Quantum entanglement is a quantum phenomenon that violates the common sense of classical physics, and is an important physical resource of quantum communication and quantum computing. Among them, high-dimensional quantum entanglement has unique advantages in many quantum information tasks. Recently, Professor Ma Xiaosong's team from the school of physics of Nanjing University reported their latest research results on the nature collaborative Journal npj quantum information Chip, the team has realized the generation, filtering, regulation and other functions of high-dimensional entangled state on silicon-based integrated optical quantum chip, and has completed the application tasks of quantum simulation and quantum precise measurement by using precise on-chip quantum regulation.
Explanation: A. three dimensional quantum entanglement chip; B. optical microscope; C. schematic diagram of experimental equipment.
Quantum entanglement is a peculiar property of quantum system. It was defined by Schrodinger in 1935. The entanglement types of quantum system mainly include multi-body quantum entanglement and multi-dimensional quantum entanglement. Among them, the high-dimensional entangled state (dimension & gt; 2) has attracted great interest due to its unique properties. With the increase of the dimension of quantum system, compared with the commonly used two-dimensional quantum system, the high-dimensional quantum system has the advantages of strong parallel computing ability, high information capacity and strong anti noise ability. As the carrier of quantum information, photons have many advantages, such as good coherence, multiple degrees of freedom, easy to control and so on. They are the ideal system to realize high-dimensional entanglement. However, how to efficiently prepare high-dimensional entangled photon pairs and carry out high-precision, programmable arbitrary coherent control is a big challenge for quantum information technology to move towards large-scale application. Professor Ma Xiaosong's team uses the micro nano processing of integrated optical chips and the third-order nonlinearity of silicon to adopt the optimized interference type micro ring resonator. By encoding the path mode of photons on the chip, the three-dimensional quantum states on the chip can be generated, filtered, controlled and other functions can be realized to form an active integrated optical quantum chip (see the figure above). Through the spontaneous four wave mixing effect in the silicon waveguide and the highly stable and reconfigurable coherent control of the linear optical path, the team has realized a two-photon source with extraction efficiency higher than 97%, without post-processing of filtering and high suppression of the pumped photons; the on-chip quantum interference visibility is higher than 96.5%, and the fidelity of the three-dimensional maximum entangled state reaches 95.5%. Based on this high-quality entangled state, the team experiment has completed the verification of the three-dimensional Bell inequality and the quantum intertextuality test without compatibility holes. In terms of quantum simulation, through the manipulation of three-dimensional entangled quantum states, the team has realized the simulation of graph theory with quantum optical devices for the first time in the world, especially through the measurement of the coherence of quantum states to directly obtain the perfect matching number of graphs. In the theory of information complexity, the perfect matching number of a graph belongs to the "p-complete" complexity. This means that the known classical algorithm can not effectively solve this problem. This work is the first to verify the feasibility of the quantum simulation experiment of the graph, and takes the first step to solve the problem of "complete P" by using quantum optics. In terms of quantum precision measurement, the applicant team also demonstrated high-precision phase measurement with quantum optical chips, breaking through the theoretical limit of the measurement accuracy of classical interferometers, and reflecting the advantages of high-dimensional quantum entanglement. This study provides an important basis for the on-chip preparation of multi-body high-dimensional quantum entanglement system and the application of quantum control technology.
This achievement was published in the nature cooperation Journal npj quantum information. Lu Liangliang, researcher of the school of physics of Nanjing University, Xia Lijun, master student and Chen Zhiyu, master student were the co authors. Chen leizhen, Yu Tonghua, Tao Tao Tao, Ma Wenchao, Professor Cai Xinlun and pan Ying from Nanjing University also made important contributions to this paper. Professor Ma Xiaosong of Nanjing University is the corresponding author of the paper. Academician Zhu shining and Professor Lu Yanqing give in-depth guidance. The research was supported by the excellence program of Nanjing University, the national key research and development program, the National Natural Science Foundation, and the special fund for basic scientific research fees of central universities. This research work is supported by the State Key Laboratory of solid microstructure, the school of physics and the collaborative innovation center of Artificial Microstructure science and technology of Nanjing University.
Article link: https://www.nature.com/articles/s41534-020-0260-x
Homepage of the research group: http://qoqi.nju.edu.cn
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Source: Nanjing University News Network
Editor: Ding Ding