We extended robust phase estimation (RPE) – a protocol for characterizing single-qubit gates – to the evaluation of energy differences in quantum simulation. We demonstrated our protocol on IBM’s Quantum Experience, verifying that it achieves optimal Heisenberg-like scaling. We also proved that our approach has a relatively high tolerance for particular coherent state preparation and measurement errors.
RPE does not require the application of controlled unitaries between an auxiliary register and a system register – in fact, it requires no auxiliary qubits leading to reductions in the required quantum resources. We expect that RPE will be most useful for simulation in the upcoming era between NISQ and fault tolerance.
For details see "Evaluating energy differences on a quantum computer with robust phase estimation", by Antonio Russo, Kenneth Rudinger, Ben Morrison, & Andrew Baczewski. arXiv:2007.08697.