An Interaction-Free Quantum Measurement-Driven Engine
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An Interaction‑Free Quantum Measurement‑Driven Engine Cyril Elouard1 · Mordecai Waegell2 · Benjamin Huard3 · Andrew N. Jordan1 Received: 16 September 2019 / Accepted: 7 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Recently highly-efficient quantum engines were devised by exploiting the stochastic energy changes induced by quantum measurement. Here we show that such an engine can be based on an interaction-free measurement, in which the meter seemingly does not interact with the measured object. We use a modified version of the Elitzur–Vaidman bomb tester, an interferometric setup able to detect the presence of a bomb triggered by a single photon without exploding it. In our case, a quantum bomb subject to a gravitational force is initially in a superposition of being inside and outside one of the interferometer arms. We show that the bomb can be lifted without blowing up. This occurs when a photon traversing the interferometer is detected at a port that is always dark when the bomb is located outside the arm. The required potential energy is provided by the photon (which plays the role of the meter) even though it was not absorbed by the bomb. A natural interpretation is that the photon traveled through the arm which does not contain the bomb—otherwise the bomb would have exploded—but it implies the surprising conclusion that the energy exchange occurred at a distance despite a local interaction Hamiltonian. We use the weak value formalism to support this interpretation and find evidence of contextuality. Regardless of interpretation, this interaction-free quantum measurement engine is able to lift the most sensitive bomb without setting it off. Keywords Quantum mechanics · Interaction-free measurement · Quantum heat engine · Single-photon effect
* Cyril Elouard [email protected] 1
University of Rochester, Rochester, NY, USA
2
Chapman University, Orange, CA, USA
3
Ecole Normale Superieure de Lyon, Lyon, France
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Foundations of Physics
1 Introduction Interaction-free measurements are often presented as a way of gaining information. Given prior knowledge, we can classically learn something nonlocally about a system by measuring where it is not. This is simply an updating of our knowledge given prior ignorance. A quantum mechanical version was introduced by Elitzur and Vaidman [1]: They envisioned an ultra sensitive bomb that would explode whenever it encountered a photon. When this bomb was placed into one arm of a tuned interferometer, detecting a photon at the dark port, i.e. the port that would normally never fire, brought simultaneously two pieces of information. First, that the interference pattern was modified, revealing that one of the arms of the interferometer must have been blocked, therefore indicating the presence of the bomb, while not exploding it. Second, that the photon was not absorbed by the bomb, which seems only compatible with the photon traveling through the arm not containing the bomb, and consequently
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