Macroscopic Quantum Measurement: In What direction does a large ensemble of Spin Points?

By Marc-Olivier Renou (Univ. Geneva)
Abstract: We introduce the concept of Macroscopic Quantum Measurement, that is, a quantum formalism models aiming to bridge the gap between well understood microscopic quantum measurements and macroscopic classical measurements describing the measurements we perform continuously in our everyday life. We idealize the problem by considering parallel spins whose direction has to be estimated. We first review the results about the optimality of different global or local measurement of such a system. We then present a physical measurement model weak enough to almost not disturb the quantum state, but strong enough to provide almost the maximal amount of information in a single shot. This model is based on a pointer measurement, where each spin component of the system is coupled to one of the 3D direction of a pointer. Lastly, we investigate relaxations of the assumptions on the state, one the initial knowledge about the state and on the control over the MQM. We show that the model is robust to these relaxations.
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