Layering and subpool exploration for adaptive Variational Quantum Eigensolvers: Reducing circuit depth, runtime, and susceptibility to noise

TL;DR

This paper enhances adaptive variational quantum eigensolvers by analyzing their layering process, developing a new selection subroutine, and demonstrating improved noise resilience, especially against amplitude-damping and dephasing noise, through circuit layering.

Contribution

It introduces a framework for understanding and optimizing the layering process in ADAPT-VQEs, including a new subroutine to reduce quantum processor calls and a numerical study on noise resilience.

Findings

Layering improves noise resilience against amplitude-damping and dephasing.

A new subroutine reduces the number of quantum-processor calls.

Layering shows no advantage against depolarizing noise.

Abstract

Adaptive variational quantum eigensolvers (ADAPT-VQEs) are promising candidates for simulations of strongly correlated systems on near-term quantum hardware. To further improve the noise resilience of these algorithms, recent efforts have been directed towards compactifying, or layering, their ansatz circuits. Here, we broaden the understanding of the algorithmic layering process in three ways. First, we investigate the non-commutation relations between the different elements that are used to build ADAPT-VQE ans\"atze. Doing so, we develop a framework for studying and developing layering algorithms, which produce shallower circuits. Second, based on this framework, we develop a new subroutine that can reduce the number of quantum-processor calls by optimizing the selection procedure with which a variational quantum algorithm appends ansatz elements. Third, we provide a thorough numerical investigation of the noise-resilience improvement available via layering the circuits of ADAPT-VQE algorithms. We find that layering leads to an improved noise resilience with respect to amplitude-damping and dephasing noise, which, in general, affect idling and non-idling qubits alike. With respect to depolarizing noise, which tends to affect only actively manipulated qubits, we observe no advantage of layering.