Reducing the Resources Required by ADAPT-VQE Using Coupled Exchange Operators and Improved Subroutines

TL;DR

This paper introduces a novel operator pool and improved subroutines for ADAPT-VQE, significantly reducing quantum resource requirements and outperforming traditional ans"atze in measurement efficiency for molecular simulations.

Contribution

The authors develop the Coupled Exchange Operator (CEO) pool and enhance subroutines, achieving substantial reductions in measurement counts, circuit depth, and CNOT operations in ADAPT-VQE.

Findings

CNOT count reduced by up to 88%

Measurement costs decreased by 99.6%

CEO-ADAPT-VQE outperforms UCCSD in all metrics

Abstract

Adaptive variational quantum algorithms arguably offer the best prospects for quantum advantage in the Noisy Intermediate-Scale Quantum era. Since the inception of the first such algorithm, the Adaptive Derivative-Assembled Problem-Tailored Variational Quantum Eigensolver (ADAPT-VQE), many improvements have appeared in the literature. We combine the key improvements along with a novel operator pool -- which we term Coupled Exchange Operator (CEO) pool -- to assess the cost of running state-of-the-art ADAPT-VQE on hardware in terms of measurement counts and circuit depth. We show a dramatic reduction of these quantum computational resources compared to the early versions of the algorithm: CNOT count, CNOT depth and measurement costs are reduced by up to 88%, 96% and 99.6%, respectively, for molecules represented by 12 to 14 qubits (LiH, H6 and BeH2). We also find that our state-of-the-art CEO-ADAPT-VQE outperforms the Unitary Coupled Cluster Singles and Doubles ansatz, the most widely used static VQE ansatz, in all relevant metrics, and offers a five order of magnitude decrease in measurement costs as compared to other static ans\"atze with competitive CNOT counts.