Optimal copying of one quantum bit

Publisher Website
Google Scholar
Abstract
A quantum copying machine producing two (in general nonidentical) copies of an arbitrary input state of a two-dimensional Hilbert space (quantum bit) is studied using a quality measure based on distinguishability of states, rather than fidelity. The problem of producing optimal copies is investigated with the help of a Bloch sphere representation, and shown to have a well-defined solution, including cases in which the two copies have an unequal quality, or the quality depends upon the input state (is “anisotropic” in Bloch sphere language), or both. A simple quantum circuit yields the optimal copying machine. With a suitable choice of parameters it becomes an optimal eavesdropping machine for some versions of quantum cryptography, or reproduces the Bužek and Hillery result for isotropic copies.
All Related Versions

This publication has 13 references indexed in Scilit: