Physical implementation of a programmable discriminator for unknown qubit states

Abstract

We present two different (but from a performance point of view) equivalent physical implementations for a programmable-state discriminator in terms of quantum circuits. The circuits that perform a positive-operator valued measure are built entirely of known logical quantum gates. The first, more-complicated circuit leads to a simpler readout, whereas the second, simpler circuit requires an extra measurement at the output. The performance of both implementations is good; it is not optimal but comes close to the optimal success probability. In the latter part of the paper we show how the necessary quantum gates can be realized in ion traps using state-of-the-art technology.