Abstract

Quantum trajectory theory is a theory of open quantum systems and the measurements that are carried out on such systems by counting the quanta emitted through their output channels. The theory uses a pure state wavefunction evolving according to a stochastic dynamic where standard quantum mechanics uses a density operator obeying a deterministic equation of motion. The stochasticity is introduced by visualizing an ideal photon counting process that converts every photon lost from the open system into a photoelectron pulse, an elementary contribution to a classical stochastic photocurrent (the measurement record). The theory provides time-domain visualizations of the quantum dynamical processes that lie behind the ensemble average in the standard quantum mechanical formalism. The pictures help one to gain an intuitive understanding of the quantum world and how its appearance alters as different kinds of observations are made. It provides a means of analyzing nontrivial conditioned measurements and is a powerful tool for simulating actual experiments.

© 1994 IEEE