Curator's Take
This article shows that by exploiting the richer two‑qubit gate repertoire now available on superconducting chips—specifically CNOT combined with CXSWAP—it is possible to implement a new family of low‑density parity‑check codes (“Bunny codes”) that match or surpass surface‑code performance without requiring long‑range couplers. The work builds on recent advances in native gate engineering and demonstrates, via exhaustive search and circuit‑level simulation, code rates up to three times higher than the toric code while achieving logical error rates an order of magnitude lower at comparable overhead. If these findings translate to hardware, they could dramatically simplify quantum processor layouts and accelerate the path toward scalable fault‑tolerant quantum computers, though experimental validation on real devices will be essential to confirm the simulated gains.
— Mark Eatherly
Summary
Drawing on advances in superconducting qubit control schemes that unlock enriched native gate sets at the hardware level, we systematically examine how harnessing this enlarged physical two-qubit gate pool -- specifically CNOT and CXSWAP -- streamlines syndrome extraction for certain qLDPC codes with nonlocal stabilizers. Through an exhaustive search, we discover a set of qLDPC codes with various stabilizer weights and distances that can be implemented on the two-dimensional nearest-neighbor qubit connectivity native to superconducting hardware while achieving performance equivalent to that of the direct CNOT implementation requiring long-range interactions. We refer to those codes as Bunny codes. Across all code distances we examine, the best Bunny codes with weight-6 stabilizers in periodic boundary conditions have a code rate approximately $3\times$ that of the toric code; when converted to open boundary conditions, they retain an approximately $2\times$ code rate advantage over the rotated surface code. In circuit-level simulation, we find that some Bunny codes exhibit logical error rates an order of magnitude lower than toric codes with comparable code rates. Our results demonstrate that high-performance quantum error correction can be achieved using an expanded gate set rather than long-range couplers, thereby significantly reducing hardware complexity.