Recently, Pan Jianwei and his colleagues Peng Chengzhi, Chen Yuao and Yin Juan from the University of Science and Technology of China (USTC) have made important experimental progress in long-distance quantum state transmission using the "Micius" quantum science experiment satellite. The experiment has for the first time realized the remote transmission of quantum states between two ground stations located 1,200 kilometers apart on Earth, taking an important step toward building a global quantum information processing and quantum communication network. The relevant research results were published online on April 26 in the internationally renowned academic journal Physical Review Letters 128, 170501 (2022).

Long distance Quantum state transfer (QST) can be realized by using quantum teleportation, which is one of the important ways to construct quantum communication network, and also a necessary element to realize a variety of quantum information processing tasks. With the aid of long-distance quantum entanglement distribution, quantum states can be transmitted over long distances by measuring and then reconstructing, and the transmission distance can be theoretically infinite. However, in the realization, the distance and quality of quantum entanglement distribution will be affected by channel loss, decoherence and other factors. How to continuously break through the transmission distance limit has been one of the important research objectives in this field.

Using spaceborne entanglement source to distribute entanglement first to two distant places, and then to prepare and reconstruct quantum states, is one of the most possible ways to realize long-distance quantum state transmission. However, due to the influence of atmospheric turbulence, it is very difficult to realize quantum state measurement based on quantum interference after photon propagation in atmospheric channel. In previous experiments, the preparation party of quantum state transmission is the owner of the quantum entanglement source, and it is impossible to realize the quantum state transmission by providing entanglement by a third party in a real sense. In 2016, with the successful launch of the "Micius" quantum science experiment satellite, the research team first realized thousand-kilometer dual-station entanglement distribution [Science356, 1140 (2017)], and the "Micius" platform provided valuable entanglement distribution resources for quantum communication experiments.

Figure 1 thousand kilometers of quantum state transmission

In order to overcome the problem of quantum light interference after long-distance turbulent atmospheric transmission, the experimental team used optical integration bonding technology to achieve ultra-stable optical interferometers that can be stabilized for a long time without active closed-loop. Based on this technological breakthrough and a quantum teleportation scheme based on two-photon pathway-polarization hybrid entangled state, the remote quantum state transmission between Yunnan Lijiang Station and Delingha ground Station has been verified. Six typical quantum states are verified in the experiment, and the transmission fidelity exceeds the classical limit. The distance of one thousand kilometers is a new record for the transmission of quantum states on the surface. This work lays an important foundation for building a global quantum information processing network in the future.

Cust postdoctoral fellow Li Bo and Associate Researcher Cao Yuan are co-first authors of the work. The work was supported by the Chinese Academy of Sciences, the National Natural Science Foundation of China, the Ministry of Science and Technology, Anhui Province, and Shanghai Municipality.

Paper link:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.170501

(Hefei National Research Center for Microscale Matter Science, School of Physics, Institute of Quantum Information and Quantum Technology Innovation, Chinese Academy of Sciences, Department of Scientific Research)