Transverse Mode-Encoded Quantum Gate on a Silicon Photonic Chip

• Published in: Physical review letters 2022-02, Vol.128 (6), p.060501-060501, Article 060501
• Main Authors: Feng, Lan-Tian, Zhang, Ming, Xiong, Xiao, Liu, Di, Cheng, Yu-Jie, Jing, Fang-Ming, Qi, Xiao-Zhuo, Chen, Yang, He, De-Yong, Guo, Guo-Ping, Guo, Guang-Can, Dai, Dao-Xin, Ren, Xi-Feng
• Format: Article
• Language: English
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.128.060501

As an important degree of freedom (d.o.f.) in photonic integrated circuits, the orthogonal transverse mode provides a promising and flexible way to increase communication capability, for both classical and quantum information processing. To construct large-scale on-chip multimode multi-d.o.f.s quantum systems, a transverse mode-encoded controlled-NOT (CNOT) gate is necessary. Here, with the help of our new transverse mode-dependent directional coupler and attenuator, we demonstrate the first multimode implementation of a 2-qubit quantum gate. The ability of the gate is demonstrated by entangling two separated transverse mode qubits with an average fidelity of 0.89±0.02 and the achievement of 10 standard deviations of violations in the quantum nonlocality verification. In addition, a fidelity of 0.82±0.01 is obtained from quantum process tomography used to completely characterize the CNOT gate. Our work paves the way for universal transverse mode-encoded quantum operations and large-scale multimode multi-d.o.f.s quantum systems.