According to the measurement postulate

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Measuring the operator Q-hat collapses the quantum state to an eigenstate corresponding to the measured eigenvalue q. Following this, a measurement of the compatible operator R-hat will yield a specific eigenvalue, altering the system's state again. Since the eigenvalues of Q-hat and R-hat are different, the subsequent measurement of Q-hat will not return to the original eigenstate but will instead yield a different result. This sequence illustrates the non-commutative nature of quantum measurements and the impact of measurement on the state of the system. Understanding these principles is crucial for interpreting quantum mechanics accurately.
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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?
 

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