Signatures of open and noisy quantum systems in single-qubit quantum annealing

Zachary Morrell, Marc Denis Vuffray, Andrey Lokhov, Andreas Baertschi, Tameem Albash, Carleton Coffrin

Abstract: We propose a quantum annealing protocol that effectively probes the dynamics of a single qubit on D-Wave’s quantum annealing hardware. This protocol uses D-Wave’s ℎ-gain schedule functionality, which allows the rapid suppression of the longitudinal magnetic field at arbitrary points during the anneal. This feature enables us to distinguish between open and closed-system dynamics as well as the presence and absence of longitudinal magnetic field noise. We show that thermal fluctuations alone are not sufficient to explain the system’s dynamics and that a prominent role is played by magnetic field fluctuations, which need to be included in an open quantum system description. Moreover, our protocol only requires single-qubit measurements, which makes it suitable as an exploration and calibration tool for large-scale quantum annealing hardware.