Abstract
The interference between two paths of a single photon at a double slit is widely considered to be the most paradoxical result of quantum theory. Here is a new interesting question to the phenomenon: can a single shutter simultaneously close two slits by effectively being in a superposition of different locations? Aharonov and Vaidman have shown that it is indeed possible to construct a quantum shutter that can close two slits and reflect a probe photon perfectly when its initial and final states are appropriately selected. Here we report the experimental demonstration of their proposal overcoming the difficulty to realize a ‘quantum shutter’ by employing photonic quantum routers. The reflectance ratio of 0.61 ± 0.027 surpasses the classical limit with 4.1 standard deviation, shedding new light on the unusual physical properties of quantum operations. This experimental demonstration, where the strong measurement and non-local superposition seem co-existing, provides an alternative to weak measurements as a way to explore the nature of quantum physics.
Highlights
The interference experiment using a single photon passing through a double slit[1,2] proves the most paradoxical claim of quantum theory, “A particle can be in different places simultaneously3–5.” It is well known that the interference fringe disappears when one monitors through which slit the photon passes[6,7,8]
The experimental results show that when the shutter photon is found in the appropriate final state, the input probe photon is reflected by the quantum shutter, with a reflectance ratio of 0.61 ± 0.027 exceeding the classical limit of 0.5 with 4.1 standard deviation
We verified that the reflected probe photon almost perfectly maintains the coherence of the input probe photon, as predicted by the original AV03 protocol
Summary
The interference experiment using a single photon passing through a double slit[1,2] proves the most paradoxical claim of quantum theory, “A particle can be in different places simultaneously3–5.” It is well known that the interference fringe disappears when one monitors through which slit the photon passes[6,7,8]. It is well known that the interference fringe disappears when one monitors through which slit the photon passes[6,7,8] This double-slit experiment continues to provide new insights into modern quantum physics; an example of this is the weak measurement to analyze the trajectory of a single photon[9]. By checking the coherence of the output probe photon, we verified that the quantum superposition of the probe photon is not destroyed by the shutter This experimental demonstration provides an alternative to weak measurements[11] as a way to explore the unusual physical properties of preselection and postselection in quantum theory, and show counterintuitive aspect of quantum theory as have been shown in three-box paradox[12], Hardy’s paradox[13], and quantum Cheshire-Cat[14]. After the interaction between the shutter and the photon (Eq (3)), the joint quantum state of the photon and the shutter is
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