Ma Xiaosong and Zhu Shining's team at Nanjing University achieve non-local multi-photon quantum interference
Quantum entanglement is a non-local quantum association between two or more particles. The 2022 Nobel Prize in Physics was awarded to Alain Aspect, John F. Clauser and Anton Zeilinger for their outstanding contributions to entangled photon experiments, violation of the Bell inequality and pioneering quantum information science. The award was given to Alain Aspect, John F. Clauser and Anton Zeilinger for their outstanding contributions to entangled photon experiments, violation of Bell's inequality and pioneering quantum information science.
Entanglement has long been recognized as a necessary condition for generating nonlocal and nonlocal multiparticle interference. Recently, a new type of nonlocal quantum interference has been realized by the team of Xiaosong Ma and Shining Zhu at the School of Physics, Nanjing University. Unlike previous nonlocal interference involving entangled multiphotons, in this work, there is no entanglement between all degrees of freedom of the photons.
In the experiment, the team successfully achieved nonlocal quantum interference by modulating and measuring only the separated states of the photons. The team further used the phase change of the undetected photons to regulate the quantum interference of the remaining detected photons, showing very different properties from the entanglement-based nonlocal interference.
Figure 1: Multi-photon quantum interference experiments with undetected photons. a. Experimental scheme of four-photon thwarted interference. b. Schematic diagram of the experimental equipment for four-photon thwarted interference.
This work is based on a nonlinear interferometer (e.g., Fig. 1a) that uses parallel incident and reflected pump light (e.g., Fig. 1b) to achieve four spontaneous parametric down-conversions on the same crystal to generate photon pairs (e.g., sources I, II, III, and IV in Fig. 1a). The two idle photon paths generated by light sources I and II are exchanged, while the signal photon paths remain unchanged. According to the principle of path full homogeneity, i.e., the spatiotemporal overlap of interfering photons leads to the property that the generated photons are indistinguishable from the light sources, four-photon blocking interference is achieved when the down-conversion photons of light sources I, II and light sources III and IV are both indistinguishable in spatiotemporal terms.
In principle, the two ends of the measurement (paths 1 and 2 and paths 3 and 4) can be separated in space and time, so that the selected events of the photon phase measurement basis vector and the photon detection events satisfy the space-like separation condition. More importantly, multiple photons in the experiment are in a simple particle number direct product state, and throughout the nonlocal interference process, no entanglement is involved, but the multiphoton interference phenomenon, which was previously thought to be generated only by entanglement, is reproduced.
Figure 2: The results of three-photon interference under the modulation of undetected photons.
Further, the team also modulates the interference of three other detected photons (paths 1, 3, and 4 in Figure 1a) by changing the phase of an independent undetected photon (path 2 in Figure 1a), and the results are shown in Figure 2.
This is fundamentally different from the entanglement-based nonlocal interference. For multi-photon entangled states, in the presence of undetected photons, the remaining photons are in a mixed state and cannot produce interference that depends on the phase of the undetected photons. This work by the team successfully demonstrates a multiphoton nonlocal quantum interference without entanglement participation and achieves multiphoton interference under the modulation of undetected photons. This work gives new insight into the sources of nonlocal interference and promises important applications in quantum-enhanced bioimaging and remote sensing techniques.
The work was recently published in the prestigious journal Nature communications under the title Multiphoton nonlocal quantum interference controlled by an undetected photon. PhD students Kingland Yi Qian and Kai Wang, PhD, School of Physics, Nanjing University, are co-first authors of the article. Prof. Xiaosong Ma, Dr. Kai Wang and Prof. Mario Krenn from Max Planck Institute, Nanjing University are the corresponding authors of the article. Academician Shining Zhu of Nanjing University provided in-depth guidance to the work.
This work was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, Frontier Technology Program of Natural Science Foundation of Jiangsu Province, Fundamental Research Funds of Central Universities, and Quantum Science and Technology Innovation Program. This work was also supported by the School of Physics, the State Key Laboratory of Solid Microstructures, the Collaborative Innovation Center of Artificial Microstructure Science and Technology, Nanjing University, the Collaborative Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, and the Hefei National Laboratory.
Subject Links:
http://qoqi.nju.edu.cn/
Link to article:
https://www.nature.com/articles/s41467-023-37228-y
