Supercompact Photonic Quantum Logic Gate on a Silicon Chip
Ming Zhang, Lan‐Tian Feng, Ming Li, Chen Yang, Long Zhang, De‐Yong He, Guo‐Ping Guo, Guang‐Can Guo, Xi‐Feng Ren, Daoxin Dai · Physical Review Letters · 2021
To build universal quantum computers, an essential step is to realize the so-called controlled-NOT (CNOT) gate. Quantum photonic integrated circuits are well recognized as an attractive technology offering great promise for achieving large-scale quantum information processing, due to the potential for high fidelity, high efficiency, and compact footprints. Here, we demonstrate a supercompact integrated quantum CNOT gate on silicon by using the concept of symmetry breaking of a six-channel waveguide superlattice. The present path-encoded quantum CNOT gate is implemented with a footprint of $4.8\ifmmode\times\else\texttimes\fi{}4.45\text{ }\text{ }\ensuremath{\mu}{\mathrm{m}}^{2}$ ($\ensuremath{\sim}3\ensuremath{\lambda}\ifmmode\times\else\texttimes\fi{}3\ensuremath{\lambda}$) as well as a high-process fidelity of $\ensuremath{\sim}0.925$ and a low excess loss of $<0.2\text{ }\text{ }\mathrm{dB}$. The footprint is shrunk significantly by $\ensuremath{\sim}10\text{ }000$ times compared to those previous results based on dielectric waveguides. This offers the possibility of realizing practical large-scale quantum information processes and paving the way to the applications across fundamental science and quantum technologies.