Quantum Information

Quantum information technology is the dominant force pushing forward the development and revolution of future information technology and industry. It will influence the whole information industry. Breakthroughs in quantum information science are the key to the development and application of quantum information technology. Currently, quantum information science and technology has entered a new era of profound development and rapid breakthroughs. The characteristic signs of a major industrial revolution are emerging. Department of Physics of Tsinghua University is one of the pioneers in quantum information studies in the world, and the department’s research covers areas such as quantum matter and material, quantum computing, quantum communication, quantum metrology and quantum devices and so on. In recent years, the University has strengthened the discipline of quantum information science, and speeded up the recruitment of young talent faculties, so as to enhance China’s research and development capability in quantum information science. For instance, two outstanding young faculty members, Dr Dong Liu from Microsoft Station-Q and Dr. Hao Zhang from Delft University of Science and Technology, have joined the department of physics recently. This has significantly strengthened the fabrication and control capabilities of topological qubit of the department.

Gui-Lu Long proposed quantum secure direct communication(QSDC) theory in 2000, which has become one of the three major theories of quantum secure communication. In the last few years, QSDC is developing fast. Guilu Long, Qikun Xue, Jianhua Lu, Lajos Hanzo et al. proposed a secure repeater quantum network, which is an evolutionary pathway for the quantum internet relying on secure classical repeaters. Guilu Long’s Group realized a 100 km fiber-based quantum secure direct communication system, paving the way to practical long-distance quantum secure direct communication application. Guilu Long’s Group experimentally demonstrated free-space quantum secure direct communication and it is the foundation for satellite-based quantum secure direct communication. Relevant national departments and Beijing Municipality attach big importance to quantum secure direct communication, and relevant policies have been written into “Construction Plan of Beijing International Science and Technology Innovation Center during the Tenth Five-Year Plan period”(released in 2021), “Implementation Plan of Beijing Municipality for Promoting Future Industrial Innovation and Development” (released in 2023) and relevant national policy documents.

Recently, the research group of Associate Professor Dong Liu proved that there is "benign" noise in the periodic quantum system, and based on this theory, developed a quantum phase estimation algorithm with remarkable anti-noise ability, and a noise detection method for quantum computing---the channel spectrum reference detection scheme. Compared with other methods, the new scheme is based on the anti-noise theorem of periodic circuits, and it does not need to control the noise scaling carefully, nor does it need to acquire noise channels, which will increase the resource consumption excessively. The results are published in Physical Review Letters and Nature Communication respectively.

Ion trap is one of the leading physical platforms to realize universal quantum computers. Coherence time of a single qubit, quantum gate fidelity and the number of computable qubits are three important indexes to evaluate the performance of a quantum computing system. Professor Kihwan Kim's team extended to coherence time of a single qubit to more than 90 minutes in 2021, which is the longest working time in all quantum computing physical systems at present. In 2020, Professor Kim's team realized a two-qubit gate with a fidelity of 99.9%, which is close to the world record of 99.94%. In terms of the number of computable qubits, Professor Kim's team realized the genuine entanglement generation of 9 phonons and the quantum simulation of more than 10 qubits. The results were published in Nature, Nature Photonics and Nature Physics respectively.