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Deutsche Physikalische Gessellschaft IOP Institute of Physics

Reflection of a particle from a quantum measurement

Jonathan B Mackrory1, Kurt Jacobs2 and Daniel A Steck1,3

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We present a generalization of continuous position measurements that accounts for a spatially inhomogeneous measurement strength. This describes many real measurement scenarios, in which the rate at which information is extracted about position has itself a spatial profile, and includes measurements that detect whether a particle has crossed from one region into another. We show that such measurements can be described, in their averaged behavior, as stochastically fluctuating potentials of vanishing time average. Reasonable constraints restrict the form of the measurement to have degenerate outcomes, which tend to drive the system to spatial superposition states. We present the results of quantum-trajectory simulations for measurements with a step-function profile (a 'which-way' measurement) and a Gaussian profile. We find that the particle can coherently reflect from the measurement region in both cases, despite the stochastic nature of the measurement back-action. In addition, we explore the connection to the quantum Zeno effect, where we find that the reflection probability tends to unity as the measurement strength increases. Finally, we discuss two physical realizations of a spatially varying position measurement using atoms.


PACS

03.65.Ta Foundations of quantum mechanics; measurement theory

42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps

02.50.Ey Stochastic processes

02.50.Cw Probability theory

Subjects

Computational physics

Optics, quantum optics and lasers

Quantum information and quantum mechanics

Dates

Issue 11 (November 2010)

Received 24 July 2010

Published 11 November 2010



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