Unitary Selective Coupled-Cluster Method

Simulating molecules using the Variational Quantum Eigensolver method is one of promising applications for NISQ-era quantum computers. Designing an efficient ansatz to represent electronic wave function crucial in such simulations. Standard unitary coupled-cluster with singles and doubles (UCCSD) tends have a large number insignificant terms that do not lower energy system. In this work, we present selective method, way construct iteratively selection procedure excitations up fourth order. This approach uses Hamiltonian matrix elements amplitudes already find important higher order add them ansatz. The feature it systematically reduces error increasing size set test molecules. main advantage proposed effort increase does require any additional measurements on computer.