Calibration and Utilization of High-Fidelity Two-Qubit Operations

Abstract

Over the past two decades, impressive strides have been made in the field of quantum computing. Quantum advantage has been reported, and there is now an ecosystem of cloud-based quantum processors and companies interested in using them. However, high error rates continue to limit circuit depth, such that solving real-world problems with today’s quantum computers remains a challenge. For quantum computing with superconducting qubits, two-qubit gates are a major source of those errors.

In this thesis, we calibrate high-fidelity CZ and CPhase gates for flux-tunable transmon qubits. We develop a new technique for mitigating coherent errors in twoqubit gates called quantum measurement emulation (QME). We use this technique to implement a novel operation called density matrix exponentiation (DME), which has applications in quantum machine learning and universal simulation. These protocols contribute to the understanding and mitigation of errors in two-qubit gates. They are a step towards fault-tolerant universal quantum computing with superconducting circuits.