China Science and Technology University realizes quantum measurement of non-local observables for the first time

China Science and Technology University realizes quantum measurement of non-local observables for the first time

[ China Instrument Network Instrument Development ] Guo Guangcan, a member of the Chinese Academy of Sciences and a professor at the University of Science and Technology of China, made new progress in the study of basic problems in quantum mechanics. The team Li Chuanfeng, Xu Xiaoye and others collaborated with the theoretical group from Europe to pass quantum measurement. The introduction of entangled probes for the first time achieved von Neumann measurements of non-local observables and was used to experimentally verify that in some cases the multiplication rule would fail. The research results were published on the International Journal of Physical Review Letters on March 15.

Quantum measurement is one of the most fundamental and core problems of quantum mechanics. According to the von Neumann measurement hypothesis, quantum measurement causes the quantum state to collapse to the eigenstate of the physical quantity to be measured. Usually the most primitive quantum measurements are also called von Neumann measurements, to distinguish them from the concepts of quantum weak measurements that were later proposed. Although quantum theory has formally included non-local variables (variables associated with multiple regions in space) from the outset, the status of non-local variables is not clear for a long time after the establishment of quantum theory. Based on the recognition that all known interactions in nature are local, it is widely believed that there is no way to directly measure non-local variables. This makes it impossible to simply refer to some local variables as observables as non-local observables. About forty years ago, Wolf Prize winner Aharonov and his collaborators pointed out in the process of systematically studying quantum field theory that there are some non-local variables that can be directly measured, and the measurement process does not lead to superluminal speed. Signal transmission.
Li Chuanfeng and Xu Xiaoye et al. first introduced von Neumann measurements of non-local observables in optical systems by introducing entangled probes in quantum measurements. They prepared two photons onto a super-entangled state in which the polarization and path were respectively in the maximum entangled state, and then realized the interaction between polarization and path, thus successfully realizing the direct measurement of polarization degree by using the path probe in the entangled state. Non-local observable measurements. Based on this non-local measurement scheme, the research team further verified that the multiplication rule would be invalid in some cases in the composite system, that is, the value of the A photon bubble operator Xa was -1, B photon bubble calculation by local measurement. The value of Yb is -1, and XaYb should be 1 according to the multiplication rule. However, the experimental result is exactly the opposite. The non-local observable XaYb measurement is -1, which is the magical point of quantum nonlocality.
The measurement of non-local observables not only deepens people's understanding of basic problems of quantum mechanics such as quantum measurement and quantum nonlocality, but also can be used technically for important quantum information such as quantum teleportation, remote quantum computation and quantum cryptography. The process will play an important role in promoting the development of quantum information.
The work was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences, Anhui Province, and the Postdoctoral Innovation Talent Support Program.
(Original title: China University of Science and Technology for the first time to achieve non-local observable quantum measurements)

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