Implementing the Variational Quantum Eigensolver with native 2-qubit interaction and error mitigation

The variational quantum eigensolver (VQE) is an algorithm that may provide near-term applications of small-scale quantum computers, in quantum chemistry and optimisation problems. In order for the VQE to provide accurate solutions to problems on real devices, methods have been proposed recently to mitigate the errors caused by imperfect gates.
In this presentation, we report a quantum chemistry simulation using the VQE on a 2-qubit superconducting device in which we use fixed frequency qubits and build the algorithm using the native 2-qubit interaction resulting from a static capacitive coupling. The hardware ansatz of the VQE is constructed by varying the timings of echo pulses to manipulate the native ZZ coupling. This method allows us to implement a VQE algorithm without needing repeated 2-qubit-gate tune-up, and enables simple and understandable implementation of error mitigation.