Charting the circuit QED design landscape using optimal control theory.

Abstract

With recent improvements in coherence times, superconducting transmon qubits have 
become a promising platform for quantum computing. They can be flexibly engineered 
over a wide range of parameters, but also require us to identify an efficient 
operating regime. Using state-of-the-art quantum optimal control techniques, we 
exhaustively explore the landscape for creation and removal of entanglement over a 
wide range of design parameters. We identify an optimal operating region outside of 
the usually considered strongly dispersive regime, where multiple sources of 
entanglement interfere simultaneously, which we name the quasi-dispersive straddling
qutrits regime. At a chosen point in this region, a universal gate set is realized 
by applying microwave fields for gate durations of 50 ns, with errors approaching 
the limit of intrinsic transmon coherence. Our systematic quantum optimal control 
approach is easily adapted to explore the parameter landscape of other quantum 
technology platforms.