Towards Total Quantum System Characterization

Quantum enabled technologies promise to deliver the next technological revolution. However, their realization requires a degree of control over quantum systems that is still elusive. The problem stems from our imperfect knowledge of the physical quantities ruling their evolution. To overcome this, system characterization tools such as Hamiltonian learning, noise spectroscopy, and state tomography have been devised. However, the success of each of these schemes often requires the knowledge provided by the other. For example, Hamiltonian learning protocols estimate the parameters of a Hamiltonian ruling the evolution of a set of qubits but require knowledge of any noise affecting them to be successful, while noise spectroscopy protocols can characterize the noise affecting the system of interest but require knowledge of the deterministic part of the Hamiltonian.
In this talk, we will present a limited-access total quantum system characterization tool. We show that it is possible to simultaneously extract the information that Hamiltonian learning, noise spectroscopy, and state tomography of a composite quantum system provide, when only limited-access is available, i.e., when fast and reliable control and measurements are possible in only a subsystem.