Representing and Probing Errors in Quantum Information Processing Devices

Abstract

The quality of quantum information processing devices has been improving at an unprecedented speed. How to faithfully represent the quality of these devices has become an increasingly imminent problem. In this thesis we focus on two aspects in representing and characterizing quantum devices. First, we discuss why most conventional quality metrics are not in principle appropriate to quantify experimentally-determined representations of gate-set elements, due to a gauge degree of freedom in quantum experiments. We then propose an operational quality measure for a gate-set and discuss its usefulness in representing degree of errors and improving experimental control. Second, we develop a protocol that separately and unambiguously characterizes state and measurement errors, relying on high-quality quantum gates. By integrating a method called randomized compiling, we derive a favorable upper bound for the effects of gate errors on the estimated parameters, and numerically demonstrate its performance in the presence of an adversarial gate error.