A bosonic topological phase in a paired superfluid

We study an effective model of two interacting species of bosons in two dimensions which is amenable to sign problem free Monte Carlo simulations In addition to conventional ground states we access a paired superfluid which is also a topological phase protected by the remaining unbroken symmetry This phase arises from the condensation of a composite object the bound state of vortices and anti vortices of one species to a boson of the second species We introduce a bulk response function the Ising analog of the quantized Hall effect to diagnose the topological phase The interplay of broken symmetry and topology leads to interesting effects such as fractionally charged vortices in the paired superfluid Possible extensions towards realistic models of cold atomic bosons will be discussed