High-order strong-coupling expansion for the Bose-Hubbard model
Tao Wang, Xuefeng Zhang, Chunfeng Hou, Sebastian Eggert, Axel Pelster
Abstract
Based on the process-chain method, we work out in detail a high-order strong-coupling expansion (HSCE) algorithm for determining the quantum phase boundary between the Mott insulator and the superfluid phase of the Bose-Hubbard model in different dimensions. A comparison with quantum Monte-Carlo results reveals the high efficiency and accuracy of the HSCE. With a symbolized evaluation of the algorithm we obtain an analytic expression for the strong-coupling boundary for different fillings up to eighth order. A subsequent Pad\'e approximation then yields a scaling function, which rescales lobes with different fillings to one lobe. As a further crosscheck, we perform a hopping expansion of the phase boundaries obtained from the effective potential Landau theory (EPLT) and find that the respective expansion coefficients coincide with those of HSCE.