Calibration-free Rydberg Atomic Receiver for Sub-MHz Wireless Communications and Sensing

TL;DR

The paper tackles sub-MHz sensing with compact, calibration-free Rydberg receivers by developing a dual-field Stark model that combines DC and AC components, $E(t)=E_{\mathrm{DC}}+E_{\mathrm{AC}}\cos(2\pi f_{\mathrm{AC}}t)$, and cycle-averaged EIT spectroscopy. A two-step MAS method retrieves $E_{\mathrm{AC}}$ from spectral fits tied to intrinsic atomic polarizability $\alpha$, yielding $\Delta f_1=\tfrac{1}{2}|\alpha|E_{\mathrm{DC}}^2$ and $\Delta f_2=2|\alpha|E_{\mathrm{AC}}E_{\mathrm{DC}}$, which leads to $E_{\mathrm{AC}}=\frac{\Delta f_2}{2\sqrt{2|\alpha|\Delta f_1}}$ and removes dependence on electrode spacing and external amplitude calibration. Experimental validation with cesium vapor at 30 kHz demonstrates a minimum detectable field of $E_{\min}=5.3$ mV/cm and demonstrates robustness against optical-power fluctuations, supported by six-level Lindblad simulations. The approach enables calibration-free, compact quantum front ends for underwater and subsurface sensing, with potential extensions to micro-cell integration and real-time demodulation.

Abstract

The exploitation of sub-MHz (\textless 1 MHz) can be beneficial for a plethora of applications like underwater vehicular communication, subsurface exploration, low-frequency navigation etc. The traditional electrical receivers in this band are either hundreds of meters long or, when miniaturized, inefficient and bandwidth-limited, making them inapplicable for practical underwater implementations. Such obstacles can be circumvented by the emerging Rydberg atomic receiving technology, which is capable of detecting fields from DC up to the terahertz regime with compact structure. Against this background, we propose a method to detect sub-MHz electric fields without further calibration. Specifically, a physics-based model of the combined DC and AC-Stark response is established. Based on the model, we modulate the DC-Stark spectrum with the received signal and extract its amplitude by fitting the cycle-averaged, symmetric Stark-split peaks. Then we map this swing directly to the intrinsic atomic polarizability. By such operations, the proposed method can remove the dependence on electrode spacing or field-amplitude references. For performance evaluation, six-level Lindblad simulations and experiments are conducted at a low-frequency field of 30 kHz demonstrate a minimum detectable field of 5.3 \text{mV}/\text{cm}, with stable readout across practical optical-power variations. The approach manages to expand operating range of Rydberg atomic receivers below 1 MHz, and enables compact, calibration-free quantum front ends for underwater and subsurface receivers.

Figures (6)

• Figure 1: (a) Energy level system and (b) experimental Setup. PD: Photodiode, DM: Dichroic Mirror. (c) Principle of the calibration-free measurement.
• Figure 2: The AC-Stark spectra of Rydberg atoms are measured (a) experimentally and (b) calculated theoretically.
• Figure 3: Experimental and theoretical spectra under a mixed electric field with a 220 mV/cm DC electric field and a 50 mV/cm, 30 kHz AC electric field.
• Figure 4: Experimental (a, c) and theoretical (b, d) spectra are measured under two conditions: (a, b) with a 220 mV/cm DC field and a 0–180 mV/cm, 30 kHz AC field, and (c, d) with a 0–360 mV/cm DC field and an 18.5 mV/cm, 30 kHz AC field.
• Figure 5: (a) Representative spectrum versus coupling-laser detuning. Vertical dashed lines mark $L=b-\Delta$ and $R=b+\Delta$; the shaded band highlights the integrated splitting region with $\Delta f_2=2\Delta$. (b) LOD analysis of the electric field measurement. Bottom: proposed Dual Field Modulated method $E_{\mathrm{MAS}}$ (red circles) plotted against the conventional AC-Stark peak-fit result $E_{\mathrm{ACM}}$ (gray diamonds). Top: deviation expressed as $20\log_{10}(E_{\mathrm{MAS}}/E_{\mathrm{ACM}})$.