Wang Ming-Feng, Jiang Nian-Quan, Zheng Yi-Zhuang
Opt Express. 2014 Apr 21;22(8):9182-92. doi: 10.1364/OE.22.009182.
The continuous-variable (CV) quadratic phase gate is one of the most fundamental CV quantum gates for universal CV quantum computation, while its experimental realization still remains a challenge. Here we propose a novel and experimentally feasible scheme to realize optical CV quadratic phase gate via Faraday interaction in an atomic ensemble. The gate is performed by simply sending an optical beam three times through an atomic medium prepared in coherent spin state. The fidelity of the gate can ideally run up to one. We show that the scheme also works well as a device to generate optical polarization squeezing. Considering the noise effects due to atomic decoherence and light losses, we find that the observed fidelities of gate operation and the attainable degree of polarization squeezing are still quite high.
连续变量（CV）二次相位门是通用CV量子计算中最基本的CV量子门之一，但其实验实现仍然是一个挑战。在此，我们提出了一种新颖且实验上可行的方案，通过原子系综中的法拉第相互作用来实现光学CV二次相位门。该门通过简单地将一束光三次穿过制备在相干自旋态的原子介质来执行。该门的保真度理论上可达1。我们表明该方案作为产生光偏振压缩的器件也能很好地工作。考虑到原子退相干和光损耗引起的噪声效应，我们发现观察到的门操作保真度和可达到的偏振压缩程度仍然相当高。
