing module calculates and outputs the magnetic field value.

[0079] This embodiment demonstrates a single-beam SERF atomic magnetometer device and method based on weak measurement of perfect vortex light. It illustrates how an elliptical polarized perfect vortex beam undergoes magneto-optical rotation after passing through an atomic gas cell, and how the rotation angle is amplified using the weak measurement principle. This allows magnetic field information to be extracted from the light intensity information after passing through the atomic gas cell, ultimately outputting the magnetic field value. Figure 2 As shown, the length of the air chamber This represents the magnetic field signal of ordinary Gaussian light. The magnetic field signal of a perfect vortex beam is nearly twice that of a regular Gaussian beam.

[0080] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement, characterized in that: It includes a light source unit (1), a perfect vortex light preparation unit (2), a polarization modulation unit (3), a gas cell coil unit (4), a polarization calibration unit (5), a weak measurement unit (6), and a detection unit (7) arranged sequentially along the optical path; the gas cell coil unit (4) includes an atomic gas cell and a coil system surrounding the atomic gas cell; The Gaussian beam emitted by the light source unit (1) enters the polarization modulation unit (3) after passing through the perfect vortex light preparation unit (2), and then enters the gas cell coil unit (4). The magnetic field to be measured acts on the atomic gas cell in the gas cell coil unit (4), and the coil system compensates for the magnetic field. The beam passes through the atomic gas cell, the polarization calibration unit (5) and the weak measurement unit (6) in sequence before entering the detection unit (7). The detection unit (7) calculates and outputs the corresponding magnetic field magnitude.

2. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that, include: The atomic gas chamber is filled with alkali metal atomic vapor in a spinless exchange relaxation state. The coil system is used to provide a compensation magnetic field to establish a near-zero magnetic field environment in the atomic gas chamber. The magnetic field to be measured acts on the atomic gas chamber and causes a magneto-optical rotation signal. The light source unit (1) emits a Gaussian beam for detection; the perfect vortex light preparation unit (2) converts the Gaussian beam emitted by the light source unit (1) into a perfect vortex beam; the polarization modulation unit (3) modulates the perfect vortex beam prepared by the perfect vortex light preparation unit (2) into an elliptic polarization state; the gas cell coil unit (4) includes an atomic gas cell and a coil system surrounding the atomic gas cell. The atomic gas cell is filled with alkali metal atomic vapor in a spinless exchange relaxation state. The coil system is used to provide a compensation magnetic field to establish a near-zero magnetic field environment at the atomic gas cell. The magnetic field to be measured acts on the atomic gas cell and causes a magneto-optical rotation signal. The polarization calibration unit (5) compensates for the residual elliptic polarization component introduced by the atomic gas cell and the optical path in the emitted beam after the action of the atomic gas cell, and restores the beam to a linear polarization state carrying only magneto-optical rotation angle information; the weak measurement unit (6) performs a post-selection operation on the beam emitted by the polarization calibration unit (5) to amplify the magneto-optical rotation signal caused by the magnetic field to be measured. The weak measurement unit (6) includes a converging lens (8), a reflecting element (9), a collimating lens (10) and a polarizer (11) arranged sequentially along the optical path. The transmission axis direction of the polarizer (11) is approximately orthogonal to the polarization direction of the emitted beam after the polarization calibration unit (5); the detection unit (7) receives the magneto-optical rotation signal amplified by the weak measurement unit (6) and converts it into an electrical signal to calculate the magnetic field information to be measured.

3. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The light source unit (1) includes a laser, the frequency of which is tuned to the near-resonance frequency of the alkali metal atom transition in the atomic chamber.

4. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The perfect vortex beam preparation unit (2) includes a spatial light modulator and a Fourier transform lens arranged in sequence. The spatial light modulator converts the incident probe beam into a Bessel-Gaussian beam, which is then subjected to Fourier transform by the Fourier transform lens to generate a perfect vortex beam.

5. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The polarization modulation unit (3) includes a half-wave plate and a quarter-wave plate. By adjusting the relative angle between the half-wave plate and the quarter-wave plate, the incident perfect vortex beam is modulated into an elliptical polarization state.

6. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The atomic chamber is filled with one of rubidium atoms, cesium atoms, potassium atoms, sodium atoms, or lithium atoms and a buffer gas; the coil system is a triaxial orthogonal Helmholtz coil group, used to generate a compensating magnetic field along three orthogonal directions to counteract the ambient magnetic field.

7. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The polarization calibration unit (5) includes a quarter-wave plate for compensating for the residual elliptic polarization component introduced by the atomic gas cell, restoring the beam to a linear polarization state.

8. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The reflective element (9) is a medium reflector or a lens coated with a highly reflective medium. The refractive index of the reflective element (9) is greater than 1, and it is used to introduce a geometric spin Hall displacement when the beam is reflected.

9. The single-beam SERF atomic magnetometer device based on perfect vortex weak light measurement according to claim 1, characterized in that: The detection unit (7) includes a photodetector and a signal processing module. The photodetector is used to convert the light intensity signal into an electrical signal. The signal processing module calculates the intensity distribution or centroid displacement of the light spot based on the electrical signal, and calculates the intensity of the magnetic field to be measured by combining the topological charge of the perfect vortex beam and the known amplification parameters of the weak measurement unit (6).

10. A single-beam SERF atomic magnetometer measurement method using the apparatus described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Construct the single-beam SERF atomic magnetometer device; S2. Start the light source unit (1) and tune the frequency to the near-resonance frequency of alkali metal atom transition in the atomic gas chamber. S3. Heat the atomic gas cell and control its temperature so that the alkali metal atom vapor inside reaches a spinless exchange relaxation state. S4. The control coil system generates a compensation magnetic field, which cancels the background magnetic field in the region where the atomic gas chamber is located to near zero. S5. Set the target topological charge in the perfect vortex beam preparation unit (2) and generate the corresponding perfect vortex beam; S6. Modulate the perfect vortex beam into an elliptic polarization state using the polarization modulation unit (3); S7. The modulated elliptic polarized perfect vortex beam is passed sequentially through the atomic gas cell, polarization calibration unit (5), and weak measurement unit (6) in a near-zero magnetic field environment. S8. When the magnetic field to be measured acts on the atomic gas cell, the detection unit (7) detects the change in the light signal after it is amplified by the weak measurement unit (6), and obtains the intensity information of the magnetic field to be measured after processing.

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