Colloquium Now Online

The ICTP colloquium by Yuval Gefen on "Weak Measurement: A Peephole
into the Quantum World" is now available online.

Gefen, who holds the Isabelle and Samuel Friedman Professorial Chair of Theoretical Physics at the Weizmann Institute, is one of the founding fathers of mesoscopic physics. One of his predictions—that currents traveling through extremely small pieces of metal or semiconductor material can be measured in single electrons—helped establish the lower limit of what characterizes the flow of electricity, and eventually led to the experimental design of a single-electron transistor.

An abstract of his talk, which he gave at ICTP on 15 February, follows:

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.