Demonstration of a large-scale quantum chemistry calculations using the Sycamore quantum processor

Variational simulation of quantum chemistry is a likely first application for noisy intermediate scale quantum (NISQ) computers in the post supremacy age. We simulate a chemistry model that is significantly larger than previous implementations on any quantum computing platform. The model is optimized through a variational outer loop and a new iterative method using an approximate Hessian. Upon application of an error mitigation scheme based on pure-state n-representability conditions our experiments run on Google’s Sycamore quantum processor achieve chemical accuracy. The model provides an efficiently verifiable circuit that has a large degree of entanglement and is a circuit primitive for broader fermionic simulation.