Rydberg Atomic Quantum Receivers for Wireless Communications: Two-Color vs. Three-Color Excitation

Abstract

An efficient three-color (3C) laser excitation-based Rydberg atomic quantum receiver (RAQR) architecture is investigated for wireless communications, utilizing a five-level (5L) electronic transition mechanism. Specifically, the conventional two-color (2C) RAQR with the four-level (4L) excitation faces three fundamental obstacles: 1) high cost and engineering challenges due to the reliance on unstable blue lasers; 2) a fundamental sensitivity limit in thermal atoms caused by residual Doppler broadening; and 3) the inability to detect low-frequency bands due to the energy-level constraint of two-photon resonance. To address these challenges, this paper analyzes a 3C5L-RAQR architecture with all-red/infrared lasers, which not only solves the engineering cost issues but also enables effective Doppler cancellation and low-frequency detection by exhibiting the three-photon resonance. Bridging atomic physics and communication theory, an end-to-end equivalent baseband signal model is derived. Furthermore, the performance of different RAQR architectures is evaluated in terms of sensitivity, achievable capacity and spectrum access range. Moreover, we provide an exact numerical solution for practical RAQRs by employing the Liouvillian superoperator formalism. Numerical results demonstrate that the exhibited 3C5L-RAQR achieves superior sensitivity compared to the conventional 2C4L-RAQR and the classical receiver based on the conductor antenna. Finally, the inherent sensitivity-capacity trade-off is revealed, showing that the 3C5L-RAQR is more suitable for deployment in power-limited communication scenarios demanding broad spectrum access.

Figures (12)

• Figure 1: Atomic energy level schemes for Cs atoms ref_prajapati_sensitivity. (a) The conventional 2C4L-RAQR with electronic transition path $6S \to 6P \to nD$, which is driven by an infrared probe laser with wavelength $\lambda_{\text{p}} = 852$ nm and a high-power blue coupling laser with wavelength $\lambda_{\text{c}} = 510$ nm. (b)The exhibited 3C5L-RAQR with transition path $6S \to 6P \to 9S \to n'P$, which uses low-cost diode lasers, i.e., an infrared probe laser with wavelength $\lambda_{\text{p}}=895$ nm, a red dressing laser with wavelength $\lambda_{\text{d}}=636$ nm, and an infrared coupling laser with wavelength $\lambda_{\text{c}}= 2245$ nm. Note that considering the same incident RF signal, the 2C4L-RAQR carry out the downward electronic transitions based on the stimulated emission mechanism 9087968, i.e., $|47D_{5/2}\rangle \to |48P_{3/2}\rangle$, while the 3C5L-RAQR achieve the upward transitions via the energy absorption, i.e., $|48P_{3/2}\rangle \to |47D_{5/2}\rangle$.
• Figure 2: EIT absorption spectrum $\Im(\hat{\rho}_{21}^{{\text{4L}}})$ vs. probe detuning $\Delta_{\text{p}}$.
• Figure 3: EIT absorption spectrum $\Im(\hat{\rho}_{21}^{{\text{4L}}})$ vs. probe detuning $\Delta_{\text{p}}$ for different thermal-atom temperature $T_\text{atom}$ of vapor cell.
• Figure 4: Transmission spectrum vs. coupling detuning $\Delta_{\text{c}}$ under room temperature $T_\text{atom}=290$K of vapor cell.
• Figure 5: SNR performance under different noise regimes of RAQRs.