On quantum coding for ensembles of mixed statesH. Barnum, C. M. Caves, C. A. Fuchs, R. Jozsa, B. W. Schumacher, On quantum coding for ensembles of mixed states. CSTR-00-015, Department of Computer Science, University of Bristol. August 2000. PDF, 242 Kbytes.
We consider the problem of optimal asymptotically faithful compression for ensembles of mixed quantum states. Although the optimal rate is unknown, we prove upper and lower bounds and describe a series of illustrative examples of compression of mixed states. We also discuss a classical analogue of the problem.