Max-Planck-Institute for Gravitational Physics, Leibniz Universität Hannover, Callinstrasse 38, D-30167 Hannover, Germany.
Opt Lett. 2012 Jun 15;37(12):2367-9. doi: 10.1364/OL.37.002367.
Squeezed states can be employed for entanglement-based continuous-variable quantum key distribution, where the secure key rate is proportional to the bandwidth of the squeezing. We produced a nonclassical cw laser field at the telecommunication wavelength of 1550 nm, which showed squeezing over a bandwidth of more than 2 GHz. The experimental setup used parametric downconversion via a periodically poled potassium titanyl phosphate crystal. We did not use any resonant enhancement for the fundamental wavelength, which should in principle allow a production of squeezed light over the full phase-matching bandwidth of several nanometers. We measured the squeezing to be up to 0.3 dB below the vacuum noise from 50 MHz to 2 GHz limited by the measuring bandwidth of the homodyne detector. The squeezing strength was possibly limited by thermal lensing inside the nonlinear crystal.
压缩态可用于基于纠缠的连续变量量子密钥分发，其中安全密钥率与压缩带宽成正比。我们在电信波长 1550nm 处产生了非经典连续波激光场，其在超过 2GHz 的带宽上显示出压缩。实验装置使用通过周期性极化磷酸钛钾晶体的参量下转换。我们没有为基频使用任何共振增强，原则上这应该允许在数纳米的整个相匹配带宽内产生压缩光。我们通过测量限制在 50MHz 至 2GHz 的同相检波器的测量带宽，测量到的压缩度最高可达真空噪声的 0.3dB。压缩强度可能受到非线性晶体内部热透镜的限制。
