Contextual Subspace Variational Quantum Eigensolver

We describe contextual subspace variational quantum eigensolver (CS-VQE), an approximation method based on standard VQE that can be adjusted to use any number of qubits to approximately simulate a given Hamiltonian. The qubits used on the quantum computer simulate the contextual part of the Hamiltonian, while the remaining, noncontextual part is simulated classically, at the cost of incurring an overall error. The more qubits used on the quantum computer, the smaller the overall error will be, providing a method that can be tailored to match available hardware.