Rydberg electromagnetic direction finding device based on spherical atomic air chamber array

Abstract

The invention relates to a Rydberg electromagnetic direction finding device based on a spherical atomic air chamber array. The Rydberg electromagnetic direction finding device is mainly composed of an antenna assembly, an antenna regulation and control assembly and a signal receiving assembly. The antenna assembly is composed of a 5 * 5 arranged spherical air chamber array, and the antenna regulation and control assembly comprises a 852 nm surface laser, a 509 nm surface laser and a 852 nm surface laser. The signal receiving assembly comprises a photoelectric detector embedded in a circuit board below each air chamber. The spherical gas chamber is filled with cesium atoms, and the lower part of the gas chamber is connected with a photoelectric detector. According to the device, the Rydberg atom spherical air chambers are adopted to form a signal receiving array, the high sensitivity of Rydberg atoms and the high sensitivity of electromagnetic field intensity measurement are utilized, and the incoming wave direction is inverted according to the weak difference of the signal intensity after electromagnetic signals emitted by an information source are sensitive in different air chambers; accurate measurement of the Rydberg atom electromagnetic sensitive system on the incoming wave direction is realized, and the Rydberg atom electromagnetic sensitive system can be used as novel electromagnetic measurement sensing equipment in the future.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic measurement, and particularly relates to a Rydberg electromagnetic direction finding device based on a spherical atomic cell array. The present invention uses Rydberg atoms as a sensitive system, utilizes the ultra-sensitive and ultra-sensitive characteristics of Rydberg atoms to electromagnetic fields, and based on the Electromagnetic Induced Transparency (EIT) and Autler-Townes effects of Rydberg atoms, senses electromagnetic signal sources through a spherical Rydberg atomic cell array, and inversely derives the direction information of the signal source relative to the sensor according to the field strength differences measured by each unit in the array. This sensor can not only accurately measure the source direction of the electromagnetic field, but also reduces the volume through an integrated design. In order to meet the electromagnetic direction finding requirements of each frequency band, the atomic energy levels can be accurately controlled by lasers to meet the response of the sensitive frequency band, and finally it can be used as a future new type of electromagnetic direction finding sensing device, with great application value. Technical Background

[0002] Electromagnetic measurement technology is a technology with a wide range of applications, high precision requirements, and many usage scenarios. The electromagnetic direction finding technology in electromagnetic measurement technology is also an important research direction. Since the development of traditional antennas, researchers have designed various antennas to meet the requirements of electromagnetic direction finding technology for different fields. However, with the continuous maturity of technology, its bottlenecks have gradually emerged. Especially under the influence of the electronic thermal noise of traditional antennas, the sensitivity and measurement accuracy of antennas can no longer be improved; moreover, due to the influence of the Chu limit, in the context of direction finding tasks in a specific electromagnetic frequency band, the antenna size cannot be made smaller, which restricts the miniaturization and integration development of antennas and payload platforms. The currently used MEMS miniaturized antennas designed with integrated circuits still have problems of low measurement accuracy and inability to break through the measurement limit.

[0003] Rydberg atoms are atoms with a very large principal quantum number, having a large electric dipole moment and extremely high sensitivity to electromagnetic fields. The measured quantity can be directly traced back to standard physical quantities, and it is a new type of and ideal electromagnetic measurement system. At present, electromagnetic measurement technology based on Rydberg atoms has achieved ultra-sensitive measurement of electromagnetic frequencies and large broadband induction. However, in the current application of electromagnetic measurement technology, the electromagnetic direction finding technology based on Rydberg atoms is in the stage of forming preliminary capabilities. This application scenario has a broad prospect and high practical value.

[0004] Rydberg atoms often use neutral alkali metal atoms as ground - state atoms, and the atoms are excited by transferring energy through laser pulses. Rydberg atoms usually adopt a three - level excitation scheme, that is, an intermediate energy level is designed between the ground state and the Rydberg state. The purpose is to achieve higher - fidelity pulsed excitation through double - pulse laser manipulation. When a continuous pulse is applied, the ground - state atoms will absorb energy to achieve distributive transition and finally reach a stable excited state. At this time, when detecting the probe light, it will be found that the spectral signal of the probe light will generate a transparent spike, that is, the electromagnetically induced transparency (EIT) effect. At this time, if there is an external electromagnetic field resonant with the Rydberg state, the Rydberg state will interact with the electromagnetic field. Under the action of the electromagnetic field, the Rydberg state and another state will have a resonant transition phenomenon. At this time, when detecting the probe light, it can be found that the original spike of the electromagnetically induced transparency has split, that is, the Autler - Townes splitting phenomenon. On the spectral image, it can be seen that the split peaks are roughly symmetric, and the sum of the absolute values of the Rabi frequencies of the two split peaks can be directly calculated through standard physical quantities to obtain the intensity of the electromagnetic field.

[0005] The electromagnetic direction - finding technology based on Rydberg atoms refers to the amplitude - method direction - finding principle in passive direction - finding technology. According to the amplitude of the signals output after each element (unit antenna) of the direction - finding antenna array receives the incoming wave signal, that is, by using the direct amplitude response or the comparative amplitude response of each antenna element, the method of measuring the direction of arrival of the incoming wave is called amplitude - method direction - finding, also known as amplitude - method direction - finding. The principle on which this method is based is that since the path lengths of the signals arriving at each element are different, the amplitudes of the signals received by each element will also be different. By analyzing these differences, the direction of the signal source can be inferred. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: aiming at the technical problem that the existing Rydberg - atom electromagnetic measurement system does not have an integrated and miniaturized electromagnetic - signal direction - finding technology, a new technical method is proposed. Aiming at the problems of the current system, such as large noise and limited signal accuracy in measuring electromagnetic signals relying only on a single atomic gas cell due to hardware limitations, the present invention designs a miniaturized spherical gas - cell array, uses a surface - mounted laser to excite cesium atoms in the gas cell, sense electromagnetic signals, and uses a photodetector embedded below the gas cell to measure the electromagnetic field strength it senses. The differences in the amplitudes of electromagnetic signals are sensed based on the differences in the spatial positions of the gas cells, and then the direction of the electromagnetic field is inversely calculated.

[0007] Secondly, aiming at the problem that the existing Rydberg - atom electromagnetic measurement system depends on laser equipment and complex optical paths, resulting in its large volume, the present invention designs an integrated Rydberg - atom electromagnetic measurement system, and its core devices are all integrated. By using a surface - mounted laser and a small spherical gas cell, the volume of the laser is greatly reduced.

[0008] The technical solution of the present invention is as follows: Aiming at the deficiency that the existing Rydberg atom electromagnetic measurement system cannot achieve electromagnetic signal direction finding in a small volume, the present invention proposes the following technical solutions: 1. Array design of spherical gas chambers. The present invention uses spherical glass gas chambers as the core units of the array, reducing the influence of the Rydberg blockade radius and irregular gas chambers on the excitation of Rydberg atoms and electromagnetic field induction. By adopting the methods of array excitation, array induction, and simultaneous measurement, it is sensitive to the external electromagnetic field strength, and the field source direction is measured by using the field strength changes of different gas chambers. 2. Integrated design. A surface light source is adopted to reduce the volume of the light source, and the devices are integrated onto the circuit board to improve the integration of the system, making it easier to carry and deploy.

[0009] The principle of the present invention is:

[0010] (1) Electromagnetically induced transparency effect

[0011] Electromagnetically induced transparency (Electromagnetic Induced Transition) is a quantum interference phenomenon of Rydberg atoms. It occurs after a three-level Rydberg atom is excited to the Rydberg state, and a penetration phenomenon occurs in the probe light between the coupled ground state and the intermediate transition state, specifically manifested as an absorption peak. It can also be considered that when the quantum state changes with the laser field, it affects the absorption of a certain special light by the medium, increasing its transmittance. When the probe light and the pump light satisfy specific resonance conditions, the transition probabilities of the two channels will cancel each other out, resulting in a transparent window at the resonance frequency, and accompanied by obvious dispersion changes.

[0012] Under the time-dependent process of the dipole approximation, the interaction between the laser and the atom can be described by the Hamiltonian:

[0013]

[0014] Under the rotating wave approximation, the Hamiltonian of the three-level atomic system is expressed as:

[0015]

[0016] In the formula, the Rabi frequencies of the probe field and the control field are respectively Ω p and Ω c , Δ1 and Δ2 are the frequency detuning amounts of the probe field and the control field respectively, ω 31 and ω 32 are the transition frequencies between the corresponding atomic energy levels. σ 21 , σ 31 and σ 32 respectively characterize the dissipation from the intermediate state to the ground state, from the excited state to the ground state, and from the excited state to the intermediate state. The system dynamic evolution process is solved by the density matrix master equation:

[0017]

[0018] Among them, the second and third terms on the right side of the equation respectively describe the spontaneous emission decay terms of |3> and |2>, and their decay rates are Γ 31 and Γ 32 . In a closed system, the energy is conserved during this interaction process, and the dephasing rates are γ2 and γ3. The total spontaneous emission decay rate Γ3 of the atomic |3> state is Γ 31 +Γ 32 . The coherent decay rate of the |3> state is γ 31 =Γ3+γ 3d , γ 32 =Γ3+γ 3d +γ 2d , γ 21 =γ 2d .

[0019] The atomic polarization intensity is:

[0020]

[0021] Assume that there are atoms per unit volume interacting with the external field. The time factor in the exponential part of the above formula comes from the transformation to the Schrödinger picture. Assume The scalar form of the polarization intensity can be obtained:

[0022]

[0023] When considering a weak probe field, the off-diagonal elements of the density matrix under the perturbation method are obtained:

[0024]

[0025] Then the linear susceptibility of the medium in the interaction picture can be obtained:

[0026]

[0027] In the formula, the real part of the linear susceptibility is:

[0028]

[0029] The imaginary part is:

[0030]

[0031] When the control field strength c is relatively weak, a very narrow transparent window, i.e., the EIT window, appears in the middle of the original Lorentz absorption peak.

[0032] (2) Autler-Townes effect

[0033] When a microwave field is introduced into the above system, if the frequency of the microwave field is close to the transition frequency between atomic energy levels, the microwave field will resonantly couple with the cesium atom, coupling the Rydberg state and another excited state to form a four-level atomic system. In the above case, the middle energy level of the atom is split into two symmetrical energy levels, and the interval of the split is the Rabi frequency of the microwave field. In the EIT signal, it is manifested as the middle main peak split into two transmission peaks. This phenomenon is the electromagnetically induced transparent Autler-Townes (EIT-AT) splitting effect.

[0034] (3) Direction finding by amplitude comparison method

[0035] Amplitude comparison direction finding is an important method in passive direction finding technology. Amplitude comparison direction finding determines the angle of arrival of a signal based on the relative amplitude of the signal received by the direction finding antenna system. A signal coming from a specific direction will be weighted differently according to the gain of different antennas, and the direction of the signal is determined by measuring these amplitude differences. The Rydberg cell array uses multiple independent antennas to generate multiple independent adjacent beams to cover 360 degrees. These antennas use the same directional pattern function and are evenly distributed. The Rydberg atomic cell array can be used as such an antenna array, with each cell being equivalent to an independent sensor for detecting signals in a specific direction.

[0036] Compared with the existing solutions, the main advantages of the solution of the present invention are:

[0037] (1) Low noise. This method uses an atomic system and can transfer classical thermal noise to quantum noise, reducing the noise by 3 orders of magnitude.

[0038] (2) Strong practicality. Rydberg atoms are sensitive to electromagnetic fields and have the advantages of not requiring calibration, being traceable to standard physical quantities, being extremely sensitive, and being able to achieve wide bandwidth sensitivity of 0-500 GHz.

[0039] (3) High integration: the gas chamber and laser are integrated into a single chip, which reduces the size and improves deployment flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of a Rydberg atomic electromagnetic direction-finding sensor based on a spherical gas cell array;

[0041] Figure 2 A top view of a Rydberg atomic electromagnetic direction-finding sensor based on a spherical gas chamber array. Specific implementation plan

[0042] First, place a 5*5 spherical cesium atomic cell 4 on the photodetector 5, embed it in the circuit board 3 according to the array, and ensure its stable position. Place three surface-emitting lasers 1, 2, and 6 around the cell array. The two lasers 2 and 6 emit lasers with wavelengths of 509 nm and 852 nm in opposite directions respectively. These two lasers are placed facing each other to ensure that they can enter the atomic cell in the same plane. At the same time, a probe laser 1 with a wavelength of 852 nm needs to be placed on one side of the cell. The laser 1 on the side will emit a beam of probe light with a wavelength of 852 nm. Then use the photodetector 5 to receive and convert the probe light signal. By accurately measuring the signal changes caused by the EIT and Autler-Townes effects, the intensity and characteristics of the electromagnetic field can be analyzed, and the signal of the photodetector is also processed to improve the signal-to-noise ratio and reduce the influence of environmental noise.

[0043] The content not described in detail in this invention book belongs to the prior art well-known to those skilled in the art.

Claims

1. A Rydberg electromagnetic direction-finding device based on a spherical atomic gas cell array, characterized in that: A new type of electromagnetic direction-finding sensor is proposed, which integrates surface-emitting light sources (1, 2, 6), a Rydberg atom cell array (4) and a photodetector (5). The four components are embedded in a circuit board (3) and connected to signal and control circuits. Through the integrated design of the surface-emitting light source, the cell and the circuit board, the overall volume of the device is reduced, realizing the miniaturization of the device.

2. The Rydberg electromagnetic direction finding device based on a spherical atomic gas cell array according to claim 1, characterized in that: A new type of electromagnetic direction-finding method is proposed. Based on the electromagnetic sensitivity effect of Rydberg atoms, a 5*5 spherical cell array is designed to be sensitive to signals from a single source. Each cell can independently receive and respond to signals. When the signals emitted by the same electromagnetic signal source are detected in different cells, there will be slight differences in signal intensity. By measuring and analyzing the signal intensity differences of the electromagnetic signals between these cells and using the intensity difference inversion technique, the direction of arrival of the electromagnetic signal can be accurately calculated.

3. The Rydberg electromagnetic direction finding device based on a spherical atomic vapor cell array according to claim 2, wherein: The electromagnetic induced transparency effect and the Autler-Townes effect of Rydberg atoms are utilized. When the surface-emitting lasers (2, 6) of 852 nm and 509 nm placed opposite each other pass through the spherical cell, cesium atoms absorb the energy of the laser in a three-level excitation mode and are excited from the ground state to the Rydberg state. Then, the 852 nm probe light emitted by the laser (1) passes through the cell and is captured by the photodetector (5). A spike will appear in the transmittance image of the generated spectral signal, which is the electromagnetic induced transparency effect. When an external electromagnetic field is applied and exactly resonates with the Rydberg state, the spike will split, and the splitting interval can be used to invert the intensity of the electromagnetic field through standard physical quantities. By calculating the different splitting intervals of the detection signals in each atomic cell, the electromagnetic field intensity sensed by each atomic cell can be obtained, and finally the source direction of the electromagnetic signal can be obtained.

Images