  Modular quantum processor architectures are envisioned as a promising
solution for the scalability of quantum computing systems beyond the Noisy
Intermediate Scale Quantum (NISQ) devices era. Based upon interconnecting tens
to hundreds of quantum cores via a quantum intranet, this approach unravels the
pressing limitations of densely qubit-packed monolithic processors, mainly by
mitigating the requirements of qubit control and enhancing qubit isolation, and
therefore enables executing large-scale algorithms on quantum computers. In
order to optimize such architectures, it is crucial to analyze the quantum
state transfers occurring via inter-core communication networks, referred to as
inter-core qubit traffic. This would also provide insights to improve the
software and hardware stack for multi-core quantum computers. To this aim, we
present a pioneering characterization of the spatio-temporal inter-core qubit
traffic in large-scale circuits. The programs are executed on an all-to-all
connected multi-core architecture that supports up to around 1000 qubits. We
characterize the qubit traffic based on multiple performance metrics to assess
the computational process and the communication overhead. Based on the
showcased results, we conclude on the scalability of the presented algorithms,
provide a set of guidelines to improve mapping quantum circuits to multi-core
processors, and lay the foundations of benchmarking large-scale multi-core
architectures.
