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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

One quantum shutter can close two slits simultaneously

Ryo Okamoto, Shigeki Takeuchi

Published Jun 1, 2017• 0 citations
Publisher

Abstract

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.

DOI
10.1109/cleoe-eqec.2017.8087302

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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.
Abstract Since its publication, Aharonov and Vaidman’s three-box paradox has undergone three major advances: i). A non-counterfactual scheme by the same authors in 2003 with strong rather than weak measurements for verifying the particle’s subtle presence in two boxes. ii) A realization of the latter by Okamoto and Takeuchi in 2016. iii) A dynamic version by Aharonov et al. in 2017, with disappearance and reappearance of the particle. We now combine these advances together. Using photonic quantum routers the particle acts like a quantum “shutter.” It is initially split between Boxes A, B and C, the latter located far away from the former two. The shutter particle’s whereabouts can then be followed by a probe photon, split in both space and time and reflected by the shutter in its varying locations. Measuring the former is expected to reveal the following time-evolution: The shutter particle was, with certainty, in boxes A+C at t1, then only in C at t2, and finally in B+C at t3. Another branch of the split probe photon can show that boxes A+B were empty at t2. A Bell-like theorem applied to this experiment challenges any alternative interpretation that avoids disappearance-reappearance in favor of local hidden variables.
The concept of wave-particle duality, which is a key element of quantum theory, has been remarkably found to manifest itself in several experimental realizations as in the famous double-slit experiment. In this specific case, a single particle seems to travel through two separated slits simultaneously. Nevertheless, it is never possible to measure it in both slits, which naturally appears as a manifestation of the collapse postulate. In this respect, one could as well ask if it is possible to "perceive" the presence of the particle at the two slits simultaneously, once its collapse could be avoided. In this article, we use the recently proposed entanglement mediation protocol to provide a positive answer to this question. It is shown that a photon which behaves like a wave, i.e., which seems to be present in two distant locations at the same time, can modify two existing physical realities in these locations. Calculations of the "weak trace" left by such photon also enforce the validity of the present argumentation.
Quantum interference is a challenging phenomenon in quantum optics. According to this principle of superposition of quantum mechanics, elementary particles such as photon can not only be in more than one place at a given time, but that an individual particle can cross its own trajectory and interfere with the direction of its path. Thomas Young devised the double slit experiment to prove that light consisted of waves. Analysis of the double slit experiment and the interference pattern indicates that each photon not only goes through both the slits simultaneously, but traverses every possible trajectory on the way to the target, not just in theory, but in fact. In the present work we have analysed the situation in terms of quantum superposition and Schrodinger cat states in quantum optics. The nature of photon in this analysis is examined
In quantum mechanics, a long-standing question remains: How does a single photon traverse double slits? One intuitive picture suggests that the photon passes through only one slit, while its wavefunction splits into an ``empty" wave and a ``full" wave. However, the reality of this empty wave is yet to be verified. Here, we present a novel experimental configuration that combines quantum memory and weak measurement to investigate the nature of the empty wave. A single atomic excitation is probabilistically split between free space and a quantum memory, analogous to the two paths in a double-slit experiment. The quantum memory serves as a path detector, where single-photon Raman scattering is enhanced due to the presence of a stored spin wave, without collapsing the quantum state. This enhancement is recorded as classical information, and the spin wave stored in the quantum memory is retrieved twice, with an interference visibility of 79%. Unlike conventional weak measurement schemes, where weak values are detected during post-selection, our approach converts the weak value into classical information before interference takes place. Our results demonstrate the potential of quantum memory as a measurement device that preserves coherence while extracting partial information, offering new insights into quantum measurement.