In quantum mechanics, this indicates that the intrinsic property of a particle, such as its spin, can be disembodied from the particle itself. The quantum Cheshire cat concept reveals an unconventional phenomenon: physical properties can be separated from the original object. In particular, under the weak measurement framework, the quantum Cheshire cat effect 29, inspired by the famous novel, “Alice in Wonderland” 30, can be achieved through appropriate pre- and post-selections. Numerous experiments based on weak measurements have been carried out for various applications, such as the observation of the spin Hall effect of light 26, direct measurement of quantum wavefunctions 27, and testing of the violation of Bell’s inequality 28.
Due to its characteristic of reducing the disturbance caused by measurement, some information of a quantum state can be extracted without collapsing the state into the eigenstate 25. In recent years, the concept of weak measurement 19, 20, 21, 22, 23, 24 has provided new ideas for addressing this challenge. Moreover, there is still considerable long-term debate regarding this puzzle 16, 17, 18.
SINGLE SLIT DIFFRACTION WAVE PARTICLE DUALITY SERIES
Although a series of outstanding theoretical and experimental works that deepen the understanding of wave‒particle duality have been reported, it remains unclear which path a single photon (or any other particle) takes when it enters the MZI (double-slit setup). Recently, several outstanding works exploring profound connotation in wave‒particle duality have been conducted, including the investigation of the linear form of duality relation with asymmetric beam interference 13, the experimental progress in the large-scale quantum nanophotonic chip 14, and theoretical achievements with the electron 15. However, after Wheeler’s “delayed-choice experiment” 7, 8 and its recent quantum versions 9, quantum wave‒particle superposition, in which both the wave and particle attributes are observed simultaneously, has been realized in experiments, including those using a single photon 10, 11 and two entangled photons 12.
As illustrated in a traditional Mach‒Zehnder interferometer (MZI), the presence or absence of the second beam splitter (BS) will determine whether the wave or particle attribute of light is observed 6, while two properties cannot be simultaneously observed. In Niels Bohr’s complementary principle 5, detecting the wave‒particle duality of light depends on the devices. Wave‒particle duality is probably one of the most intriguing counterfactual concepts in quantum mechanics, in which the interpretation of the wave and particle attributes of an objective entity is quite different from those in the classical world. The debate on whether light is a wave or a particle has lasted for hundreds of years since the seventeenth century 2, 3, 4. Based on optical phenomena, such as interference, diffraction, and scattering, light exhibits wave-like behavior, whereas according to other phenomena, such as light traveling in straight lines and the photoelectric effect, light behaves like a particle 1. Waves and particles are considered two fundamental attributes of light and matter. Our work provides a new perspective for the in-depth understanding of wave‒particle duality and promotes the application of weak measurements in fundamentals of quantum mechanics. By applying a weak disturbance to the evolution of the system, we achieve an effect similar to the quantum Cheshire cat and demonstrated the separation of the wave and particle attributes via the extraction of weak values. In this work, we experimentally separated the wave and particle attributes of a single photon by exploiting the quantum Cheshire cat concept for the first time. Furthermore, an experimental demonstration of the separation of the wave and particle attributes inspired by this scenario remains scarce. However, after the concept of the quantum Cheshire cats was proposed, which makes the separation of physical attributes from the entity possible, the premise no longer holds. This assumption is premised on the notion that physical properties are inseparable from the objective carrier. As a fundamental characteristic of physical entities, wave‒particle duality describes whether a microscopic entity exhibits wave or particle attributes depending on the specific experimental setup.
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