Figure 1
Quantifying quantum-mechanical processes. (a) Suppose that a physical process is experimentally determined by a process matrix χ expt; how a system evolves from an arbitrary initial state ρ initial to some final state ρ final is specified by the process matrix χ expt through the mapping χ expt(ρ initial) = ρ final, which preserves the Hermiticity, trace, and positivity of the system density matrix. The amount of quantumness χ Q of the process, which cannot be described at all by any classical processes χ C , can be characterized and quantified by α (composition), β (robustness), F expt (process fidelity) and S (von Neumann entropy). For instance, for a perfect (worst) experiment on a target quantum process, α, β and F expt will attain their individual maximum (minimum) values whereas S will reach the minimum (maximum) uncertainty of the quantum process. These variables have significant applications to aid in the exploration and evaluation of all physical processes described by the quantum operations formalism, such as (b,c) the dynamics of open quantum systems, (d) the generation of multipartite entanglement, and (e,f) quantum-information processing. (g) This framework shows a new correlation model in the class between genuine multipartite EPR steering and genuine multipartite entanglement, called the χ C -nonclassical correlations.
