In this talk, I will discuss unconventional superfluid states of various bosonic systems and present benchmark calculations for the ground state and finite temperature phase diagrams. The method of study is based on quantum Monte Carlo simulations by the Worm algorithm. The two qualitatively different systems to be discussed are: i) superfluidity of lower dimensional objects, i.e. dislocations and defects, embedded in solid structures both in optical lattices and in realistic systems such as 4-He. ii) the two-component Bose-Hubbard model. Bosonic optical lattice systems are also interesting for studies of quantum magnetism where under certain conditions they can be mapped onto various spin Hamiltonians. On the other hand, superfluid dislocations in 4-He are an important subject for their relevance to supersolid behavior observed in solid 4-He.
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