Charting the circuit QED design landscape using optimal control theory

TL;DR

This paper uses quantum optimal control to explore superconducting qubit design space, identifying a new optimal regime for entanglement and universal gates with high fidelity outside traditional regimes.

Contribution

It introduces the QuaDiSQ regime, a novel operating region for transmon qubits, and demonstrates high-fidelity gate implementation using optimal control techniques.

Findings

Identified the QuaDiSQ regime as optimal for entanglement.

Achieved universal gates with errors near coherence limits.

Demonstrated adaptability of control methods to other platforms.

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 (QuaDiSQ) 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.