>VITAE:
Dennis is a PhD student in Reinhard Werner's quantum information theory
group at TU Braunschweig. He currently spends an enjoyable year away from
home at Cambridge University, where he is a member of Artur Ekert's Centre
for Quantum Computation at the Department of Applied Mathematics and Theoretical
Physics. His current work lies mainly in abstract quantum information
theory, in particular channels and their capacity for classical and quantum
information transfer.



Any processing of quantum information, be it storage or transfer,
can be represented as a quantum channel: a completely positive and tracepreserving
map that transforms states on the sender's end of the channel into states
on the receiver's end. Until now most of the work on quantum channels has
concentrated on {memoryless} channels, which are characterized by the requirement
that successive channel inputs are acted on independently.
However, in many realworld applications the assumption of having uncorrelated
noise channels cannot be justified, and {memory effects} need to be taken
into account.
In this seminar talk I will present a general model to describe such memory
effects. Albeit relatively simple, this model can be shown to encompass
every stationary causal physical process, and thus is completely general.
I will then introduce capacities for the transfer of classical and quantum
information over memory channels, and discuss some simple examples in which
these can be easily evaluated.
For the general case, I will present entropic upper bounds on the various
capacities. For socalled {forgetful} channels, in which the effect of the
initializing memory dies out as time increases, these bounds can be saturated.
I will also show that generic memory channels are forgetful, and briefly
summarize what is known about nonforgetful channels. 