Efficient information extraction method based on Rydberg atom low-frequency detection and measurement system thereof

Abstract

The invention discloses an efficient information extraction method based on Rydberg atom low-frequency detection and a measurement system thereof, and the extraction method is based on the avoidance of background noise by a coherent detection technology, converts the modulation of a low-frequency electromagnetic field into quantum coherent phase change by using Rydberg atoms, and adopts the means of homodyne detection and heterodyne detection. The amplitude information and the phase information of the low-frequency electromagnetic field are accurately extracted, and the measurement sensitivity of the weak low-frequency electromagnetic field is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-frequency electromagnetic field measurement, and particularly relates to an efficient information extraction method and a measurement system for low-frequency detection based on Rydberg atoms. This method utilizes the quantum coherence effect of Rydberg atoms, combines homodyne detection and heterodyne detection, converts the modulation of the low-frequency electromagnetic field into the phase change of the optical field, and extracts the amplitude and phase information of the low-frequency electromagnetic field through coherent detection technology. It is particularly suitable for high-sensitivity measurement of weak low-frequency electromagnetic fields. Background Art

[0002] Rydberg atoms have been widely used in the precise measurement of microwave electric fields due to their extremely high sensitivity to microwave electric fields with frequency matching. Traditional electric field measurement methods usually measure the electromagnetically induced transparency (EIT)-Autler-Townes (AT) splitting and quantify this splitting as the amplitude of the electric field. This method relies on high-frequency electric fields to couple two Rydberg energy levels. So far, the electric field frequencies corresponding to the available Rydberg energy level spacings are in the MHz to GHz range. If this scheme is to be applied to the low-frequency band, the principal quantum numbers of the Rydberg energy levels required are extremely large, far exceeding the current technical level. In the initial scheme for intensity detection using EIT-AT splitting, the electric field is measured by measuring the splitting of the EIT peak in the intensity signal. The measurement accuracy of this method is limited by the broadening of the EIT peak, and in the case of weak electric fields, the measurement becomes a tiny change at the top of the EIT peak, which greatly limits the electric field measurement sensitivity of this scheme.

[0003] To address this deficiency, in recent years, new methods such as magnetic field modulation (referenced patent CN111308228A), coupling light modulation, and superheterodyne have been developed, which use modulation and demodulation methods to convert the original intensity detection into phase detection to improve the detection sensitivity of high-frequency electric fields. However, the above-mentioned schemes still rely on the EIT-AT effect and cannot fundamentally solve the technical bottleneck of low-frequency electric field measurement. In addition, these methods still face problems such as low signal-to-noise ratio and complex operation in the low-frequency band.

[0004] To further improve the efficiency and accuracy of low-frequency electric field measurement based on Rydberg atoms, the present invention proposes a phase detection scheme based on double modulation and demodulation on the basis of heterodyne detection. Different from the traditional measurement method relying on EIT-AT splitting, this scheme directly observes the modulation effect of the external field on the EIT peak, and efficiently extracts the accurate information of the low-frequency electromagnetic field through phase demodulation. Compared with the previous patent CN118465644A, the present invention improves the detection end, focusing on optimizing the optical path design of the phase detection scheme. On the one hand, it breaks through the problem of low intensity detection slope, and on the other hand, the double modulation and demodulation avoid the problem of phase locking required by traditional homodyne detection and heterodyne detection. This technical path effectively overcomes the problem of insufficient measurement sensitivity in the low-frequency band, significantly improves the detection sensitivity, and expands the applicability of the measurement technology. Summary of the Invention

[0005] The object of the present invention is to propose an efficient information extraction method and its measurement system for low-frequency electric field detection based on Rydberg atoms, and through the extraction of specific frequency components, realize the efficient information processing of the electromagnetically induced transparency (EIT) spectrum modulated by the electromagnetic field. When a low-frequency electromagnetic field is applied to the atomic gas cell, the intensity and phase of the signal light passing through the atomic gas cell will be modulated. The probe light is split before entering the atomic gas cell. The laser that does not pass through the atomic gas cell corresponds to the heterodyne detection scheme and the homodyne detection scheme respectively according to whether frequency shifting is performed. The local oscillator light that does not pass through the atomic gas cell is combined with the signal light passing through the gas cell, and a signal is obtained through a detector. For the detected signal, the in-phase signal and the quadrature signal are obtained through two mixing operations respectively, and they are converted into amplitude signals and phase signals through further data processing. This method can simultaneously obtain the amplitude and phase of the signal, so as to realize the complete description of the signal. For the obtained phase signal, further spectral analysis is performed on it, and the external field amplitude and phase information are extracted according to the phase signal. Through coherent detection technology, the present invention significantly avoids the interference of background noise and improves the sensitivity of electric field detection. At the same time, this method can realize the real-time extraction of signal changes, which not only improves the efficiency of low-frequency electric field detection, but also expands the application range of the Rydberg atom technology.

[0006] The technical solution of the present invention is as follows: According to the first aspect of the present invention, there is provided an efficient information extraction method for low-frequency detection based on Rydberg atoms, characterized by including: Providing a probe light and a coupling light, and frequency stabilizing the probe light frequency to the resonance frequency range of the atomic ground state energy level and the atomic excited state energy level respectively, and frequency stabilizing the coupling light frequency to the resonance frequency range of the atomic excited state energy level and the Rydberg energy level respectively; Make the probe light and the coupling light propagate in opposite directions collinearly in the atomic gas cell to generate a quantum coherence effect; Apply a DC bias field and the low-frequency alternating electromagnetic field to be measured to the atomic gas cell, and convert the electromagnetic field information into optical field phase information through Rydberg state modulation; Adopt homodyne detection or heterodyne detection, and extract the phase signal through coherent detection technology; Perform spectral analysis on the phase signal to obtain the amplitude and phase information of the low-frequency electromagnetic field.

[0007] Furthermore, the homodyne detection includes: Split the probe light into a signal light and a local oscillator light, and recombine the signal light with the local oscillator light after the signal light interacts with the atoms; Use a third laser to generate a phase-locked light, and stabilize the optical path phase through a Mach-Zehnder interferometer; Separate the in-phase signal and the quadrature signal through a polarization beam splitter prism; Collect the in-phase signal and the quadrature signal respectively through a balanced detector, and extract the electromagnetic field information through spectral analysis.

[0008] Furthermore, the heterodyne detection includes: Split the probe light into a signal light and a local oscillator light, and shift the frequency of the local oscillator light through an acousto-optic modulator; Recombine the signal light and the reference light with the local oscillator light respectively; Demodulate through a mixer to obtain two sets of in-phase signals and quadrature signals; Perform differential processing on the two sets of signals to extract the phase information.

[0009] Furthermore, the atomic gas cell contains alkali metal atoms or alkaline earth metal atoms.

[0010] Furthermore, for obtaining the amplitude and phase information of the low-frequency electromagnetic field based on homodyne detection, the formula is as follows: where and are the quadrature components of the two modulation and demodulation outputs respectively, is the photocurrent response coefficient of the detector, is the amplitude of the local oscillator optical vector, is the amplitude of the signal optical vector, is the total phase difference caused by the optical path difference during the process of splitting to recombining the light, is the phase change caused by the applied magnetic field on the interaction between light and atoms.

[0011] Further, based on heterodyne detection, the amplitude of the low-frequency electromagnetic field is obtained and the phase information , and the formula is as follows: Wherein, and are respectively the quadrature components of the outputs of two modulation and demodulation processes, is the photocurrent response coefficient of the detector, is the amplitude of the local oscillator optoelectronic vector, is the amplitude of the signal optoelectronic vector, is the amplitude of the reference signal, is the total phase difference caused by the optical path difference during the process of splitting light to combining light, is the phase difference between the reference signal and the output signal of the detector, is the phase change caused by the applied magnetic field on the interaction between light and atoms.

[0012] In a second aspect, the present invention also provides a measurement system for implementing the above method, characterized in that it includes: Laser module: at least including a probe light laser and a coupled light laser; Optical frequency stabilization module: used to lock the laser frequency to the atomic transition energy level; Atomic interaction module: including an atomic gas cell and an electromagnetic field application device; Coherent detection module: including a beam splitter, a beam combiner, an interferometer and a detector, wherein, for the homodyne detection scheme, it includes a Mach-Zehnder interferometer, and for the heterodyne detection scheme, it includes an acousto-optic modulator and a mixer; Signal processing module: used for signal demodulation and spectrum analysis.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) By adopting a phase detection scheme, wherein the phase change amount of the probe light field is proportional to the ratio of the amplitude of the alternating current field to its frequency. Compared with the traditional intensity detection scheme, phase detection can effectively amplify the response to the electromagnetic field in low-frequency detection, thereby significantly improving the detection sensitivity of the system, especially in the application of weak field and low-frequency bands.

[0014] 2) In the homodyne detection scheme, the feedback loop introduces a certain degree of operational complexity. However, by locking the interferometer arms with the reference light, the need for using complex radio frequency signals is avoided. In the heterodyne detection scheme, additional radio frequency signals are required for modulation and demodulation processing, but the operation of locking the interferometer is avoided. Each scheme has its own advantages. However, regardless of which scheme is used, through optimized design and processing, high-precision and stable processing of the phase signal can be achieved, thus ensuring the reliability of the detection system.

[0015] 3) Both the probe light and the coupling light are stably controlled through frequency locking operations. Coherently exciting the atoms to the Rydberg state effectively reduces the laser phase noise, which is beneficial for the subsequent extraction of signals. At the same time, combined with the use of the reference light, the interference of factors such as common-mode noise on the signal is effectively reduced. This design significantly improves the signal-to-noise ratio of the system, thereby enhancing the accuracy and stability of the detection.

[0016] 4) The adopted detection and data processing techniques can accurately and efficiently extract the amplitude and phase information related to the electric field from the modulated signal, which is beneficial for improving the detection sensitivity. Brief Description of the Drawings

[0017] Figure 1 is a schematic flow diagram of homodyne detection and heterodyne detection; Figure 2 is a schematic optical path diagram for phase extraction using the homodyne detection scheme; Figure 3 is a schematic optical path diagram for phase extraction using the heterodyne detection scheme; Figure 4 is a schematic energy level diagram for measuring low-frequency electromagnetic fields based on Rydberg atoms. Detailed Embodiments

[0018] The present invention will be further described below in conjunction with the embodiments and the drawings, but the protection scope of the present invention should not be limited thereby.

[0019] Please refer to Figure 1 , an efficient information extraction method for low-frequency electromagnetic fields of Rydberg atoms based on homodyne detection, including the following steps: Step 1. Frequency stabilization and beam splitting of the probe light: Use the first laser to emit the probe light. After frequency stabilization processing, the frequency of the probe light is locked to the resonance frequencies of the atomic ground state energy level and the excited state energy level , and is split into two beams by the first beam splitter. Among them, one beam is used as the local oscillator light for subsequent interference detection; the other beam is used as the signal light and enters the atomic gas cell through the first dichroic mirror to interact with the atoms; Step 2. Coupling light excitation and EIT spectrum observation: Use a second laser to emit coupling light, and after frequency stabilization processing, the frequency of the coupling light is locked to the resonance frequencies of the atomic excited state energy level and the Rydberg state energy level , and enter the atomic gas cell through reflection by a second dichroic mirror; Adjust the optical path to ensure that the signal light and the coupling light are anti-parallel and collinear and coincide in the atomic gas cell, and scan the frequency of the coupling light to observe the spectral signal generated by the quantum coherence effect.

[0020] Step 3: Phase-locked light stabilization interferometer: Use a third laser to emit phase-locked light. After frequency stabilization processing, the phase-locked light forms a Mach-Zehnder interferometer through a beam splitter. One beam of light enters the atomic gas cell and is combined with another reference light at the first beam splitter. A balanced detector is used to receive the differential signal and feedback it to the piezoelectric ceramic mirror to dynamically adjust the optical path difference and stabilize the interference phase; Step 4: Electric field application and signal extraction: Apply a DC bias field and a low-frequency alternating electromagnetic field to be measured to the atomic gas cell through parallel capacitor plates. The total electromagnetic field acts on the Rydberg state and causes energy level modulation. The signal light modulated by the atomic gas cell and the local oscillator light are combined through the first beam splitter. A polarization beam splitter prism is used to separate the in-phase signal and the quadrature signal, and they are detected by a balanced detector; Step 5: Data processing and information extraction: Perform data processing on the in-phase signal and the quadrature signal to convert them into amplitude signals and phase signals; the extracted signals contain the information of the quantum coherence effect spectrum line under the modulation of the electromagnetic field; Perform spectral analysis on the phase signal to extract the amplitude information and relative phase information at the frequency of the low-frequency electromagnetic field, and achieve accurate measurement and complete characterization of the low-frequency electromagnetic field.

[0021] For the signal light passing through the atomic gas cell in Step 1, its electric vector is , where is the signal intensity, is the optical frequency of the signal light, is the phase on the signal light, represents the imaginary number, and t represents time.

[0022] For the local oscillator light in Step 1, its electric vector is , and in the homodyne detection scheme, the local oscillator light frequency , is all the phase differences caused by the optical path difference during the splitting to combining process of the light.

[0023] The signal obtained by applying a low-frequency electromagnetic field to the atomic gas cell and performing beam combination in Step 4 is ; Among them, is the photocurrent response coefficient of the detector. Under the modulation of the low-frequency electromagnetic field, taking the application of a low-frequency electric field as an example, where is the amplitude of the applied low-frequency field, is the frequency of the low-frequency field, is the phase of the low-frequency field. The intensity and phase of the signal light will be modulated due to atomic interactions. Taking the EIT resonance as an example, the phase is proportional to the electric field, denoted as , where is the amplitude at the alternating current field frequency , is the alternating current field frequency at the relative phase.

[0024] Since the detector adopts an AC coupling mode, the actual output electrical signals finally obtained are respectively ; Among them, and represent the output electrical signals separated by the polarization beam splitter prism to two balanced probes, namely the in-phase signal and the quadrature signal.

[0025] The amplitude signal and the phase signal in the fifth step are respectively ; .

[0026] For the phase signal read the spectrum in the fifth step, the amplitude information at the low-frequency electromagnetic field frequency and the relative phase information can be extracted. Finally, through a calibration method, the corresponding relationship between the amplitude information and the phase information and the amplitude and phase of the electromagnetic field is established, so as to realize the efficient information reading of the low-frequency electromagnetic field based on Rydberg atoms.

[0027] According to the second aspect of the present invention, there is provided an efficient information extraction method for the low-frequency electromagnetic field of Rydberg atoms based on heterodyne detection, which is characterized by including the following steps: Step 1: Use a first laser to generate a probe light. After the probe light is frequency-stabilized, the frequency is fixed to the atomic ground state energy level and the excited state energy level Near the resonance frequency, the probe light is split by a first beam splitter. One of the split beams is frequency-shifted to serve as the local oscillator light in heterodyne detection, and the other beam is guided into the atomic gas cell through a first dichroic mirror as the signal light for interaction with atoms.

[0028] Step 2: Use a second laser to generate coupling light. After the coupling light is frequency-stabilized, its frequency is fixed to the resonance frequency of the atomic excited state energy level and the Rydberg state energy level Near the resonance frequency, the coupling light is guided into the atomic gas cell through a second dichroic mirror; adjust the optical path to ensure that the signal light and the coupling light are anti-parallel and collinear in the atomic gas cell; when scanning the frequency of the coupling light, the spectral signal generated by the quantum coherence effect can be observed.

[0029] Step 3: Use the first laser to split the reference light through a second beam splitting prism. After the reference light is frequency-stabilized, its frequency is exactly the same as that of the signal light. The reference light is guided into the atomic gas cell through the first dichroic mirror and adjusted to be parallel to the signal light. The reference light and the local oscillator light are combined through a second combiner to obtain the first set of in-phase signals and quadrature signals.

[0030] Step 4: Apply a DC bias field and the low-frequency AC electromagnetic field to be measured to the atomic gas cell. The total electromagnetic field acts on the Rydberg state and causes energy level modulation. The signal light passing through the atomic gas cell is combined with the local oscillator light through a first combiner to obtain the second set of in-phase signals and quadrature signals.

[0031] Step 5: Process the two sets of in-phase signals and quadrature signals obtained by combining the signal light and the reference light with the local oscillator light respectively, and convert them into amplitude signals and phase signals. Subtract the two sets of amplitude signals and phase signals to significantly improve the signal-to-noise ratio. At the same time, as the reference of the signal light, eliminate the influence of factors such as common-mode noise on the signal. The extracted signal contains the modulation information of the electromagnetic field on the quantum coherence effect spectrum line. Further perform spectral analysis on the phase signal to extract the amplitude and phase information of the low-frequency electromagnetic field.

[0032] For the signal light passing through the atomic gas cell in Step 1, its electric vector is where is the signal intensity, is the optical frequency of the signal light, is the phase on the signal light, represents the imaginary number, and t represents time.

[0033] For the local oscillator light in Step 1, its electric vector is In the heterodyne detection scheme, the local oscillator light frequency , is the difference frequency between the local oscillator light and the signal light, is all the phase differences caused by the optical path difference during the process of splitting light to combining light.

[0034] The signal obtained by applying a low-frequency electromagnetic field to the atomic gas cell and performing beam combination in Step 4 is where is the photocurrent response coefficient of the detector. After being modulated by the low-frequency electromagnetic field, taking the low-frequency electric field as an example, a low-frequency electric field is applied, where is the amplitude of the applied low-frequency field, is the frequency of the low-frequency field, is the phase of the low-frequency field. The intensity and phase of the signal light will be modulated due to atomic interactions. Taking the EIT resonance as an example, the phase is proportional to the electric field, denoted as where is the amplitude at the alternating current (AC) field frequency and is the relative phase at the AC field frequency .

[0035] Since the detector adopts an AC coupling mode, the actually output electrical signal is .

[0036] In Step 5, to ensure that the difference frequency signal is in a lower frequency range for easy resolution by the detector, the signal is subjected to modulation and demodulation processing. Specifically, the signal detected by the detector is mixed on two mixers with two sets of orthogonal reference signals and , where is the reference signal frequency, is the reference signal amplitude, is the reference signal phase. Further, the outputs of the mixers after low-pass filtering are respectively ; .

[0037] By further calculation, the corresponding amplitude signal and phase signal can be obtained. The formulas are as follows: ; .

[0038] In Step 5, by reading the spectrum of the phase signal , the amplitude information at the low-frequency electromagnetic field frequency and the relative phase information Finally, by calibration, the conversion relationships between the amplitude information and phase information and the amplitude and phase of the electromagnetic field are determined, realizing efficient information reading based on Rydberg low-frequency measurement.

[0039] Embodiment: Taking the example of using alkali metal or alkaline earth metal atoms, exciting them to the Rydberg state, and detecting low-frequency electromagnetic fields: Referring to Figure 2 , Figure 2 is a schematic optical path diagram for phase extraction by the homodyne detection scheme. As shown in the figure, it includes: The first laser 2-1, which generates the probe light, and its frequency is stabilized to the resonance frequencies of the atomic ground state energy level and the excited state energy level ; The second laser 2-12, which generates the coupling light, and its frequency is stabilized to the resonance frequencies of the excited state energy level and the Rydberg energy level ; The third laser 2-14, which generates the phase-locked light for stabilizing the interferometer optical path.

[0040] The atomic gas cell 2-5, filled with alkali metal atoms, is used to generate the Rydberg EIT effect; The parallel capacitor plates 2-6, which apply a DC bias electric field and the low-frequency AC electric field to be measured; The Mach-Zehnder interferometer: It is composed of the first beam-splitting prism 2-3, the second beam-splitting prism 2-11, the mirror 2-8, the mirror 2-21 with a piezoelectric ceramic, and the third balanced detector 2-20, and is used for phase locking.

[0041] The third polarization beam-splitting prism 2-16 and the fourth polarization beam-splitting prism 2-17 separate the in-phase signal (X) and the quadrature signal (Y), which are respectively collected by the first balanced detector 2-18 and the second balanced detector 2-19.

[0042] The frequency locking based on the ultra-stable cavity 2-15 can effectively reduce the linewidth of the used laser, improve the coherence of the Rydberg EIT and Autler-Townes and other quantum optical effects generated by the interaction of the two laser beams with atoms, and is beneficial to improving the signal-to-noise ratio of the final detection signal.

[0043] Combined with referring to Figure 4 , Figure 4 is the energy level schematic diagram of the Rydberg atom for detecting low-frequency electric fields in the present invention, which is applicable to various atoms including typical alkali metal atoms such as Rb, Cs, K, Na, and typical alkaline earth metal atoms such as Yb, Sr: As shown in the figure, the probe light 4-4 with a Rabi frequency of excites the atom from the ground state 4-1 to the excited state 4-2, the Rabi frequency is of the coupling light 4-5 to excite the atom from the excited state 4-2 to a specific Rydberg state 4-3, the response of the Rydberg state to the external electromagnetic field is shown in 4-7. When an external electromagnetic field 4-6 is applied to the atomic cell, the low-frequency electric field to be measured is converted from the Rydberg state to the low-frequency energy level oscillation 4-8.

[0044] Combined with Figure 1 As shown in the schematic flow chart of an efficient information extraction method based on Rydberg atom low-frequency detection of the present invention, Example 1 can be given in detail. Using 87 Rb atoms, which are excited to the Rydberg state as an example for illustration. The atomic transition frequency corresponding to its probe light 4-4 is 384.2346 THz, and the atomic transition frequency corresponding to its coupling light 4-5 is 312.3886 THz. It includes the following steps: Step 1, the first laser 2-1 uses a 780 nm laser as the probe light. The probe light is divided into two paths by the first polarization beam splitter prism 2-2. One path is input into the ultra-stable cavity 2-15 for frequency stabilization, and the frequency is fixed to the resonance frequencies of the atomic ground state energy level and the excited state energy level which is 384.2346 THz. The other path is split by the first beam splitter prism 2-3. One beam is used as the local oscillator light, and after passing through the mirror 2-21 with a piezoelectric ceramic and the 1 / 2 wave plate 2-9 in sequence, it is directly used for interference measurement; the other beam is used as the signal light, which is guided by the first dichroic mirror 2-4 into the atomic cell 2-5, interacts with the coupling light in a counter-propagating and collinear manner, excites the Rydberg state, and is transmitted by the second dichroic mirror 2-7.

[0045] Step 2, the second laser 2-12 uses a 480 nm laser as the coupling light. The coupling light is divided into two paths by the second polarization beam splitter prism 2-13. One path is input into the ultra-stable cavity 2-15 for frequency stabilization, and the frequency is fixed to the resonance frequency of the atomic excited state energy level Rydberg energy level which is 312.3886 THz, ensuring the high coherence of the Rydberg EIT effect generated by the interaction of the two laser beams with the atoms. The other path is reflected by the second dichroic mirror 2-7 into the atomic cell 2-5 and is reflected by the first dichroic mirror 2-4. Adjust the optical path so that the signal light and the coupling light coincide in a counter-propagating and collinear manner within the atomic cell 2-5, and the atoms can be excited to On the Rydberg energy level, the EIT effect is formed. By scanning the frequency of the coupling light, the Rydberg EIT spectral line can be observed.

[0046] Step 3: The third laser 2-14 uses 795 nm as the reference light. After frequency stabilization, through the Mach-Zehnder interferometer composed of the second beam splitter prism 2-11 and the first beam splitter prism 2-3, the interference arms are locked. After the reference light is split by the second beam splitter prism 2-11, one beam passes through the mirror 2-8, the second dichroic mirror 2-7, enters the atomic gas cell 2-5, and then passes through the first dichroic mirror 2-4. At the first beam splitter prism 2-3, it is combined with the other beam of light passing through the mirror 2-21 with a piezoelectric ceramic. The generated differential signal is received by the third balanced detector 2-20 and fed back to the piezoelectric ceramic on the mirror 2-21 with a piezoelectric ceramic to achieve phase stability between the two arms of the interferometer. This reference light completely coincides with the signal light in Step 1.

[0047] Step 4: Apply a DC bias electric field and the low-frequency AC electric field to be measured to the atomic gas cell 2-5 through the parallel capacitor plates 2-6. The total electric field acts on the Rydberg state and causes energy level modulation. Combine the signal light and the local oscillator light in Step 1 at the second beam splitter prism 2-11. Use mirrors, the third polarization beam splitter prism 2-16, and the fourth polarization beam splitter prism 2-17 to generate in-phase signals and collect them by the first balanced detector 2-18, and collect orthogonal signals by the second balanced detector.

[0048] Step 5: Further process the combined in-phase signals and orthogonal signals, and convert them into amplitude signals and phase signals. The extracted signals contain information on the quantum coherence effect spectral line under the modulation of the electromagnetic field. By performing spectral analysis on the phase signals, the amplitude and phase information of the low-frequency electromagnetic field can be further extracted to achieve accurate measurement and complete characterization of the low-frequency electromagnetic field.

[0049] The optical electric vector of the signal light passing through the atomic gas cell in Step 1 is: In the formula, is the signal light intensity, is the optical frequency of the signal light, is the phase of the signal light.

[0050] The optical electric vector of the local oscillator light is: In the formula, is the local oscillator light intensity, is the optical frequency of the local oscillator light, , It is the local oscillator light phase, which is all the phase differences caused by the optical path difference during the process of splitting light to combining light.

[0051] In step four, a low-frequency electromagnetic field is applied to the atomic gas cell and beam combination is performed. The signal after beam combination is In the formula, is the photocurrent response coefficient of the detector.

[0052] Under the modulation of the low-frequency electric field, taking the application of the low-frequency electric field as an example, the intensity and phase of the signal light will be modulated due to atomic interaction. Taking the EIT resonance as an example, the phase is proportional to the electric field, denoted as .

[0053] Since the detector adopts the AC coupling mode, the actual output electrical signals finally obtained are respectively Calculate the amplitude and the phase , and the formula is as follows: ; .

[0054] Perform spectrum analysis on the phase to extract the amplitude information at the frequency of the low-frequency electromagnetic field and the phase information . Finally, through the calibration method, the corresponding relationship between the amplitude information and the phase information and the amplitude and phase of the electromagnetic field is established, so as to realize the efficient information reading of the low-frequency electromagnetic field based on Rydberg atoms.

[0055] Refer to Figure 3 , Figure 3 is a schematic optical path diagram for phase extraction using the heterodyne detection scheme. As shown in the figure, it includes the first laser 2-1, the second laser 2-12, the first polarization beam splitter prism 2-2, the second polarization beam splitter prism 2-13, the ultra-stable cavity 2-15, the first beam splitter prism 2-3, the second beam splitter prism 3-4, the first dichroic mirror 2-4, the atomic gas cell 2-5, the parallel capacitor plates 2-6, the second dichroic mirror 2-7, the acousto-optic modulator 3-9, the third beam splitter prism 3-10, the fourth beam splitter prism 3-11, the fifth beam splitter prism 3-16, the first balanced detector 3-12, the first mixer 3-19, the second mixer 3-20, the second balanced detector 3-17, the third mixer 3-21, the fourth mixer 3-22, and the radio frequency source 3-18. Combined with Figure 1The schematic flow chart of an efficient information extraction method based on Rydberg atom low-frequency detection according to the present invention can give Embodiment 1 in detail. Taking 87 Rb atoms as an example, which are excited to the Rydberg state for illustration. The atomic transition frequency corresponding to the probe light 4-4 is 384.2346 THz, and the atomic transition frequency corresponding to the coupling light 4-5 is 312.3886 THz. The method includes the following steps: Step 1: The first laser 2-1 uses a 780 nm laser as the probe light, which is split by the first polarization beam splitter prism 2-2. One beam is input into the ultra-stable cavity 2-15 for frequency stabilization, and the frequency is fixed to the resonance frequencies of the atomic ground state energy level and the excited state energy level , with a frequency of 384.2346 THz. The probe light is split by the first beam splitter prism 2-3. One path passes through the acousto-optic modulator 3-9 as the local oscillator light, and the radio frequency signal of the acousto-optic modulator through which the local oscillator light is frequency-shifted is provided by the radio frequency source 3-18. The other beam of light is guided into the atomic cell 2-5 through the first dichroic mirror 2-4 as the signal light.

[0056] Step 2: The second laser 2-12 uses a 480 nm laser as the coupling light, which is split by the second polarization beam splitter prism 2-13. One beam is input into the ultra-stable cavity 2-15 for frequency stabilization, and the frequency is fixed to the resonance frequency of the atomic excited state energy level Rydberg energy level , with a frequency of 312.3886 THz, to ensure the high coherence of the Rydberg EIT effect generated by the interaction of the two laser beams with the atoms. The signal light is transmitted into the atomic cell 2-5 through the first dichroic mirror 2-4 and is transmitted by the second dichroic mirror 2-7; the coupling light is reflected into the atomic cell 2-5 through the second dichroic mirror 2-7 and is reflected by the first dichroic mirror 2-4; the optical path is adjusted so that the signal light and the coupling light are reversely collinear and coincide inside the atomic cell 2-5, and the atoms can be excited to the Rydberg energy level; by scanning the frequency of the coupling light, the Rydberg EIT spectrum can be observed.

[0057] Step 3: Using the first laser, the reference light is obtained by splitting the beam through the second beam splitter prism 3-4. After the reference light undergoes frequency stabilization processing, its frequency is exactly the same as that of the signal light. The reference light is guided into the atomic gas cell through the first dichroic mirror 2-4, and is adjusted to be parallel to the signal light. The reference light and the local oscillator light are combined by the third beam splitter prism 3-11, and the signal is detected by the first balanced detector 3-12. Two reference signals with frequencies consistent with the driving radio frequency signal of the acousto-optic modulator and orthogonal to each other are generated by the radio frequency source 3-18, and are mixed with the combined signal in the first mixer 3-19 and the second mixer 3-20 respectively to obtain the first group of in-phase signals and the first quadrature signal 3-24.

[0058] Step 4: A DC bias electric field and the low-frequency AC electric field to be measured are applied to the atomic gas cell 2-5 through the parallel capacitor plates 2-6. The total electric field acts on the Rydberg state and causes energy level modulation. The local oscillator light is split by the third beam splitter prism 3-10 and combined with the signal light at the fifth beam splitter prism 3-16. The signal is detected by the second balanced detector 3-17. Two reference signals with frequencies consistent with the driving radio frequency signal of the acousto-optic modulator and orthogonal to each other are generated by the radio frequency source 3-18, and are mixed with the combined signal in the third mixer 3-21 and the fourth mixer 3-22 respectively to obtain the second group of in-phase signals and the second quadrature signal 3-23.

[0059] Step 5: The two groups of in-phase signals and the first and second quadrature signals obtained by combining the signal light and the reference light with the local oscillator light respectively are processed and converted into amplitude signals and phase signals. The two groups of amplitude signals and phase signals are subtracted to significantly improve the signal-to-noise ratio. At the same time, as the reference of the signal light, the influence of factors such as common-mode noise on the signal is eliminated. The extracted signal contains the modulation information of the electromagnetic field on the quantum coherence effect spectrum line. Further spectral analysis of the phase signal can extract the amplitude and phase information of the low-frequency electromagnetic field.

[0060] For the signal light passing through the atomic gas cell in Step 1, its electric vector is , where is the signal intensity, is the optical frequency of the signal light, is the phase on the signal light.

[0061] For the local oscillator light in Step 1, its electric vector is , in the heterodyne detection scheme , is all the phase differences caused by the optical path difference during the process of splitting to combining the light.

[0062] The signal obtained by applying the low-frequency electromagnetic field to the atomic gas cell and performing beam combination in Step 4 is where, is the photocurrent response coefficient of the detector. After being modulated by a low-frequency electromagnetic field, taking the low-frequency electric field as an example, a low-frequency electric field is applied After that, the signal light intensity and phase will be modulated due to atomic interactions. Taking the EIT resonance as an example, the phase is proportional to the electric field, denoted as Since the detector adopts an AC coupling mode, the actually output electrical signal is In step five, to ensure that the difference frequency signal is in a relatively low frequency range, facilitating the detector to distinguish, the signal is subjected to modulation and demodulation processing. Specifically, the signal detected by the detector On the mixer, is mixed with two sets of orthogonal reference signals and where is the reference signal frequency. Further, the outputs of the mixer after low-pass filtering are respectively ; and By further calculation, the corresponding amplitude signal and phase signal can be obtained. The formulas are as follows: In step five, for the phase signal Reading the spectrum, the amplitude information at the low-frequency electromagnetic field frequency and the relative phase information can be extracted. Finally, by calibration, the conversion relationships between the amplitude information and phase information and the amplitude and phase of the electromagnetic field are determined, realizing efficient information reading based on Rydberg low-frequency measurement.

[0063] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An efficient information extraction method based on low-frequency detection of Rydberg atoms, characterized in that: include: Provides detection light and coupling light, and stabilizes the detection light frequency to the atomic ground state energy level and atomic excited state energy levels The frequency of the coupled light is stabilized to the atomic excited state energy level within the resonant frequency range. and Rydberg levels Within the resonant frequency range; The detection light and the coupling light are made to propagate in opposite directions and collinearly in the atomic gas chamber, producing a quantum coherence effect; Apply a DC bias field and a low-frequency AC electromagnetic field to be measured to the atomic gas chamber, and convert the electromagnetic field information into optical field phase information through Rydberg state modulation; Use homodyne detection or heterodyne detection to extract phase signals through coherent detection technology; Perform spectrum analysis on the phase signal to obtain the amplitude and phase information of the low-frequency electromagnetic field.

2. The efficient information extraction method based on Rydberg atom low-frequency detection according to claim 1 is characterized in that: The homodyne detection comprises: Splitting the detection light into signal light and local oscillator light, wherein the signal light interacts with the atoms and then combines with the local oscillator light; A third laser is used to generate phase-locked light, and the phase of the optical path is stabilized by a Mach-Zehnder interferometer; Separate the in-phase signal and the orthogonal signal by a polarization beam splitter; The in-phase signal and the orthogonal signal are collected respectively by a balanced detector, and the electromagnetic field information is extracted by spectrum analysis.

3. The efficient information extraction method based on Rydberg atom low-frequency detection according to claim 1 is characterized in that: The heterodyne detection comprises: Splitting the detection light into signal light and local oscillator light, wherein the local oscillator light is frequency-shifted by an acousto-optic modulator; Combine the signal light and the reference light with the local oscillator light respectively; Through mixer demodulation, two sets of in-phase signals and orthogonal signals are obtained; The two sets of signals are differentially processed to extract phase information.

4. The efficient information extraction method based on low-frequency detection of Rydberg atoms according to any one of claims 1 to 3, characterized in that: The atomic gas cell contains alkali metal atoms or alkaline earth metal atoms.

5. The efficient information extraction method based on Rydberg atom low-frequency detection according to any one of claims 1 to 3, characterized in that: Obtaining the amplitude of low-frequency electromagnetic field based on homodyne detection and phase information , the formula is as follows: in, and are the orthogonal components of the two modulation and demodulation outputs, is the photocurrent response coefficient of the detector, is the local oscillator photoelectric vector amplitude, is the signal photoelectric vector amplitude, It is the total phase difference caused by the optical path difference in the process of light splitting and light combining. The phase change caused by the interaction between light and atoms due to the application of a magnetic field.

6. The efficient information extraction method based on low-frequency detection of Rydberg atoms according to any one of claims 1 to 3, characterized in that: Acquisition of low frequency electromagnetic field amplitude based on heterodyne detection and phase information , the formula is as follows: in, and are the orthogonal components of the two modulation and demodulation outputs, is the photocurrent response coefficient of the detector, is the local oscillator photoelectric vector amplitude, is the signal photoelectric vector amplitude, is the reference signal amplitude, It is the total phase difference caused by the optical path difference in the process of light splitting and light combining. is the phase difference between the reference signal and the detector output signal, The phase change caused by the interaction between light and atoms due to the application of a magnetic field.

7. A measurement system for implementing the method according to any one of claims 1 to 4, characterized in that: include: Laser module: at least includes a detection light laser and a coupling light laser; Optical frequency stabilization module: used to lock the laser frequency at the atomic transition energy level; Atomic interaction module: including atomic gas chamber and electromagnetic field application device; Coherent detection module: includes a beam splitter, a beam combiner, an interferometer and a detector. For homodyne detection, it includes a Mach-Zehnder interferometer, and for heterodyne detection, it includes an acousto-optic modulator and a mixer. Signal processing module: used for signal demodulation and spectrum analysis.

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