Direct characterization of quantum dynamics: General theory

The characterization of the dynamics of quantum systems is a task of both fundamental and practical importance. A general class of methods which have been developed in quantum information theory to accomplish this task is known as quantum process tomography (QPT). In an earlier paper M. Mohseni and D. A. Lidar Phys. Rev. Lett. 97 170501 (2006) we presented an algorithm for direct characterization of quantum dynamics (DCQD) of two-level quantum systems. Here we provide a generalization by developing a theory for direct and complete characterization of the dynamics of arbitrary quantum systems. In contrast to other QPT schemes, DCQD relies on quantum error-detection techniques and does not require any quantum state tomography. We demonstrate that for the full characterization of the dynamics of n d-level quantum systems (with d prime), the minimal number of required experimental configurations is reduced quadratically from d⁴ⁿ in separable QPT schemes to d²ⁿ in DCQD.