Strongly Interacting Two-component Coupled Bose Gas in 1D Optical Lattice

We study one-dimensional strongly interacting two-component bosons in an optical lattice with tunable same-site and nearest neighboring sites intercomponent coupling. Previous work studying two-component Bose–Hubbard model in deep Mott regime without consideration of coupling shows z anti-ferromagnetic and x-y ferromagnetic spin phases in spin-1/2 (New J. Phys. 5 113, 2003) and Mott and x-y ferromagnetic spin phases in spin-1 (Phys. Rev. A 92, 041602(R), 2015). Such a system is experimentally realizable as two component bosons (envisoned as two internal levels of an atom) in a tilted optical lattice. We introduce couplings via nearly resonant microwave field, and the intra-component tunnelings via light-assisted Raman transition. Coupling of the components substantially alters the previously observed spin phases revealing fascinating non-trivial spin correlations. The present consideration of inter-component coupling for unit occupancy gives rise to novel effective ordering of the spins leading to unprecedented spin phases: site-dependent z-x spin configuration with tunable (by hopping parameter) proclivity of spin alignment along z. The examination goes beyond the mean-field approximation by employing exact analysis and Variational Monte Carlo with stochastic minimization on Entangled Plaquette states (EPS). The possibility of the exotic spin phases persisting at occupancy greater than unity and with complex intra-component tunnelings and inter-component coupling are discussed.