Initial-State Dependent Optimization of Controlled Gate Operations with Quantum Computer

TL;DR

This paper introduces AQCEL, a quantum circuit optimizer that reduces redundant controlled operations based on initial states, improving efficiency and fidelity of quantum circuits on near-term devices.

Contribution

The paper presents AQCEL, a novel optimizer that removes unnecessary controls from multi-controlled gates depending on initial states, even with entangled qubits, using polynomial resources.

Findings

AQCEL reduces gate count in quantum circuits for modeling physics phenomena.

AQCEL maintains high fidelity when approximating original circuits on noisy quantum hardware.

The method is broadly applicable to various quantum algorithms for circuit simplification.

Abstract

There is no unique way to encode a quantum algorithm into a quantum circuit. With limited qubit counts, connectivity, and coherence times, a quantum circuit optimization is essential to make the best use of near-term quantum devices. We introduce a new circuit optimizer called AQCEL, which aims to remove redundant controlled operations from controlled gates, depending on initial states of the circuit. Especially, the AQCEL can remove unnecessary qubit controls from multi-controlled gates in polynomial computational resources, even when all the relevant qubits are entangled, by identifying zero-amplitude computational basis states using a quantum computer. As a benchmark, the AQCEL is deployed on a quantum algorithm designed to model final state radiation in high energy physics. For this benchmark, we have demonstrated that the AQCEL-optimized circuit can produce equivalent final states with much smaller number of gates. Moreover, when deploying AQCEL with a noisy intermediate scale quantum computer, it efficiently produces a quantum circuit that approximates the original circuit with high fidelity by truncating low-amplitude computational basis states below certain thresholds. Our technique is useful for a wide variety of quantum algorithms, opening up new possibilities to further simplify quantum circuits to be more effective for real devices.