Southwest Quantum Information and Technology

An adaptive algorithm for ansatz construction with condensed quantum circuits

Presenting Author: Panagiotis Anastasiou, Virginia Tech
Contributing Author(s): Yanzhu Chen, Sophia E. Economou, Edwin Barnes, Nicholas J. Mayhall

Quantum simulation of strongly correlated systems is expected to be the “killer” application of quantum computing on noisy intermediate scale quantum (NISQ) devices. One of the most promising NISQ algorithms, the variational quantum eigensolver (VQE), brings down the quantum resource requirements by leveraging the power of classical optimization, yet the gap between the most compact and accurate known ansätze and the coherence properties of our best quantum hardware is still too wide for the VQE to offer a quantum advantage. Recent progress on the theoretical side has reduced the resource requirements with an adaptive algorithm for problem-tailored ansatz construction called ADAPT-VQE. The algorithm uses local energy gradient information to iteratively construct a VQE ansatz specific to the problem at hand, one unitary at a time. In this work, we introduce a variation of the algorithm, which modifies the way the ansatz is created by adding multiple unitaries at a time. Our algorithm results in denser but significantly shallower circuits, without increasing the number of CNOT gates or variational parameters. Moreover, the expensive step of measuring the energy gradient with respect to each candidate unitary at each iteration is performed only a fraction of the time compared to the original ADAPT-VQE. These improvements can contribute to the challenging goal of demonstrating useful quantum advantage with NISQ hardware.

(Session 5 : Thursday from 5:00 pm - 7:00 pm)