Quantum Divide and Compute: Hardware Demonstrations and Noisy
  Simulations
Noisy, intermediate-scale quantum computers come with intrinsic limitations
in terms of the number of qubits (circuit "width") and decoherence time
(circuit "depth") they can have. Here, for the first time, we demonstrate a
recently introduced method that breaks a circuit into smaller subcircuits or
fragments, and thus makes it possible to run circuits that are either too wide
or too deep for a given quantum processor. We investigate the behavior of the
method on one of IBM's 20-qubit superconducting quantum processors with various
numbers of qubits and fragments. We build noise models that capture
decoherence, readout error, and gate imperfections for this particular
processor. We then carry out noisy simulations of the method in order to
account for the observed experimental results. We find an agreement within 20%
between the experimental and the simulated success probabilities, and we
observe that recombining noisy fragments yields overall results that can
outperform the results without fragmentation.
Thomas Ayral François-Marie Le Régent Zain Saleem Yuri Alexeev Martin Suchara