Logical-to-Physical Compilation for Reducing Depth in Distributed Quantum Systems

TL;DR

This paper introduces a compiler that reduces circuit depth in distributed quantum computing by smartly scheduling and decomposing logical operations to enhance reliability in noisy intermediate-scale quantum (NISQ) devices.

Contribution

It presents a novel depth-aware compilation technique that combines logical-to-physical decomposition with parallel scheduling to improve distributed quantum circuit performance.

Findings

Consistently reduces circuit depth for sequential CNOT structures.

Leaves already parallel circuits unchanged.

Improves the fidelity of distributed quantum computations.

Abstract

Quantum computing is expected to become a foundational technology for solving problems that exceed the capabilities of classical systems. As quantum algorithms and hardware technologies continue to advance, the need for scalable architectures becomes increasingly clear. Distributed quantum computing offers a promising path forward by interconnecting multiple smaller processors into a larger, more powerful system. However, distributed quantum computing introduces significant circuit depth overhead, as logical operations are typically decomposed into sequential physical procedures that require entanglement generation. These sequential operations limit the reliability of quantum algorithms in the NISQ era due to noise. In this work, we present a compiler that integrates logical-to-physical decomposition with depth-aware rescheduling to reduce the execution cost of distributed quantum circuits. The compiler identifies sequences of logical CNOT gates that share a control or target qubit, reschedules them into parallel instruction groups, and applies decompositions that allow multiple gates to be executed simultaneously using distributed shared entanglement resources. An algorithm is proposed that ensures parallelism is created when possible while keeping logical equivalence and that circuit depth is never increased. Benchmark results demonstrate that the compiler consistently reduces circuit depth for circuits containing inherently sequential CNOT structures, while leaving already-parallel circuits unchanged. These results highlight the value of combining scheduling and hardware-aware decomposition, and establish the compiler as a practical tool for improving the fidelity of distributed quantum computations.