Greatly improved higher-order product formulae for quantum simulation

Quantum algorithms for simulation of Hamiltonian evolution are often based on product formulae. The fractal method of Suzuki gives a systematic way to find arbitrarily high-order product formulae, but results in a large number of exponentials. On the other hand, product formulae with fewer exponentials can be found by numerical solution of simultaneous nonlinear equations. It is also possible to reduce the cost of long-time simulations by processing, where a kernel is repeated and a processor need only be applied at the beginning and end of the simulation. In this work, we found thousands of new product formulae of both 8th and 10th order, and numerically tested these formulae, together with many formulae from prior literature. We provide methods to fairly compare product formulae of different lengths and different orders. We have found a new 8th order processed product formula with exceptional performance, that outperforms all other tested product formulae for about eight orders of magnitude in system parameters T (time) and ϵ (allowable error). That includes most reasonable combinations of parameters to be used in quantum algorithms.