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The cartoon of 'Quantum Twisted Loong' (Cover). CREDIT Science China Press

Abstract:
Quantum mechanics, as a pillar of modern civilization, has benefited human society for a century, in which wavefunctions played a crucial role. In the past 100 years, what most people did was 'Shut up and calculate', and wavefunctions always gave us a correct probability list of measurement outcomes. However, the debate on the following deeper philosophical issue behind it still persists: whether wavefunctions describe the reality of quantum entities' existence and dynamic trajectory. In various delayed-choice experiments that are dedicated to this issue, Copenhagen interpretation denied the reality of wavefunctions for avoiding the paradox of a choice made in the present to alter a photon's past behavior. However, the determinists argued that the past of photons should be realistic and deterministic prior to the detection, as Einstein's famous question states: Do you really believe the moon exists only when you look at it?

Quantum twisted Loong confirms the physical reality of wavefunctions

Beijing, China | Posted on September 23rd, 2017

Recently, to address this long-standing issue, Profs. Bao-Sen Shi's research group from the University of Science and Technology of China collaborated with Prof. Zhi-Han Zhu from Harbin University of Science and Technology and other collaborators to propose and demonstrate a quantum twisted double-slit experiment, in which photonics orbital angular momentum (OAM) and its group velocity slowing-down feature are employed to extract photons' propagation history after detections. Specifically, first, the state (wavefunction) of signal photons diffracted from the twisted double slits is transformed into a superposition state between different OAM modes and Gaussian mode; second, the photons are observed only in Gaussian mode (selecting particle behavior); and then, a Hong-Ou-Mandel (HOM) interference between signal and reference photons provides the arrival times of signal photons that allow one to investigate photons' propagation history.

The results obtained from the experiment tell us that the nature of the photon prior to the measurement is pre-existing, just as described by the wavefunction. Thus, the physical reality and nonlocality of wavefunctions are confirmed. This finding clarifies the long-held misunderstanding of the role of wavefunctions and their collapses in the evolution of quantum entities. In addition, they present a cartoon titled "Quantum Twisted Loong", which is shown in the Cover and Fig. 5 in the article, as shown in Fig. 1, to illustrate the propagation behavior of photons in a double-slit apparatus. Unlike the cartoon titled "Great Smoky Dragon" created by Miller and Wheeler in 1983, as shown in Fig.2, where the body of the dragon is unknown and smoky, the body of Loong is deterministic, i.e., the two bodies coexist simultaneously (representing wave nature) before their collapse.

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This work is supported by the National Natural Science Funds for Distinguished Young Scholar of China (Grant No. 61525504); the National Natural Science Foundation of China (Grant Nos. 11574065, 11604322, 61275115, 61378003, 61435011, 61605194); China Postdoctoral Science Foundation (Grant No. 2016M590570); the Fundamental Research Funds for the Central Universities No. 11604322), and the Key Programs of the Natural Science Foundation of Heilongjiang Province of China (Grant No. ZD201415).

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Contacts:
B.-S. Shi

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