Terminology for m_ops in stochastic solvers

[BenjaminDAnjou]

Describe the Issue!

I noticed some terminology used in the QuTip documentation that I think is not quite accurate.

The description of "m_ops" in the stochastic solver options states:

List of operators representing the measurement operators.

However, it is clear from the example given here that "m_ops" represents the observable being measured and not the measurement operator.

The distinction is that the term "measurement operator" usually refers to an (efficient) quantum operation that brings a pure state to a pure state. The measurement operators are the operators that generate the stochastic evolution and are akin to "sc_ops", not to "m_ops".

The operators "m_ops" used by the stochastic solver define the POVM elements, i.e., they define the probabilities of measurement outcomes. This is not the same as a measurement operator.

For more detail, see the first chapter of the standard textbook by Wiseman and Milburn.

P.S. Note that Wiseman also calls the POVM elements "effects", which I think is dreadfully confusing. But I think there is pretty universal agreement that "measurement operator" should refer to the quantum maps.