A Multiplicative Ergodic Theorem for Repeated Bistochastic Quantum Interactions with Applications to Entanglement

We consider compositions of random bistochastic completely positive (bcp) maps driven by an ergodic dynamical system. Our main result is the explicit description of Oseledets's Multiplicative Ergodic Theorem (MET) for such compositions in terms of the random multiplicative domains corresponding to the random bcp maps in the compositions. By applying our main theorem, we classify when compositions of random bcp maps are asymptotically entanglement breaking, and use this classification to show that occasionally PPT maps are asymptotically entanglement breaking, i.e., if compositions of random bcp maps contain PPT bcp maps with positive probability, then they are asymptotically entanglement breaking almost surely. We then strengthen our results in the case of compositions of i.i.d. random bcp maps, and, by an application of the theory of random walks on linear groups, we prove a generalization of a theorem of Kuperberg for compositions of i.i.d. random bcp maps. We conclude with a cursory discussion of how to use our methods to move beyond asymptotics and find random finite times at which compositions of random bcp maps are entanglement breaking.
Comment: 29 pages; the author was supported in part by US National Science Foundation Grant No. DMS-2153946; comments welcome