Abstract. The quantum variance of a self-adjoint operator depends on a density matrix whose particular example is a pure state (formulated by a projection). A general variance can be obtained from certain variances of pure states. This is very different from the probabilistic case.
AMS Subject Classification
(1991): 81Q50, 40C05
Keyword(s):
density matrix,
pure state,
projection,
variance
Received November 3, 2011, and in revised form February 18, 2012. (Registered under 57/2011.)
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