Rapid measurement of quantum systems using feedback control

Abstract

We introduce a feedback control algorithm that increases the speed at which a measurement extracts information about a d-dimensional system by a factor that scales as d2. Generalizing this algorithm, we apply it to a register of n qubits and show an improvement of O(n). We derive analytical bounds on the benefit provided by the feedback and perform simulations that confirm that this speedup is achieved. © 2008 The American Physical Society.