“…In the Noisy Intermediate-Scale Quantum (or NISQ) era, quantum computers are still rapidly evolving but still present several limitations: Firstly, quantum computing as a field has not yet settled on a particular physical realization for quantum hardware [25]; leading candidate implementations include those constructed from superconducting qubits [26], VOLUME 4, 2016 [27], [28], [29], [30], [19], trapped-ion qubits [31], [32], [33], [34], as well as other proposals [35], [36], [37], [38], [39]. Secondly, many devices exhibit fixed and finite connectivity constraints between neighboring qubits (a notable exception to this is trapped-ion technology, in which one can in principle produce "all-to-all" connectivity [31]).…”