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Sensing Low-Frequency Field with Rydberg Atoms via Quantum Weak Measurement

Ding Wang, Shenchao Jin, Xiayang Fan, Hongjing Li, Jiatian Liu, Jingzheng Huang, Guihua Zeng, Yuan Sun

Abstract

Recently, Rydberg atom has emerged as an attractive choice to realize quantum sensing of low-frequency electric field. The progress so far has mostly utilized the intensity and phase changes in probe laser and the corresponding detection mechanism still remains classical. Nevertheless, external field acting on the Rydberg state can induce the polarization variation of probe laser in the Rydberg electromagnetically induced transparency (EIT) system embedded in realistic multi-state atoms. We experimentally observe this phenomenon and realize signal extraction by appropriately utilizing the polarization degrees of freedom. Based on such a mechanism, we further design and implement a quantum weak measurement scheme, which clearly suppresses the technical noise and leads to considerable improvement of performance. Evaluation of the sensitivities across different post-selection angles demonstrates that the weak measurement results agree well with the theoretical model predictions. The advantages of our method are analyzed from multiple aspects, including characterizing the responses over different frequencies and comparing the responses of the weak measurement scheme and the traditional transmission-based method. After accounting for the screening effect of a measured ratio 17\% where the $^\text{87}$Rb atoms experience a substantially reduced field inside the glass cell, the performance reaches 33 $μ\text{V}~\text{cm}^\text{-1}~\text{Hz}^\text{-1/2}$ in sensitivity and 1.0 $μ\text{V/cm}$ in minimal detectable field for an integration time of 1000 s, as perceived by the atoms.

Sensing Low-Frequency Field with Rydberg Atoms via Quantum Weak Measurement

Abstract

Recently, Rydberg atom has emerged as an attractive choice to realize quantum sensing of low-frequency electric field. The progress so far has mostly utilized the intensity and phase changes in probe laser and the corresponding detection mechanism still remains classical. Nevertheless, external field acting on the Rydberg state can induce the polarization variation of probe laser in the Rydberg electromagnetically induced transparency (EIT) system embedded in realistic multi-state atoms. We experimentally observe this phenomenon and realize signal extraction by appropriately utilizing the polarization degrees of freedom. Based on such a mechanism, we further design and implement a quantum weak measurement scheme, which clearly suppresses the technical noise and leads to considerable improvement of performance. Evaluation of the sensitivities across different post-selection angles demonstrates that the weak measurement results agree well with the theoretical model predictions. The advantages of our method are analyzed from multiple aspects, including characterizing the responses over different frequencies and comparing the responses of the weak measurement scheme and the traditional transmission-based method. After accounting for the screening effect of a measured ratio 17\% where the Rb atoms experience a substantially reduced field inside the glass cell, the performance reaches 33 in sensitivity and 1.0 in minimal detectable field for an integration time of 1000 s, as perceived by the atoms.
Paper Structure (1 section, 5 equations, 4 figures)

This paper contains 1 section, 5 equations, 4 figures.

Table of Contents

  1. Acknowledgments

Figures (4)

  • Figure 1: a, Schematic diagram. b, Energy level. c, Polarization measurement result for the Stokes parameters $S_x$ and $S_z$. The abbreviations in the figure are as follows: P: polarizer, DM: dichroic mirror, HWP: half-wave plate, QWP: quarter-wave plate, PBS: polarization beam splitter, M: mirror, BPD: balanced photodetector.
  • Figure 2: Comparison between the traditional transmission measurement and the WM scheme. Scanning two-photon detuning of the Rydberg EIT is realized by scanning the frequency of 480 nm laser, which changes Rydberg atoms' response to LF field. The shaded regions represent one standard deviation derived from five independent measurements.
  • Figure 3: Experimental and theoretical sensitivity as a function of the post-selection angle. The error bars represent one standard deviation from five independent measurements. The theoretical fitting is provided (see Supplementary S4) by modeling the post-selection process.
  • Figure 4: a, Measured sensitivity across different AC electric field frequencies. The shaded region denotes one standard deviation from five independent measurements. b, Measured minimal detectable field strength versus RBW. The dashed lines are linear fittings according to the function $E_\mathrm{min} = k/\sqrt{T}$, where $k$ is the fitting parameter. Data are shown for a transmission measurement where the probe light at the photodiode was attenuated to match the optical power of the WM case. Insets: SNR extracted from the FFT spectrum for a $4.8~\mathrm{kHz}$, $0.18~\mathrm{mV/cm}$ electric field, with standardized y-axis limits for comparative purpose.