Physics – Quantum Physics
Scientific paper
2011-07-11
Physics
Quantum Physics
Review+new. 161 pages Latex, 15 figures. Comments are welcome
Scientific paper
The quantum measurement problem, that is, understanding why a unique outcome is obtained in each individual experiment, is tackled. A review of the various approaches is presented. Next, a rather realistic model, describing a measurement of the $z$-component of a spin through interaction with a magnetic memory, is fully solved. This Curie--Weiss magnet includes $N\gg1$ spins weakly coupled to a phonon bath. The Hamiltonian evolution exhibits several time scales. The reduction, a rapid decay of the off-diagonal blocks of the density matrix, arises from the many degrees of freedom of the pointer. The "which basis" paradox does not show up, reduction takes place continuously on the basis set by the interaction between the system and the apparatus. Recurrences are ruled out either by randomness in the system-pointer coupling, or by a resonance between phonon and spin frequencies. The apparatus is prepared in a metastable paramagnetic state and would, by itself, go to either its up or down ferromagnetic state. This process is triggered by the measurement, which breaks the ergodicity and produces a stable final state, thus registering the measurement. Conditions are given for ensuring ideality of the measurement. Irreversibility is ensured by the macroscopic size of the apparatus. This study inspires various pedagogical exercises, and suggests lessons for future work on models. The outcome supports a specified version of the statistical interpretation of quantum mechanics, which is promoted for teaching. The solution of the quantum measurement problem relies on the dynamics of the process, on the reduction, on the system--pointer correlations created during the registration and on thermodynamic stability of the final state. Standard quantum statistical mechanics is sufficient to explain the emergence of classicality and the production of a unique answer for the outcome of each run.
Allahverdyan Armen E.
Balian Roger
Nieuwenhuizen Theo M.
No associations
LandOfFree
Understanding quantum measurement from the solution of dynamical models does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Understanding quantum measurement from the solution of dynamical models, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Understanding quantum measurement from the solution of dynamical models will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-564345