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Measurement in quantum mechanics is still so weird and foreign to me, even as a postdoc in quantum optics. It will never amaze me how many weird and amazing thi
by bowsamic 4y ago
Measurement in quantum mechanics is still so weird and foreign to me, even as a postdoc in quantum optics. It will never amaze me how many weird and amazing things we know about measurement, while still not having defined or understood what a measurement really is! Quantum mechanics is terrifying in its opaqueness, it is almost less like a physical theory and more like a mathematical tool
- Strilanc 4y agoThe Zeno effect can still occur if there's no measurements. Let there be a qubit B and a register of N qubits C[0], C[1], ..., C[N-1]. Now repeat the following N times: rotate B by an N'th of a full turn and then perform C[k] ^= B (a CNOT controlled by B targeting C[k] where k is the index of the iteration). These are all unitary operations; no measurement. If you consider doing this for larger and larger N, you find that if B started in the |0> state then B ends up nearer and nearer the |0> state as N increases. B's final density matrix limits to |0><0| as N goes to infinity.
- bowsamic 4y agoInteresting! This seems related to the idea that quantum measurement is nothing but unitary evolution with a large number of degrees of freedom