Time versus Hardware: Reducing Qubit Counts with a (Surface Code) Data
  Bus
We introduce a data bus, for reducing the qubit counts within quantum
computations (protected by surface codes). For general computations, an
automated trade-off analysis (software tool and source code are open sourced
and available online) is performed to determine to what degree qubit counts are
reduced by the data bus: is the time penalty worth the qubit count reductions?
We provide two examples where the qubit counts are convincingly reduced: 1)
interaction of two surface code patches on NISQ machines with 28 and 68 qubits,
and 2) very large-scale circuits with a structure similar to state-of-the-art
quantum chemistry circuits. The data bus has the potential to transform all
layers of the quantum computing stack (e.g., as envisioned by Google, IBM,
Riggeti, Intel), because it simplifies quantum computation layouts, hardware
architectures and introduces lower qubits counts at the expense of a reasonable
time penalty.
Daniel Herr Alexandru Paler Simon J. Devitt Franco Nori