Parallel Driving for Fast Quantum Computing Under Speed Limits

Abstract

Increasing quantum circuit fidelity requires an efficient instruction set to minimize errors from decoherence. The choice of a two-qubit (2Q) hardware basis gate depends on a quantum modulator's native Hamiltonian interactions and applied control drives. In this paper, we propose a collaborative design approach to select the best ratio of drive parameters that determine the best basis gate for a particular modulator. This requires considering the theoretical computing power of the gate along with the practical speed limit of that gate, given the modulator drive parameters. The practical speed limit arises from the couplers' tolerance for strong driving when one or more pumps is applied, for which some combinations can result in higher overall speed limits than others. Moreover, as this 2Q basis gate is typically applied multiple times in succession, interleaved by 1Q gates applied directly to the qubits, the speed of the 1Q gates can become a limiting factor for the quantum circuit, particularly as the pulse length of the 2Q basis gate is optimized. We propose parallel-drive to drive the modulator and qubits simultaneously, allowing a richer capability of the 2Q basis gate and in some cases for this 1Q drive time to be absorbed entirely into the 2Q operation. This allows increasingly short duration 2Q gates to be more practical while mitigating a significant source of overhead in some quantum systems. On average, this approach can decrease circuit duration by 17.8% and decrease infidelity for random 2Q gates by 10.5% compared to the currently best reported basic 2Q gate, √iSWAP.