Scalable Circuit Cutting and Scheduling in a Resource-Constrained and Distributed Quantum System

Despite rapid developments in quantum computing, current systems remain limited in practical applications due to their constrained qubit counts and quality. Technologies such as superconducting, trapped ions, and neutral atom quantum computing are progressing towards fault tolerance. However, they face challenges in scalability and control. Recent efforts have concentrated on multi-node quantum systems that connect smaller quantum devices to execute larger circuits. Future demonstrations aim to utilize quantum channels for system coupling, but current methods often resort to classical communication with circuit cutting techniques. This involves dividing large circuits into smaller subcircuits and reconstructing them after execution. Existing cutting methods face challenges such as lengthy search times with increasing numbers of qubits and gates. Moreover, they often struggle to efficiently use resources across various worker configurations in a multi-node system. To address these challenges, we propose FitCut, a novel approach that transforms quantum circuits into weighted graphs. FitCut employs a community-based, bottom-up approach to cut circuits based on resource constraints such as qubit counts on each worker. Additionally, it includes a scheduling algorithm that optimizes resource utilization across workers. Implemented with Qiskit and evaluated extensively, FitCut significantly outperforms existing tools such as Qiskit Circuit Knitting Toolbox, reducing time costs by factors ranging from 3 to 2000 and improving resource utilization rates by up to 388% on the worker side, leading to a system-wide improvement of 286% in accumulated circuit depth.