Comparative study of quantum error correction strategies for the
  heavy-hexagonal lattice
Topological quantum error correction is a milestone in the scaling roadmap of
quantum computers, which targets circuits with trillions of gates that would
allow running quantum algorithms for real-world problems. The square-lattice
surface code has become the workhorse to address this challenge, as it poses
milder requirements on current devices both in terms of required error rates
and small local connectivities. In some platforms, however, the connectivities
are kept even lower in order to minimise gate errors at the hardware level,
which limits the error correcting codes that can be directly implemented on
them. In this work, we make a comparative study of possible strategies to
overcome this limitation for the heavy-hexagonal lattice, the architecture of
current IBM superconducting quantum computers. We explore two complementary
strategies: the search for an efficient embedding of the surface code into the
heavy-hexagonal lattice, as well as the use of codes whose connectivity
requirements are naturally tailored to this architecture, such as
subsystem-type and Floquet codes. Using noise models of increased complexity,
we assess the performance of these strategies for IBM devices in terms of their
error thresholds and qubit footprints. An optimized SWAP-based embedding of the
surface code is found to be the most promising strategy towards a near-term
demonstration of quantum error correction advantage.
César Benito Esperanza López Borja Peropadre Alejandro Bermudez