USC and Quantum Elements Breakthrough Paves Way for Next-Gen Quantum Computing Hardware

Researchers from the University of Southern California (USC) and Quantum Elements have made significant strides in quantum computing by demonstrating subthreshold surface code scaling on IBM's heavy-hex processors. The breakthrough, published in Nature Communications, confirms that physical quantum processors can achieve distance-scaling error suppression without a native square-grid lattice.

The study utilized 156-qubit IBM Heron-generation superconducting QPUs and overcame connectivity constraints by co-designing a depth-minimizing 'fold-unfold' SWAP embedding using bridge ancillas alongside robust dynamical decoupling (DD). The team's implementation, via Quantum Elements' Orbit Qiskit Function, successfully suppressed idle-time noise, allowing directional subthreshold scaling as the surface code distance expanded from d = 3 to anisotropic configurations.

The researchers introduced a novel SPAM-aware Entanglement Fidelity (EF) metric that accurately isolates per-cycle logical error rates without assuming stationary noise. The study also warned against 'spurious subthreshold claims' and demonstrated the importance of advanced DD error suppression in hardware control sequences.