nLab
quantum measurement

Context

Physics

physics, mathematical physics, philosophy of physics

Surveys, textbooks and lecture notes


theory (physics), model (physics)

experiment, measurement, computable physics

Quantum measurement

Idea

Quantum measurement is measurement in quantum mechanics.

Definition

In terms of mixed quantum states represented by density matrices, a quantum measurement is a quantum operation which is given by a positive-operator valued measure

The “measurement problem”

In the context of interpretation of quantum mechanicsit is common to speak of the “measurement problem” when referring to the tension between regarding quantum physics as a probabilistic theory and the idea of realism.

Namely by the above a quantum measurement is formally reflected in a change of probabilities. But since in any given measurement experiment one definite outcome is observed, one may wonder how that particular outcome was actually chosen, given that the theory only gives its probability.

References

The article

points out that for symmetric systems with a symmetric ground state, already a tiny perturbation mixing the ground state with the first excited state causes spontaneous symmetry breaking in a suitable limit, and suggests that this already resolves the measurement problem.

Last revised on July 17, 2016 at 04:28:23. See the history of this page for a list of all contributions to it.