The non-classical light resonant on the cesium D1 (894.6 nm) line has important applications in solid-state quantum information networks due to its unique advantages. The cesium D1 line has the merit of simplified hyperfine structure for experimental realization of a light-atom interface. It also lies well within the wavelength regime of excitonic transition in InAs/GaAs quantum dots for integrated quantum interfaces between light and solid-state systems. We prepare the vacuum squeezed light at cesium D1 line with continuous-wave quasi-phase-matching degenerate optical parametric oscillator (OPO), which is pumped by 447.3 nm blue laser generated via frequency doubling of 894.6 nm laser at cesium D1 line. The SHG cavity is a two-mirror standing-wave cavity with a PPKTP crystal as the nonlinear medium. The input coupler has a transmissivity of 5% at 894.6 nm and is highly reflecting at 447.3 nm, while the output coupler is highly reflecting at 894.6 nm and has a transmissivity of 95% at 447.3 nm. The power of generated blue laser is 32 mW when the incident infrared power is 120 mW. In our previous work, we demonstrated 2.8 dB quadrature squeezed vacuum light at cesium D1 line in an OPO with a periodically poled KTP (PPKTP) crystal. Here, we use super-polished and optimal coating cavity mirrors to improve the nonlinear process in OPO. The OPO is a two-mirrors standing-wave cavity with a PPKTP crystal. The input coupler has a transmissivity of 10% at 447.3 nm and is highly reflecting at 894.6 nm, while the output coupler is highly reflecting at 447.3 nm and has a transmissivity of 9.5% at 894.6 nm. The threshold of OPO is reduced to 28 mW. The squeezing level of generated quadrature squeezed vacuum light is increased to 3.3 dB when the pump power is 15 mW. The spectrum analyzer is setting on zero-span mode at 1 MHz. The resolution bandwidth is 30 kHz and the video bandwidth is 100 Hz. Taking into account the overall detection efficiency, the actual squeezing reaches 5.5 dB. We inject a weak signal beam into the OPO cavity to run it as an optical parametric amplifier (OPA), the generated bright squeezed light can be continuously tuned over a range around 80 MHz across D1 line of cesium, offering the possibility for the efficient coupling between the non-classical source and solid medium in the process of quantum interface.
下载:
