QuCLEAR: Clifford Extraction and Absorption for Quantum Circuit Optimization

TL;DR

QuCLEAR is a novel quantum circuit optimization framework that reduces gate count and circuit depth by extracting and classically processing Clifford subcircuits, improving the efficiency of quantum algorithms on noisy devices.

Contribution

The paper introduces Clifford Extraction and Clifford Absorption, two new techniques for optimizing quantum circuits by leveraging Clifford circuit properties.

Findings

Up to 77.7% reduction in CNOT gate count.

Up to 84.1% reduction in entangling depth.

Effective on quantum simulation circuits and near-term algorithms.

Abstract

Quantum computing carries significant potential for addressing practical problems. However, currently available quantum devices suffer from noisy quantum gates, which degrade the fidelity of executed quantum circuits. Therefore, quantum circuit optimization is crucial for obtaining useful results. In this paper, we present QuCLEAR, a compilation framework designed to optimize quantum circuits. QuCLEAR significantly reduces both the two-qubit gate count and the circuit depth through two novel optimization steps. First, we introduce the concept of Clifford Extraction, which extracts Clifford subcircuits to the end of the circuit while optimizing the gates. Second, since Clifford circuits are classically simulatable, we propose Clifford Absorption, which efficiently processes the extracted Clifford subcircuits classically. We demonstrate our framework on quantum simulation circuits, which have wide-ranging applications in quantum chemistry simulation, many-body physics, and combinatorial optimization problems. Near-term algorithms such as VQE and QAOA also fall within this category. Experimental results across various benchmarks show that QuCLEAR achieves up to a $77.7\%$ reduction in CNOT gate count and up to an $84.1\%$ reduction in entangling depth compared to state-of-the-art methods.