A Multi-Qubit SFQ Control Architecture Using Recycled Bias Current

High-frequency input signals from room-temperature microwave sources present a major bottleneck for scaling qubit numbers in universal quantum computers. To address this challenge, we previously developed a superconducting single-flux quantum (SFQ) qubit control circuit (SQCC) capable of generating precise SFQ pulse sequences using only DC bias. This approach eliminates traditional microwave signal chains and enables scalable, low-loss DC-based interconnects. However, as the number of SQCCs increases, the total required bias current grows linearly, leading to significant cable-induced thermal dissipation that limits scalability. In this work, we propose and implement an architecture using recycled bias current to scale up multiple SQCCs (RB-MSQCC). Theoretical analysis indicates that the recycling method can reduce thermal load by a factor of 100 to 1000 compared to conventional biasing. A key enabler of this architecture is a custom-designed driver-receiver pair (DRP) cell, which supports SFQ signal transmission across isolated ground planes using the SIMIT Nb03 process. Based on this, we demonstrate a 4-bit RB-MSQCC prototype. Experimental results confirm stable SFQ pulse generation across all four channels, with output frequencies ranging from 3.42 to 5.27 GHz, consistent with prior results (2.40-8.11 GHz). These findings validate the feasibility and robustness of the proposed scheme under current fabrication constraints. Our study offers both theoretical and experimental support for scalable, energy-efficient SFQ-based qubit control, representing a critical step toward large-scale superconducting quantum processors.