An efficient information extraction method and measurement system based on low-frequency detection of Rydberg atoms

Abstract

A high-efficiency information extraction method and measurement system based on Rydberg atom low-frequency detection. This extraction method is based on the avoidance of background noise by coherent detection technology, uses Rydberg atoms to convert the modulation of low-frequency electromagnetic fields into quantum coherent phase changes, and adopts homodyne detection and heterodyne detection to accurately extract the amplitude and phase information of the low-frequency electromagnetic field, significantly improving the measurement sensitivity of weak low-frequency electromagnetic fields.

Description

Technical Field

[0001] This invention belongs to the field of low-frequency electromagnetic field measurement technology, specifically a highly efficient information extraction method and measurement system based on low-frequency detection of Rydberg atoms. This method utilizes the quantum coherence effect of Rydberg atoms, combined with homodyne and heterodyne detection, to convert the modulation of the low-frequency electromagnetic field into phase variations in the optical field. Through coherent detection technology, the amplitude and phase information of the low-frequency electromagnetic field are extracted. This method is particularly suitable for high-sensitivity measurement of weak low-frequency electromagnetic fields. Background Art

[0002] Rydberg atoms, due to their exceptional sensitivity to frequency-matched microwave electric fields, have been widely used for precision microwave electric field measurements. Conventional electric field measurement methods typically measure the electromagnetically induced transparency (EIT)-Autler-Townes (AT) splitting, quantifying this splitting as the magnitude of the electric field. This method relies on coupling two Rydberg energy levels via a high-frequency electric field. To date, the available electric field frequencies for the Rydberg energy level spacings have been in the MHz to GHz range. Application of this approach to lower frequencies requires an extremely large principal quantum number of Rydberg energy levels, far exceeding current technological capabilities. Initial approaches to utilizing EIT-AT splitting for intensity detection measured the splitting of the EIT peak in the intensity signal. This method's accuracy is limited by the broadening of the EIT peak. Furthermore, in weak electric fields, the measurement results in small variations at the EIT peak's top, significantly limiting the sensitivity of this approach.

[0003] To address this shortcoming, recent developments have leveraged modulation and demodulation techniques, such as magnetic field modulation (cited in patent CN111308228A), coupled optical modulation, and superheterodyne technology. These methods transform intensity detection into phase detection, improving sensitivity for high-frequency electric fields. However, these approaches still rely on the EIT-AT effect and fail to fundamentally address the technical bottleneck of low-frequency electric field measurement. Furthermore, these methods still face challenges in low signal-to-noise ratio and complex operation at low frequencies.

[0004] In order to further improve the efficiency and accuracy of low-frequency electric field measurements based on Rydberg atoms, the present invention proposes a phase detection scheme based on dual modulation and demodulation on the basis of heterodyne detection. Unlike the traditional measurement method that relies on EIT-AT splitting, this scheme directly observes the modulation effect of the external field on the EIT peak, and efficiently extracts the precise information of the low-frequency electromagnetic field through phase demodulation. Compared with the previous patent CN118465644A, the present invention makes improvements at the detection end, focusing on optimizing the optical path design of the phase detection scheme. On the one hand, it solves the problem of low intensity detection slope. On the other hand, the dual modulation and demodulation avoids the problem of phase locking required for traditional zero-difference detection and heterodyne detection. This technical path effectively overcomes the problem of insufficient measurement sensitivity in the low-frequency band, and while significantly improving the detection sensitivity, it expands the applicability of the measurement technology. Summary of the Invention

[0005] The present invention aims to provide an efficient information extraction method and measurement system based on low-frequency electric field detection of Rydberg atoms. By extracting specific frequency components, this method enables efficient information processing of electromagnetically induced transparency (EIT) spectroscopy modulated by electromagnetic fields. When a low-frequency electromagnetic field is applied to an atomic gas cell, the intensity and phase of the signal light passing through the cell are modulated. The probe light is split before entering the cell. The laser light that does not pass through the cell is used for heterodyne or homodyne detection, depending on whether or not it undergoes frequency shifting. The local oscillator light that does not pass through the cell is combined with the signal light that does pass through the cell, and the signal is obtained by a detector. The detected signal is mixed twice to obtain an in-phase signal and a quadrature signal, respectively. Further data processing converts these signals into amplitude and phase signals. This method simultaneously obtains both the amplitude and phase of the signal, thus achieving a complete description of the signal. The obtained phase signal is further spectrally analyzed to extract the external field amplitude and phase information. By utilizing coherent detection technology, the present invention significantly mitigates background noise interference and improves the sensitivity of electric field detection. At the same time, this method can realize real-time extraction of signal changes, which not only improves the efficiency of low-frequency electric field detection, but also expands the application scope of Rydberg atom technology.

[0006] The technical solutions of the present invention are as follows:

[0007] According to a first aspect of the present invention, there is provided an efficient information extraction method based on low-frequency detection of Rydberg atoms, which is characterized by comprising:

[0008] Provides probe light and coupling light, and stabilizes the probe 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 resonance frequency range. and Rydberg levels within the resonant frequency range;

[0009] 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;

[0010] Apply a DC bias field and a low-frequency AC 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;

[0011] Using homodyne detection or heterodyne detection, the phase signal is extracted through coherent detection technology;

[0012] Perform spectrum analysis on the phase signal to obtain the amplitude and phase information of the low-frequency electromagnetic field.

[0013] Furthermore, the homodyne detection includes:

[0014] Splitting the probe light into signal light and local oscillator light, wherein the signal light interacts with the atoms and then combines with the local oscillator light;

[0015] A third laser is used to generate phase-locked light, and the optical path phase is stabilized by a Mach-Zehnder interferometer.

[0016] Separate the in-phase signal and the orthogonal signal through a polarization beam splitter;

[0017] The in-phase signal and the orthogonal signal are collected separately by a balanced detector, and the electromagnetic field information is extracted through spectrum analysis.

[0018] Furthermore, the heterodyne detection includes:

[0019] Splitting the probe light into signal light and local oscillator light, wherein the local oscillator light is frequency-shifted by an acousto-optic modulator;

[0020] Combine the signal light and the reference light with the local oscillator light respectively;

[0021] Through mixer demodulation, two sets of in-phase signals and orthogonal signals are obtained;

[0022] The two sets of signals are differentially processed to extract phase information.

[0023] Furthermore, the atomic gas cell contains alkali metal atoms or alkaline earth metal atoms.

[0024] Furthermore, the amplitude of the low-frequency electromagnetic field is obtained based on homodyne detection. and phase information , the formula is as follows:

[0025]

[0026]

[0027] 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 to light combining. The phase change caused by the interaction between light and atoms due to the applied magnetic field.

[0028] Furthermore, the amplitude of the low-frequency electromagnetic field is obtained based on heterodyne detection. and phase information , the formula is as follows:

[0029]

[0030]

[0031] 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 to 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 applied magnetic field.

[0032] In a second aspect, the present invention further provides a measurement system for implementing the above method, which is characterized in that it includes:

[0033] Laser module: at least includes detection light laser and coupling light laser;

[0034] Optical frequency stabilization module: used to lock the laser frequency to the atomic transition energy level;

[0035] Atomic interaction module: includes atomic gas chamber and electromagnetic field application device;

[0036] Coherent detection module: includes a beam splitter, a beam combiner, an interferometer, and a detector. For homodyne detection, it includes a Mach-Zehnder interferometer; for heterodyne detection, it includes an acousto-optic modulator and a mixer.

[0037] Signal processing module: used for signal demodulation and spectrum analysis.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1) A phase detection scheme is adopted, in which the phase change of the detected light field is proportional to the ratio of the AC field amplitude 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 applications with weak fields and low frequencies.

[0040] 2) In the homodyne detection scheme, the feedback loop introduces a certain degree of operational complexity, but the interferometer arms are locked by reference light, avoiding the need to use complex RF signals; in the heterodyne detection scheme, additional RF signals are required for modulation and demodulation, but the operation of locking the interferometer is avoided. Both schemes have their own advantages, but no matter which scheme is used, high-precision and stable processing of the phase signal can be achieved through optimized design processing, thereby ensuring the reliability of the detection system.

[0041] 3) Both the probe and coupling beams are frequency-locked for stable control, exciting atoms to Rydberg states with high coherence, effectively reducing laser phase noise and facilitating subsequent signal extraction. Furthermore, the use of reference beams effectively reduces signal interference from factors such as common-mode noise. This design significantly improves the system's signal-to-noise ratio, thereby enhancing detection accuracy and stability.

[0042] 4) The detection and data processing technology used can accurately and efficiently extract the amplitude and phase information related to the electric field from the modulated signal, which is conducive to improving the detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of homodyne detection and heterodyne detection;

[0044] Figure 2 This is a schematic diagram of the optical path for phase extraction using a homodyne detection scheme;

[0045] Figure 3 It is a schematic diagram of the optical path for phase extraction using a heterodyne detection scheme;

[0046] Figure 4 This is a schematic diagram of measuring low-frequency electromagnetic field energy levels based on Rydberg atoms. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the embodiments and drawings, but the scope of protection of the present invention should not be limited thereto.

[0048] See also Figure 1 A method for efficiently extracting information from the low-frequency electromagnetic field of Rydberg atoms based on homodyne detection comprises the following steps:

[0049] Step 1: Frequency stabilization and beam splitting of the detection light:

[0050] A first laser is used to emit a probe light, which is frequency-locked to the atomic ground state energy level after frequency stabilization. and excited state energy levels The resonant frequency is obtained by the first beam splitter and is divided into two beams, one of which is used as the local oscillator light for subsequent interference detection; the other is used as the signal light and enters the atomic gas chamber through the first dichroic mirror to interact with the atoms;

[0051] Step 2: Coupled optical excitation and EIT spectral observation:

[0052] A second laser is used to emit coupled light, which is frequency-locked to the atomic excited state energy level after frequency stabilization. and Rydberg state energy levels The resonant frequency of the electrons is reflected by the second dichroic mirror and enters the atomic gas chamber;

[0053] The optical path is adjusted to ensure that the signal light and the coupled light overlap in the opposite collinear direction in the atomic gas chamber, and the coupled light frequency is scanned to observe the spectral signal generated by the quantum coherence effect.

[0054] Step 3: Phase-locked optical interferometer:

[0055] A third laser is used to emit phase-locked light. After frequency stabilization, the phase-locked light passes through a beam splitter to form a Mach-Zehnder interferometer. One beam enters the atomic gas chamber and is combined with a reference beam at the first beam splitter. A balanced detector receives the differential signal and feeds it back to a piezoelectric ceramic mirror to dynamically adjust the optical path difference and stabilize the interference phase.

[0056] Step 4: Electric field application and signal extraction:

[0057] A DC bias field and a low-frequency AC electromagnetic field to be measured are applied 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 is combined with the local oscillator light through a first beam combiner. The in-phase signal and the orthogonal signal are separated by a polarization beam splitter prism and detected by a balanced detector.

[0058] Step 5: Data processing and information extraction:

[0059] Performing data processing on the in-phase signal and the quadrature signal to convert them into amplitude signals and phase signals; the extracted signals contain information on the spectral lines of the quantum coherence effect under electromagnetic field modulation;

[0060] Perform spectrum analysis on the phase signal to extract the amplitude information and relative phase information at the low-frequency electromagnetic field frequency, thereby achieving accurate measurement and complete characterization of the low-frequency electromagnetic field.

[0061] The electric vector of the signal light passing through the atomic gas chamber in step 1 is ,in is the signal strength, is the signal light frequency, is the phase of the signal light, represents an imaginary number, and t represents time.

[0062] The local oscillator photoelectric vector in step 1 is , in the homodyne detection scheme, the local oscillator frequency , It is the total phase difference caused by the optical path difference in the process of light splitting to light combining.

[0063] The signal obtained by applying a low-frequency electromagnetic field to the atomic gas chamber and combining the beams in step 4 is

[0064] ;

[0065] in, is the photocurrent response coefficient of the detector, which is modulated by a low-frequency electromagnetic field and applied with a low-frequency electric field. For example, To apply the low frequency field amplitude, is the low-frequency field frequency, is the low-frequency field phase. The signal light intensity and phase will be modulated due to atomic interaction. Taking the EIT resonance as an example, the phase is proportional to the electric field and is recorded as ,in, is the AC field frequency The amplitude at is the AC field frequency The relative phase of .

[0066] Since the detector adopts AC coupling mode, the actual output electrical signals are

[0067] ;

[0068]

[0069] in, and They represent the output electrical signals separated by the polarization beam splitter to the two balanced probes, namely the in-phase signal and the orthogonal signal.

[0070] The amplitude signal in step five With phase signal They are

[0071] ;

[0072] .

[0073] In step 5, the phase signal By reading the spectrum, the low-frequency electromagnetic field frequency can be extracted Amplitude information at and relative phase information ,Finally, through the calibration method, the correspondence between the amplitude information and phase ,information and the amplitude and phase of the electromagnetic field is established, ,thus achieving efficient information reading of the low-frequency electromagnetic field based on ,Rydberg atoms.

[0074] According to a second aspect of the present invention, there is provided a method for efficiently extracting information from the low-frequency electromagnetic field of Rydberg atoms based on heterodyne detection, which is characterized in that it comprises the following steps:

[0075] Step 1: Use the first laser to generate the probe light. After the probe light is stabilized, the frequency is fixed to the atomic ground state energy level. and excited state energy levels Near the resonance frequency of the probe light, the probe light is split by the first beam splitter, one beam is frequency-shifted and used as the local oscillator light in heterodyne detection, and the other beam is guided into the atomic gas chamber through the first dichroic mirror as the signal light for interacting with the atoms.

[0076] Step 2: Use a second laser to generate coupled light. After the coupled light is frequency-stabilized, the frequency is fixed to the atomic excited state energy level. and Rydberg state energy levels The coupled light is guided into the atomic gas chamber through a second dichroic mirror near the resonance frequency of the atomic gas chamber; the optical path is adjusted to ensure that the signal light and the coupled light coincide in the opposite directions in the atomic gas chamber; when the frequency of the coupled light is scanned, the spectral signal generated by the quantum coherence effect can be observed.

[0077] Step 3: Use the first laser to split the reference light through the second beam-splitting prism. After the reference light is frequency-stabilized, its frequency is completely consistent with the signal light. The reference light is guided into the atomic gas chamber through the first dichroic mirror and adjusted to be parallel to the signal light. The reference light is combined with the local oscillator light through the second beam combiner to obtain the first set of in-phase signals and orthogonal signals.

[0078] Step 4: A DC bias field and a low-frequency AC electromagnetic field to be measured are applied 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 the first beam combiner to obtain a second set of in-phase and quadrature signals.

[0079] Step 5: The two sets of in-phase and quadrature signals obtained by combining the signal light and reference light with the local oscillator light are processed and converted into amplitude and phase signals. These two sets of amplitude and phase signals are subtracted to significantly improve the signal-to-noise ratio. They also serve as a reference for the signal light, eliminating the effects of common-mode noise and other factors on the signal. The extracted signal contains information about the modulation of the electromagnetic field on the quantum coherence effect spectrum. Further spectrum analysis of the phase signal can extract the amplitude and phase information of the low-frequency electromagnetic field.

[0080] The electric vector of the signal light passing through the atomic gas chamber in step 1 is ,in is the signal strength, is the signal light frequency, is the phase of the signal light, represents an imaginary number, and t represents time.

[0081] The local oscillator photoelectric vector in step 1 is , in the heterodyne detection scheme, the local oscillator frequency , is the difference frequency between the local oscillator light and the signal light, It is the total phase difference caused by the optical path difference in the process of light splitting to light combining.

[0082] The signal obtained by applying a low-frequency electromagnetic field to the atomic gas chamber and combining the beams in step 4 is

[0083]

[0084] in, 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. ,in, To apply the low frequency field amplitude, is the low-frequency field frequency, is the low-frequency field phase. The signal light intensity and phase will be modulated due to atomic interaction. Taking the EIT resonance as an example, the phase is proportional to the electric field and is recorded as ,in, is the AC field frequency The amplitude at is the AC field frequency The relative phase of .

[0085] Since the detector adopts AC coupling mode, the actual output electrical signal is

[0086] .

[0087] In step 5, the signal is modulated and demodulated to ensure that the difference frequency signal is in a lower frequency range, so as to facilitate the detection of the detector. On the two mixers, two sets of orthogonal reference signals as well as Mixing is performed, where is the reference signal frequency, is the reference signal amplitude, is the reference signal phase. Further, the outputs of the mixer after low-pass filtering are

[0088] ;

[0089] .

[0090] Through further calculation, the corresponding amplitude signal can be obtained With phase signal , the formula is as follows:

[0091] ;

[0092] .

[0093] In step 5, the phase signal By reading the spectrum, the low-frequency electromagnetic field frequency can be extracted Amplitude information at and relative phase information Finally, the conversion relationship between amplitude information and phase information and the amplitude and phase of the electromagnetic field is determined by calibration, and efficient information reading based on Rydberg low-frequency measurement is achieved.

[0094] Example:

[0095] Take the example of using alkali metal or alkaline earth metal atoms and exciting them to Rydberg states and performing low-frequency electromagnetic field detection:

[0096] See Figure 2 , Figure 2 This is a schematic diagram of the optical path for phase extraction using a homodyne detection scheme, as shown in the figure, including:

[0097] The first laser 2-1 generates probe light and stabilizes its frequency to the atomic ground state energy level. and excited state energy levels The resonant frequency of

[0098] The second laser 2-12 generates coupled light and stabilizes the frequency to the excited state energy level and Rydberg levels The resonant frequency of

[0099] The third laser 2-14 generates phase-locked light to stabilize the interferometer optical path.

[0100] Atomic gas chambers 2-5 are filled with alkali metal atoms to produce the Rydberg EIT effect;

[0101] Parallel capacitor plates 2-6, applying a DC bias electric field and a low-frequency AC electric field to be measured;

[0102] Mach-Zehnder interferometer: consists of a first beam splitter prism 2-3, a second beam splitter prism 2-11, a reflector 2-8, a reflector with piezoelectric ceramics 2-21 and a third balanced detector 2-20, and is used for phase locking.

[0103] The third polarization splitter prism 2-16 and the fourth polarization splitter prism 2-17 separate the in-phase signal (X) and the orthogonal signal (Y), which are collected by the first balanced detector 2-18 and the second balanced detector 2-19 respectively.

[0104] Frequency locking based on the ultrastable cavity 2-15 can effectively reduce the linewidth of the laser used and improve the coherence of quantum optical effects such as Rydberg EIT and Autler-Townes produced by the interaction between the two laser beams and atoms, which is beneficial to improving the signal-to-noise ratio of the final detection signal.

[0105] See also Figure 4 , Figure 4 This is a schematic diagram of the energy levels of the Rydberg atom probe low-frequency electric field in the present invention, which is applicable to a variety of atoms including typical alkali metal atoms such as Rb, Cs, K, and Na, and typical alkaline earth metal atoms such as Yb and Sr. As shown in the figure, the Rabi frequency is The probe light 4-4 excites the atom from the ground state 4-1 to excited state 4-2, the Rabbi frequency is The coupled light 4-5 excites the atoms 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 the external electromagnetic field 4-6 is applied to the atomic gas cell, the low-frequency electric field to be measured is transformed from the Rydberg state to the low-frequency energy level oscillation 4-8.

[0106] Combine Figure 1 The schematic diagram of the process flow of the present invention is a method for extracting information efficiently based on low-frequency detection of Rydberg atoms. Example 1 is given in detail. 87 Rb atoms, which are excited to Taking the Rydberg state as an example, the atomic transition frequency corresponding to the detection light 4-4 is 384.2346 THz, and the atomic transition frequency corresponding to the coupling light 4-5 is 312.3886 THz. The following steps are included:

[0107] Step 1: The first laser 2-1 uses a 780nm laser as the detection light. The detection light is divided into two paths by the first polarization beam splitter prism 2-2, one of which is input into the ultrastable cavity 2-15 for frequency stabilization, and the frequency is fixed to the atomic ground state energy level. and excited state energy levels The resonant frequency of the coupled light is 384.2346 THz. The other beam is split by the first beamsplitter prism 2-3. One beam is used as the local oscillator light, which is then directly used for interferometry after passing through the piezoelectric ceramic reflector 2-21 and the half-wave plate 2-9. The other beam is used as the signal light, which is guided by the first dichroic mirror 2-4 into the atomic gas chamber 2-5. There, it interacts in the opposite direction and is collinear with the coupled light, exciting the Rydberg state and is transmitted by the second dichroic mirror 2-7.

[0108] Step 2: The second laser 2-12 uses a 480nm laser as coupling light. The coupling light is split into two paths by the second polarization beam splitter 2-13, one path is input into the ultrastable cavity 2-15 for frequency stabilization, and the frequency is fixed to the atomic excited state energy level. Rydberg levels The resonant frequency of the laser beam is 312.3886 THz, which ensures the high coherence of the Rydberg EIT effect generated by the interaction between the two laser beams and the atoms. The other path is reflected by the second dichroic mirror 2-7 and enters the atomic gas chamber 2-5, and is reflected by the first dichroic mirror 2-4. The optical path is adjusted so that the signal light and the coupled light overlap in the opposite direction in the atomic gas chamber 2-5, and the atoms can be excited to The EIT effect occurs at the Rydberg energy level. By scanning the frequency of the coupled light, the Rydberg EIT spectrum can be observed.

[0109] In step 3, the third laser 2-14 uses 795nm as the reference light. After the frequency stabilization process, the interference arm is locked by the Mach-Zehnder interferometer composed of the second beam splitter prism 2-11 and the first beam splitter prism 2-3. After the reference light is split by the second beam splitter prism 2-11, one beam passes through the reflector 2-8 and the second dichroic mirror 2-7, enters the atomic gas chamber 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 passing through the reflector 2-21 with piezoelectric ceramics. The generated differential signal is received by the third balanced detector 2-20 and fed back to the piezoelectric ceramics on the reflector 2-21 with piezoelectric ceramics to achieve phase stability between the two arms of the interferometer. The reference light completely overlaps with the signal light in step 1.

[0110] In step 4, a DC bias electric field and a low-frequency AC electric field to be measured are applied to the atomic gas chamber 2-5 through the parallel capacitor plate 2-6. The total electric field acts on the Rydberg state and causes energy level modulation. The signal light and the local oscillator light in step 1 are combined at the second beam splitter prism 2-11. A reflector, a third polarization beam splitter prism 2-16 and a fourth polarization beam splitter prism 2-17 are used to generate an in-phase signal and collect it by the first balanced detector 2-18, and an orthogonal signal and collect it by the second balanced detector.

[0111] In step 5, the combined in-phase and quadrature signals are further processed to convert them into amplitude and phase signals. The extracted signals contain information about the spectral lines of the quantum coherence effect under electromagnetic field modulation. Spectral analysis of the phase signal further extracts the amplitude and phase information of the low-frequency electromagnetic field, enabling precise measurement and complete characterization of the low-frequency electromagnetic field.

[0112] The photoelectric vector of the signal passing through the atomic gas chamber in step 1 for:

[0113]

[0114] Where, is the signal light intensity, is the signal light frequency, is the signal light phase.

[0115] local oscillator photoelectric vector for:

[0116]

[0117] Where, is the local oscillator light intensity, is the local oscillator light frequency, , It is the local oscillator light phase, which is the total phase difference caused by the optical path difference in the process of light splitting to light combining.

[0118] In step 4, a low-frequency electromagnetic field is applied to the atomic gas chamber and beam-combined. The signal after beam combination is

[0119]

[0120] Where, is the photocurrent response coefficient of the detector.

[0121] Under the modulation of low-frequency electric field, For example, the signal light intensity and phase will be modulated due to atomic interaction. Taking the EIT resonance as an example, the phase is proportional to the electric field, which is recorded as .

[0122] Since the detector adopts AC coupling mode, the actual output electrical signals are

[0123]

[0124]

[0125] Calculate amplitude and phase , the formula is as follows:

[0126] ;

[0127] .

[0128] Phase Perform spectrum analysis to extract low-frequency electromagnetic field frequencies Amplitude information at and phase information Finally, through the calibration method, the corresponding relationship between the amplitude information and phase information and the amplitude and phase of the electromagnetic field is established, thereby realizing efficient information reading of the low-frequency electromagnetic field based on Rydberg atoms.

[0129] See Figure 3 , Figure 3This is a schematic diagram of the optical path for phase extraction using a heterodyne detection scheme. As shown, the optical path includes a first laser 2-1, a second laser 2-12, a first polarization beam splitter prism 2-2, a second polarization beam splitter prism 2-13, an ultrastable cavity 2-15, a first beam splitter prism 2-3, a second beam splitter prism 3-4, a first dichroic mirror 2-4, an atomic gas cell 2-5, parallel capacitor plates 2-6, a second dichroic mirror 2-7, an acousto-optic modulator 3-9, a third beam splitter prism 3-10, a fourth beam splitter prism 3-11, a fifth beam splitter prism 3-16, a first balanced detector 3-12, a first mixer 3-19, a second mixer 3-20, a second balanced detector 3-17, a third mixer 3-21, a fourth mixer 3-22, and a radio frequency source 3-18.

[0130] Combine Figure 1 The schematic diagram of the process flow of the present invention is a method for extracting information efficiently based on low-frequency detection of Rydberg atoms. Example 1 is given in detail. 87 Rb atoms, which are excited to Taking the Rydberg state as an example, the atomic transition frequency corresponding to the detection light 4-4 is 384.2346 THz, and the atomic transition frequency corresponding to the coupling light 4-5 is 312.3886 THz. The following steps are included:

[0131] 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 2-2. One beam is input into the ultrastable cavity 2-15 for frequency stabilization, and the frequency is fixed to the atomic ground state energy level. and excited state energy levels The resonance frequency of the probe light is 384.2346 THz. The probe light is split by the first beam splitter prism 2-3 and passes through the acousto-optic modulator 3-9 as the local oscillation light. The radio frequency signal of the acousto-optic modulator through which the local oscillation light is shifted is provided by the radio frequency source 3-18. The other beam of light is guided by the first dichroic mirror 2-4 into the atomic gas chamber 2-5 as the signal light.

[0132] 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 2-13. One beam is input into the ultrastable cavity 2-15 for frequency stabilization, and the frequency is fixed to the atomic excited state energy level. Rydberg levels The resonant frequency of the laser beam is 312.3886 THz, which ensures the high coherence of the Rydberg EIT effect generated by the interaction between the two laser beams and the atoms. The signal light is transmitted through the first dichroic mirror 2-4 into the atomic gas chamber 2-5 and is transmitted by the second dichroic mirror 2-7; the coupled light is reflected by the second dichroic mirror 2-7 into the atomic gas chamber 2-5 and is reflected by the first dichroic mirror 2-4; the optical path is adjusted so that the signal light and the coupled light overlap in the opposite collinear direction in the atomic gas chamber 2-5, and the atoms can be excited to At the Rydberg energy level; by scanning the coupled light frequency, the Rydberg EIT spectrum line can be observed.

[0133] Step 3, using the first laser, splitting the reference light through the second beam splitting prism 3-4 to obtain the reference light. After the reference light is frequency-stabilized, its frequency is completely consistent with the signal light. The reference light is guided into the atomic gas chamber through the first dichroic mirror 2-4 and adjusted to be parallel to the signal light. The reference light is combined with the local oscillator light through the third beam splitting prism 3-11, and the signal is detected by the first balanced detector 3-12. The RF source 3-18 is used to generate two reference signals whose frequencies are consistent with the RF signal driven by the acousto-optic modulator and are orthogonal to each other. The combined signals are mixed with the combined signals in the first mixer 3-19 and the second mixer 3-20 respectively to obtain a first group of in-phase signals and a first quadrature signal 3-24.

[0134] Step 4, apply a DC bias electric field and a low-frequency AC electric field to be measured to the atomic gas chamber 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 the signal light is combined at the fifth beam splitter prism 3-16, the signal is detected by the second balanced detector 3-17, and two reference signals are generated by the RF source 3-18, which have the same frequency as the RF signal driven by the acousto-optic modulator and are orthogonal to each other, and are mixed with the combined signal in the third mixer 3-21 and the fourth mixer 3-22 respectively to obtain a second group of in-phase signals and a second orthogonal signal 3-23.

[0135] In step 5, the two 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 are processed and converted into amplitude and phase signals. These two amplitude and phase signals are subtracted to significantly improve the signal-to-noise ratio. These signals also serve as a reference for the signal light, eliminating the effects of common-mode noise and other factors on the signal. The extracted signal contains information about the modulation of the electromagnetic field on the quantum coherence effect spectrum. Further spectrum analysis of the phase signal can extract the amplitude and phase information of the low-frequency electromagnetic field.

[0136] The electric vector of the signal light passing through the atomic gas chamber in step 1 is ,in is the signal strength, is the signal light frequency, is the phase of the signal light.

[0137] The local oscillator photoelectric vector in step 1 is , in the heterodyne detection scheme , It is the total phase difference caused by the optical path difference in the process of light splitting to light combining.

[0138] The signal obtained by applying a low-frequency electromagnetic field to the atomic gas chamber and combining the beams in step 4 is

[0139]

[0140] in, 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. After that, the signal light intensity and phase will be modulated due to the atomic interaction. Taking the EIT resonance as an example, the phase is proportional to the electric field and is expressed as

[0141] Since the detector adopts AC coupling mode, the actual output electrical signal is

[0142]

[0143] In step 5, the signal is modulated and demodulated to ensure that the difference frequency signal is in a lower frequency range, so as to facilitate the detection of the detector. At the mixer, two sets of orthogonal reference signals as well as Mixing is performed, where is the reference signal frequency. Further, the outputs of the mixer after low-pass filtering are

[0144] ;

[0145] as well as

[0146]

[0147] Through further calculation, the corresponding amplitude signal can be obtained With phase signal , the formula is as follows:

[0148]

[0149]

[0150] In step 5, the phase signal By reading the spectrum, the low-frequency electromagnetic field frequency can be extracted Amplitude information at and relative phase information Finally, the conversion relationship between amplitude information and phase information and the amplitude and phase of the electromagnetic field is determined by calibration, and efficient information reading based on Rydberg low-frequency measurement is achieved.

[0151] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection 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 resonance 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 cell, and convert the electromagnetic field information into optical field phase information through Rydberg state modulation; Using homodyne detection or heterodyne detection, the phase signal is extracted 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 probe 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 optical path phase is stabilized by a Mach-Zehnder interferometer. Separate the in-phase signal and the orthogonal signal through a polarization beam splitter; The in-phase signal and the orthogonal signal are collected separately by a balanced detector, and the electromagnetic field information is extracted through 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 probe 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 Rydberg atom low-frequency detection 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 fields 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 to light combining. The phase change caused by the interaction between light and atoms due to the applied 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: Obtaining the amplitude of low-frequency electromagnetic fields 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 to 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 applied 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 detection light laser and coupling light laser; Optical frequency stabilization module: used to lock the laser frequency to the atomic transition energy level; Atomic interaction module: includes 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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