Method for improving sensitivity of Rydberg atom microwave measurement based on atomic velocity selection

Abstract

The invention discloses a Rydberg atom microwave measurement sensitivity improving method based on atom velocity selection, and relates to the field of Rydberg atom microwave measurement, and the method comprises the steps: moving the frequency of probe light to an energy level resonance transition position of cesium atoms from a ground state to an excited state, scanning the frequency of the coupled light within a Rydberg state energy level preset range, and observing an EIT signal; the frequency of the detection light is changed, the detuning amount of the detection light is selected to enable the EIT signal to reach the maximum, and the frequency of the detection light is locked to the frequency corresponding to the maximum position of the EIT signal; meanwhile, a local oscillation field signal generator in the Rydberg atomic microwave sensitivity measurement device is turned on, and corresponding EIT-AT splitting is generated; the frequency of the coupling light is locked to the coupling light laser frequency corresponding to the lowest point of EIT-AT splitting, and the Rydberg atom microwave measurement sensitivity reaches the maximum. The cesium atom speed is screened and controlled, and the signal-to-noise ratio of the measurement signal is improved, so that the measurement sensitivity is improved.

Description

Technical Field

[0001] The present application relates to the field of Rydberg atom microwave measurement, and in particular to a method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection. Background Art

[0002] In recent years, with the development of quantum technology, Rydberg atoms have shown great application prospects in the field of microwave precision measurement. Due to their ultra-high principal quantum number, Rydberg atoms are extremely sensitive to external electromagnetic fields and have become an important research object in the field of new system microwave measurement. Although they have made remarkable achievements in the field of microwave measurement, how to improve the signal-to-noise ratio and measurement accuracy in microwave measurement has always been an important technical bottleneck. Summary of the invention

[0003] The purpose of this application is to provide a method for improving the sensitivity of Rydberg atomic microwave measurements based on atomic velocity selection, which improves the signal-to-noise ratio of the measurement signal by screening and controlling the cesium atom velocity, thereby improving the measurement sensitivity.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] A method for improving the sensitivity of Rydberg atomic microwave measurements based on atomic velocity selection, the method for improving the sensitivity of Rydberg atomic microwave measurements is applied to a Rydberg atomic microwave measurement sensitivity device, the Rydberg atomic microwave measurement sensitivity device comprising a detection light laser generator, a coupling light laser generator and a cesium atomic vapor pool; the detection light laser generator is used to emit detection light, the coupling light laser generator is used to emit coupling light, the interior of the cesium atomic vapor pool is filled with cesium atoms, the cesium atoms themselves are in a ground state, under the action of the detection light, the cesium atoms in the ground state are excited to an excited state, and then the excited state cesium atoms are made to reach the Rydberg state through the coupling light, generating an EIT signal;

[0006] The method for improving the sensitivity of Rydberg atom microwave measurement comprises:

[0007] The frequency of the detection light is moved to the energy level resonant transition of the cesium atom from the ground state to the excited state, and the frequency of the coupled light is scanned within the preset range of the Rydberg state energy level to observe the EIT signal;

[0008] The frequency of the detection light is changed, and the detuning amount of the detection light is adjusted to maximize the EIT signal, and the frequency of the detection light is locked to the frequency corresponding to the maximum position of the EIT signal; at the same time, the local oscillator field signal generator in the Rydberg atomic microwave measurement sensitivity device is turned on to generate the corresponding EIT-AT splitting;

[0009] By locking the frequency of the coupled light to the coupled light laser frequency corresponding to the lowest point of the EIT-AT splitting, the sensitivity of Rydberg atom microwave measurement reaches the maximum.

[0010] According to the specific embodiments provided in this application, this application has the following technical effects:

[0011] The present application provides a method for improving the sensitivity of Rydberg atomic microwave measurements based on atomic speed selection. Through the interaction between detection light, coupling light and cesium atoms, the detection light that originally interacts with a small number of zero-speed cesium atoms is frequency-detuned, the frequency of the detection light is changed, and the detection light interacts with a large number of high-speed cesium atoms, thereby improving the signal strength of the interaction between the detection light, coupling light and cesium atoms, improving the signal-to-noise ratio of the measurement signal, and thus improving the sensitivity of Rydberg atomic microwave measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 This is a schematic diagram of the structure of the Rydberg atom microwave measurement sensitivity device;

[0014] Figure 2 A schematic flow chart of a method for improving the sensitivity of microwave measurements of Rydberg atoms based on atomic velocity selection provided in one embodiment of the present application;

[0015] Figure 3 Schematic diagram of the energy level transition of the Rydberg atom;

[0016] Figure 4 Figure 3 is the amplitude diagram of the EIT signal corresponding to different detuning amounts and the amplitude diagram of the superheterodyne measurement beat signal, where (a) is the amplitude diagram of the EIT signal at resonance, (b) is the amplitude diagram of the EIT signal at the optimal detuning amount, (c) is the amplitude diagram of the superheterodyne measurement beat signal at resonance, and (d) is the amplitude diagram of the superheterodyne measurement beat signal at the optimal detuning amount. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] The present application provides a method for improving the sensitivity of Rydberg atom microwave measurements based on atomic velocity selection. The principle is that the velocity distribution of cesium atoms in a cesium atom vapor pool satisfies the Maxwell velocity distribution. When the frequency of the detection light resonates with the energy level of the cesium atom, the detection light will excite the cesium atoms with a velocity of '0' to a high state (i.e., an excited state). When the frequency of the detection light is detuned, the detection light will select to excite the cesium atoms with a non-'0' velocity by utilizing the Doppler effect. In this way, under different frequency detuning states of the detection light, different numbers of cesium atoms will participate in the interaction. By selecting an appropriate detuning amount of the detection light, the most cesium atoms can participate in the interaction. At this time, under the joint action of the detection light and the coupling light, the most cesium atoms are excited to the Rydberg state, thereby obtaining more Rydberg atoms (i.e., cesium atoms in the Rydberg state). The method utilizes the Doppler velocity selection technology to optimize the number of Rydberg atom excitations, thereby significantly improving the detection sensitivity of microwave signals.

[0019] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0020] In an exemplary embodiment, a method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection is provided. The method is applied to Figure 1 The Rydberg atomic microwave measurement sensitivity device shown. The Rydberg atomic microwave measurement sensitivity device comprises a detection light laser generator 1, a coupling light laser generator 17 and a cesium atomic vapor pool 10. The detection light laser generator 1 is used to emit detection light, and the coupling light laser generator 17 is used to emit coupling light. The interior of the cesium atomic vapor pool 10 is filled with cesium atoms, and the cesium atoms themselves are in the ground state. Under the action of the detection light, the cesium atoms in the ground state are excited to the excited state, and then the excited state cesium atoms are made to reach the Rydberg state through the coupling light, generating an EIT signal.

[0021] like Figure 1 As shown, the Rydberg atomic microwave measurement sensitivity device specifically includes:

[0022] Probe light laser generator 1: used to emit probe light;

[0023] Reflector 2: used to reflect the detection light at a 45-degree angle with high efficiency;

[0024] Probe light polarization splitter prism (PBS1) 3: used to split the probe light into two beams of horizontal polarization (transmission) and vertical polarization (reflection);

[0025] Detection light half wave plate 4: used to change the polarization direction of the detection light;

[0026] Detection light collimator 5: used to connect the detection light emitted by the detection light laser generator 1 to the experimental platform;

[0027] Local oscillator field speaker 6: used to radiate the signal of the local oscillator field signal generator 8 into free space;

[0028] Signal field speaker 7: used to radiate the signal of the signal field signal generator 9 into free space;

[0029] Local oscillator signal generator 8: outputs a waveform with adjustable frequency and amplitude to the local oscillator speaker 6;

[0030] Signal field signal generator 9: outputs a waveform with adjustable frequency and amplitude to the signal field speaker 7;

[0031] Cesium atomic vapor pool 10: a place where the detection light and the coupling light interact with the cesium atoms, and the interior is filled with cesium atoms;

[0032] Dichroic mirror 11: used to highly reflect the detection light in a certain wavelength range and to highly transmit the coupling light in a certain wavelength range.

[0033] Differential photodetector 12: performs differential operation on two beams of light and detects the result;

[0034] A coupling light polarization splitter prism (PBS2) 13 is used to split the coupling light into two beams of horizontal polarization (transmission) and vertical polarization (reflection);

[0035] The beam collector 14 is used to collect the redundant beams to prevent them from escaping into the space;

[0036] Coupling light half wave plate 15: used to change the polarization direction of the coupling light;

[0037] Coupling light collimator 16: used to connect the coupling light emitted by the coupling light laser generator 17 to the experimental platform;

[0038] Coupling light laser generator 17: used to emit coupling light.

[0039] The working principle of the Rydberg atomic microwave measurement sensitivity device is as follows:

[0040] After the detection light emitted by the detection light laser generator 1 enters the experimental platform through the optical fiber input port of the detection light collimating head 5, it is divided into two beams by the half wave plate 4 and the polarization beam splitter prism 3. One beam and the coupling light overlap in the cesium atomic vapor pool 10 and interact with the cesium atoms in the cesium atomic vapor pool 10 to prepare Rydberg atoms, and enters one end of the differential photodetector 12 through the cesium atomic vapor pool 10 and the dichroic mirror 11. The other beam, as a reference light, also reaches the cesium atomic vapor pool 10 after passing through the reflector 2, but it does not interact with the coupling light. Its function is to enter the other end of the differential photodetector 12 and perform differential operation with the detection light, so that the intensity noise of the detection light itself can be subtracted, the signal-to-noise ratio is improved, and the measurement result is more accurate.

[0041] The coupling light emitted by the coupling light laser generator 17 enters the device through the optical fiber input port of the coupling light collimating head 16, propagates through the half wave plate 15 and the polarization beam splitter prism 13, and the transmitted horizontally polarized light is then transmitted through the dichroic mirror 11 into the cesium atomic vapor pool 10 to interact with the detection light. The coupling light reflected by the polarization beam splitter prism 13 is collected in the beam collector 14 to prevent it from being scattered into space.

[0042] Among them, in the cesium atomic vapor pool 10, the detection light and the coupling light are incident in opposite directions and overlap, and interact with the cesium atoms inside the cesium atomic vapor pool 10 to prepare Rydberg atoms. When only the detection light passes through, the cesium atoms absorb the detection photons and are excited from the ground state to the excited state. When the coupling light is added, the cesium atoms transition from the excited state to the Rydberg state. Under the action of the coupling light, the transmitted detection light generates an electromagnetically induced transparency (EIT) signal in the cesium atomic vapor pool 10 and enters the differential photodetector 12 for detection. The differential photodetector 12 is used to convert the optical signal into an electrical signal. Electromagnetic induced transparency (EIT): refers to the phenomenon that the absorption of the detection light by the medium is reduced under the action of the electromagnetic field. It is a quantum coherence effect. In a three-level atomic system, it is the result of the coherent destructive effect between two possible excitation channels.

[0043] The local oscillator field signal generator 8 and the signal field signal generator 9 are used to output two microwave signals with similar frequencies, respectively, as the local oscillator field and the unknown signal field, with a frequency difference of Δf, so that the two beat at the cesium atomic vapor pool 10. At this time, the Rydberg atom acts as a mixer, so that the output signal laser generates an oscillation signal with a frequency of Δf. The amplitude of the oscillation signal is proportional to the intensity of the unknown signal field. Therefore, the intensity of the unknown signal field can be measured according to the amplitude of the oscillation signal.

[0044] The signals from the local oscillator field signal generator 8 and the signal field signal generator 9 are mixed at the cesium atomic vapor pool 10. The Rydberg atoms act as mixers to generate a frequency of Δf (Δf = 20 kHz in this experiment, i.e. Figure 4 An oscillation signal of the beat frequency oscillation signal frequency) is generated. Prior to this, Rydberg atoms are prepared by detection light and coupling light, so the detection light will carry the Rydberg atom information after interacting with the microwave beat frequency signal into the differential photodetector 12, and this oscillation signal can be observed.

[0045] P=E LO +E SIG cos(2πΔft+4φ)

[0046] E LO and E SIG are the electric field strength of the local oscillator field and the unknown signal field (sent by the signal field signal generator 9), Δφ is the phase difference between the local oscillator field and the unknown signal field, and t is time. When the electric field strength of the local oscillator field is known, the electric field strength of the unknown signal field can be directly solved according to the size of the difference frequency signal P.

[0047] Based on the above Rydberg atom microwave measurement sensitivity device, the Rydberg atom microwave measurement sensitivity improvement method based on atomic velocity selection provided in the present application includes:

[0048] S1: Move the frequency of the detection light to the energy level resonant transition of the cesium atom from the ground state to the excited state, scan the frequency of the coupled light within the preset range of the Rydberg state energy level, and observe the EIT signal.

[0049] Lock the power of the probe light in the above device and shift the frequency of the probe light to the ground state 6S of the cesium atom 1 / 2 (F=4)→excited state 6P 3 / 2 At the (F=5) energy level resonant transition, the frequency of the coupled light is scanned near the Rydberg state energy level and an EIT signal is observed.

[0050] S2: Change the frequency of the detection light, select the detuning amount of the detection light to maximize the EIT signal, lock the frequency of the detection light to the frequency corresponding to the maximum position of the EIT signal; at the same time, turn on the local oscillator field signal generator in the Rydberg atomic microwave measurement sensitivity device to generate the corresponding EIT-AT splitting.

[0051] By changing the frequency of the detection light emitted by the detection light laser generator 1, it can be observed that the size of the generated EIT signal will change when the frequency of the detection light is changed. The relationship between the two is as follows: the change in the size of the EIT signal is due to the increase and decrease in the number of Rydberg atoms. The velocity distribution of the cesium atoms in the cesium atomic vapor pool 10 satisfies the Maxwell velocity distribution. When the frequency of the detection light resonates with the energy level of the cesium atoms, the detection light will excite the cesium atoms with a velocity of '0' to a high state, and when detuned, the detection light will choose to excite the cesium atoms with a non-'0' velocity. In this way, under different sizes of detection light detuning states, different numbers of cesium atoms will participate in the interaction. The detuning amount of the detection light is selected to maximize the EIT signal, thereby obtaining more Rydberg atoms. At this time, the frequency of the detection light is locked to the frequency corresponding to the maximum position of the EIT signal (when the EIT signal reaches the maximum, the number of cesium atoms in the Rydberg state is the largest), and the local oscillator field signal generator 8 is turned on at the same time to generate the corresponding EIT-AT splitting.

[0052] The relationship between the detuning amount of the detection light and the EIT signal is:

[0053]

[0054] Among them, σ(v) is the EIT signal size when the cesium atom velocity is v, Γ is the spontaneous emission rate of the excited state, Δ P and Δ C are the detuning amounts of the detection light and the coupling light, k P and k C is the wave vector of the probe light and the coupled light, k C and Ω c are the Rabi frequencies of the probe light and the coupled light respectively, and i is an imaginary number.

[0055] S3: Lock the frequency of the coupled light to the coupled light laser frequency corresponding to the lowest point of the EIT-AT splitting, and the sensitivity of the Rydberg atom microwave measurement reaches the maximum.

[0056] The frequency of the coupled light laser generator 17 is locked to the coupled light laser frequency corresponding to the lowest point of the EIT-AT splitting. At this time, the sensitivity of the entire Rydberg atomic sensor system reaches the maximum. At this time, the signal field signal generator 9 is turned on and the total field strength felt is P = E LO +E SIG cos(2πΔft+4φ), so the signal of the detection light transmission has a sinusoidal oscillation, and its oscillation amplitude is proportional to the Rabi frequency of the unknown signal field. The frequency and phase of the oscillation depend on the relative frequency and relative phase between the LO field (local oscillator field) and the SIG field (unknown signal field). This quantum beat frequency method can be used to achieve precise measurement of weak fields.

[0057] like Figure 3As shown in the figure, the cesium atom itself is in the ground state. Under the action of the detection light, the ground state cesium atom is excited to the excited state, and then the cesium atom is made to reach the Rydberg state through the coupling light, generating an EIT signal. Figure 3 In, ω p is the frequency of the detection light, ω0 is the resonance frequency of the cesium atom, and the Doppler frequency shift of the detection light felt by the cesium atom due to the non-zero speed movement of the cesium atom is Δp=kv, ω0=ω p -Δp, k is the wave vector, and v is the velocity of the cesium atom itself. When the frequency of the probe light does not completely match the transition energy level relative to the frequency of the resonant probe light, "detuning" occurs. At this time, although the system deviates from the original resonant frequency, the layout distribution during the excitation process is changed, allowing more cesium atoms to transition from the ground state to the excited state, so that the number of atoms in the system that eventually reach the Rydberg state will be increased, achieving an improvement in the system sensitivity.

[0058] Figure 4 (a) is the amplitude diagram of the EIT signal at resonance. Figure 4 (b) is the amplitude diagram of the EIT signal at the optimal detuning amount (220MHz). Figure 4 (c) is a schematic diagram of the beat frequency signal generated by the signal field and the local oscillator field after the detection light frequency is locked to the resonant transition and the coupling light frequency is locked to the lowest point of the EIT-AT splitting. Figure 4 (d) is a schematic diagram of the beat signal generated when the detection light frequency is locked to the optimal detuning position, and the frequencies of the two beat oscillation signals are both 20kHz; it can be seen that the amplitude of the EIT signal has increased by nearly 8 times, that is, the signal-to-noise ratio has been greatly improved, which makes the sensitivity of the entire system relatively improved a lot, further illustrating that the method provided in this application can improve the sensitivity of the system.

[0059] The method for improving the microwave measurement sensitivity of Rydberg atoms based on atomic velocity selection provided in this application utilizes the principle that the atomic velocity distribution satisfies the Maxwell velocity distribution, and realizes atomic velocity selection by detuning the frequency of the detection light, utilizing the Doppler effect, and optimizing the quantum state distribution of Rydberg atoms, thereby significantly improving the detection sensitivity of microwave signals. Compared with the prior art, this application uses a simple laser frequency tuning technology to improve the measurement sensitivity of microwave signals, and can achieve higher measurement accuracy in complex electromagnetic environments, and is particularly suitable for high-sensitivity microwave spectrum analysis, quantum sensor applications, and other scenarios that require extremely high measurement sensitivity.

[0060] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection, characterized in that: The Rydberg atomic microwave measurement sensitivity improvement method is applied to a Rydberg atomic microwave measurement sensitivity device, which includes a detection light laser generator, a coupling light laser generator and a cesium atomic vapor pool; the detection light laser generator is used to emit detection light, the coupling light laser generator is used to emit coupling light, the interior of the cesium atomic vapor pool is filled with cesium atoms, and the cesium atoms themselves are in a ground state. Under the action of the detection light, the cesium atoms in the ground state are excited to an excited state, and then the excited state cesium atoms are made to reach the Rydberg state through the coupling light, thereby generating an EIT signal; The method for improving the sensitivity of Rydberg atom microwave measurement comprises: The frequency of the probe light is moved to the energy level resonant transition of the cesium atom from the ground state to the excited state, and the frequency of the coupled light is scanned within the preset range of the Rydberg state energy level to observe the EIT signal; The frequency of the detection light is changed, the detuning amount of the detection light is selected to maximize the EIT signal, and the frequency of the detection light is locked to the frequency corresponding to the maximum position of the EIT signal; at the same time, the local oscillator field signal generator in the Rydberg atomic microwave measurement sensitivity device is turned on to generate the corresponding EIT-AT splitting; By locking the frequency of the coupled light to the coupled light laser frequency corresponding to the lowest point of the EIT-AT splitting, the sensitivity of Rydberg atom microwave measurement reaches the maximum.

2. The method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection according to claim 1, characterized in that: The velocity distribution of cesium atoms in the cesium atomic vapor pool satisfies the Maxwell velocity distribution.

3. The method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection according to claim 1, characterized in that: When the frequency of the detection light resonates with the energy level of the cesium atoms, the detection light will excite the cesium atoms with a speed of '0' to an excited state. When the frequency of the detection light is detuned, the detection light will selectively excite the cesium atoms with a non-'0' speed by utilizing the Doppler effect. Under different frequency detuning states of the detection light, different numbers of cesium atoms will participate in the interaction.

4. The method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection according to claim 1, characterized in that: When the EIT signal reaches a maximum, the number of cesium atoms in the Rydberg state is the largest.

5. The method for improving the sensitivity of Rydberg atom microwave measurement based on atomic velocity selection according to claim 1, characterized in that: The relationship between the detuning amount of the detection light and the EIT signal is: Among them, σ(v) is the EIT signal size when the cesium atom velocity is v, Γ is the spontaneous emission rate of the excited state, Δ P and Δ C are the detuning amounts of the detection light and the coupling light, k P and k C is the wave vector of the probe light and the coupled light, k C and Ω c are the Rabi frequencies of the probe light and the coupled light respectively, and i is an imaginary number.

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