Optimization of VQE-UCC Algorithm Based on Spin State Symmetry

Abstract

The accurate calculation of molecular energy spectra, a very complicated work, is of importance in many applied fields. Relying on the VQE-UCC algorithm, it is very possible to calculate the molecular energy spectrum on a noisy intermediate scale quantum computer. However, due to the limitation of the number of qubits and coherent time in quantum computers, the complexity of VQE-UCC algorithm still needs to be reduced in the simulation of macromolecules. We develop a new VQE-UCC method to calculate the ground state of the molecule according to the symmetry of the system, the complexity of which is reduced. Using this method we get the ground and excite state of four kinds of molecules. The method and the results are of great significance for the promotion of quantum chemical simulations.

Quantum computing of the $^6$Li nucleus via ordered unitary coupled cluster

“…The unitary coupled clusters ansatz (UCC) is widely used to obtain a correlated ground-state from an initial Hartree-Fock solution |ψ 0 in quantum chemistry and nuclear physics [28,29,40]. It lets the Hartree-Fock state evolve according to the cluster operator T .…”

“…The former is as shallow as possible in the circuit architecture, with the smallest number of CNOT gates executable on NISQ devices, whereas the latter is built according to properties of the underlying physical system. Although VQE simulations have been widely and successfully used in quantum chemistry [20,21,[26][27][28][29][30], there are fewer applications in nuclear physics [6,12,[14][15][16]. While both fields share many similarities, such as being formulated as non-relativistic quantum field theories in second quantization, they differ in many other aspects.…”