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China University of Science and Technology for the first time realizes direct measurement of entangled system wave function
[ 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's Li Chuanfeng and Xu Xiaoye and the University of Stockholm Dr. Yaron Kedem first proposed and The experiment realized the direct measurement of multi-body non-local wave function. The research results were published on the International Journal of Physical Review Letters on October 9 and were selected as "Editor's Choice" papers. The "Physical News and Reviews" section of the American Physical Society website reports the results in a special article entitled "Direct Measurement of Entangled States".
Wave function is one of the core concepts of quantum mechanics. Whether it is a single or multi-body quantum system, its state can be completely characterized by wave function. At present, the most commonly used method for measuring the wave function is quantum state tomography. However, as the scale of the system to be tested increases, the consumption of resources increases exponentially. In 2011, scientists proposed a direct measurement method for single-photon spatial wave function based on weak measurement and Weak Value, which avoids the complex reconstruction process in quantum chromatography. However, for the direct measurement of multi-body, especially the wave function containing entangled quantum systems, it has not been able to make a breakthrough. The difficulty lies in the inability to extract the weak values ​​of non-local observables of multi-body systems.
After the first implementation of non-local observable quantum measurements [Phys. Rev. Lett. 122, 100405 (2019)], Li Chuanfeng's research team has taken a different approach with Yaron Kedem to achieve a multi-body system localization by cleverly constructing Hamiltonian quantities. The measurement of the Modular Value of the sum of the measurements is then used to directly give the latter the value of the mathematical relationship with the weak values ​​of the non-local observables. This method successfully solves the problem of extracting the weak values ​​of non-local observables of multi-body systems, and can be easily applied to the measurement of multi-body non-local wave functions. The experimental team successfully demonstrated the direct measurement of the two-photon non-local wave function by using two-photon super-entanglement. They prepare two photons to the super-entangled state where the polarization and path are respectively in the maximum entangled state, and then realize the interaction between polarization and path. Finally, the two-photon polarization state is directly measured by counting the path pointer under different projection bases. Wave function.
For the first time, this achievement realizes the direct measurement of the wave function of multi-body entanglement system. The article "Direct Measurement of Entangled State" comments on this result provides an efficient method for detecting large-scale entanglement systems in future quantum information technology. The work also clarified that the direct measurement technique of the wave function originates from weak values ​​rather than weak measurements, and more importantly, direct measurement of the wave function of the multi-body quantum system containing entanglement proves that this is a pure quantum technique. Instead of a classic intervention process. This method brings new ideas to the research of basic problems of quantum physics and plays an important role in promoting the development of quantum information technology.
The first author of the paper is Pan Weiwei, a Ph.D. student in the Key Laboratory of Quantum Information of the Chinese Academy of Sciences, and Xu Xiaoye, a special associate researcher. 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.