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Nonuniqueness of generalized quantum master equations for a single observable
Nathan Ng1, David T Limmer2, Eran Rabani2
1Department of Physics, University of California, Berkeley, California 94720, USA.
Abstract:
When deriving exact generalized master equations for the evolution of a reduced set of degrees of freedom, one is free to choose what quantities are relevant by specifying projection operators. However, obtaining a reduced description does not always need to be achieved through projections-one can also use conservation laws for this purpose. Such an operation should be considered as distinct from any kind of projection; that is, projection onto a single observable yields a different form of master equation compared to that resulting from a projection followed by the application of a constraint. We give a simple example to show this point and give relationships that the different memory kernels must satisfy to yield the same dynamics.
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