Fine-tuning of a squeezed state across the hyperfine transition in a cesium D 1 line

Squeezed states tuned to alkali atomic transitions are essential for developing atom–light quantum interfaces. We experimentally demonstrate a frequency-tunable quadrature squeezed state across the hyperfine transition of F =4(6 2 S 1/2 )→ F ′ =3(6 2 P 1/2 ) of a cesium ( 133 Cs) D 1 line at 894.6 nm. Using a compact semi-monolithic optical parametric oscillator (OPO) operating below threshold, we achieve up to −4.1 dB squeezing below the standard quantum limit. When reconfigured as an optical parametric amplifier (OPA), the system generates bright squeezed light that can be finely tuned over a 50 MHz range, which is verified using electromagnetically induced transparency (EIT) spectroscopy. This portable and tunable quantum light source provides a promising platform for cesium-based quantum interfaces in emerging quantum networks.