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Prof. Zhang xiangdong, Sun houjun with their research groups have made significant progress in cooperative research

release date :2019-05-26 05:49:00  |   [ close window ]ViewCount:

    Translator:  Lv Rong, News Agency of BIT

    Editor: News Agency of BIT

  Recently, Professor Zhang Xiangdong from School of Physics and Sun Houjun from School of Information and Electronics of Beijing Institute of Technology, lead their research groups to cooperative research on Microwave signal processing and topological entanglement entropy. Significant progress has been made and related research findings are published in  the  recent Nature Communications (Vol.10, 1557 (2019)) and Optics Express(Vol. 27, 436-460 (2019))and other important journals. Professor Kou Supeng from The Department of Physics of Beijing Normal University and Dr. Liu Yulong from School of Physics of BIT offered their help in the study of topological entanglement entropy.

Figure 1: CMGS Implementation in Classical Microwave and Circuit Systems

  In the field of microwave signal processing, the existing information technology was developed based on the traditional classical theory. However, with the development of society and the demand for big data processing, the slow speed of information processing gradually surface and become a problem apparently. Compared with the classical information processing method, quantum information processing technology based on quantum mechanics embodies its superiority. Nevertheless, a special quantum environment needs to be established in order to achieve its implementation. In such an environment, it is easily affected by decoherence and scalability, which seriously restricts its practical application.

  Recently, the two research groups cooperated closely together to construct a classical microwave graph state (CMGS) based on classical microwaves and circuits (shown in Figure 1), and proved that CMGS possesses similar characteristics to quantum patterns. Based on this kind of state, the unitary transformation and quantum search algorithms have been completed, demonstrating similar functions to one-way quantum computing.Related work is published in Optics Express (Vol. 27, 436-460 (2019)).Zhang Shihao, PhD student of the School of Physics, BIT, Zhang Yi, PhD student of the School of Information and Electronics, and Dr. Sun Yifan, School of Physics, are the co-first authors of the paper.

Figure 2 Description of the quantum minimum entropy state

  Based on the above research on microwave signal processing, the research on topological entanglement entropy is further carried out.Topological entanglement entropy is a physical quantity proposed by Kitaev and Wen Xiaogang when studying entanglement property of topological order a few years ago.It is a unique state that can exhibit many novel physical properties, and its long-range entanglement property is one of its important features.Although the theoretical study shows that topological entanglement entropy can describe the topological order and its long-range entanglement property well , it has not been experimentally confirmed.

  Recently, the research group put forward an experimental scheme to study topological entanglement entropy based on minimum entropy states.The minimum entropy state is a multi-qubit entangled that can be used to observe the topological order (as shown in Figure 2). It would be usual to construct a multi-particle entangled state (quantum minimum entropy state) in a quantum many-body system, and then conduct several experimental researches based on a pure quantum information processing platform. Yet execution in this way is very difficult to implement.The reason is that it requires at least 90% of the fidelity of the multi-particle entangled state to observe the topological entanglement entropy, and the 12-qubit entangled state fidelity constructed on the IBM quantum computer platform at present is less than 44%.

Figure 3 Comparison of topological entanglement entropy experiments and theoretical results

Figure 4 Experimental observation of the transition from Z2 topologically ordered state to topologically trivial state

  The research group constructed the classical minimum entropy state (CMES) based on classical microwaves and circuits, and its construction method is similar to that of the classical microwave pattern mentioned above. The research group found that CMES constructed in this way has similar correlation properties with the quantum minimum entropy state. Based on CMES, a linear relationship between topological entanglement entropy and size is observed (as shown in Figure 3), which is consistent with theoretical predictions. Furthermore, the transition from Z2 topologically ordered state to topologically trivial state are observed (as shown in Figure 4). 
       Related content was published in Nature Communications (Vol. 10, 1557 (2019)).Associate Professor Chen Tian and PhD student Zhang Shihao of the School of Physics, BIT, are the co-first authors of the paper; Zhang Yi, PhD student of School of Information and Electronics and Dr. Liu Yulong, School of Physics, BIT, are the co-authors of the paper. Professor Sun Houjun from the School of Information and Electronics, and Professor Zhang Xiangdong from the School of Physics,BIT, are the corresponding author of the paper; Professor Kou Supeng from Beijing Normal University is the co-corresponding author of the paper.

  The work above has been funded by the National Key Research and Development Program of China and the National Natural Science Foundation of China.

  

Link to the paper:

https://www.nature.com/articles/s41467-019-09584-1;
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-2-436

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