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Realization of quantum Wheeler's delayed-choice experiment


Light is believed to exhibit wave–particle duality1 depending on the detecting devices, according to Bohr's complementarity principle2, as has been demonstrated by the ‘delayed-choice experiment’ with classical detecting devices3,4,5,6,7,8,9. A recent proposal10 suggests that the detecting device can also occupy a quantum state, and a quantum version of the delayed-choice experiment can be performed. Here, we experimentally realize the quantum delayed-choice experiment and observe the wave–particle morphing phenomenon of a single photon. We also illustrate, for the first time, the behaviour of the quantum wave–particle superposition state of a single photon. We find that the quantum wave–particle superposition state is distinct from the classical mixture state because of quantum interference between the wave and particle states. Our work reveals the deep relationship between the complementarity principle and the superposition principle, and it may be helpful in furthering understanding of the behaviour of light.

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Figure 1: Logic diagrams of the classical and quantum delayed-choice experiments.
Figure 2: Experimental set-up.
Figure 3: Probabilities of finding a photon in path 1.
Figure 4: Three quantities (centre, visibility and ratio) derived from Fig. 3.


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The authors thank H.-Q. Ni for sample growth. This work was supported by the National Fundamental Research Program, National Natural Science Foundation of China (grant nos 60921091, 10874162 and 10734060).

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Authors and Affiliations



C-F.L. and J-S.T. planned and designed the experiments. J-S.T., Y-L.L. and G-Y.X. implemented the experiments. G-C.G., J-S.T. and X-Y.X. carried out the theoretical analysis and developed the interpretation. C-F.L. and J-S.T. wrote the paper and all authors discussed its contents. C-F.L. supervised the project.

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Correspondence to Chuan-Feng Li.

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The authors declare no competing financial interests.

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Tang, JS., Li, YL., Xu, XY. et al. Realization of quantum Wheeler's delayed-choice experiment. Nature Photon 6, 600–604 (2012).

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