Precision microwave detection method based on transmission enhanced spectrum without population inversion

Abstract

The invention discloses a microwave precision detection method based on a transmission enhancement spectrum without population inversion, and belongs to the technical field of microwave quantum detection, the method abandons an electromagnetic induction transparency mechanism depended on by a traditional atom microwave electric field meter, and realizes a transmission field enhancement effect under the condition without population inversion through periodically coupled pulsed light. And a transmission spectrum is further generated. Precise detection of a microwave field is realized by using a linear relation between a peak-to-peak distance of a medium transmission spectrum and microwave field intensity. Compared with the prior art, the spectral line width of transmission light is remarkably compressed, the measurement sensitivity and precision are greatly improved, and the wide application potential is shown. In addition, the invention provides a brand new generation mechanism for the design of the atomic microwave electric field meter, and opens up a new way for the development of a microwave electric field precision detection technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave quantum detection, and particularly relates to a microwave precision detection method based on the enhanced transmission spectrum without population inversion. Background Art

[0002] In traditional methods, the measurement of microwave electric fields mainly relies on dipole antennas, but this method has some limitations. Dipole antennas are usually made of metal and use metal transmission lines, which may cause the microwave field to be measured to be interfered by the conductive material during the measurement process. Although the spatial resolution can be improved by reducing the probe size, this method still cannot achieve sub-wavelength measurement.

[0003] Rydberg atoms are extremely sensitive to external electromagnetic fields, so they show great potential in achieving high-precision measurement of microwave electric fields. Traditional Rydberg-atom-based microwave electric field meters mainly rely on the electromagnetically induced transparency spectrum generated by the interaction between a continuous detection field and a coupling field and Rydberg atoms. When a microwave field is applied on this basis, the electromagnetically induced transparency spectrum will undergo peak-to-peak splitting, and the peak-to-peak spacing of the two transmission spectra is proportional to the microwave field strength, thereby achieving precise measurement of the microwave field. However, the spectral line width of the electromagnetically induced transparency spectrum is relatively wide, which limits the measurement accuracy and sensitivity. Therefore, researchers usually need to further compress the spectral line width by means of the resonant cavity method, the grating method or the superheterodyne method.

[0004] The Rydberg-atom microwave electric field precision detection scheme disclosed by the present invention is significantly different from traditional Rydberg-atom electric field meters in terms of working principle. The present invention does not rely on the electromagnetically induced transparency effect, but uses the enhanced transmission spectrum without population inversion caused by the coherence of the sideband radiation field and the detection field to achieve quantum precision measurement of microwave electric fields. Compared with traditional Rydberg-atom electric field meters, the transmission spectral line width of the present invention is narrower, thus significantly improving the accuracy and sensitivity of microwave field detection. This improvement not only enhances the measurement accuracy, but also broadens the application prospects of microwave quantum precision detection technology. Summary of the Invention

[0005] Aiming at the above problems existing in the prior art, the present invention proposes a microwave precision detection method based on the enhanced transmission spectrum without population inversion, which is reasonably designed, solves the deficiencies of the prior art, and has good effects.

[0006] A microwave precision detection method based on the enhanced transmission spectrum without population inversion includes the following steps:

[0007] Step 1: Build a detection system, and the detection system includes An atomic gas cell, a frequency-stabilized laser system, a microwave horn antenna, a signal generator, a photodetector, a spectrum analyzer, an electro-optic modulator, two lenses, and a half-wave plate. The frequency-stabilized laser system includes a probe field laser and a coupling field laser;

[0008] Step 2: The output end of the probe field laser is connected to the electro-optic modulator through an optical fiber, and the output end of the coupling field laser is connected to the signal generator through an optical fiber. The probe light and the coupling light pass through the atomic gas cell in opposite directions to form a probe field and a coupling field. The microwave horn antenna is used to generate the microwave field to be measured;

[0009] Step 3: Modulate the detuning of the probe field through the electro-optic modulator, and use the photodetector and the spectrum analyzer to detect the transmission spectrum of the probe field;

[0010] Step 4: Utilize the linear relationship between the peak-to-peak spacing of the enhanced transmission spectrum of the probe field and the microwave electric field strength to achieve precise detection of the microwave field.

[0011] Further, in Step 2, the probe light emitted by the probe field laser sequentially passes through the electro-optic modulator, the first lens, the first half-wave plate, the atomic gas cell, and the second lens and then is input to the photodetector. After the photodetector performs photoelectric conversion, it is input to the spectrum analyzer; the coupling light emitted by the coupling field laser sequentially passes through the signal generator and the second half-wave plate, the second lens, the atomic gas cell, the first half-wave plate, and the first lens.

[0012] Further, the lasers output by the probe field laser and the coupling field laser are both continuous light, with wavelengths of 480 nm and 780 nm respectively. The continuous coupling light is modulated by the signal generator into a periodic laser pulse train, and its pulse waveform, single-pulse height, full width at half maximum, and the distance between two adjacent pulses are all adjustable.

[0013] Further, the microwave generated by the horn antenna passes through the atomic gas cell in a direction perpendicular to the optical path. The probe field is coupled with the state , phase, and the coupling field is coupled with the state , phase. The microwave field is coupled with the state , phase.

[0014] Further, in Step 4, the linear relationship between the peak-to-peak spacing of the enhanced transmission spectrum of the probe field and the microwave electric field strength is obtained through pre-calibration, so as to achieve the detection of the microwave electric field strength.

[0015] The beneficial technical effects brought by the present invention:

[0016] The microwave quantum precision detection method based on Rydberg atoms involved in the present invention has a fundamental difference in the working principle from the traditional Rydberg atom microwave electrometer. Its working mechanism does not rely on the electromagnetically induced transparency phenomenon, but is realized by the enhanced transmission spectrum of non-population-inverted light caused by the coherence between the sideband radiation field and the detection field. The beneficial technical effects brought by this invention are as follows:

[0017] 1. High-sensitivity detection: By means of the enhanced transmission spectrum technology of non-population-inverted light, this method significantly improves the detection sensitivity of microwave electric fields and can detect very weak microwave electric fields.

[0018] 2. High-precision measurement: Utilizing the linear relationship between the peak-to-peak spacing of the enhanced transmission spectrum and the microwave electric field intensity, this method can achieve high-precision measurement of the microwave electric field intensity.

[0019] 3. Wide-band measurement ability: The present invention does not rely on a specific frequency, so it can achieve wide-band microwave electric field measurement, covering a wide range of applications from low frequency to high frequency.

[0020] 4. Strong anti-interference ability: Due to the high sensitivity of Rydberg atoms to external fields, this invention can reduce the interference of conductive materials on the measurement and improve the measurement accuracy.

[0021] 5. Self-calibration ability: The Rydberg atom electrometer can be traced back to fundamental physical constants and can perform self-calibration using atomic parameters, reducing the complexity and uncertainty in the calibration process.

[0022] 6. Sub-wavelength electric field imaging: This invention can also measure the polarization direction of microwave electric fields and achieve sub-wavelength electric field imaging, providing a more refined measurement of the spatial distribution of microwave fields.

[0023] 7. System stability and repeatability: By means of regular calibration and digital signal processing, this invention improves the measurement accuracy and stability of the system and ensures the repeatability of measurement results.

[0024] 8. Flexibility and tunability: The pulse shape, modulation depth, and frequency of the periodic laser pulse train can be adjusted according to actual detection requirements, making this method highly flexible and adaptable. Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of the detection system in the present invention;

[0026] wherein, 1 - Atomic gas cell; 2 - Probe field laser; 3 - Coupling field laser; 4 - Microwave horn antenna; 5 - Signal generator; 6 - Photoelectric detector; 7 - Spectrum analyzer; 8 - Electro - optic modulator; 9 - First lens; 10 - Second lens; 11 - First half - wave plate; 12 - Second half - wave plate;

[0027] Figure 2 is the microwave field intensity Set to 0, and the probe field and the coupling field are detuned and Under the condition that both are 0, the imaginary part of the medium polarizability versus time Variation relationship curve graph;

[0028] Figure 3 For the microwave field intensity Set to 0, the coupling field is detuned Set to 0, the medium transmission spectrum versus the probe field detuning and time Variation relationship graph;

[0029] Figure 4 For the microwave field intensity Set to 0.5×2π MHz, the coupling field is detuned Set to 0, the medium transmission spectrum versus the probe field detuning and time Variation relationship graph;

[0030] Figure 5 is the linear relationship graph between the peak - to - peak spacing of the medium transmission enhancement spectrum and the microwave field intensity ;

[0031] Figure 6 is the relationship graph of the medium transmission spectrum T versus the probe field detuning variation; Specific implementation mode

[0032] The following further illustrates the specific implementation mode of the present invention in combination with specific embodiments:

[0033] Most of the detection fields and coupling fields selected by traditional Rydberg-atom-based atomic microwave electric field meters are continuous light or long-pulse lasers. For a three-level ladder atomic system, when the transition between two low energy levels (ground state and excited state) matches the frequency of the detection light, the atom will absorb the light and become opaque. When a strong coupling light field acts on the transition between the excited state and the Rydberg state, it will cause the electrons to transition back and forth between these two energy levels, forming a coherent state. This coherence effect makes the detection light that could originally be absorbed no longer absorbed, thus making the medium transparent to light of this frequency. This phenomenon is called electromagnetically induced transparency (EIT). Traditional atomic microwave electric field meters achieve precise measurement of microwave electric fields based on the EIT phenomenon.

[0034] In the present invention, a pulsed laser chain with adjustable pulse width, spacing between two adjacent pulses, and pulse shape, etc., is used as the coupling field. When the coupling field is turned off, some of the particles in the ground state are excited to the excited state through single-photon resonant transition . When the strong coupling field is turned on, it couples the excited state and the Rydberg state , and generates two new dressed states. At this time, the particles in the ground state will no longer transition to the excited state, but , the particles on the energy levels will return to the ground state due to the sideband effect. The sideband radiation light coherently enhances with the detection field, generating a transmission enhancement spectrum without population inversion. The present invention utilizes this enhanced transmission spectrum to achieve quantum precise detection of microwave electric fields. A microwave precision detection method based on the transmission enhancement spectrum without population inversion includes the following steps:

[0035] Step 1: Build a detection system. As shown in Figure 1 , the detection system includes an atomic gas cell 1, a frequency-stabilized laser system, a microwave horn antenna 4, a signal generator 5, a photodetector 6, a spectrum analyzer 7, an electro-optic modulator 8, two lenses, and a half-wave plate. The frequency-stabilized laser system includes a detection field laser 2 and a coupling field laser 3; these components together constitute the experimental platform of the present invention for achieving precise detection of microwave electric fields;

[0036] Step 2: The output end of the detection field laser 2 is connected to the electro-optic modulator 8 through an optical fiber, and the output end of the coupling field laser 3 is connected to the signal generator 5 through an optical fiber. The detection light and the coupling light pass through the atomic gas cell 1 in opposite directions to form a detection field and a coupling field. The microwave horn antenna 4 is used to generate the microwave field to be measured;

[0037] Step 3: Modulate the probe field detuning through the electro-optic modulator 8, and use the photodetector 6 and the spectrum analyzer 7 to detect the probe field transmission spectrum; this step is the key to realizing the precise detection of the microwave electric field. By adjusting the detuning amount, the detection effect of the probe light transmission spectrum can be optimized;

[0038] Step 4: Utilize the linear relationship between the peak-to-peak spacing of the enhanced transmission spectrum of the probe field and the microwave electric field intensity to achieve the precise detection of the microwave field. This step reflects the core advantage of the present invention, that is, by precisely controlling the detuning amount, high-precision measurement of the microwave electric field intensity can be achieved.

[0039] The physical mechanism of this microwave quantum precise detection method is the enhanced transmission spectrum without population inversion caused by the coherence of the sideband radiation field and the probe field, and this mechanism is different from the traditional Rydberg atom electric field meter.

[0040] Specifically, in the detection system, the photodetector and the spectrum analyzer are used as detection tools, and other detection tools such as oscilloscopes and single-photon detectors can also be selected; in actual use, the detection system is calibrated regularly to maintain the measurement accuracy and stability of the system.

[0041] Specifically, in Step 2, the probe light emitted by the probe field laser 2 passes through the electro-optic modulator 8, the first lens 9, the first half-wave plate 11, the atomic gas cell 1, the second lens 10 in sequence and then is input to the photodetector 6. After the photodetector 6 performs photoelectric conversion, it is input to the spectrum analyzer 7; the coupling light emitted by the coupling field laser 3 passes through the signal generator 5 and the second half-wave plate 12, the second lens 10, the atomic gas cell 1, the first half-wave plate 11 and the first lens 9.

[0042] Specifically, the lasers output by the probe field laser 2 and the coupling field laser 3 are both continuous light, with wavelengths of 480 nm and 780 nm respectively. The continuous coupling light is modulated by the signal generator 5 into a periodic laser pulse train, and its pulse waveform (such as Gaussian type, step type, etc.), single-pulse height, full width at half maximum, and the distance between two adjacent pulses and other parameters are adjustable. This modulation method provides the necessary time structure for subsequent detection.

[0043] Specifically, the atomic gas cell is used to provide the detection medium for the microwave electric field to be measured, in the atomic gas cell 1 87 the Rb atoms adopt a four-level atom, where the states , , and represent respectively the , , and Four energy levels, the energy level is adjusted according to the frequency of the microwave field to be measured. The probe light and the coupling light pass through the atomic gas cell in opposite directions, while the microwave generated by the horn antenna passes through the atomic gas cell perpendicular to the optical path. The probe field is coupled to the states and , the coupling field is coupled to the states and , and the microwave field is coupled to the states and . The detunings ( , and ) and intensities ( , and ) of the probe field, coupling field, and microwave field are all characterized. Under such conditions, the atomic medium polarizability can be expressed as:

[0044]

[0045] In the above formula, is the atomic density, is the vacuum permittivity, , and , where represents the spontaneous decay rate of the atomic state. Under such conditions, the atomic medium transmission spectrum function can be expressed as:

[0046]

[0047] where, is the frequency of the probe field, is the length of the atomic gas cell, is the imaginary part of the medium polarizability, is the speed of light in free space.

[0048] In the simulation of this embodiment, the intensity of the probe field is set to , and the intensity of the coupling light changes with time and is given by , where represents the amplitude of the coupled pulsed light, and is the duration of a single pulse. For the atomic gas cell, its spatial length is set to , and the decay rates of the , , energy levels of the atoms are respectively set to , , . The simulation results reveal the following phenomena:

[0049] When the microwave field is turned off: In the case where the probe field and the coupling field are in resonance (i.e., ), the imaginary part of the dielectric susceptibility evolves periodically with time to show negative values, as shown in Figure 2 , which indicates that negative absorption of the probe field can be observed within a specific time period. The corresponding enhanced transmission spectrum distribution of the atomic medium is as shown in Figure 3 . It can be clearly seen from the figure that when the probe field is in resonance (i.e., ), a periodically enhanced transmission spectrum without population inversion appears.

[0050] When the microwave field is turned on: When the microwave field acts between two Rydberg energy levels of the atom, it will cause the corresponding Rydberg energy levels to undergo Autler - Townes (A - T) splitting. This A - T splitting phenomenon of the energy levels will induce the splitting of the enhanced transmission spectrum without population inversion at the resonance excitation of the probe field. Specifically, as shown in Figure 4 , when the microwave field intensity is set to and the coupling field detuning is 0, the originally enhanced transmission spectrum at the resonance excitation of the probe field splits into two transmission spectra, and the peak - to - peak spacing of these two transmission spectra is both 0.5×2π MHz. By changing the intensity of the microwave field, it can be observed that there is a proportional relationship between the peak - to - peak spacing of the two enhanced transmission spectra without population inversion and the microwave field intensity, as shown in Figure 5 . This figure not only intuitively presents the direct connection between the two, but also provides a theoretical basis for the quantum precision detection of microwave electric fields using this linear relationship. By accurately measuring the peak - to - peak spacing of the medium transmission spectrum, the intensity of the microwave field can be accurately deduced, thereby realizing high - precision quantum detection of the microwave electric field intensity.

[0051] Further simulation results show that under the condition that the microwave field intensity is set to 0.5×2π MHz and the coupling field detuning is 0, as shown in Figure 6 , the full width at half maximum of the enhanced transmission spectrum in this scheme is significantly reduced compared to the transmission spectrum's full width at half maximum in the traditional Rydberg - atom - based microwave detection scheme under the same conditions (replacing the coupling field with continuous light and keeping the maximum amplitude unchanged), and is only 1 / 3 of the latter. Under the same conditions, that is, when the coupling field is replaced with continuous light and the maximum amplitude is kept unchanged, the present invention can significantly improve the accuracy and sensitivity of microwave quantum precision detection. This improvement not only enhances the measurement accuracy but also broadens the application prospects of microwave quantum precision detection technology.

[0052] In Step 4, the linear relationship is obtained through pre-calibration to ensure the measurement accuracy of the microwave electric field intensity. The linear relationship between the peak-to-peak spacing of two electromagnetically induced transparency enhanced spectra and the microwave electric field intensity is expressed as: , where is the peak-to-peak spacing of the medium transmission enhancement spectrum, is the proportionality coefficient, is the intensity of the microwave field to be measured.

[0053] In summary, in this embodiment, by precisely controlling the intensities and temporal characteristics of the probe field and the coupling field, and by utilizing the characteristics of Rydberg atoms, high-sensitivity and high-precision detection of the microwave electric field are achieved, demonstrating the significant advantages of the present invention in the field of microwave quantum precision measurement.

[0054] Certainly, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A microwave precision detection method based on non-particle population inversion transmission enhancement spectroscopy, characterized in that: The following steps are involved: Step 1: Build a detection system, which includes An atomic gas chamber, a frequency-stabilized laser system, a microwave horn antenna, a signal generator, a photodetector, a spectrum analyzer, an electro-optic modulator, two lenses and a half-wave plate, wherein the frequency-stabilized laser system includes a detection field laser and a coupling field laser; Step 2: The output end of the detection field laser is connected to the electro-optic modulator through an optical fiber, and the output end of the coupling field laser is connected to the signal generator through an optical fiber. The detection light and the coupling light are The atoms pass through the gas chamber in opposite directions to form a detection field and a coupling field. The microwave horn antenna is used to generate the microwave field to be measured; Step 3: modulate the detection field detuning by an electro-optic modulator, and detect the detection field transmission spectrum by using a photodetector and a spectrum analyzer; Step 4: Use the linear relationship between the peak-to-peak spacing of the detection field enhancement transmission spectrum and the microwave electric field intensity to achieve precise detection of the microwave field.

2. The microwave precision detection method based on non-particle population inversion transmission enhancement spectroscopy according to claim 1 is characterized in that: In the step 2, the detection light emitted by the detection field laser passes through the electro-optic modulator, the first lens, the first half-wave plate, The coupled light emitted by the coupled field laser passes through the signal generator and the second half-wave plate, the second lens, Atomic gas cell, first half-wave plate and first lens.

3. The microwave precision detection method based on non-particle population inversion transmission enhancement spectroscopy according to claim 2 is characterized in that: The lasers output by the detection field laser and the coupling field laser are both continuous light with wavelengths of 480 nm and 780 nm respectively. The continuous coupling light is modulated into a periodic laser pulse chain by a signal generator, and its pulse waveform, single pulse height and half-maximum full width, and the distance between two adjacent pulses are all adjustable.

4. The microwave precision detection method based on non-particle population inversion transmission enhancement spectroscopy according to claim 3 is characterized in that: The microwaves generated by the horn antenna pass through the Atomic gas chamber, detecting fields and states , Phase coupling, coupled field and state , Phase coupling, microwave field and state , Phase coupling.

5. The microwave precision detection method based on non-particle population inversion transmission enhancement spectroscopy according to claim 4 is characterized in that: In the step 4, the linear relationship between the peak-to-peak spacing of the detection field enhanced transmission spectrum and the microwave electric field intensity is obtained by pre-calibration, thereby realizing the detection of the microwave electric field intensity.

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