Quantum Computation and Information Seminar 

31/03/2006, 15:00 — 16:00 — Room P4.35, Mathematics Building
Christopher Fuchs, Bell Laboratories

Maximally Sensitive Quantum States and a Measure of Quantumness

In quantum Shannon theory, the calculational task for any given quantum channel is to find a set of quantum states that are maximally resistant to distortion by the channel. In quantum cryptography, however, one welcomes the circumstance that quantum states are sensitive to their environments; for it is a feature that can be used to detect eavesdropping. When an eavesdropper gathers information on the identity of one of a set of nonorthogonal states, she necessarily causes a disturbance to those states. This situation calls for a means to quantify how sensitive to eavesdropping one alphabet of quantum states is over another. We explore one such measure, and use it to define a set of maximally sensitive quantum states. Sets of such maximally sensitive quantum states have several interesting properties that indicate they may be of wider interest than the problem from which they came.