Extended Data Fig. 1: Details of the entire experimental set-up.
From: Continuous wideband microwave-to-optical converter based on room-temperature Rydberg atoms
a, Laser system. A narrowband fiber laser at 1,560 nm serves as a frequency reference for the entire system. The laser is amplified via erbium-doped fiber amplifier (EDFA) and the frequency is doubled using a second-harmonic generation (SHG) process to 780 nm. The 960 nm external-cavity diode laser (ECDL) is amplified using a tapered amplifier (TA) and frequency-doubled via cavity-enhanced SHG to yield a coupling field at 480 nm. The 960 nm laser is stabilized to the master laser of 1,560 nm using a common cavity. A similar independent system is introduced for the stabilization of decoupling (1,258 nm) laser, likewise for local oscillator (LO) 776 nm laser. The second harmonic of the 1,560 nm fiber laser serves as a reference for offset-locking of the probe laser in an optical phase-locked loop (PLL). b, Microwave generation system. The generated microwaves are attenuated adequately and split into the spectrum analyzer for power and frequency references and to the antenna. c, Thermal image of the cell and cell holder. The constant temperature of the cell is assured with hot-air heating via hollow channels in the 3D-printed cell holder. d, The generated signal light exits the converter in a beam with a Gaussian profile shown in the image. e, Heterodyne measurement with LO yields spectrum of the converted signal: the residual broadening of Γsig = 86 × 2π kHz FWHM is due to collective laser-locking phase noise. f, Scheme of the experimental setup: probe, coupling and decoupling laser beams are combined with dichroic mirrors (DM) into a collinear configuration, and focused inside a rubidium vapor cell of length 50 mm and diameter 25 mm with a MW helical antenna pointed there. The circular polarization of lasers is assured with quarter-wave plates (QWP). The probe (780 nm) signal is registered by an avalanche photodiode (APD), which enables laser calibration by observation of EIT features. Converted 776 nm signal is spectrally separated and coupled into a single-mode fiber. g, Different setups are used for detection, with single setup being used at a time. The detection setups include direct photon counting with optional attenuation, cavity-filtered photon counting, photon autocorrelation with two channels simultaneously, and heterodyne detection. For photon counting, a multichannel superconducting nanowire single-photon detector (SNSPD) is used. For heterodyne measurement we combine the signal with LO using a polarization beam splitter (PBS) and split the combined signal 50:50 with a half-wave plate (HWP) and a second PBS. The signal is then registered on a differential photodiode (PD).
