Weak Measurement: A Peephole into the Quantum World - ICTP Colloquium

by Prof. Yuval Gefen ABSTRACT: The measurement of observables in quantum mechanics is a probabilistic process, traditionally described by von Neumann’s projection postulate. Each eigenvalue of the observable happens to be a possible outcome of the measurement process with a given probability, and the original state of the system collapses into the corresponding eigenstate. Weakly measuring an observable (i.e., coupling the system weakly to the measuring device), perturbs the former weakly, yet, at the same time, provides only partial information on the state of the measured system. Employing composite measurement protocols, e.g., a weak measurement followed by a strong one, opens new horizons. Such composite protocols can be employed, inter alia, for efficient weak signal amplification; they provide a tool for quantum state discrimination, and may facilitate direct, yet non-destructive, observation of quantum virtual states. A very recent challenge is their utility in probing topological states of matter. I will address the principles and applications—present and future-- of weak measurement protocols, paying particular attention to the arena of solid state physics.