基于减光子技术的薛定谔猫态的实验制备

The control of quantum systems not only have important scientific interest but also promises powerful technical applications. These years, Schrödinger cat states became another central requirement for quantum information science and technology except Fock states and quantum entaglment. High fidelity and large-amplitude cat states will be useful for encoding of logical qubits in coherent states, fault-tolerant quantum computing, super-resolution metrology and and so on. In this project, the cat state is generated by subtracting a single-photon from a squeezed vacuum state based on non-Gaussian operation, which is a third or higher order optical non-linear process and is involved in photon creation and annihilation operators. The main proposal of the project is: 1) Generate a squeezed vacuum state with high purity by a stable and lossless optical parametric oscillator. Improve the state purity by decreasing the optical loss and improving the phase noise and so on. 2) Filter the optical mode to remove all the non-degenerate modes by filter system, reconstruct the generated state and experimentally observed Schrödinger cat state. Furthermore, implementation of arbitrary quantum qubits based on quantum manipulation of cat state provide better insight into quantum computing, quantum communication and quantum precision measurement.

对量子态进行操控不仅有着重要的科学意义而且具有极高的技术应用价值。近二十年来，除各类光子数态和各类纠缠态之外，薛定谔猫态成为近年来量子信息处理系统中的重要资源。具有高保真度和大幅值的薛定谔猫态是目前的一个研究热点，因为它可以用于编码完美的量子比特、容错量子计算、超分辨率量子计量等。本项目在线性光学系统中通过对高斯态进行非高斯操作来实现态的制备，即通过对压缩真空态操控，进行减光子操作来制备薛定谔猫态。本项目主要研究：1）利用高稳定性、低损耗的光学参量振荡器制备高纯度、高压缩度(8dB)的真空压缩态光场；2）利用两级频率过滤装置搭建减光子系统，平衡零拍测量重构量子态，完成减光子操作制备具有高保真度和大幅值的薛定谔猫态。本项目为下一步对猫态进行量子操控实现任意量子比特的制备提供了基础，并将拓展其在量子计算、量子通讯、量子精密测量等方面的应用。

在基金的资助下，主要开展了高纯度、高压缩度的真空压缩态和基于减光子技术的薛定谔猫态的理论和实验研究。利用基于PPKTP晶体构成的I类光学参量振荡器，实验获到了1064nm真空压缩态光场，最大压缩度为7.1dB，考虑到测量损耗后，光场的真空压缩度可达8.7dB；在低泵浦功率下，实验获得了压缩度为3.2dB、纯度为93.3%的真空压缩态光场。利用减光子技术和量子层析技术初步制备和重构了条件制备态，条件制备态为幅值约等于1、保真度为36.8%的薛定谔奇猫态。实验中相关的实验技术成果申请了国家发明专利3项、实用新型专利3项，均已授权。通过本项目，课题组掌握了一系列的实验技术，为下一步提高猫态幅值和保真度，对猫态进行量子操控等实验提供了坚实的基础，这些研究将拓展薛定谔猫态在量子计算、量子纠缠纯化、量子信息处理等领域的应用。