Coherent feedback that beats all measurement-based feedback protocols

Abstract

We show that when the speed of control is bounded, there is a widely applicable minimal-time control problem for which a coherent feedback protocol is optimal, and is faster than all measurement-based feedback protocols, where the latter are defined in a strict sense. The superiority of the coherent protocol is due to the fact that it can exploit a geodesic path in Hilbert space, a path that measurement-based protocols cannot follow.

4 pages, revtex4-1, 1 png figure; v2: new (now optimal) coherent protocol, new author