Pushing the Limit of Quantum Chemistry Simulations with Ion-Trap Hardware

The variational quantum eigensolver (VQE) is a promising approach to simulate molecular systems in the NISQ era, as it requires much shallower quantum circuits than quantum phase estimation. However, the low gate fidelity of currently available quantum computers severely limits its quantum chemistry application. In this work, we aim to push the limit of VQE chemistry simulations using the high-fidelity, 11-qubit ion-trap quantum computers provided by IonQ. By testing the IonQ quantum computer with 2-electron, 4-qubit problems with error mitigation techniques, we have obtained results with improved accuracy compared to previous demonstration of benchmarks. As we shall show in our latest results for 2-electron, 6-qubit metal hydrides simulations, ion trap quantum computer's all-to-all connectivity offers a great deal of flexibility to optimize the VQE circuits by reducing the number of two-qubit entangling gates. Pairing the optimized circuit with error detection techniques based on symmetry verification, hidden inverse, and density matrix purification, we simulate small molecular systems such as metal hydrides with a 2-electron, 6-qubit active space and beyond to chemical accuracy.