Calculating the Dissociation Curve of Molecular Nitrogen on a Superconducting Quantum Computer

The contextual subspace variational quantum eigensolver (CS-VQE) is a hybrid quantum-classical algorithm that approximates the ground-state energy of a given Hamiltonian. In this work we present an experimental demonstration of the CS-VQE algorithm on superconducting quantum hardware. We compute the potential energy curve for molecular nitrogen, where a dominance of static correlation in the dissociation limit proves challenging for many conventional quantum chemistry techniques. The CS-VQE methodology is competitive with standard subspace methods used in quantum chemistry, but at a considerable saving of quantum resource, meaning different active spaces can be treated for a fixed qubit allowance.