A low-noise on-chip coherent microwave source

Abstract

The increasing need for scaling up quantum computers operating in the microwave domain calls for advanced approaches for control electronics. To this end, integration of components at cryogenic temperatures hosting also the quantum devices seems tempting. However, this comes with the limitations of ultra-low power dissipation accompanied by stringent signalquality requirements to implement quantum-coherent operations. Here, we present a device and a technique to provide coherent continuous-wave microwave emission. We experimentally verify that its operation characteristics accurately follow our introduced theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. From phase noise measurements, we evaluate that the infidelity of typical quantum gate operations owing to this cryogenic source is less than 0.1% up to 10-ms evolution times, which is well below the infidelity caused by dephasing of the state-of-the-art superconducting qubits. Our device provides a coherent tone of 25 pW, corresponding to the total power needed in simultaneous control of thousands of qubits. Thus, together with future cryogenic amplitude and phase modulation techniques, our results may open pathways for scalable cryogenic control systems for quantum processors.

Charge dynamics in quantum-circuit refrigeration: Thermalization and microwave gain

“…Interestingly, biasing the quantum dot QCR with an appropriate voltage, we find that the excitation rates are much higher than the relaxation rates. Thus, the dot QCR provides effectively negative damping into the microwave resonator, a phenomenon observed in other types of devices, such as voltage-biased Josephson junctions, 59 to lead to coherent microwave emission. In this regime we can solve the master equation under the assumption that the excitation rates are dominant.…”