Designs for quantum error correction depend strongly on the connectivity of the qubits. For
solid-state qubits, the most straightforward approach is to have connectivity constrained to a
planar graph. Practical considerations may also further restrict the connectivity, resulting in a
relatively sparse graph such as the heavy-hexagonal (“heavy-hex”) architecture of current
IBM Quantum devices. In such cases, it is hard to use all qubits to their full potential. Instead,
in order to emulate the denser connectivity required to implement well-known quantum error …