Eveson, S.P., Fewster, C.J. and Verch, R. (2005) Quantum inequalities in quantum mechanics. Annales Henri Poincare, 6 (1). pp. 130. ISSN 14240661
Abstract
We study a phenomenon occurring in various areas of quantum physics, in which an observable density (such as an energy density) which is classically pointwise nonnegative may assume arbitrarily negative expectation values after quantization, even though the spatially integrated density remains nonnegative. Two prominent examples which have previously been studied are the energy density (in quantum field theory) and the probability flux of rightwardsmoving particles (in quantum mechanics). However, in the quantum field context, it has been shown that the magnitude and spacetime extension of negative energy densities are not arbitrary, but restricted by relations which have come to be known as quantum inequalities. In the present work, we explore the extent to which such quantum inequalities hold for typical quantum mechanical systems. We derive quantum inequalities of two types. The first are kinematical quantum inequalities where spatially averaged densities are shown to be bounded below. Specifically, we obtain such kinematical quantum inequalities for the current density in one spatial dimension (imposing constraints on the backflow phenomenon) and for the densities arising in Weyl–Wigner quantization. The latter quantum inequalities are direct consequences of sharp Gårding inequalities. The second type are dynamical quantum inequalities where one obtains bounds from below on temporally averaged densities. We derive such quantum inequalities in the case of the energy density in general quantum mechanical systems having suitable decay properties on the negative spectral axis of the total energy. Furthermore, we obtain explicit numerical values for the quantum inequalities on the onedimensional current density, using various spatial averaging weight functions. We also improve the numerical value of the related backflow constant previously investigated by Bracken and Melloy. In many cases our numerical results are controlled by rigorous error estimates.
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Institution:  The University of York 
Academic Units:  The University of York > Mathematics (York) 
Depositing User:  York RAE Import 
Date Deposited:  13 Aug 2009 10:31 
Last Modified:  13 Aug 2009 10:31 
Published Version:  http://dx.doi.org/10.1007/s0002300501979 
Status:  Published 
Publisher:  Birkhäuser Basel 
Identification Number:  10.1007/s0002300501979 