5 ms·

If you're measuring a bit and it's not 0, what is the only other value it can be?

• Koshkin 8y ago
  In the case of an "interaction-free" measurement (i.e. one that supposedly would not disturb the system), as mentioned by the parent, if the interaction did not happen, then the system continues to be in a superposition of the two base states (0 and 1, in your example).
  • amluto 8y ago
    Citation needed. In a two-level quantum system, if I make any measurement of a particle such that the distribution of outcomes depends on whether the particle is in state 0 or 1, then I have disturbed the state of the system. This is true no matter how fancy the measurement is. This can’t even be avoided with hacks that depend on detailed knowledge of the system. If the initial state is |0>+|1>, then, sure, I can measure and then reset the state. But if the initial state was entangled with some far-away particle, I can’t reset the state of the nearby particle without completely forgetting the outcome of the measurement.
    • Koshkin 8y ago
      Yeah, this "interaction-free" measurement didn't sit well with me, either.