Accelerated Variational Quantum Eigensolver

The problem of finding the ground state energy of a Hamiltonian using a quantum computer is currently solved using either the quantum phase estimation (QPE) or variational quantum eigensolver (VQE) algorithms. For precision ε, QPE requires O(1) repetitions of circuits with depth O(1/ε), whereas each expectation estimation subroutine within VQE requires O(1/ε^{2}) samples from circuits with depth O(1). We propose a generalized VQE algorithm that interpolates between these two regimes via a free parameter α∈[0,1], which can exploit quantum coherence over a circuit depth of O(1/ε^{α}) to reduce the number of samples to O(1/ε^{2(1-α)}). Along the way, we give a new routine for expectation estimation under limited quantum resources that is of independent interest.