Abstract
We address the issue of coupling variables whichare essentially classical to variables that are quantum.Two approaches are discussed. In the first, continuousquantum measurement theory is used to construct a phenomenological description of theinteraction of a quasiclassical variable X with aquantum variable x, where the quasiclassical nature ofX is assumed to have come about as a result ofdecoherence. The state of the quantum subsystem evolvesaccording to the stochastic nonlinear Schrodingerequation of a continuously measured system, and theclassical system couples to a stochastic c-number\(\overline x \left( t \right)\) representing the imprecisely measured value of x. The theorygives intuitively sensible results even when the quantumsystem starts out in a superposition of well-separatedlocalized states. The second approach involves a derivation of an effective theory from theunderlying quantum theory of the combinedquasiclassical-quantum system, and uses the decoherenthistories approach to quantum theory.
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Halliwell, J.J. Two Approaches to Coupling Classical and Quantum Variables. International Journal of Theoretical Physics 38, 2969–2986 (1999). https://doi.org/10.1023/A:1026612300318
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DOI: https://doi.org/10.1023/A:1026612300318