Beyond asymptotic reasoning: a practical ground state projector based on the wall-Chebyshev expansion

Abstract: We introduce a quantum algorithm for ground-state preparation based on a Chebyshev series approximation to the wall function. This projector can be efficiently implemented as a product of Hamiltonian operators, enabling a straightforward realization via the linear combinations of unitaries method. We analyze the asymptotic scaling and provide numerical benchmarks, demonstrating that the wall-Chebyshev projector achieves competitive performance with leading methods based on imaginary time evolution and alternative projector function approximations. Notably, our approach exhibits superior robustness and convergence in scenarios where accurate ground-state energy estimates are unavailable, showing promise for realistic chemistry problems.