Digital Coherent Control of a Superconducting Qubit

Superconducting qubits are conventionally controlled with shaped microwave pulses from a microwave carrier tone. This works well for small systems, but is difficult to scale up to the millions of qubits needed for a general-purpose quantum computer. Instead, the authors suggest irradiating a qubit with trains of quantized flux pulses derived from single flux quantum (SFQ) digital logic. The pulses are generated by an SFQ driver circuit cofabricated on the qubit chip. This work opens the door to tight integration of a quantum array with a classical coprocessor, to lower wiring heat load, latency, and overall system footprint.