A method for reducing noise in electromagnetic measurements of rydberg atoms

Abstract

This invention discloses a noise reduction method for electromagnetic measurements of Rydberg atoms. This method constructs a 509nm coupled optical closed-loop circulation system comprising a polarization beam splitter, a half-wave plate, and a high-reflection mirror. This enables multiple reciprocating propagations of the laser within the atomic gas chamber. Utilizing the optical path circulation mechanism, the coupling strength between light and atoms is significantly improved without increasing the laser source power, thus greatly enhancing the excitation efficiency of Rydberg states. Simultaneously, this structure allows the intermediate frequency carrier signal to linearly and coherently superimpose with the number of cycles, while the laser background noise accumulates incoherently only according to a square root law, thereby significantly improving the measurement signal-to-noise ratio. This invention solves the problems of low excitation efficiency and difficulty in eliminating laser background noise in existing single-path optical systems, providing a new solution with high excitation efficiency and high signal-to-noise ratio for high-sensitivity microwave electric field measurements.

Description

Technical Field

[0001] This invention relates to the field of quantum precision measurement technology, and in particular to Rydberg atomic microwave sensing technology. Background Technology

[0002] Rydberg atoms possess extremely large electric dipole moments, extremely wide microwave response bands, and ultra-high electric field sensitivity. Microwave electric field measurement technology based on Rydberg atoms can achieve self-calibration, interference-free, and high-precision measurements over a wide frequency band. Researchers have used Rydberg atoms to achieve accurate measurements of large bandwidth, extremely low frequency, and very high frequency electromagnetic fields. The measurement sensitivity far exceeds that of traditional antennas, making it a core solution for next-generation microwave electric field metrology, electromagnetic compatibility testing, and wireless communication signal detection.

[0003] Current conventional microwave measurement schemes for Rydberg atoms generally employ a single-path optical design: a 509nm coupling light passes through the cesium atom gas cell in a single pass, exciting the atoms from an intermediate state to a highly excited Rydberg state. This, combined with an 852nm probe light, achieves electromagnetically induced transparency (EIT) effect, and microwave electric field information is obtained by detecting the AT splitting of the EIT spectrum. This scheme has the following core drawbacks: 1. Low Rydberg state excitation efficiency: The effective coupling density between the 509nm coupled light and atoms is low under a single optical path, resulting in low preparation efficiency of atoms excited to the Rydberg state. This leads to weak contrast of the EIT signal and limited signal-to-noise ratio, which directly limits the measurement sensitivity. 2. Poor noise suppression capability: In order to improve signal strength, conventional solutions use multiple repeated measurements and averaging to reduce noise. The signal-to-noise ratio can only be improved with the square root of the measurement time, which not only greatly prolongs the measurement time, but also introduces systematic errors such as environmental temperature drift and laser frequency drift. 3. Large systematic error: In order to improve the efficiency of Rydberg atom preparation, the output power of the 509nm coupling light needs to be increased. High-power lasers will introduce serious problems such as optical frequency shift, power saturation effect, and atomic decoherence, which will reduce the accuracy of microwave electric field measurement. Summary of the Invention The technical problem solved by this invention is noise reduction in Rydberg atomic electromagnetic measurements.

[0004] The technical solution of this invention is to allow the 509nm coupled light to pass through the same atomic gas cell multiple times through a closed-loop circulating optical path, which greatly improves the excitation efficiency of the Rydberg state, realizes coherent signal superposition and incoherent noise cancellation, fundamentally improves the measurement signal-to-noise ratio and sensitivity, and reduces system error.

[0005] The principle of this invention is: (1) Electromagnetically induced transparency (EIT) effect This invention utilizes a cesium atom Λ-type three-level system to realize the EIT effect. The system energy levels are defined as: |1 ground state of cesium atoms , |2 excited state , |3 The high-excitement state is nS / nD in the Rydberg region. The 852nm probe-coupled transition is |1 |2 509nm coupled optical coupling transition |2 |3 .

[0006] Under the electric dipole approximation and the rotating wave approximation, the Hamiltonian of the system in the interaction representation is: (1) In the formula, The Rabi frequency of the probe light at 852nm. The Rabi frequency of the coupled light at 509 nm. is the reduced Planck constant.

[0007] The Schrödinger equation under the interaction representation is: (2) In the formula, For state vectors, It is the Hamiltonian of the light-cesium atom interaction under the electric dipole approximation.

[0008] Expand the state vector using basis vectors: (3) In the formula, , , Given the probability amplitude, we can obtain the following from formulas (2) and (3). (4) Combining the normalization conditions: (5) Solving (6) The atom is in energy level |2 The probability is Then, in the stable state, the atom does not occupy the excited state |2. The atoms do not interact effectively with the probe light, and the probe light is not absorbed by the medium, forming an EIT transparent window.

[0009] (2) AT (Autler-Townes) splitting effect Based on the aforementioned three-level EIT system, a Rydberg state |3 coupled to the microwave electric field under test is introduced. With adjacent Ridburg state |4 This constitutes a four-level measurement system.

[0010] The interaction between the measured microwave electric field and atoms can be described by the microwave Rabi frequency: (7) In the formula, For |3 |4 Microwave electric dipole moment of transition, The amplitude of the microwave electric field to be measured is denoted as .

[0011] Under the electric dipole approximation and the rotating wave approximation, the Hamiltonian of the system in the interaction representation is: (8) Under the influence of a microwave field, |3 and |4 Coupling occurs, and the original energy level undergoes AC-Stark splitting, forming two decorated eigenlevels with an energy difference of: (9) Frequency spacing of transmission peaks satisfy: (10) From formulas (9) and (10), the quantitative relationship between the measured microwave electric field intensity and the splitting distance can be obtained: (11) Therefore, by collecting the transmission spectrum of the 852nm probe light and extracting the AT splitting distance, the field strength, frequency, and other parameters of the microwave electric field to be measured can be obtained by inversion.

[0012] (3) Cyclic excitation denoising and signal-to-noise ratio (SNR) enhancement principle This invention achieves multiple recycling of 509nm coupled light through a closed-loop annular optical path. The core physical mechanism of its noise reduction and signal enhancement is as follows: 1. Coherent superposition of signals and enhancement of effective interaction length. In a traditional single-path optical system, the population efficiency of Rydberg states is limited by the single-pass interaction distance of the 509nm coupled light and the finite Rabi frequency. In the cyclic excitation system of this invention, the 509 nm coupled light passes through the same cesium atom ensemble multiple times, which is equivalent to increasing the interaction time density between the atoms and the light field. Let the effective interaction length of the 509 nm coupled light passing through the cesium atom gas cell in a single pass be... Given that the number of optical path cycles is N, and under the premise that polarization control, collimation, and focusing ensure spatial coincidence and constant phase of the optical field, the equivalent effective interaction length between the atom and the optical field can be expressed as: (12) The corresponding 509nm effective pull ratio frequency of the coupled light meets the requirements. ( (This refers to the Rabi frequency under single-pass conditions). Within a unit of time, the coupling light in each cycle maintains spatial overlap and a constant phase correlation with the 852nm probe light. The optical field amplitude of the EIT signal coherently superimposes with the number of cycles. If the optical field amplitude of the EIT signal under single-pass conditions is... Then, after N cycles, the total optical field amplitude of the EIT signal is: (13) The corresponding EIT signal intensity is This allows for coherent superposition of EIT signals, thereby significantly improving the contrast of transparent peaks in the detection spectrum and making it easier to accurately extract the AT splitting interval.

[0013] 2. Incoherent cancellation of random noise and statistical gain According to the error propagation law, laser power fluctuation noise and electronic shot noise in a measurement system typically exhibit random processes that vary over time. Because cyclic excitation acts on the same atomic group, the resulting EIT response is highly coherent, and the signal strength... With the number of loops It exhibits linear or quasi-linear growth. The phases of the relative intensity noise and quantum shot noise of the laser at different cycle time points are randomly distributed, belonging to incoherent superposition, and the total noise amplitude only increases with... Growth. Therefore, the final signal-to-noise ratio of the system: (14) Compared to traditional single-measurement post-processing averaging, this cyclic superposition within the optical path suppresses random noise from its physical source without increasing the total measurement time, greatly shortening the integration time required for high-precision measurements.

[0014] 3. System error suppression and optical frequency shift optimization In high-precision measurements, simply increasing the power of a single-pass laser to enhance the signal can lead to serious systematic errors, such as power broadening and AC Stark displacement.

[0015] The cyclic excitation method of this invention allows for the equivalent high-power excitation population effect to be achieved through multiple coherent superpositions under relatively low incident power conditions, thereby avoiding the drastic Rydberg level drift and spectral broadening caused by high-power laser incident. Simultaneously, the closed-loop optical path, by passing through the atomic gas cell multiple times, improves the uniformity of the optical field distribution within the atomic gas cell, reduces atomic phase competition and local decoherence induced by laser spatial mode inhomogeneity, and enhances the accuracy and robustness of microwave electric field measurements.

[0016] The cyclic excitation scheme of this invention enables coherent superposition of EIT signals and incoherent superposition of random noise such as laser power noise and shot noise, which significantly improves the spectral signal-to-noise ratio, reduces the extraction error of AT splitting distance, and realizes high-precision, low-noise, and high-robust measurement of microwave electric fields.

[0017] Compared with existing solutions, the main advantages of this invention are: (1) The present invention proposes a noise reduction method for electromagnetic measurement of Rydberg atoms. Compared with the traditional single-path optical measurement method, this method is less sensitive to environmental interference such as laser power noise and shot noise, and can significantly improve the excitation efficiency of Rydberg states and the measurement signal-to-noise ratio, thereby achieving better microwave electric field measurement results.

[0018] (2) The present invention adopts a closed-loop optical path with multiple coherent excitation paths. Compared with the traditional noise reduction method of multiple repeated measurements and averaging, this method has higher excitation fidelity and measurement accuracy, while effectively suppressing systematic errors such as optical frequency shift and environmental drift. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the optical path. Detailed Implementation

[0020] First, system initialization and optical path calibration are performed. The 509nm coupling beam and 852nm probe beam are activated and locked to the corresponding transition lines of cesium atoms. The optical paths are adjusted to ensure that the two beams propagate coaxially and oppositely within the cesium atom gas cell, with the beam spots completely overlapping. Simultaneously, the polarization state of the cyclic excitation optical path is matched to stabilize the gas cell's operating conditions. Subsequently, the 509nm coupling beam passes through a closed-loop annular optical path, passing through a mirror, polarization control unit, polarization beam splitter, dichroic mirror, and focusing collimation unit, repeatedly exciting the same cesium atom ensemble. This, combined with the 852nm probe beam, generates an electromagnetically induced transparent EIT signal carrying Rydberg state population information. Multiple cyclic excitations achieve coherent superposition of the EIT signal, while random noise such as laser power noise and shot noise is incoherently superimposed, thus improving the signal-to-noise ratio. The microwave electric field to be measured acts on the cesium atom gas cell, causing the Rydberg AT level to split, and the EIT spectrum subsequently carries microwave field information. Finally, the 852nm transmission spectrum was collected by the detection module, the AT splitting distance was extracted, and the field strength and frequency of the microwave electric field were calculated by combining the electric dipole moment of the Rydberg atom, thus achieving high-precision measurement.

[0021] The contents not described in detail in this invention are existing technologies known to those skilled in the art.

Claims

1. A noise reduction method for Rydberg atomic electromagnetic measurements, characterized in that, A cyclic closed-loop excitation system is constructed based on a laser emission module, a cyclic excitation optical path module, an atomic gas cell module, a microwave coupling module, and a detection and acquisition module. This system is used to repeatedly introduce 509nm coupling light into the atomic gas cell module, allowing the 509nm coupling light to act on the same cesium atom ensemble multiple times per unit time. The atomic gas cell module includes a cesium atom gas cell, which provides the cesium atom ensemble that interacts with the laser. The microwave coupling module is used to apply the microwave electric field to be measured to the cesium atom gas cell. The detection and acquisition module is used to acquire the transmission signal of the 852nm probe light and extract the parameter information of the microwave electric field to be measured.

2. The measurement method according to claim 1, characterized in that, Includes the following steps: S1 System Initialization and Optical Path Calibration: Turn on the 509nm laser and the 852nm laser, lock the two laser beams to the transition lines corresponding to the cesium atoms respectively, adjust the optical path so that the 509nm coupling light and the 852nm probe light propagate coaxially and oppositely in the cesium atom gas cell and the light spots completely overlap, adjust the polarization matching of the cyclic excitation optical path, and stabilize the working state of the cesium atom gas cell; S2 Cyclic Excitation and Rydberg State Excitation Efficiency Enhancement: The cyclic excitation optical path module includes a first mirror, a second mirror, a polarization control unit, a polarization beam splitter, a dichroic mirror, and a focusing and collimating unit. After the 509nm coupled light enters the closed-loop optical path, it is reflected by the first and second mirrors, its polarization state is adjusted by the polarization control unit, and then reflected by the polarization beam splitter. It is then focused by the focusing and collimating unit into the cesium atom gas cell, where it interacts with the 852nm probe light in the opposite direction to the cesium atom ensemble. The 509nm coupled light passing through the cesium atom gas cell is collimated by the focusing and collimating unit and then incident on the dichroic mirror. After being reflected by the dichroic mirror, it is incident on the first mirror, completing one closed-loop cycle and realizing multiple cyclic excitations of the same cesium atom ensemble. The 852nm probe light and the cyclically excited 509nm coupled light interact with the atom ensemble to generate an electromagnetically induced transparent signal carrying Rydberg state population information. S3 Noise Suppression and Signal Acquisition: Multiple cyclic excitations enable coherent superposition of the EIT signal, while random noises such as laser power noise and shot noise are incoherently superimposed, thus improving the signal-to-noise ratio; the microwave electric field to be measured acts on the cesium atom gas cell, causing the Rydberg level to split into AT levels, and the EIT spectrum carries the information of the microwave electric field to be measured; the transmission spectrum signal of the 852nm probe light is acquired through the detection and acquisition module. S4 Microwave Electric Field Information Extraction: The acquired spectral signal is processed to extract the AT splitting distance. Combined with the electric dipole moment of the Rydberg atom, the field strength, frequency and other parameters of the microwave electric field to be measured are calculated to complete the high-precision microwave electric field measurement.

3. The measurement method according to claim 2, characterized in that, The polarization control unit is a zero-order half-wave plate with a working wavelength matched to 509nm. It is used to adjust the polarization state of the 509nm coupled light to ensure the reflection efficiency of the polarization beam splitter during the cycle. The dichroic mirror is a 509nm high-reflectivity and 852nm high-transmission dichroic mirror. It is used to separate the cyclic 509nm coupled light from the 852nm probe light to prevent the probe light transmission spectrum from mixing into the cyclic optical path spectrum.

4. The measurement method according to claim 2, characterized in that, The focusing and collimating unit includes a first convex lens and a second convex lens, which are respectively disposed at both ends of the cesium atom gas cell for focusing and collimating the 509nm coupling light and the 852nm probe light.

Images