Quantum algorithm

Quantum mechanics

Computational science

Algorithm

Quantum computer

Supramolecular chemistry

Supersymmetric quantum mechanics

Quantum circuit

Quantum chemistry

Coupled cluster

Molecule

Computer science

Mathematical optimization

Hamiltonian (control theory)

The Imaginary

Ansatz

Physics

Imaginary time

Quantum phase estimation algorithm

Psychology

Quantum dynamics

Mathematics

Quantum network

Psychotherapist

Artificial intelligence

Quantum

Heuristic

Qubit

Quantum simulator

Journal of Chemical Theory and Computation

We develop a resource-efficient step-merged quantum imaginary time evolution approach (smQITE) to solve for the ground state of a Hamiltonian on quantum computers. This heuristic method features a fixed shallow quantum circuit depth along the state evolution path. We use this algorithm to determine the binding energy curves of a set of molecules, including H2, H4, H6, LiH, HF, H2O, and BeH2, and find highly accurate results. The required quantum resources of smQITE calculations can be further reduced by adopting the circuit form of the variational quantum eigensolver (VQE) technique, such as the unitary coupled cluster ansatz. We demonstrate that smQITE achieves a similar computational accuracy as VQE at the same fixed-circuit ansatz, without requiring a generally complicated high-dimensional nonconvex optimization. Finally, smQITE calculations are carried out on Rigetti quantum processing units, demonstrating that the approach is readily applicable on current noisy intermediate-scale quantum devices.

Efficient Step-Merged Quantum Imaginary Time Evolution Algorithm for Quantum Chemistry