Title:	Functional integral treatment of some quantum nondemolition systems
Authors:	Banerjee, Subhashish Ghosh, R.
Issue Date:	Feb-2007
Publisher:	IOP Publishing Ltd.
Citation:	Journal of Physics A, 2007, Vol.40, p1273
Abstract:	In the scheme of a quantum nondemolition (QND) measurement, an observable is measured without perturbing its evolution. In the context of studies of decoherence in quantum computing, we examine the 'open' quantum system of a two-level atom or, equivalently, a spin-1/2 system, in interaction with quantum reservoirs of either oscillators or spins, under the QND condition of the Hamiltonian of the system commuting with the system-reservoir interaction. For completeness, we also examine the well-known non-QND spin-Bose problem. For all these many-body systems, we use the methods of functional integration to work out the propagators. The propagators for the QND Hamiltonians are shown to be analogous to the squeezing and rotation operators, respectively, for the two kinds of baths considered. Squeezing and rotation being both phase-space area-preserving canonical transformations, this brings out an interesting connection between the energy-preserving QND Hamiltonians and the homogeneous linear canonical transformations.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/4137
ISSN:	1751-8113 1751-8121 (Online)
Alternative Location:	http://arxiv.org/abs/quant-ph/0611127 http://dx.doi.org/ 10.1088/1751-8113/40/6/006 http://adsabs.harvard.edu/abs/2007JPhA...40.1273B
Copyright:	2007, IOP Publishing Ltd
Appears in Collections:	Research Papers (TP)

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