Receiving Wi-Fi Signal with Warm Rydberg Atoms*

Rydberg atoms exhibit both remarkable sensitivity to electromagnetic fields making them promising candidates for revolutionizing field sensors and, unlike conventional antennas, they neither disturb the measured field nor necessitate extensive calibration procedures. In this study, we propose a receiver design for data-modulated signal reception near the 2.4 GHz Wi-Fi frequency band, harnessing the capabilities of warm Rydberg atoms. In the experiment, we consider a 5-level energy ladder of 85Rb. In the following setup, the probe laser is tuned to the D2 transition  between ground state 5²S_1/2 (𝐹 = 3) and 5²P_3/2 (𝐹 = 4). The second and third fields coupled to the 5²P_3/2 (𝐹 = 4) → 5²D_5/2 (𝐹 = 5) and 5²D_5/2 (𝐹 = 5) → 32²F_7/2 transitions respectively. The

last 32²F_7/2 → 32²G_9/2 transition is in the considered microwave regime. The fields excite atoms to the Rydberg state and cause the electromagnetically induced absorption effect to emerge, which can be interpreted as the interference of electromagnetically induced transparencies. To perform the heterodyne detection we introduce an additional microwave field acting as a local

oscillator. The main goal of the experiment is to receive data encoded into the signal through modulation of the microwave field, using the quadrature amplitude modulation (QAM) scheme. In this scheme, the signal is generated from the amplitude-modulated I (in-phase) and Q (quadrature) components shifted in phase by 𝜋/2. The components define two-dimensional IQ space, in which QAM can be described as an even symmetrical points distribution around the origin. We consider various transmission frequencies for QAM4, QAM16 and QAM64 and its influence on chanel capacity using Voronoi diagrams. We also offer a characterization of our setup, encompassing the atomic response frequency range, attainable electric field amplitudes, and sensitivity.