Quantum computers are expected to outperform conventional computers for a range of
important problems, from molecular simulation to search algorithms, once they can be
scaled up to large numbers of quantum bits (qubits), typically millions. For most solid-state
qubit technologies, eg those using superconducting circuits or semiconductor spins, scaling
poses a significant challenge as every additional qubit increases the heat generated, while
the cooling power of dilution refrigerators is severely limited at their operating temperature …