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Evaluating Energy Differences on a Quantum Computer with Robust Phase Estimation

Antonio E. Russo, K. Rudinger, Benjamin C. A. Morrison, A. Baczewski

Physical Review Letters, 2020

62 citations

Abstract

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.

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