Long-lived superconducting quantum circuits toward fault-tolerant quantum computing

Abstract:
Superconducting quantum circuits represent fully engineerable quantum systems, positioning them as a leading platform for large-scale quantum computing. Despite recent milestones like surface code demonstrations and achieving quantum supremacy, scaling up to millions of qubits for fault-tolerant operations remains a significant challenge. Our research focuses on enhancing qubit lifetimes within superconducting quantum circuits to reduce resource requirements significantly. We pursue two primary strategies: Firstly, we investigate the loss mechanisms affecting state-of-the-art superconducting qubit lifetimes. By careful optimization of the fabrication process, sample packaging, and cryogenic wiring, we demonstrate long-lived superconducting qubits, recording one of the best qubit lifetimes (> 0.5 milliseconds). By leveraging these long-lived qubits as quantum sensors, we identify a new loss mechanism attributed to mechanical shocks from the pulse tube cooler of a dilution refrigerator. This discovery suggests new error mitigation strategies by isolating superconducting qubits from mechanical environments. Secondly, we introduce mechanical oscillators based on circuit optomechanics, facilitated by a novel nanofabrication process involving silicon-etched trenches. This breakthrough enables the realization of ultra-coherent and highly scalable systems (> 10 milliseconds and > 20 modes), leading to the first demonstrations of tracking the thermalization of a mechanical squeezed state and engineering topological optomechanical lattices. These advancements not only bring insights into decoherence mechanisms but also pave the way for scalable fault-tolerant quantum computing.