Energy gap calculation on near-term quantum hardware with robust phase estimation*

Can alternative approaches to phase estimation yield better results for chemical simulation on NISQ hardware? Robust phase estimation (RPE) calculates the difference in phases between two eigenstates of a unitary, provided oracular access to that unitary and the relevant eigenstates. In contrast to conventional phase estimation, it does not require a controlled-U and is naturally resistant to state preparation and measurement errors.

We evaluate the suitability of RPE on near-term hardware. In particular, we calculate the energy landscapes of H₂ and H₃ on extant quantum hardware (pre-compiling to emulate hardware with significantly higher fidelities). Resource requirements for larger molecules are considered.