POVM stands for Positive Operator-Valued Measure. It is a formalism used in quantum mechanics to describe measurements that are not necessarily projective measurements, which are the more traditional way to represent quantum measurements. In quantum mechanics, a measurement is typically represented by a set of projectors that correspond to the possible outcomes of the measurement. These projectors are mathematically represented by Hermitian operators that satisfy certain properties, such as being positive semi-definite and summing to the identity operator.
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