High fidelity unitary evolution using constrained control fields.

The problem of coherent errors, where the quantum unitary evolution is corrupted by populating spurious states (leakage error) or accumulates the wrong phase (phase error), is generic to a variety of situations. This type of errors often arise because it is a difficult task to find control fields that would generate with high accuracy a desired unitary evolution. The task becomes even more complex when taking into account experimental constraints: unavailable control fields, bandwidth limitations, amplitude limitations, etc. Here we attack a class of problems where suitable controls are known in an idealized scenario, but unwanted perturbative interactions disrupt the desired unitary evolution. We show how a recently-proposed Magnus expansion based algorithm for quantum control [1] can be modified to find control fields that both suppress coherent errors and are compatible with experimental constraints. In this talk, we focus on presenting the general method and revisit the problem of single qubit gates in a transmon qubit.
[1] H. Ribeiro, A. Baksic, and A. A Clerk, Phys. Rev. X 7, 011021 (2017).