- View PDF version of TR-2001-01 (88905 bytes)
- View PostScript version of TR-2001-01
- Save PostScript version of TR-2001-01
- Save gzipped PostScript version of TR-2001-01 (25769 bytes)

- Quantum Signal Propagation in Depolarizing Channels, March 28, 2001 Nicholas Pippenger, 7 pages
Quantum Signal Propagation in Depolarizing Channels Nicholas Pippenger Abstract: Let X be an unbiassed random bit, let Y be a qubit whose mixed state depends on X, and let the qubit Z be the result of passing Y through a depolarizing channel, which replaces Y with a completely random qubit with probability p. We measure the quantum mutual information between X and Y by T(X; Y) = S(X) + S(Y) - S(X,Y), where S(...) denotes von Neumann's entropy. (Since X is a classical bit, the quantity T(X; Y) agrees with Holevo's bound chi(X; Y) to the classical mutual information between X and the outcome of any measurement of Y.) We show that T(X;Z) <= (1-p)^2 T(X;Y). This generalizes an analogous bound for classical mutual information due to Evans and Schulman, and provides a new proof of their result.

If you have any questions or comments regarding this page please send mail to help@cs.ubc.ca.