Southwest Quantum Information and Technology

Richardson extrapolation for small diatomic molecules on the QSCOUT device

Presenting Author: Oliver Maupin, Tufts University
Contributing Author(s): Ashlyn D. Burch, Chrisopher G. Yale, Brandon Ruzic, Andrew J. Landahl, Peter J. Love, Kenneth M. Rudinger, Antonio Russo, Ryan Shaffer

Current noisy intermediate-scale quantum (NISQ) ion-trap devices are subject to gate errors around 0.1% for two qubit gates. These errors significantly impact the accuracy of calculations if left unchecked. Error mitigation techniques such as Richardson extrapolation can reduce these errors without incurring a qubit overhead. We demonstrate and optimize this extrapolation on Sandia's QSCOUT device in order to calculate the ground state energy of the HeH+ molecule using VQE. This work uses two methods of scaling our noise: time-stretching our gates and unitary folding. Using simulations, we study how to best integrate Richardson extrapolation into an optimization procedure. We further study the effects of the order of extrapolation on the accuracy and precision of the final energy estimate in order to maximize its effectiveness given a limited sampling budget. Experimental results show that such extrapolation methods can be effective in a vacuum, but may require a large sampling overhead and are sensitive to coherent errors in the circuit.

(Session 5 : Thursday from 5:00 - 7:00 pm)