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arXiv:quant-ph/0206074 · Physical Review A

How one shutter can closeNslits

Yakir Aharonov, Lev Vaidman A

Published Apr 22, 2003• 20 citations
arXivHTMLPDF

Abstract

It is shown that a quantum shutter, preselected and postselected in particular quantum states, can close simultaneously arbitrary number of slits preventing the passage of a single photon in an arbitrary state. A set of K preselected and postselected shutters can close the slits preventing the passage of K or less photons. This result indicates that the surprising properties of preselected and postselected quantum systems are even more robust than previously expected.

DOI
10.1103/physreva.67.042107

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It is shown that a quantum shutter, preselected and postselected in particular quantum states, can close simultaneously arbitrary number of slits preventing the passage of a single photon in an arbitrary state. A set of K preselected and postselected shutters can close the slits preventing the passage of K or less photons. This result indicates that the surprising properties of preselected and postselected quantum systems are even more robust than previously expected.
Summary form only given. 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 [1]. Here we report the experimental demonstration of their proposal overcoming the difficulty to realize a quantum shutter' by employing photonic quantum routers [2]. 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.
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.
It is well known that spontaneous parametric down-conversion can be used to probabilistically prepare single-photon states. We have performed an experiment in which arbitrary superpositions of zero- and one-photon states can be prepared by appropriate postselection. The optical phase, which is meaningful only for superpositions of photon number, is related to the relative phase between the zero- and one-photon states. Whereas the light from spontaneous parametric down-conversion has an undefined phase, we show that this technique collapses one beam to a state of well-defined optical phase when a measurement succeeds on the other beam.
The “N‐box experiment” is a much‐discussed thought experiment in quantum mechanics. It is claimed by some authors that a single particle prepared in a superposition of N+1 box locations and which is subject to a final “post‐selection” measurement corresponding to a different superposition can be said to have occupied “with certainty” N boxes during the intervening time. However, others have argued that under closer inspection, this surprising claim fails to hold. Aharonov and Vaidman have continued their advocacy of the claim in question by proposing a variation on the N‐box experiment, in which the boxes are replaced by shutters and the pre‐ and post‐selected particle is entangled with a photon. These authors argue that the resulting “N‐shutter experiment” strengthens their original claim regarding the N‐box experiment. It is argued in this article that the apparently surprising features of this variation are no more robust than those of the N‐box experiment and that it is not accurate to say that the particle is “with certainty” in all N shutters at any given time.Shutters, Boxes, but No Paradoxes: Time Symmetry Puzzles in Quantum TheoryAll authorsRuth E. Kastner https://doi.org/10.1080/02698590412331289279Published online:14 October 2010 Figure 1 Hilbert Space of the Shutter Particle. Display full size Figure 1 Hilbert Space of the Shutter Particle.