Multi-photon phase detection method, device and system based on closed-loop quantum coherence and clock transition

Abstract

The invention discloses a multi-photon phase detection method, device and system based on closed-loop quantum coherence and clock transition, and aims to solve the problems that the working frequency of an existing atom sensor is limited and the existing atom sensor is easily interfered by amplitude noise. According to the method, a closed ring is constructed in an atomic medium by applying a light field, a working alternating-current magnetic field and an auxiliary alternating-current magnetic field. The sum of the working frequency and the auxiliary frequency is set to be equal to the transition frequency of the first-order magnetic insensitive clock of the atom, so that decoupling of the working frequency to be measured and the inherent frequency of the atom is realized, and continuous tuning can be performed in a broadband range from Hertz to gigahertz. To-be-measured phase information is carried in a global phase of a closed loop, and is extracted by measuring an optical response signal and performing synchronous demodulation. According to the scheme, the self-consistency of the closed loop phase and the stability of clock transition are utilized, the influence of driving field amplitude noise and environment magnetic field fluctuation is effectively restrained, and the method is suitable for the fields of high-precision electromagnetic detection, broadband communication and the like.

Description

Technical Field

[0001] The present invention relates to electromagnetic induction detection, and in particular to a system based on quantum coherent closed-loop transition contour multi-photon transition phase detection. Background Art

[0002] Precision measurement of the phase of the electromagnetic field is a core basic capability in the frontier exploration of modern science and technology and high-end engineering applications. Compared with the amplitude information of the electromagnetic field, the phase information often carries richer and more stable physical connotations. It can not only reveal the dispersion and absorption characteristics of the wave in the propagation medium, but also characterize the electromagnetic response of the target object or the dynamic evolution process of the oscillation source. Therefore, the development of high-sensitivity and high-stability phase detection technology has important research significance and application value in many key fields. For example, in the field of underwater communication and target identification, by analyzing the phase delay of the secondary induction field, the target material and geometric structure can be effectively identified; in geophysical exploration, the phase spectrum of the electromagnetic field is the key observation quantity for inverting the conductivity distribution of the underground medium; in basic physics research, precise measurement of the weak phase shift caused by specific interactions is an important way to test basic physical laws and explore new physical phenomena.

[0003] Currently, precision measurement technology based on coherent manipulation of atomic quantum states has become a research hotspot in this field. In the existing technology, a variety of measurement schemes using atomic ensembles as sensing media have been developed. For example, the atomic magnetometer based on the SERF (spin exchange relaxation free) mechanism achieves extremely high sensitivity detection of near-DC or low-frequency magnetic fields by monitoring the optical rotation caused by the precession of atomic spins in a near-zero magnetic field environment. Its detection information mainly comes from the magnetic field amplitude. In the radio frequency and microwave bands, atomic sensors based on electromagnetically induced transparency (EIT) or coherent population trapping (CPT) effects have demonstrated superior performance. These sensors use two-photon resonance technology to establish quantum coherence between the two ground state energy levels of an atom. Their resonant frequency is usually locked to the intrinsic transition frequency determined by the atomic hyperfine structure, such as rubidium-87 ( 87 These technologies have reached a high level of sophistication within their respective optimal operating frequency bands and have been successfully applied in magnetic anomaly detection, atomic clocks, and quantum storage.

[0004] However, existing technologies still face several deep-seated technical bottlenecks when seeking a balance between broadband frequency adaptability and high measurement stability. These bottlenecks are mainly reflected in the rigid coupling between the operating frequency and the atomic intrinsic structure, and the excessive dependence of measurement accuracy on the stability of the driving field amplitude. Specifically, existing technologies have the following problems: First, there is an inherent contradiction between the flexibility of the detection frequency and the stability of the system. On the one hand, in order to obtain the highest stability to resist environmental magnetic field noise, existing solutions tend to use clock transitions that are insensitive to magnetic fields, but this will rigidly lock the operating frequency of the system to a specific microwave frequency band (such as 87 The 6.835 GHz of the Rb-based CMOS makes it impossible to directly detect signals in other important frequency bands, such as very low frequency (VLF) or medium frequency (MF). Furthermore, detecting signals at these non-natural frequencies requires forgoing the stability advantages offered by clock transitions and instead employing other magnetic-field-sensitive transition pathways, making the system highly susceptible to interference from ambient magnetic field fluctuations. This rigid coupling between the operating frequency and the atomic intrinsic energy level structure prevents a single device from achieving both broadband frequency adaptability and high stability, limiting its application in complex electromagnetic environments and multi-task scenarios. Furthermore, existing solutions generally rely on measuring the amplitude of the resonant signal, such as detecting the height or depth of the EIT / CPT resonance peak. This amplitude-encoded detection mechanism has an inherent drawback: the measurement results are extremely sensitive to fluctuations in the driving field amplitude. Slight drifts in laser power and jitter in the RF driving field intensity directly translate into fluctuations in the signal baseline and distortion of the resonance line shape, ultimately adding noise to the measurement results, significantly reducing the achievable signal-to-noise ratio and measurement accuracy. This problem is particularly prominent in weak signal detection scenarios requiring long integration times. Summary of the Invention

[0005] The purpose of the invention is to provide a multi-photon phase detection method, device and system based on closed-loop quantum coherence and clock transition in order to solve the above-mentioned problems existing in the prior art.

[0006] The technical solution is a multi-photon phase detection method based on closed-loop quantum coherence and clock transitions, including: applying a group driving field to the atomic medium to construct a closed loop in the atomic medium, wherein the driving field comprises a light field, a working AC magnetic field, and an auxiliary AC magnetic field; Setting the working frequency of the working AC magnetic field and the auxiliary frequency of the auxiliary AC magnetic field, wherein the frequency combination is related to the natural transition frequency of the atomic medium, so as to achieve decoupling of the working frequency and the natural transition frequency; Obtaining the optical response signal generated by the interaction between the closed ring and the atomic medium; Based on the optical response signal, the working phase of the working AC magnetic field is analyzed.

[0007] A multi-photon phase detection system based on closed-loop quantum coherence and clock transition, comprising: An atomic cell module configured to accommodate an atomic medium; A laser system configured to generate and guide an optical field through the atomic cell module; A magnetic field module configured to generate a working AC magnetic field and an auxiliary AC magnetic field within the atomic cell module; A photodetector disposed on the transmission path of the optical field, for converting the optical field transmitted through the atomic cell module into an optical response signal; A control and signal processing unit operatively coupled to the laser system, the magnetic field module and the photodetector, The control and signal processing unit is configured to: By controlling the laser system and the magnetic field module, a closed loop is constructed in the atomic medium; The working frequency of the working AC magnetic field and the auxiliary frequency of the auxiliary AC magnetic field are set to be related to the inherent transition frequency of the atomic medium, so as to realize the decoupling of the working frequency and the inherent transition frequency; Receiving and processing the optical response signal, and analyzing the working phase of the working AC magnetic field.

[0008] A multi-photon phase detection device, comprising: An atomic cell for accommodating an atomic medium; A first magnetic field generating unit for generating a frequency-adjustable first AC magnetic field and applying it to the atomic cell; A second magnetic field generating unit for generating a second AC magnetic field and applying it to the atomic cell, the frequency of the second AC magnetic field being equal to the sum of the frequency of the first AC magnetic field and the clock transition frequency of the atomic medium; A laser source for generating a laser field corresponding to the clock transition frequency and incident on the atomic cell; A detection unit for detecting the change of the optical signal transmitted through the atomic cell; Wherein, the first magnetic field generating unit and the second magnetic field generating unit are configured to construct a closed transition path containing a virtual intermediate energy level between two ground state energy levels of the atomic medium, and the frequency of the first AC magnetic field is adjustable in the range of 1 Hz to 10 GHz.

[0009] Beneficial effect: A closed-loop quantum interference path is constructed by combining the light field and the AC magnetic field, and the first-order Zeeman frequency shift is suppressed by clock transitions. The phase change of the signal field to be measured is mapped to the change of the atomic population through quantum interference. The multi-photon transition technology breaks the inherent transition frequency limit of atoms and realizes continuous adjustment of the signal field frequency in the range of 1Hz-10GHz. The total phase of the closed loop is determined by the phase of the AC magnetic field, which suppresses the combined influence of environmental noise and system parameter drift. The system is suitable for electromagnetic induction detection (such as secondary magnetic field phase analysis caused by underground or underwater targets) and communication applications, including but not limited to ultra-low frequency, very low frequency (1Hz-30kHz) signal detection and microwave frequency band (1GHz-10GHz) data transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural diagram of the system of the present invention.

[0011] Figure 2 and Figure 3 It is a schematic diagram of the present invention.

[0012] Figure 4 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments and features in the embodiments of this application can be combined with each other unless there is a conflict.

[0014] Example 1: This example provides a basic process for a phase detection method. This method maps the phase information of the AC magnetic field to be measured into a measurable optical signal by constructing a quantum coherent closed loop, while decoupling the operating frequency from the atomic natural frequency.

[0015] Specifically, the method of this embodiment includes the following steps: Step S101 : applying a set of driving fields to the atomic medium, wherein the driving fields include a light field, a working AC magnetic field, and an auxiliary AC magnetic field, so as to construct a closed loop in the atomic medium.

[0016] In this step, the atomic medium can be an alkali metal atomic vapor. For example, in a specific application scenario, rubidium-87 ( 87 Rb) atoms are encapsulated in a glass cavity to form an atomic vapor chamber. A buffer gas, such as nitrogen (N2), can be added to reduce the decoherence effect of collisions between the atoms and the bubble wall. To achieve a sufficient atomic vapor density, the atomic vapor chamber is typically heated to a specific operating temperature, such as between 85°C and 120°C.

[0017] The driving field is a set of precisely controlled electromagnetic fields that act synergistically on the atomic medium. Specifically: The light field is usually generated by one or more laser beams. In a preferred embodiment, a wavelength-locked laser beam can be used. 87 Laser light from the Rb atomic D1 line (approximately 795 nm) is modulated by an electro-optic modulator (EOM) or acousto-optic modulator (AOM) to produce two coherent light components with a frequency interval equal to the atomic ground-state clock transition frequency (approximately 6.835 GHz). These two light components work together to drive the transition of the atoms between the ground and excited states.

[0018] The working AC magnetic field is the target signal field that carries the phase information to be measured. For example, when detecting underwater targets, this magnetic field is the secondary electromagnetic field driven by the target. Its frequency f _LF and the phase to be measured φ _LF It is the core measurement object of this method.

[0019] According to one aspect of the present application, this magnetic field is both a magnetic field that drives atomic transitions in a closed loop and an excitation magnetic field that excites a secondary magnetic field of the same frequency in the target object. The combined magnetic field of the two constitutes a new working magnetic field, and its phase is the main detection target.

[0020] The auxiliary AC magnetic field is a reference magnetic field generated by a local signal source, and its frequency f _HF and phase φ _HF All are known and controllable.

[0021] A closed loop is a circuit that constructs a closed quantum transition path between specific atomic energy levels through the combination of the aforementioned driving fields. For example, this loop can involve two ground-state energy levels, |g1> and |g2>, and one excited-state energy level, |e>. The working AC magnetic field and the auxiliary AC magnetic field jointly drive the transition between |g1> and |g2>, while the light field couples |g1>, |g2>, and |e>, forming a closed loop such as |g1> → |g2> → |e> → |g1>. The existence of this closed loop is a prerequisite for quantum interference effects and phase-sensitive responses.

[0022] Step S102 : setting the working frequency of the working AC magnetic field and the auxiliary frequency of the auxiliary AC magnetic field, wherein the frequency combination is associated with the natural transition frequency of the atomic medium to achieve decoupling of the working frequency and the natural transition frequency.

[0023] In this step, the intrinsic transition frequency refers to a specific transition frequency determined by the internal structure of the atom and not easily changed by the external environment. In the present invention, preferably, the frequency is a clock transition frequency that is insensitive to magnetic fields, for example 87 6.835GHz for Rb atoms.

[0024] The frequency combination is related to the natural transition frequency, which refers to the operating frequency f _LF and auxiliary frequency f _HF A specific mathematical relationship needs to be satisfied. In this embodiment, the relationship is set such that the sum of their frequencies is equal to the natural transition frequency, i.e., f _LF +f _HF =f _clock .

[0025] By establishing the above relationship, the decoupling of the operating frequency and the natural transition frequency is achieved. The principle is that the resonance condition of the system no longer directly depends on the operating frequency f _LF itself, but depends on f _LF and f _HF Therefore, f _LF It is no longer limited to a few specific resonance frequencies inherent in atoms, but can be freely selected within a wide range. It only needs to adjust f accordingly. _HF This mechanism solves the technical problem of limited operating frequency of traditional atomic sensors, making it possible to detect signals of any frequency.

[0026] Step S103: acquiring an optical response signal generated by the interaction between the closed loop and the atomic medium.

[0027] When the closed loop is formed, due to the quantum interference effect, the absorption or dispersion characteristics of the atomic medium to the light field will affect the total phase Φ of the driving field. _total It shows an extremely sensitive dependence. This phase-sensitive property will be directly reflected in the light field after passing through the atomic medium.

[0028] Specifically, the process for acquiring the optical response signal is as follows: After the light field passes through the atomic vapor cell, a photodetector is placed. This photodetector measures the intensity change of the transmitted light. Optionally, a polarization analysis element (such as a polarization beam splitter and a λ / 4 wave plate) can be placed before the photodetector, and the polarization rotation angle change of the transmitted light can be measured by balancing the photodetector. Both the intensity and polarization changes constitute the original optical response signal that carries phase information.

[0029] Step S104: analyzing the working phase of the working AC magnetic field based on the optical response signal.

[0030] Since the amplitude of the optical response signal is directly related to the global phase Φ _total , and the working phase to be measured φ _LF is Φ _total is a component of φ, so φ can be inverted by analyzing the optical response signal _LF .

[0031] One specific implementation is to process the electrical signal output from the photodetector by a control and signal processing unit (e.g. a digital phase-locked amplifier based on FPGA or DSP). The unit can execute a configured algorithm, for example, by calculating the phase φ _HF of the auxiliary magnetic field from the detected response component of the optical response signal corresponding to the modulation frequency of the first AC magnetic field. _LF The process will be further described in subsequent embodiments.

[0032] Through the above steps, the present embodiment can efficiently and accurately convert the phase information of an AC magnetic field with an arbitrary frequency into an optical signal that is easy to measure, and finally demodulate it. The entire process has good suppression ability to the amplitude noise of the driving field and the fluctuation of the environmental magnetic field.

[0033] According to an aspect of the present application, the process can also be described as: applying a first AC magnetic field and a second AC magnetic field to atoms in an atomic cell; building a closed loop containing a virtual intermediate level between two ground state levels of the atoms by the first AC magnetic field and the second AC magnetic field; applying a laser field corresponding to the clock transition frequency to the atomic cell, and then detecting the change of the optical signal transmitted through the atomic cell, the change of the optical signal being related to the phase of the first AC magnetic field, i.e. obtaining the working phase.

[0034] Preferably, the closed condition of the closed transition path is changed by adjusting the frequency of the first AC magnetic field.

[0035] Preferably, the frequency of the first AC magnetic field ranges from 1 Hz to 10 GHz. The sum of the frequency of the first AC magnetic field and the frequency of the second AC magnetic field is equal to the clock transition frequency of the atoms.

[0036] Preferably, the clock transition is the transition between |F=1, m F =0> state and |F=2, m F =0> state of alkali atoms; The laser field includes a carrier light and a sideband light generated by modulation, and the frequency difference between the carrier light and the sideband light is equal to the clock transition frequency.

[0037] Preferably, the phases of the first AC magnetic field and the second AC magnetic field are kept coherent, wherein the total phase Φ of the closed transition path satisfies: Φ = φ LF - (φ HF + φ L1 + φ L2 ) wherein φ LF is the phase of the first AC magnetic field, and φHF is the phase of the second AC magnetic field, φ L1 and φ L2 are the phases of the two frequency components in the laser field; By scanning the phase φ of the second AC magnetic field HF To read the phase φ of the first AC magnetic field LF .

[0038] Example 2: This example is based on Example 1 and further elaborates on the specific implementation of frequency decoupling and how to achieve broadband frequency tuning based on this.

[0039] In this embodiment, step S102 of the first embodiment is optimized and refined.

[0040] In step S201 , the frequency combination is associated with the inherent transition frequency of the atomic medium, which means that the sum of the operating frequency and the auxiliary frequency is equal to the clock transition frequency of the atomic medium.

[0041] In this embodiment, a clear and preferred mathematical definition is given to the concept of frequency combination association. 87 Rb atoms act as atomic media, and their ground state 5S 1 / 2 There are two hyperfine structure energy levels F = 1 and F = 2. Among them, the transition between the two magnetic sub-energy levels |F = 1, mF = 0> and |F = 2, mF = 0> is insensitive to the first-order change of the external magnetic field and is called a clock transition. The corresponding transition frequency f _clock It is a very stable physical constant, approximately 6.835GHz.

[0042] Set the working frequency of the working AC magnetic field to f _LF , the auxiliary frequency of the auxiliary AC magnetic field is f _HF The core of this step is to control the signal sources that generate the two magnetic fields so that their frequencies strictly meet the following conditions: _LF +f _HF =f _clock (i.e. 6.835GHz).

[0043] This embodiment uses the clock transition frequency as a reference benchmark. Since the clock transition itself is insensitive to the magnetic field, the resonance condition of the entire system is highly robust to slow drift or noise of the ambient magnetic field, thereby improving the stability and accuracy of phase detection.

[0044] Step S202 , adjusting the operating frequency within a preset wideband frequency range, and changing the auxiliary frequency synchronously and inversely with the adjustment, so as to constantly maintain the sum of the operating frequency and the auxiliary frequency equal to the clock transition frequency throughout the adjustment process.

[0045] This step describes the specific operational process for implementing broadband frequency scanning and adaptive adjustment. The preset broadband frequency range can be determined based on actual application requirements. Thanks to the frequency decoupling mechanism of the present invention, this range can be very wide. For example, its span can extend from the extremely low frequency (ULF) band covering 1 Hz to the microwave band of 10 gigahertz (GHz). This makes the present invention applicable to fields such as geophysical exploration and underwater communications that require extremely low frequencies, as well as fields such as microwave radar and wireless communications that require high frequencies.

[0046] The synchronous and reverse changes refer to a dynamic, real-time frequency compensation process, which is automatically performed by the system's control and signal processing units.

[0047] For example: Suppose you need to detect a frequency f _LF_initial =10kHz signal. At this time, the control unit will automatically set the auxiliary frequency f _HF_initial =6.835GHz-10kHz=6,834,990,000Hz.

[0048] When the detection frequency needs to be switched to f _LF_new =1MHz, the operator or upper-level application only needs to issue a new operating frequency instruction to the control unit. While the control unit adjusts the frequency of the signal source generating the working magnetic field from 10kHz to 1MHz (the frequency increases by Δf=990kHz), it will also synchronously instruct the signal source generating the auxiliary magnetic field to change its frequency from f _HF_initial Reduce Δf by the same value.

[0049] The new auxiliary frequency becomes: f _HF_new =f _HF_initial -Δf=6,834,990,000Hz-990,000Hz=6,834,000,000Hz. At this point, the new frequency and still satisfy f _LF_new +f _HF_new =1MHz+6.834GHz=6.835GHz.

[0050] Through this synchronous compensation mechanism, regardless of the operating frequency f _LF How it changes in the broadband range is related to the auxiliary frequency f _HF The sum is always locked to a constant clock transition frequency f _clock This ensures that the quantum coherence conditions are continuously satisfied throughout the entire tuning range, thus achieving truly broadband, continuously adjustable phase detection.

[0051] Embodiment 3: This embodiment is based on embodiment 1 and elaborates on the physical connotation of the optical response signal and the preferred technical solution for accurately demodulating the working phase to be measured therefrom.

[0052] In the embodiment, steps S103 and S104 of the first embodiment are further deepened and specified.

[0053] In step S301, the optical response signal carries information of a global phase, and the working phase to be demodulated is one of multiple branch phases forming a closed loop.

[0054] In this step, the branch phase refers to the independent phase of each driving field (including optical field and alternating magnetic field) participating in forming the closed loop. The global phase, denoted as Φ _total , is the effective total phase formed by the branch phases according to a specific combination and determining the quantum interference result of the whole system. It is not a simple phase algebraic sum, but a result of quantum mechanical evolution path coherent superposition.

[0055] In a specific implementation, the global phase Φ _total can be represented by the following formula: Φ _total = φ _LF - (φ _HF + φ _L1 + φ _L2 ) Wherein: φ _LF is the working phase of the working alternating magnetic field to be demodulated. φ _HF is the auxiliary phase of the auxiliary alternating magnetic field. φ _L1 and φ _L2 are the phases of two coherent components of the optical field driving the atomic transition.

[0056] In the closed loop, the atom evolves from the initial state back to the initial state, which can go through multiple different quantum paths, and the probability amplitudes of these paths will interfere. Finally, the atomic population and the macroscopic optical response (such as light absorption or polarization rotation) related thereto do not depend on the absolute parameters of a certain driving field, but are strongly dependent on the degree of constructive or destructive interference of these paths, which is uniquely determined by the global phase Φ _total . Therefore, the intensity I _out of the optical response signal can be represented as a function of Φ _total , for example, I _out ∝ cos(Φ _total ). It can be seen that the working phase φ _LF to be demodulated is one of the key variables determining this macroscopic measurable signal.

[0057] Step S302, the process of demodulating the working phase is to apply a periodic scan to a reference branch phase not to be measured among the multiple branch phases, thereby generating a synchronous modulation on the optical response signal, and deconstructing the synchronous modulation to separate the working phase.

[0058] This step describes a process from being _total The single target phase φ is extracted from the locked optical response signal with high precision and high signal-to-noise ratio. _LF The preferred method is synchronous demodulation technology (or phase-locked amplification technology).

[0059] The specific implementation is as follows: Selecting a reference shunt phase includes: selecting a phase that is not to be measured, generated by the system, and easy to accurately control from multiple components of the global phase as the reference shunt phase. A preferred choice is the phase φ of the auxiliary AC magnetic field. _HF .

[0060] Applying periodic scanning, including: through the control and signal processing unit, the reference phase φ _HF Apply a periodic modulation with a known parameter. For example, apply a sinusoidal modulation with a frequency of f_mod (e.g. 1kHz) and an amplitude of A_mod, i.e. φ _HF (t)=φ _HF 0+A_mod*sin(2π*f_mod*t), where φ _HF 0 is its initial phase.

[0061] Generate synchronous modulation, including: due to φ _HF is periodically scanned, the global phase Φ _total is modulated accordingly with the frequency f_mod. This results in the final optical response signal I _out On the basis of its DC or slowly varying component, an AC component with a frequency of f_mod and its harmonics that is synchronized with the reference scanning signal is superimposed.

[0062] Deconstruction and separation, including: inputting the optical response signal with synchronous modulation into a phase-locked amplifier. The phase-locked amplifier uses a reference scanning signal with a frequency of f_mod as a reference. Through internal orthogonal phase-sensitive detection and low-pass filtering, the phase-locked amplifier can extremely accurately extract the amplitude and phase of the signal component in the optical signal that is completely synchronized with the f_mod frequency. The amplitude of the output signal is proportional to the working phase φ to be measured. _LF There is a definite, usually linear, dependency on φ _LF Precise deconstruction and measurement.

[0063] Because direct measurement of DC changes in optical signals is susceptible to interference from low-frequency noise such as laser power drift and electronics noise (particularly 1 / f noise), applying a high, periodic modulation frequency (e.g., 1kHz) away from the main noise band shifts the useful phase information to a clean frequency band. A lock-in amplifier acts as an extremely narrow-bandwidth filter, responding only to signals of a specific frequency. This significantly suppresses noise at other frequencies, improving the signal-to-noise ratio by several orders of magnitude and being the key to achieving high-precision phase measurement.

[0064] Example 4: This example describes in detail, from a physical perspective, how to construct an efficient closed loop that is highly robust to external environmental fluctuations.

[0065] In step S401 , in order to enhance the robustness of the closed loop to external magnetic field fluctuations, the natural transition frequency is selected as a clock transition frequency that is first-order insensitive to magnetic field changes.

[0066] This step clarifies the preferred physical nature of the intrinsic transition frequencies in Examples 1 and 2. In atomic physics, atomic energy levels undergo Zeeman splitting in an external magnetic field, with the magnitude of the splitting proportional to the magnetic field strength. This causes the frequencies of most atomic transitions to drift with magnetic field fluctuations, a major source of noise in atomic sensors.

[0067] In terms of specific implementation, the present invention deliberately selects two specific magnetic sub-energy levels whose energy shifts (i.e., first-order Zeeman shifts) in the external magnetic field are equal in magnitude and in the same direction, or their first-order Zeeman shifts are both zero. The transition frequency between these two energy levels is, in a first-order approximation, independent of the external magnetic field strength. This kind of transition that is insensitive to magnetic fields is called a clock transition. For example, for 87 For Rb atom, the transition between the ground state |F=1,mF=0> energy level and the |F=2,mF=0> energy level is a typical clock transition.

[0068] Set the system's core frequency reference (i.e. f _clock ) is locked to the clock transition frequency. The motivation is to suppress the interference of environmental magnetic field fluctuations on the measurement results from the physical root. When the environmental magnetic field (such as daily fluctuations in the earth's magnetism and stray magnetic fields generated by surrounding electrical equipment) changes, the clock transition frequency itself is not sensitive to this, and the resonance condition f of the system is _LF +f _HF =f _clock This means that the method of the present invention can achieve high-stability and high-precision phase measurement in ordinary laboratory environments or even in field environments without relying on expensive and bulky multi-layer magnetic shielding devices, greatly improving the practicality and environmental adaptability of the system.

[0069] In step S402, the structure of the closed loop is defined as follows: the working AC magnetic field and the auxiliary AC magnetic field work together to open an atomic transition channel containing a virtual intermediate energy level between the two ground state energy levels of the atomic medium; at the same time, the light field connects the ground state energy level with an excited state energy level, thereby completing the closure of the loop.

[0070] This step defines in detail the topology of the quantum paths that are used to achieve the above functions, that is, the connection between energy levels. Specifically, the topology can be described as follows: Constructing atomic transition channels involves: selecting two ground state energy levels, e.g. 87 The clock transition energy levels of Rb are |g1﹥=|F=1,mF=0﹥ and |g2﹥=|F=2,mF=0﹥. It is forbidden to directly drive the transition between these two energy levels with a single electromagnetic field (selection rule ΔF=±1,ΔmF=0,±1). The present invention applies a working AC magnetic field (frequency ω _LF ) and auxiliary AC magnetic field (frequency ω _HF ), using the two-photon transition mechanism, an effective transition channel was constructed between |g1﹥ and |g2﹥.

[0071] The introduction of virtual intermediate energy levels includes: This two-photon transition process can be understood as being completed through a virtual intermediate energy level |virtual>. This is not a real atomic intrinsic energy level, but a mathematical construction in the multiphoton transition theory. The atom first absorbs an ω _LF The photon jumps from |g1> to |virtual> and then emits an ω _HF The photon (or vice versa) jumps from |virtual> to |g2>. The condition for this process to occur is exactly ω _LF +ω _HF Equal to the energy difference between |g1> and |g2>, that is, ω _clock .

[0072] The light field closed loop includes: at the same time, as the two-color light field of embodiment 1, its two frequency components ω _L1 and ω _L2 Couple the ground state energy levels |g1﹥, |g2﹥ and a common excited state energy level |e﹥ (e.g. 5P1 / 2|F'=1﹥). For example, ω _L1 Drive |g1﹥→|e﹥ transition, ω _L2 Drive the |g2﹥→|e﹥ transition.

[0073] In summary, a complete closed loop is formed, and its topological path can be expressed as: |g1>--(ω _LF ,ω _HF Two-photon)-->|g2﹥--(ω _L2 Photon)-->|e﹥--(ω_L1 Photon)-->|g1>.

[0074] Through magnetically induced two-photon transition, the limitation of atomic selection rule is cleverly circumvented, and the frequency and f are introduced. _LF +f _HF , thus achieving frequency decoupling. Simultaneously, this magnetic induction channel is connected to an excited state via an optical field, forming an all-optical-magnetic hybrid closed loop, allowing the resulting interference effect to be detected using simple optical means. This structural design combines the flexibility of frequency tuning, immunity to magnetic field noise, and convenient signal readout.

[0075] Example 5: This example fully demonstrates the application of the phase detection method of the present invention through a specific and reproducible numerical calculation and operation case. The application scenario of this case is to perform high-precision phase detection on a very low frequency (VLF) signal through electromagnetic induction.

[0076] In this example, we assume that we need to detect the secondary induced magnetic field generated by an underwater metal target under active electromagnetic field excitation. This secondary induced magnetic field is the working AC magnetic field in the method of the present invention, and its phase carries key information about the target's conductivity, geometry, and other aspects.

[0077] 1. Scene and parameter settings Atomic medium: Rubidium-87 ( 87 Rb) atomic vapor is encapsulated in a spherical glass chamber filled with 50 Torr nitrogen (N2) as a buffer gas.

[0078] System operating temperature: The atomic gas chamber is heated and maintained at 95°C by a non-magnetic heating device.

[0079] Target signal (working AC magnetic field) parameters: Operating frequency f _LF : 20kHz. This is a typical VLF frequency band used for underwater detection.

[0080] Working phase to be measured φ _LF : This is the unknown physical quantity that needs to be measured by this method.

[0081] Atomic intrinsic transition frequency (reference frequency): Selection 87 The clock transition of the Rb ground state, that is, the transition between the |F=1,mF=0﹥ and |F=2,mF=0﹥ energy levels.

[0082] The corresponding clock transition frequency f _clock =6,835,000,000Hz.

[0083] 2. Specific operations and calculation process Step A: System initialization and driving field application First, the system is initialized. The three-axis magnetic field compensation coil group is started to compensate the geomagnetic field and environmental stray magnetic field in the atomic gas chamber area to a level close to zero magnetic field. Then, the laser system is started to generate a laser beam with a wavelength of 795nm. It is modulated into two two-color light fields with frequencies of f_laser-3.4175GHz and f_laser+3.4175GHz through a microwave modulator. The frequency difference between the two components is exactly f _clock The two-color light field is polarized and then passes through the atomic gas chamber.

[0084] At the same time, the magnetic field module is started to apply the working AC magnetic field, and its frequency is set to the frequency of the target signal, that is, f _LF =20,000Hz.

[0085] Step B: Frequency decoupling setting According to the frequency decoupling core condition f _LF +f _HF =f _clock , the control and signal processing unit needs to calculate the auxiliary frequency f corresponding to the current operating frequency _HF .

[0086] Calculation process: f _HF =f _clock -f _LF f _HF =6,835,000,000Hz-20,000Hzf _HF =6,834,980,000Hz.

[0087] The control unit then instructs the multi-channel signal generator in the magnetic field module to generate a 20,000 Hz signal on one channel (to drive the coil to produce the working magnetic field) and a 6,834,980,000 Hz signal on the other channel (to drive the coil to produce the auxiliary magnetic field). This completes the establishment of a drive field that meets the quantum coherence requirements.

[0088] Step C: Acquisition of optical response signals Under the combined action of the above driving fields, the atomic gas chamber 87 The Rb atoms form a closed ring as in Example 4. The transmission intensity or polarization state of the laser passing through the atomic gas chamber will change with the global phase Φ _total The photodetector behind the gas cell converts this optical change into a continuous voltage signal, which is the optical response signal. The voltage value V(t) of this signal is related to the global phase Φ _totalRelated, V(t)∝cos(Φ _total (t)).

[0089] Through step C, the phase shift of the working magnetic field can be obtained.

[0090] Preferably, the method may further include step D: phase extraction based on synchronous demodulation.

[0091] In order to obtain the Φ _total Accurately separate the φ to be measured _LF ,This case adopts the synchronous demodulation method.

[0092] It should be noted that step D is not necessary, but is used to perform denoising in some cases to obtain more accurate data.

[0093] Applying reference phase modulation: the control unit applies a phase modulation to the signal channel generating the auxiliary AC magnetic field.

[0094] Modulation waveform: sine wave.

[0095] Modulation frequency f_mod: 1kHz.

[0096] Modulation depth A_mod: 0.1rad. At this time, the instantaneous value of the auxiliary phase is φ _HF (t)=φ _HF 0+0.1*sin(2π*1000*t).

[0097] Lock-in amplifier processing: The voltage signal V(t) output by the photodetector is input into a digital lock-in amplifier. At the same time, a 1kHz sine wave used for phase modulation is also input into the lock-in amplifier as a reference signal.

[0098] Demodulation and calculation: The lock-in amplifier will output two DC components, namely the in-phase component X and the orthogonal component Y. These two components are related to the phase φ to be measured. _LF The relationship is as follows: X∝sin(φ _LF -φ_offset); Y∝cos(φ _LF -φ_offset); Where φ_offset is determined by other fixed phases in the system (such as φ _HF 0,φ _L1 ,φ _L2 and circuit delays) to form a constant phase offset.

[0099] Finally, by calculating the inverse tangent of these two components, the phase to be measured can be obtained: _LF _measured=arctan(X / Y) The result φ_LF _measured is φ _LF -φ_offset. The value of φ_offset can be determined through a one-time calibration process: replace the signal to be measured with a reference signal with a known phase, and use the same method to measure a φ_ref_measured, then φ_offset = φ_ref_known - φ_ref_measured. In subsequent actual measurements, the measured φ _LF _measured plus the calibrated φ_offset, the working phase φ can be obtained _LF The absolute value of .

[0100] Through the above steps, this embodiment fully demonstrates how to use the method of the present invention to accurately measure the phase of a very low frequency signal with a frequency of 20 kHz, transforming the abstract theory and method flow into a set of specific, operational and reproducible engineering practices, fully demonstrating the feasibility and practicality of the present invention.

[0101] Example 6 For the sake of clarity, a specific embodiment of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that this embodiment is only used to illustrate the present invention and is not intended to limit the scope of protection of the present invention.

[0102] This embodiment provides a phase detection system, including: an atomic gas cell module 1 configured to accommodate an atomic medium; a laser system 2 configured to generate a light field and direct the light field through the atomic gas cell module; a magnetic field module configured to generate a working AC magnetic field and an auxiliary AC magnetic field in the atomic gas cell module; A photodetector, which is arranged on the transmission light path of the light field and is used to convert the light field transmitted through the atomic gas cell module 10 into an optical response signal; A control and signal processing unit is operatively coupled to the laser system, the magnetic field module, and the photodetector.

[0103] The atomic gas chamber module is constructed as an integrated physical environment, the core of which contains an atomic gas chamber filled with alkali metal atoms and buffer gas. The module further integrates a magnetic field compensation coil group surrounding the atomic gas chamber and a temperature control device for maintaining its operating temperature.

[0104] Specifically, the atomic gas chamber is a sealed glass container filled with, for example, rubidium-87 ( 87 Rb) as the atomic medium, and filled with nitrogen (N2) at a specific pressure as a buffer gas, its role is to slow down 87The collisions between Rb atoms and the chamber walls extend the atomic coherence time. The magnetic field compensation coil assembly 12 is typically a three-axis Helmholtz coil, driven by an external precision current source (not shown). Its function is to offset the geomagnetic field and other stray magnetic fields in the environment, creating a near-zero magnetic environment for the atomic medium, thereby eliminating interference from the background magnetic field on the measurement. The temperature control device can be a non-magnetic electric heating film or heating wire attached to the outer wall of the atomic chamber. A temperature sensor and a PID controller (integrated into the control and signal processing unit) form a closed-loop control to precisely heat and maintain the atomic chamber at an operating temperature of, for example, 85°C to ensure a sufficient and stable atomic vapor density. This integrated design integrates the core physical conditions required to provide a stable atomic state into a compact module, providing a foundation for achieving high-precision quantum coherent manipulation.

[0105] The laser system is physically located on one side of the atomic gas cell module. The light field it generates propagates along the Z-axis (defined as an example) and is guided through the atomic gas cell. In a preferred embodiment, to enhance system robustness by utilizing a clock transition that is first-order insensitive to magnetic field variations, the laser system includes a modulator configured to convert monochromatic light into a two-color light field, with the frequency spacing of the two-color light field locked to the frequency of the clock transition.

[0106] Specifically, the laser system 20 may include a distributed Bragg reflector (DBR) laser with a wavelength of 795 nm. The monochromatic laser output by the DBR laser is first coupled to an optical fiber and then enters an electro-optic modulator (EOM) or a microwave resonant cavity as a modulator. The modulator is driven by the control and signal processing unit 50, and the frequency of the driving signal is precisely set to 87 Half the transition frequency of the Rb atomic clock, that is, 3.4175 GHz. Through carrier suppressed double-sideband modulation technology, the modulator outputs a two-color light field containing two frequency components, and the frequency interval of the two components is precisely 6.835 GHz. This design enables the light field to coherently interact with atoms in the two ground state energy levels involved in the clock transition at the same time, which is the key to constructing a closed loop such as the method embodiment. Optionally, the modulator can also be implemented using other technologies, such as cascading acousto-optic modulators or directly high-speed modulation by injecting current into the laser.

[0107] The function of the magnetic field module is to generate the two key AC magnetic fields required by the present invention. Figure 2The module can include at least two sets of RF coils. For example, one set of Helmholtz coils arranged along the X-axis is used to generate a working AC magnetic field, and another set of Helmholtz coils arranged along the Y-axis is used to generate an auxiliary AC magnetic field. These two sets of coils are spatially orthogonal to reduce crosstalk. They are each connected to the RF output port of the control and signal processing unit via a coaxial cable. By passing an AC current of a specific frequency and phase through these two sets of coils, the required working AC magnetic field and auxiliary AC magnetic field can be induced in the central region of the atomic gas chamber.

[0108] The photodetector 40 is physically located on the other side of the atomic gas cell module, facing the laser system. Its function is to convert the light field carrying phase information after passing through the atomic medium into an electrical signal. In one specific embodiment, the photodetector can be a high-speed, low-noise balanced photodetector. A set of polarization optical elements, such as a λ / 4 wave plate and a polarizing beam splitter (PBS), can be placed in front of the detector to detect small rotations in the polarization angle of the light field. Compared with direct light absorption detection, this polarization rotation detection scheme generally has a higher signal-to-noise ratio and better suppression of laser intensity noise.

[0109] The control and signal processing unit (CPU) is the brains of the entire system, typically composed of hardware such as a field-programmable gate array (FPGA), a digital signal processor (DSP), and a microcontroller (MCU). It is operationally coupled to all other components, including the laser system 20, the magnetic field module 30, and the photodetector 40, through various interfaces (such as digital-to-analog converters (DACs), analog-to-digital converters (ADCs), and radio frequency signal sources). It is configured to perform a series of complex control and signal processing tasks, including generating and precisely controlling the microwave signals that drive the modulator in the laser system; generating and precisely controlling the radio frequency signals that drive the two sets of coils in the magnetic field module; and receiving and processing the optical response signals output by the photodetector.

[0110] Ultimately, the unit is configured to: control the laser system and magnetic field module to form a closed loop within the atomic medium; set the operating frequency of the working AC magnetic field and the auxiliary frequency of the auxiliary AC magnetic field so that their frequency combination is correlated to an intrinsic transition frequency of the atomic medium, thereby achieving decoupling of the operating frequency and the intrinsic transition frequency; and receive and process the optical response signal to demodulate the operating phase of the working AC magnetic field. The specific control law and signal processing flow will be detailed in the next embodiment.

[0111] According to one aspect of the present application, in one embodiment, the apparatus includes an atomic gas chamber module 1, a laser system 2, a photoelectric detection module 3, an RF coil assembly 4, a bias / compensation magnetic field coil 5, and a signal source and lock-in amplifier 6. The three-dimensional layout adopts a structure in which the optical axis is along the Z axis and the coil is coaxial with the gas chamber. Example 7. This example, based on Example 6, details the specific control law and signal processing flow executed by the control and signal processing unit to achieve frequency decoupling and phase demodulation.

[0112] Reference Figure 1 To achieve frequency decoupling, the control and signal processing unit's internal hardware and firmware are configured to support specific functions. Specifically, to achieve frequency decoupling, the magnetic field module includes at least two independently frequency-controlled signal channels, one for generating the working AC magnetic field and the other for generating the auxiliary AC magnetic field.

[0113] These two signal channels can be physically implemented by two independent direct digital synthesizers (DDS) or phase-locked loop (PLL) circuits within the control and signal processing unit. The outputs of these two channels are connected to at least two sets of radio frequency coils, which are configured to drive the working AC magnetic field and the auxiliary AC magnetic field within the atomic gas cell module, respectively.

[0114] On this hardware basis, the control and signal processing unit is configured to implement a control law that forces the operating frequency f _LF With auxiliary frequency f _HF The sum is always equal to the one-clock transition frequency f of the atomic medium _clock Furthermore, the control law further includes a synchronous compensation logic, and the control and signal processing unit operates at the operating frequency f according to the synchronous compensation logic. _LF When the auxiliary frequency f is adjusted _HF An equal and opposite synchronous compensation is applied to dynamically maintain the sum of frequencies constant.

[0115] For example, when the system receives a command to adjust the operating frequency from 20kHz to 25kHz (a 5kHz increase), the synchronous compensation logic is immediately triggered. The control and signal processing unit updates the frequency of the signal channel generating the operating magnetic field while precisely reducing the frequency of the signal channel generating the auxiliary magnetic field by 5kHz. This process is completed in microseconds, ensuring that quantum coherence conditions are not destroyed during frequency scanning or switching, thus achieving seamless broadband tuning.

[0116] In addition, in order to demodulate the working phase, the control and signal processing unit is configured to execute a process including two core steps. First, it instructs the magnetic field module to adjust the auxiliary phase φ of the auxiliary AC magnetic field. _HFSpecifically, the waveform generator inside the control unit generates a sine or triangle wave digital sequence with a frequency of f_mod (e.g. 1kHz), and superimposes it on the phase accumulator of the signal channel that generates the auxiliary AC magnetic field, thereby achieving the φ _HF Precise periodic modulation.

[0117] Secondly, the control unit receives the synchronously modulated optical response signal from the photodetector in response to the periodic scan, and demodulates the signal with reference to the preset periodic scan to extract the working phase φ _LF Specifically, the analog signal output by the photodetector, which has been frequency modulated at 1kHz, is digitized via a high-speed analog-to-digital converter (ADC). Subsequently, within the FPGA, the digital signal stream is fed into a digital orthogonal lock-in amplifier module. This module uses an internally generated 1kHz reference signal as a reference, and calculates the in-phase component X and the orthogonal component Y of the signal through digital mixing and low-pass filtering. Finally, the inverse tangent values ​​of X and Y are calculated using the CORDIC (Coordinate Rotation Digital Computer) algorithm to obtain the working phase φ to be measured. _LF This fully digital phase-locked demodulation solution has higher accuracy, lower drift and greater flexibility than traditional analog lock-in amplifiers.

[0118] Example 8: As an alternative or improved implementation of the above embodiment, this embodiment provides a more specific physical structure of a magnetic field module in a phase detection system. This structure is intended to optimize the uniformity of the applied AC magnetic field and reduce crosstalk between fields, thereby further improving the overall performance of the system.

[0119] In this embodiment, the coil portion of the magnetic field module is designed as a nested structure. The structure includes a main coil and a secondary coil nested therein. The main coil can be a multi-turn solenoid arranged along the Z axis (i.e., the direction of light field propagation), which is large enough to completely cover the core area of ​​the atomic gas chamber module. The secondary coil can be a pair of small-sized Helmholtz coils, which are precisely fixed at the geometric center of the main coil, and their axial directions are, for example, arranged along the X axis, perpendicular to the axis of the main coil. Both the main coil and the secondary coil are made of non-magnetic, high-temperature resistant materials (such as ceramics or polytetrafluoroethylene) as a skeleton to avoid deformation or unnecessary electromagnetic loss under heating and strong radio frequency field environments.

[0120] During the connection and operation, the primary and secondary coils are respectively connected to two independent signal channels of the control and signal processing unit. Specifically, the signal channel for generating a high-frequency auxiliary AC magnetic field is connected to the primary coil, while the signal channel for generating a low-frequency operating AC magnetic field is connected to the secondary coil. When the system is operating, a high-frequency current (e.g., a frequency close to 6.8GHz) flows through the primary coil, generating a highly uniform auxiliary AC magnetic field B along the Z-axis in the central area where the atomic gas chamber is located. _HF At the same time, a low-frequency current (e.g., a frequency in the range of 1 Hz to 10 GHz) flows through the secondary coil, generating a uniform working AC magnetic field B along the X-axis in the same area. _LF Since the two coils are spatially orthogonal and have a large size difference, this structure naturally provides good electromagnetic isolation and effectively reduces the crosstalk between the two frequency components.

[0121] The functional principle and technical effect of this nested coil structure design are as follows: Under normal circumstances, the frequency of the auxiliary AC magnetic field is much higher than the working AC magnetic field, and its field strength and uniformity are crucial to maintaining a stable quantum coherence effect. Using a larger solenoid as the main coil to generate the high-frequency field can form a wide-range, highly uniform magnetic field distribution in its central area, ensuring that the entire atomic medium sample is under basically the same driving conditions, thereby obtaining an optical response signal with higher contrast and narrower linewidth. Placing the secondary coil used to generate the working magnetic field in the center of the main coil ensures that the working magnetic field to be measured is also applied to the area where the atoms are most sensitive and respond most consistently. In summary, this structural design directly improves the quality of the driving field by optimizing the physical layout, which ultimately translates into improved phase detection sensitivity and accuracy.

[0122] As an optional solution and equivalent variant, the coil structure of the magnetic field module is not limited to this. In some optional embodiments, the main coil and the secondary coil can both be in the form of a Helmholtz coil pair and can be mounted on the same support structure in an orthogonal manner. In addition, a more complex coil design can also be used, such as a non-standard shape coil manufactured using 3D printing technology and optimized for magnetic field simulation, to achieve higher magnetic field uniformity in a smaller volume. In terms of material selection, for the auxiliary magnetic field coil operating in the microwave frequency band, its conductor can be made of silver-plated copper wire or Litz wire to reduce the skin effect loss at high frequencies and improve the quality factor (Q value) of the coil.

[0123] Example 9: As a supplement to the previous example, this example is intended to illustrate that the technical solution of the present invention has good versatility and is not limited to the use of specific atomic species. This example provides a phase detection system based on cesium-133 (¹³³Cs) atoms.

[0124] Structurally, the system in this embodiment shares a fundamentally similar core architecture to that of the system in Example 6, including the atomic gas chamber module, laser system, magnetic field module, photodetector, and control and signal processing unit. The primary difference lies in adaptive adjustments to key system parameters and components to accommodate changes in the atomic medium.

[0125] Specifically, in this embodiment, the core of the atomic gas cell module, namely the atomic gas cell, is filled with cesium-133 (¹³³Cs) atomic vapor. Accordingly, the laser in the laser system is replaced with a device capable of generating laser light with a wavelength of the cesium atomic D2 line (approximately 852nm). To utilize the clock transition of cesium atoms to enhance robustness, the modulator in the laser system is configured to convert 852nm monochromatic light into a two-color light field, and its frequency interval is precisely locked to the ground state clock transition frequency of cesium-133 atoms, which is f _clock About 9.192631770GHz.

[0126] In the connection relationship and action process, the internal firmware and software algorithms of the control and signal processing unit have also been modified accordingly. The frequency decoupling control law f _LF +f _HF =f _clock Still valid, but as a benchmark f _clock The value is updated to 9.192...GHz for cesium atoms. Therefore, when the operating frequency f _LF After being set, the control unit will calculate a new auxiliary frequency f _HF value, and instruct the magnetic field module to generate the corresponding AC magnetic field.

[0127] This example demonstrates that the phase detection mechanism based on frequency decoupling and closed-loop coherence proposed in this invention is a universal physical principle, not just a special case applicable to rubidium-87 atoms. By simply replacing the atomic medium and adjusting the matching laser wavelength and RF frequency, the entire technical solution can be transplanted to another atomic system and achieve the same functionality. This greatly expands the scope of application and implementation flexibility of the present invention. For example, the phase detection system of the present invention can be constructed by leveraging existing mature cesium atomic clock technology and the related industrial chain.

[0128] As an alternative and equivalent variant, in addition to rubidium-87 and cesium-133, the principles of this invention can also be applied to other alkali metal atoms with similar hyperfine energy level structures, such as potassium (K) or sodium (Na), simply by equipping them with corresponding laser systems and radio frequency sources. Furthermore, the optimal operating temperature required for different atoms may also vary. For example, for cesium atoms, the operating temperature is typically set in the lower range of 25°C to 40°C to achieve a suitable vapor density.

[0129] Embodiment 10: This embodiment is intended to illustrate the specific application of the phase detection method and system of the present invention in the field of communications, and provides a method for phase shift keying (PSK) data demodulation using a phase detection system.

[0130] First, in a typical binary phase shift keying (BPSK) communication scenario, the transmitter modulates a binary digital bit stream (containing 0s and 1s) onto a high-frequency carrier signal. In this embodiment, the carrier signal is the working AC magnetic field to be measured, and its carrier frequency (i.e., the working frequency f _LF ) is set to a microwave frequency band, such as 5 GHz. Its phase φ _LF It switches between two discrete values ​​depending on the bit data to be transmitted: for example, a phase of 0° represents a bit 0, and a phase of 180° (π radians) represents a bit 1.

[0131] The phase detection system of the present invention acts as a communication receiver in this scenario. Its working process is as follows: the system first calculates the phase detection signal according to the known carrier frequency f. _LF =5GHz, configure its own operating parameters. Specifically, the control and signal processing unit is based on f _LF +f _HF =f _clock The principle (based on 87 Take the Rb system as an example, f _clock =6.835GHz), calculate the required auxiliary frequency f _HF =6.835GHz-5GHz=1.835GHz, and drives the magnetic field module to generate the corresponding auxiliary AC magnetic field.

[0132] Then, the system enters the continuous phase measurement mode, as in the fifth embodiment, to measure the phase φ of the received 5 GHz working AC magnetic field in real time and continuously. _LF , and outputs a series of phase measurement values.

[0133] Finally, the digital signal processing module within the control and signal processing unit performs demodulation and decision-making on this series of phase measurements. This module incorporates decision logic. For example, for each bit period, it compares the measured phase value with a decision threshold (e.g., 90°). If the measured value falls near 0° (e.g., between -90° and +90°), the bit is judged to be 0; if the measured value falls near 180° (e.g., between +90° and +270°), the bit is judged to be 1. In this way, the system restores the received phase information to the original binary bit stream, completing the communication demodulation process.

[0134] This embodiment demonstrates that the system of the present invention can be used as a highly sensitive, broadband tunable communications receiver. Because its detection principle is phase-based, it is inherently robust to channel amplitude fading. Its broadband frequency tuning capability enables the receiver to flexibly operate across a wide spectrum, from extremely low frequencies to microwaves, adapting to diverse communications application requirements.

[0135] Alternatively, the method can be easily extended to more complex modulation schemes. For example, in quadrature phase-shift keying (QPSK), the phase can take on four values: 0°, 90°, 180°, and 270°. In this case, only three decision thresholds (e.g., 45°, 135°, and 225°) need to be set in the control unit to correctly demodulate the measured phase value into two binary digits (00, 01, 10, 11).

[0136] Example 11: This example is a preferred or improved configuration of Example 6, and aims to elaborate on the role of actively applying a bias magnetic field to further improve the stability and measurement accuracy of the system.

[0137] In this embodiment, the magnetic field compensation coil assembly not only compensates for the ambient magnetic field but also has an active control function: after compensating for the ambient magnetic field and creating a near-zero magnetic background, it applies a weak, stable, and precisely controllable DC magnetic field in a specific direction (for example, along the Z-axis of light propagation). This bias magnetic field is driven by a control and signal processing unit via a high-precision DC current source, with its field strength typically set at a few microteslas (μT).

[0138] The principle behind applying this bias magnetic field is to define a clear quantization axis for the atomic system. In an ideal zero-magnetic field environment, the atomic magnetic sublevels (for example, the F=1 energy level, which contains the three sublevels mF=-1, 0, and +1) are degenerate, meaning they have exactly the same energy. This degenerate state is unfavorable for precise quantum state manipulation, as the applied driving field may non-selectively interact with multiple sublevels simultaneously, leading to coherence destruction and reduced signal contrast.

[0139] By applying a bias magnetic field along the Z axis, this degeneracy is broken, and each mF sub-energy level will undergo energy splitting due to the Zeeman effect, and the energy difference of the splitting is proportional to the strength of the bias magnetic field. This is like establishing a clear coordinate system inside the atom, making different quantum states clearly distinguishable. The direct technical effect brought about by this is that |F=1,m F=0> and |F=2,mF=0>, the transition frequencies of the two clock transition energy levels are separated from other transition frequencies involving mF≠0. Therefore, when applying light fields and AC magnetic fields, it can be ensured that these driving fields mainly interact with our desired mF=0 energy level, while forming a detuned state with other irrelevant transition paths, thereby greatly suppressing the noise and interference that may be introduced by these irrelevant paths. Ultimately, this active definition and control of the quantized axis can significantly improve the signal-to-noise ratio and contrast of the optical response signal, and is one of the key practical steps to achieve high-precision and high-stability phase measurement.

[0140] As an option, the direction of the bias magnetic field can be optimized according to the specific experimental configuration. For example, if linearly polarized light is used for detection, the direction of the bias magnetic field can be set to be perpendicular to the polarization and propagation direction of the light to meet specific quantum transition selection rules, thereby maximizing the response of the target signal. The strength of the bias magnetic field is also a parameter that needs to be optimized: it needs to be strong enough to clearly separate the various magnetic sublevels, but not too strong to avoid introducing a non-negligible second-order Zeeman frequency shift, which will negatively affect the stability of the clock transition frequency.

[0141] Example 12: According to one aspect of the present application, a quantum coherent closed-loop phase detection system based on multi-photon transitions is provided. A closed transition path is constructed by applying multiple light fields and AC magnetic fields, and a clock transition is used to suppress magnetic field interference. oh LF ) as the working signal field carrying phase information. The detection system detects signals through changes in the polarization state and / or intensity of the transmitted light after the atomic gas cell, performs spectrum analysis on the output signal, and extracts the phase-frequency response function.

[0142] Among them, the present invention uses a multi-photon transition path (such as |g, F =1﹥ω LF ∣Virtual﹥ωHF∣ F =2﹥ωL2∣e, F =1﹥ωL1|g, F =1>) to build a closed loop, and its total transition phase is determined by the AC magnetic field phase: F=f LF –(f HF +f L1 +f L2 ).

[0143] By adjusting oh LFThe frequency (in the range of 1Hz-10GHz) changes the closure condition of the transition path. Apply an AC magnetic field between the two ground state energy levels to realize a closed loop, add a virtual intermediate energy level, and use multiple oscillating AC magnetic fields to replace a single AC magnetic field to realize a closed loop. Among the multiple AC magnetic fields, one is used as the working magnetic field for detection. As long as the frequency combination of each AC magnetic field is reasonable and meets the transition selection rule, the frequency of the working magnetic field is no longer limited by the frequency of the clock transition, so that the working magnetic field frequency is free from the limitation of the inherent frequency of the atomic clock transition. The clock transition used is, for example, 87Rb 5 S 1 / 2 |F g =1,m F =0﹥→|F g =2,m F =0﹥,6.835GHz,the excited state used can be 5 P 1 / 2 |F e =1,m F =1>or 5 P 1 / 2 |F e =1,m F =-1﹥.

[0144] According to one aspect of the present application, a multi-photon phase detection system is provided, comprising: Atomic gas chamber, used to contain atomic medium; a first magnetic field generating unit, configured to generate a first alternating magnetic field with adjustable frequency and apply the magnetic field to the atomic gas chamber; A second magnetic field generating unit is used to generate a second AC magnetic field and apply it to the atomic gas chamber, wherein the sum of the frequency of the second AC magnetic field and the frequency of the first AC magnetic field is equal to the clock transition frequency of the atomic medium; A laser source, used for generating a laser field corresponding to the clock transition frequency and injecting the laser field into the atomic gas chamber; A detection unit, used to detect changes in light signals passing through the atomic gas chamber; The first magnetic field generating unit and the second magnetic field generating unit are configured to construct a closed transition path including a virtual intermediate energy level between two ground state energy levels of the atomic medium, and the frequency of the first AC magnetic field is adjustable in the range of 1 Hz to 10 GHz.

[0145] Among them, the laser source includes: A master laser for generating carrier light; An optical modulator, selected from an electro-optic modulator or an acousto-optic modulator, is used to modulate the carrier light to generate sideband light with a frequency of f0±fRF, where f0 is the carrier light frequency and f RF is the modulation frequency; Here, the modulation frequency fRF is equal to the clock transition frequency.

[0146] Wherein, the first magnetic field generating unit includes: A frequency synthesizer, configured to generate a first AC signal with adjustable frequency; a power amplifier connected to a frequency synthesizer; a coil (such as a Helmholtz coil or a solenoid), connected to the power amplifier, for converting the first AC signal into a first AC magnetic field; The phase control circuit is used to control the phase of the first AC signal.

[0147] The detection unit includes: A photodetector, used to convert the light signal transmitted through the atomic gas chamber into an electrical signal; a lock-in amplifier connected to the photodetector and configured to extract a signal component related to the phase of the first AC magnetic field from the electrical signal using the frequency of the second AC magnetic field as a reference frequency; a phase demodulation circuit connected to the lock-in amplifier and configured to demodulate the phase information of the first AC magnetic field from the signal component; The time constant of the lock-in amplifier is set to be greater than 10 times the period of the first AC magnetic field.

[0148] Specifically, the equipment used in this technical solution includes an atomic gas chamber module, a laser system, a magnetic field module, and a lock-in amplifier: Atomic gas cell module: Alkali metal gas cell (such as 87Rb), filled with buffer gas (such as N2), temperature controlled by non-magnetic electric heating device (85-120℃); magnetic shielding device (optional, can be used for performance evaluation or calibration) or three-axis magnetic field compensation coil assembly; Laser system: Optical path: laser → laser modulator → beam expander → circular polarization optical element → gas chamber → photodetector (or → polarization beam splitter → balanced photodetector); Magnetic field module: bias magnetic field coil and current source; RF coil assembly and signal generator (AC magnetic field initial phase coherent output); The technical solution includes two parts: testing and data analysis. The specific steps are as follows: Step 1): Heat the alkali metal gas chamber to a set temperature (e.g., the rubidium atom gas chamber is heated to 85°C) and apply a bias magnetic field; Adjust the laser wavelength (e.g. 795nm for the D1 line of 87Rb) and generate two-color sideband light (separated by 6.835GHz) using electro-optical modulation or microwave modulation, and lock it to the clock transition; Step 2): Apply an AC magnetic field oh LF and oh HF , apply working magnetic field oh LFBetween 1Hz–10GHz (amplitude such as 50nT); The sum frequency of the working signal ωLF and the auxiliary signal ωHF must be precisely aligned with the clock transition frequency. When adjusting ωLF, ωHF must be changed synchronously to keep the sum of the two constant.

[0149] Step 3): The transmitted light signal depends on the global phase Φ = f LF -( f HF+ f L1+ f L2). Therefore, a single measurement can obtain the target observation quantity f LF. For easier reading f The value of LF can be obtained by π Scan within a cycle f Phase realization of HF.

[0150] The multiphoton transition closed-loop design enables an operating frequency (ωLF) range of 1Hz–10GHz. The phase-frequency response depends solely on the closed-loop phase condition, suppressing AC magnetic field amplitude fluctuations and light intensity drift. The application of clock transition technology significantly suppresses the effects of ambient magnetic field perturbations, as the transition frequency is independent of the applied magnetic field at its dominant order. The device is compatible with a variety of lasers and magnetic field control devices, and is suitable for different alkali metal atoms (such as 87Rb and 133Cs).

[0151] In the traditional two-photon coherent population trapping (CPT) system, two driving beams ( oh 1 and oh 2) Through the two-photon resonance condition ( oh 1- oh 2 = Δhyperfine) excited ground state | F =1﹥and∣ F =2>. However, its frequency tuning capability is limited by the intrinsic hyperfine splitting frequency of the atom (such as 6.8 GHz for 87Rb).

[0152] The present invention extends this model by introducing multiple AC magnetic field closed loops (Closed-loop transition contour): AC magnetic field phase coordination: Apply two AC magnetic fields ( oh 1, oh 2), forming a closed transition path (such as | F =1﹥→∣Virtual﹥→∣ F =2﹥→∣ F =1﹥). Among them, the virtual intermediate energy level (|Virtual﹥) is determined by the AC magnetic field oh 1 and oh 2's joint coupling effect is generated.

[0153] Total phase closure condition: The optical properties of the atomic medium depend on the global phase of all driving fields in the closed loop: Φ = f LF-( f HF+ φL 1+ φL 2). Therefore, based on the quantum interference effect, the optical response characteristics of the atomic medium essentially depend on the relative phase of the low-frequency driving magnetic field (RF field) f LF, this phase is the target observation.

[0154] In a multi-photon quantum coherence system, the steady-state distribution of atomic populations is determined by the closed-loop phase, rather than the absolute phase of a single AC magnetic field. Specifically: Phase-sensitive detection mechanism: Phase fluctuations of the AC driving magnetic field induce changes in the atomic population in the closed loop, which manifests as observable changes in the intensity and / or polarization state of the transmitted light.

[0155] Frequency tuning freedom: by adjusting multiple The frequency (1Hz-10GHz) is increased by adding virtual intermediate energy levels, and multiple oscillating AC magnetic fields are used to replace the previous AC magnetic field to achieve a closed loop. Among the multiple AC magnetic fields, one is used as the working magnetic field for detection. As long as the frequency combination of each AC magnetic field is reasonable and meets the transition selection rule, the frequency of the working magnetic field is no longer limited to the frequency of the clock transition, and the closed loop closing condition (Φtotal= f ref), which frees the system operating frequency from the inherent transition frequency limit of atoms.

[0156] Magnetic field noise suppression: Select the magnetically insensitive clock transition path (such as 87Rb| F =1, mF =0﹥‹-›∣ F =2, mF =0﹥), its Zeeman frequency shift is zero, making the closed loop phase robust to external magnetic field fluctuations.

[0157] Amplitude fluctuation suppression: Phase detection results only depend on the relative phase of the AC magnetic field (φ f L1, φ f L2, φ f LF ), and the AC magnetic field amplitude ( A L1, A L2, A LF ), thus suppressing the magnetic field amplitude noise.

[0158] This invention describes a multiphoton phase detection system and method based on closed-loop quantum coherence and clock transitions. This system constructs virtual intermediate energy levels through a closed multiphoton transition loop, utilizes clock transitions to suppress magnetic field interference, and enables wideband (1Hz-10GHz) signal analysis through phase detection. The device used in this invention comprises an atomic gas cell module, a laser system, an AC magnetic field module, and a lock-in amplifier.

[0159] Atomic gas chamber module: An alkali metal gas chamber (such as rubidium-87 or cesium-133) is placed in a multi-layer magnetic shielding barrel (optional, can be used for performance evaluation or calibration) or a magnetic field active stabilization system. The gas chamber is filled with nitrogen (N2) as a buffer gas and the temperature is controlled (85-120°C) by a non-magnetic electric heating device.

[0160] A triaxial magnetic field compensation coil assembly surrounds the gas chamber to compensate for the residual magnetic field and apply a background magnetic field when needed.

[0161] Laser system: Pumping optical path (along the z-axis): pumping laser (wavelength 795 nm, corresponding to 87RbD1 line) → beam expander → circular polarization optical element (λ / 4 wave plate) → gas cell.

[0162] The pump light generates two-color sideband light (with an interval of 6.835 GHz) and is locked to the clock transition (|F=1,mF=0﹥→|F=2,mF=0﹥).

[0163] AC magnetic field module: This module uses an AC magnetic field coil assembly (variable frequency range 1Hz-10GHz) driven by a multi-channel signal generator, with phase-coherent output from each channel. The AC magnetic field includes a low-frequency working field (ωLF) and a high-frequency auxiliary field (ωHF).

[0164] The bias / compensation magnetic field coil utilizes a three-axis Helmholtz structure to generate a uniform static magnetic field and offset environmental disturbances. The RF coil assembly comprises two physical channels, one energizing the low-frequency working field ωLF and the other energizing the high-frequency auxiliary field ωHF. Together with the optical field, these channels form a closed transition path. A closed transition path is a circular multiphoton transition channel formed by the coupling of the optical field and the AC magnetic field, with the ground state sublevel and the excited state as vertices. Virtual energy levels are intermediate states that are not physically occupied and result from the combined coupling of multiple fields.

[0165] Specifically, a Z-axis coil provides the bias field; coupled coils or microstrip antennas are placed in the Z or X / Y directions to apply the ωLF and ωHF, respectively. The two channels are geometrically offset by 10–30 mm and employ independent shielding and matching networks to minimize crosstalk. A phase-synchronized multichannel signal source drives the two channels, maintaining a coherent reference with the optical field modulator. Frequency linkage maintains sum-frequency constraints. Multiple AC magnetic fields replace a single magnetic field to form a closed loop, freeing up the operating frequency degree of freedom. Clock transition paths are exploited to reduce first-order Zeeman sensitivity.

[0166] Optionally, a body coil can be used to improve uniformity in the low-frequency band (≤kHz); microstrip loop / patch antennas can be used to improve coupling in the MHz–GHz band. Multiple layers of magnetic shielding can be added for laboratory calibration, while active compensation alone can be used in engineering deployments. Regarding parameters, the bias field is adjustable from 0–100 µT, preferably operating at near-zero or low bias. The amplitude of the ωLF reaching the center of the gas chamber is approximately 50 nT. The ωLF frequency can be set within 1 Hz–10 GHz, and ωHF is linked to the sum frequency. The coil Q value can be low in the low-frequency band to widen the bandwidth, while a 50 Ω match is used in the high-frequency band. The sum frequency relationship is: sum frequency constraint ωLF + ωHF = ωclock, where ωLF is the operating low-frequency field angular frequency, in rad / s, with a range of 1 Hz–10 GHz; ωHF is the auxiliary high-frequency field angular frequency, in rad / s; and ωclock is the clock transition angular frequency, in rad / s, which for 87Rb is approximately equal to 2π·6.835×10 9 ; Approximately equal to means the calibration value is subject to the standard and ±10 is allowed -7 Relative deviation.

[0167] In some embodiments, the primary laser is locked near the 795 nm linear spectrum peak, and a microwave-driven EOM is used to generate double-sideband (DSB) output, with a frequency-locked loop maintaining the sideband spacing at 6.835 GHz. σ polarization is controlled by adjusting the waveplate angle. If polarization readout is used, a PBS is added to the gas cell output and connected to a balanced detector. This step is used to establish a steady-state CPT dark state, improve the phase response signal-to-noise ratio, and reduce sensitivity to amplitude drift.

[0168] Optionally, the detection channel can be replaced with a weak 780 nm probe light, detuned by about 0.5 nm to reduce absorption; the pump power can be adjusted between 0.5–5 mW to compromise linewidth and contrast; the polarization can be selected σ + or σ - To adapt to specific mF paths. Regarding parameters, the EOM RF power is set based on the device's Vπ, typically optimized within the range of 0–27 dBm; the beam waist is 1–3 mm; and the CPT linewidth is typically in the hundreds of Hz to kHz range, affected by air pressure and light intensity.

[0169] In this embodiment, a coherent reference distribution is achieved throughout the system using a 10 MHz reference. Drives such as ωLF and ωHF share this reference and maintain phase programmability within a DDS / PLL. The phase response of the transmitted signal is acquired via a lock-in amplifier. The term global phase Φ refers to the algebraic combination of all drive field phases along the closed-loop path. Phase sweeping involves linearly sweeping Φ by varying the reference phase ϕHF while fixing the target phase ϕLF.

[0170] Specifically, each channel of the signal source uses a common 10 MHz reference input, sets the phase zero point, and records the phase delay. A lock-in amplifier references the phase of the ωHF channel. The software performs a 0–2π sweep of the φHF channel and records the transmitted signal. This step stably maps the phase of the field to be measured to the phase value of the optical readout, facilitating calibration and traceability.

[0171] Optionally, the reference distribution network can incorporate a phase-stable distributor and temperature-controlled cables. A phase noise analyzer can be used for auxiliary calibration in the high-frequency band. The reference source phase noise is preferably less than −120 dBc / Hz at 1 kHz offset; the phase-locking time constant, 1–100 ms, is selected based on the frequency band. The global phase relationship is: Global Phase Φ = φLF − (φHF + φL1 + φL2). Where: Φ is the total closed-loop phase, in rad; φLF is the operating low-frequency field phase, in rad, which is the target observation; φHF is the auxiliary high-frequency field phase, in rad; φL1 is the phase of pump field sideband 1, in rad; and φL2 is the phase of pump field sideband 2, in rad. Transmission signal model: Transmission signal I(Φ)=I0+A·cos(Φ+Φbias); where: I(Φ) is the transmitted photoelectric signal voltage, unit is V; I0 is the DC baseline, unit is V; A is the coherent modulation amplitude, unit is V; Φbias is the equivalent bias phase, unit is rad, which is used to absorb the constant term introduced by the fixed delay and path difference of the device.

[0172] In this embodiment, φHF is scanned to sample a 2π phase cycle, I(Φ) is fitted to obtain Φ, and φLF is inverted. ωLF is set according to application requirements within a wide frequency band, and the above process is repeated to obtain the phase-frequency response function. The term phase-frequency response function refers to the functional relationship of φLF with frequency and is used for target field phase extraction or communication demodulation. The coil constant kcoil refers to the proportional coefficient between the coil center field and the coil current.

[0173] Specifically, uniform phase sampling is performed at N points (e.g., N = 16 / 32 / 64) under a fixed ωLF condition. Sine fitting is used to obtain A, I0, Φbias, and Φ. φLF is calculated from Φ and the known φHF, φL1, and φL2. By varying ωLF and linking ωHF to maintain the sum-frequency constraint, φLF(f) is obtained and archived. The equivalent magnetic field phase is obtained by coil calibration using B = kcoil·ILF. This step separates the phase measurement deviation into reference phase drift and optical path drift, allowing for zero-point correction.

[0174] Optionally, a dual-reference method can be used to simultaneously scan φHF and φL1 to improve suppression of optical phase drift. Time window averaging can be used to improve SNR in low-frequency bands, while bandpass filtering can be used in high-frequency bands. Regarding parameters, the number of sampling points N and the phase-locking time constant jointly determine the total measurement time. The fitting residual threshold can be set to be less than 1–5% of the baseline to determine validity. The coil relationship is: Magnetic Field at the Coil Center B ≈ kcoil·ILF; where B is the magnetic flux density at the coil center, in T; kcoil is the coil constant, in T / A, determined by geometry and materials and calibrated through field measurements; ILF is the coil current applied to the ωLF channel, in A; ≈ denotes a linear approximation that ignores higher-order edge effects and mutual inductance.

[0175] In this embodiment, the closed-loop path uses 87Rb 5S1 / 2|Fg=1,mF=0〉|Fg=2,mF=0〉 as the clock transition channel, and the excited state can be selected as 5P1 / 2|Fe=1,mF=±1〉. The AC magnetic field satisfies the selection rule of ΔmF=0 or ±1. The term "selection rule" means that the polarization, frequency, and spatial direction of each coupled field are consistent with the energy level transition rules. Specifically, the light field adopts σ polarization; the AC magnetic field is arranged in a direction orthogonal to or parallel to the quantization axis to obtain the desired ΔmF; and a closed loop is constructed by combining frequency and polarization: |Fg=1〉→|Virtual〉→|Fg=2〉→|Fe=1〉→|Fg=1〉. This step ensures that the quantum interference path is closed and controllable.

[0176] Alternatively, the atoms can be replaced with 133Cs and the clock transition frequency adjusted accordingly. Differential measurements can also be performed using different mF substates to assess the system's systematic errors. Regarding parameters, the polarization extinction ratio is preferably ≥100:1; the quantization axis is defined by the bias field, and its direction is consistent with the coil layout.

[0177] Implementation steps (taking rubidium-87 atoms as an example): Step 1: System Initialization The rubidium gas chamber was heated to 85°C, and the bias magnetic field was stabilized by a three-axis compensation coil.

[0178] The pump laser wavelength was adjusted to 795 nm, and a microwave modulator was used to generate two-color sideband light (±3.4175 GHz sidebands), which was locked to the clock transition.

[0179] The detection laser wavelength was tuned to 780 nm and detuned by 0.5 nm, and the polarization beam splitter was adjusted to return the balanced detector baseline to zero.

[0180] Step 2: Apply the driving magnetic field Apply driving magnetic field: ω LF (Working signal field): The frequency is selected in the range of 1 Hz to 10 GHz according to the application requirements (such as detection depth), and the amplitude is fixed at 50 nT.

[0181] ω HF (Auxiliary field): The frequency must satisfy ω LF +ω HF ≡clock transition frequency. When ω LF When making any adjustment, you need to adjust ω synchronously HF To keep the sum of the two frequencies constant.

[0182] Step 3: Phase signal acquisition The transmitted light signal depends on the global phase Φ=φφ LF -(φφ HF +φφ L1 +φ L2 ). Therefore, a single measurement can obtain the target observation φ LF To facilitate reading φ LF The value of φ can be obtained by scanning φ over a complete 2π period. HF Phase realization.

[0183] By introducing an auxiliary AC magnetic field and constructing a closed loop with the frequency locked to the atomic clock transition, the present invention successfully achieves the decoupling between the detection frequency and the atomic intrinsic structure, giving a single device the ability to perform broadband frequency detection while maintaining high stability. This effect is achieved due to its unique frequency coordination mechanism: by executing f _LF +f _HF =f _clock The control law of the system, the resonance condition of the system is no longer determined by the operating frequency f _LF is determined independently, but by its relationship with the auxiliary frequency f _HF Therefore, f _LF It can be freely selected in a wide range from Hz to Gigahertz, and only needs to compensate f synchronously and inversely. _HF At the same time, since the frequency reference f _clock Locked to a clock transition that is insensitive to magnetic fields, the system inherits the stability of the clock transition and effectively suppresses ambient magnetic field fluctuations. Specifically, in marine electromagnetic detection, for example, the same device can operate in very low frequency bands (such as 20kHz) that require deep penetration to detect large underwater targets, while also seamlessly switching to microwave bands (such as 5GHz) for high-speed underwater communications. This resolves the inherent contradiction in existing technologies between frequency flexibility and system stability.

[0184] The present invention encodes the phase information to be measured in the global phase of the closed loop and uses synchronous demodulation technology for signal extraction, which fundamentally solves the dependence of the measurement results on the fluctuation of the driving magnetic field amplitude and significantly improves the measurement accuracy and long-term stability of the phase. This effect is achieved in the following way: the optical response of the system directly depends on the global phase Φ composed of the phases of each branch._total , rather than the amplitude of the resonance signal. The phase to be measured φ _LF The change of Φ directly leads to _total By changing the phase of a known reference (such as φ _HF ) applies periodic scanning and uses this information as a reference for phase-locked amplification, which can separate φ from the complex signal with high signal-to-noise ratio. _LF In weak signal detection scenarios requiring long integration times, such as geophysical exploration, slow drift of laser power or fluctuations in RF amplifier gain are fatal noise sources in traditional amplitude detection schemes. However, due to its phase encoding characteristics, the present invention treats this amplitude noise as common-mode interference and suppresses it, ensuring the reliability and repeatability of the measurement results.

[0185] While solving the core technical problems, the technical solution of the present invention also brings about an innovation in the application form of the system, that is, it realizes multi-functional and multi-task coverage with a single hardware platform, significantly improving the application versatility of the system and reducing the overall cost of use for users. This effect is a direct reflection of the two major technological innovations mentioned above: broadband frequency adaptability enables the same device to replace the task combination that previously required multiple dedicated atomic sensors of different frequency bands to complete. For example, a comprehensive scientific research platform no longer needs to purchase and maintain atomic magnetometers for low-frequency magnetic anomaly detection and atomic receivers for microwave measurement separately, but only needs to adjust the operating frequency f of the system of the present invention through software instructions. _LF , which can meet the needs of different experiments. From the perspective of user experience, this ability to quickly switch between different application scenarios without replacing hardware provides unprecedented operational flexibility, greatly simplifies the experimental process, shortens task preparation time, and objectively improves the efficiency of scientific research and engineering applications.

[0186] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the scope of protection of the present invention.

Claims

1. A multi-photon phase detection method based on closed-loop quantum coherence and clock transition, characterized in that: include: applying a group driving field to the atomic medium to construct a closed loop in the atomic medium, wherein the driving field comprises a light field, a working AC magnetic field, and an auxiliary AC magnetic field; Setting the working frequency of the working AC magnetic field and the auxiliary frequency of the auxiliary AC magnetic field, wherein the frequency combination is related to the natural transition frequency of the atomic medium, so as to achieve decoupling of the working frequency and the natural transition frequency; Obtaining the optical response signal generated by the interaction between the closed ring and the atomic medium; Based on the optical response signal, the working phase of the working AC magnetic field is analyzed.

2. The method according to claim 1, characterized in that The frequency combination is related to the intrinsic transition frequency of the atomic medium, specifically: The sum of the operating frequency and the auxiliary frequency is equal to the clock transition frequency of the atomic medium.

3. The method according to claim 2, characterized in that Also includes: The operating frequency is adjusted within a preset broadband frequency range, and the auxiliary frequency is changed synchronously and inversely with the adjustment, so that the sum of the operating frequency and the auxiliary frequency is constantly maintained equal to the clock transition frequency during the entire adjustment process.

4. The method according to claim 1, wherein The optical response signal carries information of the global phase, which is a composite phase formed by quantum interference of multiple branch phases constituting a closed loop, and the working phase to be demodulated is one of the multiple branch phases.

5. The method according to claim 1, wherein To enhance the robustness of the closed loop to external magnetic field fluctuations, the intrinsic transition frequency is selected as a clock transition frequency that is first-order insensitive to magnetic field changes.

6. The method according to claim 1, characterized in that The closed loop transition loop structure is configured as follows: The working AC magnetic field and the auxiliary AC magnetic field work together to form an atomic transition channel containing a virtual intermediate energy level between two ground state energy levels of the atomic medium to meet the transition selection rule.

7. The method according to claim 3, characterized in that The operating frequency is adjusted within a broadband frequency range that spans from very low frequencies covering 1 Hz to microwave frequencies covering 10 GHz.

8. A multi-photon phase detection system based on closed-loop quantum coherence and clock transitions, characterized in that: include: an atomic gas cell module configured to accommodate an atomic medium; a laser system configured to generate a light field and direct the light field through the atomic gas cell module; a magnetic field module configured to generate a working AC magnetic field and an auxiliary AC magnetic field in the atomic gas chamber module; A photodetector, which is arranged on the transmission light path of the light field and is used to convert the light field transmitted through the atomic gas cell module into an optical response signal; a control and signal processing unit operatively coupled to the laser system, the magnetic field module, and the photodetector, The control and signal processing unit is configured as follows: By controlling the laser system and magnetic field module, a closed loop is constructed in the atomic medium; Setting the working frequency of the working AC magnetic field and the auxiliary frequency of the auxiliary AC magnetic field so that their frequency combination is associated with the inherent transition frequency of the atomic medium, thereby achieving decoupling of the working frequency and the inherent transition frequency; Receive and process the optical response signal, and analyze the working phase of the working AC magnetic field.

9. The system according to claim 8, characterized in that To achieve frequency decoupling, The magnetic field module includes at least two signal channels with independently controllable frequencies, which are used to generate a working AC magnetic field and an auxiliary AC magnetic field respectively; The control and signal processing unit is configured to execute a control law that forces the sum of the operating frequency and the auxiliary frequency to be always equal to the clock transition frequency of the atomic medium.

10. The system according to claim 8, wherein: In order to enhance the robustness of the system by utilizing the clock transition that is first-order insensitive to magnetic field changes, the laser system includes a modulator configured to convert a monochromatic light into a two-color light field, and the frequency interval of the two-color light field is locked to the frequency of the clock transition.

11. The system according to claim 9, wherein: At least two signal channels of the magnetic field module are electrically connected to at least two groups of radio frequency coils respectively. The at least two groups of radio frequency coils are configured to drive the working AC magnetic field and the auxiliary AC magnetic field respectively in the atomic gas chamber module.

12. The system according to claim 9, wherein: The control law further includes a synchronous compensation logic. According to the synchronous compensation logic, the control and signal processing unit applies synchronous compensation of equal magnitude and opposite direction to the auxiliary frequency when the operating frequency is adjusted to dynamically maintain the constant sum of the frequencies.

13. The system according to claim 8, wherein: The atomic gas cell module includes: an atomic gas chamber filled with alkali metal atoms and a buffer gas; A magnetic field compensation coil assembly surrounding the atomic gas chamber; A temperature control device used to maintain its operating temperature.

14. A multi-photon phase detection device, characterized in that: include: Atomic gas chamber, used to contain atomic medium; a first magnetic field generating unit, configured to generate a first alternating magnetic field with adjustable frequency and apply the magnetic field to the atomic gas chamber; A second magnetic field generating unit is used to generate a second AC magnetic field and apply it to the atomic gas chamber, wherein the sum of the frequency of the second AC magnetic field and the frequency of the first AC magnetic field is equal to the clock transition frequency of the atomic medium; A laser source, used for generating a laser field corresponding to the clock transition frequency and injecting the laser field into the atomic gas chamber; A detection unit, used to detect changes in light signals passing through the atomic gas chamber; The first magnetic field generating unit and the second magnetic field generating unit are configured to construct a closed loop transition path including a virtual intermediate energy level between two ground state energy levels of the atomic medium, and the frequency of the first AC magnetic field is adjustable in the range of 1 Hz to 10 GHz.

15. The device according to claim 14, characterized in that: Laser sources include: A master laser for generating carrier light; an optical modulator selected from an electro-optic modulator or an acousto-optic modulator, for modulating the carrier light to generate sideband light with a frequency of f0±fRF, wherein f0 is the carrier light frequency and fRF is the modulation frequency; Here, the modulation frequency fRF is equal to the clock transition frequency.

16. The device according to claim 14, characterized in that: The first magnetic field generating unit includes: A frequency synthesizer, configured to generate a first AC signal with adjustable frequency; a power amplifier connected to a frequency synthesizer; a coil, connected to the power amplifier, and configured to convert the first AC signal into a first AC magnetic field; The phase control circuit is used to control the phase of the first AC signal.

Images