Fine-tuning of a squeezed state across the hyperfine transition in a cesium <i>D</i> 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 <i>F</i>=4(6²<i>S</i>_1/2)→<i>F</i>^<i>'</i>=3(6²<i>P</i>_1/2) of a cesium (¹³³Cs) <i>D</i>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.