Quantum process

In quantum mechanics, a quantum process is a somewhat ambiguous term which usually refers to the time evolution of an (open) quantum system. Under very general assumptions, a quantum process is described by the quantum operation formalism (also known as a quantum dynamical map), which is a linear, trace-preserving, and completely positive map from the set of density matrices to itself.

For instance, in quantum process tomography, the unknown quantum process is assumed to be a quantum operation.

However, not all quantum processes can be captured within the quantum operation formalism;^[1][2] in principle, the density matrix of a quantum system can undergo completely arbitrary time evolution.

References

1. ↑ Philip Pechukas, "Reduced Dynamics Need Not Be Completely Positive", Phys. Rev. Lett. 73, 1060 (1994).
2. ↑ Anil Shaji and E.C.G. Sudarshan "Who's Afraid of not Completely Positive Maps?", Physics Letters A Volume 341, 20 June 2005, Pages 48–54

• M. Nielsen and I. Chuang, Quantum Computation and Quantum Information, Cambridge University Press, 2000