Evaluating energy differences on a quantum computer with robust phase estimation

• Main Authors: Russo, A. E, Rudinger, K. M, Morrison, B. C. A, Baczewski, A. D
• Format: Journal Article
• Language: English
• Published: 17-07-2020
• Subjects: Physics - Quantum Physics
• DOI: 10.48550/arxiv.2007.08697

Phys. Rev. Lett. 126, 210501 (2021) We adapt the robust phase estimation algorithm to the evaluation of energy
differences between two eigenstates using a quantum computer. This approach
does not require controlled unitaries between auxiliary and system registers or
even a single auxiliary qubit. As a proof of concept, we calculate the energies
of the ground state and low-lying electronic excitations of a hydrogen molecule
in a minimal basis on a cloud quantum computer. The denominative robustness of
our approach is then quantified in terms of a high tolerance to coherent errors
in the state preparation and measurement. Conceptually, we note that all
quantum phase estimation algorithms ultimately evaluate eigenvalue differences.