Source: China University of Science and Technology News
The team of Academician Guo Guangcan of our university has made important progress in the research of optical quantum chips. In cooperation with the Dai Dao Zinc team of the College of Optoelectronic Science and Engineering of Zhejiang University/State Key Laboratory of Modern Optical Instruments, the team achieved the operation of a two-bit quantum logic gate encoded by on-chip waveguide mode for the first time in the world, and the related results were published in the internationally renowned academic journal Physical Review Letters on February 11.

Both classical and quantum information applications need to greatly improve the information processing and communication capabilities of photonic chips to meet the growing needs of optical communication and interconnection. In order to realize large-scale optical quantum systems, multi-photon, multi-degree of freedom and high-dimensional coding are inevitable approaches. The unique properties of multimode waveguide modes, such as high dimensional extensibility, compactness and arbitrary coherence conversion with other degrees of freedom, make waveguide mode coding have a wide prospect in the field of integrated photonics. Therefore, waveguide mode coding has attracted much attention in recent years.

Ren Xifeng's research group and Dai Dao Zinc team of Zhejiang University have been committed to the research of silicon-based optical quantum devices and chips for a long time and have made a series of important progress: (1) Waveguide mode encoding is used for quantum information processing for the first time in the world, and coherent transformation between waveguide mode, polarization and path encoding entangled states is realized (Nat Commun 7, 11985, 2016); (2) The first waveguide mode encoded entangled light source was fabricated (npj Quantum Inf 5, 2, 2019); (3) Construct the world's smallest optical quantum controlled non-gate (Phys Rev Lett.126.130501 (2021)) based on dense waveguide superlattice arrays. On this basis, two new multi-mode photonic devices such as waveguide mode coupler (TMDDC) and mode attenuator (MMA) have been designed and developed independently by the two parties, which are used to realize specific functions of mode dependent coupling and mode dependent attenuation respectively. Furthermore, these new photonic functional devices are integrated on a single chip, and the two-bit controlled ungated operation of waveguide mode coding is demonstrated for the first time in the world.

Figure 1. Schematic diagram of photonic waveguide mode encoded quantum control non-gate chip

The results pave the way for waveguide mode coded quantum manipulation, and can also be used for on-chip multi-degree-of-freedom optical quantum information processing. The reviewers agree that this is an important research work and give high evaluation: "The two new components TMDDC and MMA invented here are important", "I believe that the work. presented in this letter will provide essential tools in that field. Presented in this letter will provide essential tools in that field.

Professor Ren Xifeng, Key Laboratory of Quantum Information, Chinese Academy of Sciences, and Professor Dai Daoxin, State Key Laboratory of Modern Optical Instruments, College of Optoelectronic Science and Engineering, Zhejiang University are co-corresponding authors of the paper. Feng Lantian, special associate researcher, Key Laboratory of Quantum Information, Chinese Academy of Sciences, and Zhang Ming, assistant researcher, Zhejiang University are co-first authors of the paper. The work was funded by the Ministry of Science and Technology, the National Foundation of China, the Chinese Academy of Sciences, Anhui Province, and the University of Science and Technology of China.

Paper link:https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.060501

(Key Laboratory of Quantum Information, Academy of Quantum Information and Quantum Technology Innovation, Scientific Research Department, Chinese Academy of Sciences)