Flux-bias-free flux qubit driven by low-power single-flux-quantum driver on monolithically integrated circuit

Single-flux-quantum (SFQ) cryogenic control circuits are a promising approach for realizing scalable superconducting quantum processors. However, previous studies have primarily relied on conventional SFQ technologies with Josephson junction critical current densities ( \(JC\) ) of about 1 kA/cm 2 and critical currents ( \(IC\) ) of several hundred microamperes. Such large critical currents can increase power dissipation and induce nonequilibrium quasiparticles that degrade qubit performance. In this study, we demonstrate coherent control of a flux-bias-free (FBF) flux qubit using a low-power SFQ driver monolithically integrated on the same chip. The SFQ driver was fabricated using epitaxial NbN/AlN/NbN Josephson junctions with critical currents of only a few microamperes, approximately two orders of magnitude smaller than those used in conventional SFQ circuits. Using this low- \(IC\) SFQ driver, we found that the energy relaxation time, \(T₁\) , of the FBF qubit remains comparable to that obtained under conventional microwave control, indicating that the low- \(IC\) SFQ driver does not introduce a measurable degradation of qubit performance in the present device.