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Any effect that is conditional on the state and thermodynamically irreversible counts as a measurement. One way to do a partial measurement is to make the cond
by Strilanc 11y ago
Any effect that is conditional on the state and thermodynamically irreversible counts as a measurement.
One way to do a partial measurement is to make the conditional effects less orthogonal to each other, e.g. cause a target qubit to conditionally rotate by 22 degrees instead of a full 180 degrees.
Another possible concept for a partial measurement is not distinguishing between all of the cases. For example, if a system can be in the x=-1, x=0, or x=1 cases then it's possible to do a measurement that distinguishes x=-1 from x in {0,1} without collapsing all the way down to x=0 or x=1.
- Keyframe 11y agoand thermodynamically irreversible So anything related to light then as well?
- kawa 11y agoIf you make the opening shot in billiards, the balls are all over the table in the end. In principle you could now make another shot which restores the original, ordered position, but in practice it's impossible. So the opening shot is called 'irreversible'. Same thing goes for many things, for example letting some hydrogen gas out of a gas bottle: The gas will never go back into the bottle by itself (even if there is a very very small probability that this may happen, in practice it never will). Because the behavior of this kind of systems is described in thermodynamics those systems are called "thermodynamically irreversible". In the end it simply means that its much more easy to break things than to assemble them again (which also leads to the concept of the always increasing entropy).