Fast state preparation for molecular simulation by direct pulse optimization: ctrl-VQE

The variational quantum eigensolver (VQE) is a hybrid quantum-classical algorithm to simulate stationary states of molecular systems, which classically optimizes a parameterized quantum circuit to minimize the expectation value of a molecular Hamiltonian. Due to the ability of the variational principle to absorb circuit errors, VQE is uniquely positioned for deployment on NISQ devices. However, in order to obtain sufficiently accurate results, the depth of the parameterized circuits can easily exceed what is experimentally realizable within device coherence times. In this talk, I will discuss recent progress we have made which dramatically reduces the coherence time demands by replacing the parameterized quantum circuit component with a direct pulse optimization. Compared to UCCSD, direct pulse optimization achieves 1000x faster state preparation for LiH molecule on four qubits.