According to the measurement postulate

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Homework Statement

according to the measurement postulate of quantum mechanics what happens if Q-hat is measured, followed immediately by a measurement of a compatible quantity R-hat and then a further measurement of Q-hat? you may assume that the eigenvalues of Q-hat and the eigenvalue of R-hat are all different

The Attempt at a Solution

looking it up didn't help

 

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Take it step by step. First, say you measure Q and get the result q. What can you say about the state of the system right after the measurement?