  We study information storage in noisy quantum registers and computers using
the methods of statistical dynamics. We develop the concept of a strictly
contractive quantum channel in order to construct mathematical models of
physically realizable, i.e., nonideal, quantum registers and computers.
Strictly contractive channels are simple enough, yet exhibit very interesting
features, which are meaningful from the physical point of view. In particular,
they allow us to incorporate the crucial assumption of finite precision of all
experimentally realizable operations. Strict contractivity also helps us gain
insight into the thermodynamics of noisy quantum evolutions (approach to
equilibrium). Our investigation into thermodynamics focuses on the
entropy-energy balance in quantum registers and computers under the influence
of strictly contractive noise. Using entropy-energy methods, we are able to
appraise the thermodynamical resources needed to maintain reliable operation of
the computer. We also obtain estimates of the largest tolerable error rate.
Finally, we explore the possibility of going beyond the standard circuit model
of error correction, namely constructing quantum memory devices on the basis of
interacting particle systems at low temperatures.
