利用“魔术”条件提高中性原子量子比特门操作保真度

The neutral atom system has some advantages, which makes it very suitable for demonstrating the quantum information and quantum computation. The coupling of the neutral atom to the external electromagnetic field is weak, which indicates a long coherence time of a neutral atom. In addition, single neutral atoms can be easily scaled to 2D or 3D arrays. Furthermore, the strong interaction between Rydberg atom can indirectly accomplish atom-atom entanglement, and then realize efficient double-qubit logic gates operation, which provides a good experimental platform for the quantum computation. To perform fault-tolerant quantum computations via quantum error correction protocols, it requires that errors in quantum logic gates are small enough. Normally, the tolerable error varies among correction strategies, and the commonly accepted error threshold per gate is 10−4. Specifically, in neutral atom quantum computation. In contrast to trapped ion qubits, microwave-driven gates on neutral atomic qubits undergo large errors. Therefore, it is of great significance to further improve the fidelity of quantum logic gate of neutral atoms. Increasing the coherence time is the key to the improvement of the fidelity of quantum logic gate. In this project, by constructing a "magic" dipole trap to reduce the decoherence of qubit caused by atomic motion, the fidelity of quantum logic gate can be improved. Using this method, the fidelity of the single qubit gate is expected to be improved to over 99.99%, and the double-qubit gate to over 99%, which lays a foundation for the development of quantum information and quantum computing.

由于中性原子系统不易受外界电磁场的干扰，极易扩展成阵列，相干性较好，里德堡相互作用较大，成为演示量子信息和量子计算的重要系统。要想实现基于量子纠错协议的容错量子计算，量子逻辑门的误差需要足够小，通常可接受的误差阈值为10-4。相比与离子系统，中性原子量子比特门操作的保真度相差甚远。因此进一步提高中性原子量子比特门操作的保真度具有重要的研究意义。量子比特门操作保真度的提高，关键之处在于量子比特相干时间的提高。本项目拟在中性冷原子系统中，通过构建“魔术”偶极阱来减小原子运动导致的量子比特的退相干，从而实现量子比特门操作保真度的提高。采用这种方法，有望将单量子比特门操作的保真度提高到99.99%以上，双量子比特门操作的保真度提高到99%以上，为量子信息和量子计算的发展奠定了基础。

由于中性原子系统不易受外界电磁场的干扰，极易扩展成阵列，相干性较好，里德堡相互作用较大，成为演示量子信息和量子计算的重要系统。本项目在中性冷原子系统中，利用“魔术”偶极阱来减小基态原子的差分光频移，将基态原子量子比特的相干时间提高到秒量级；利用“魔术”偶极阱囚禁里德堡原子，将里德堡原子的相干时间延长，从而使得里德堡单光子源的纯度和全同度同时提升至99.9%以上，并利用该单光子源实现了国际上最高保真度的光量子逻辑门。该研究成果有望为光量子信息处理和分布式光量子系统等重要量子应用开辟新的前景。