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## Summary:

- I'm unsure of what it means for a system or state to have various 'quantum coherences' which can be selected.

I have recently been reading some stuff on quantum information in the physics literature which refers to 'a mechanism by which a measurement in A determines

I am aware of the meaning of the terms 'decoherence' and 'coherent state', but could someone clarify for me what it means for a system to have several 'quantum coherences' which can be chosen from?

Also in a paper 'On the role of complex phases in the quantum statistics of weak measurements', I have seen the following quotation:

''As early as 1995, Steinberg pointed out that weak measurements provide a natural deﬁnition of conditional probabilities in quantum mechanics. However, the mathematically consistent deﬁnition of such weak conditional probabilities results in complex numbers originating from the

Again, could someone explain what it means for the initial and final states to have 'quantum coherences'?

**quantum coherences**in B', where A and B are subsystems of a larger system.I am aware of the meaning of the terms 'decoherence' and 'coherent state', but could someone clarify for me what it means for a system to have several 'quantum coherences' which can be chosen from?

Also in a paper 'On the role of complex phases in the quantum statistics of weak measurements', I have seen the following quotation:

''As early as 1995, Steinberg pointed out that weak measurements provide a natural deﬁnition of conditional probabilities in quantum mechanics. However, the mathematically consistent deﬁnition of such weak conditional probabilities results in complex numbers originating from the

**quantum coherences**of the initial and ﬁnal states''.Again, could someone explain what it means for the initial and final states to have 'quantum coherences'?