Effect of spin fluctuations in ultracold bosons coupled to dynamical Z₂gauge fields

We study the Z₂ Bose-Hubbard model [1] that describes a strongly correlated bosonic system coupled to lattice degrees of freedom. This model has been proposed to describe spatial modulation of the hopping. The lattice degrees of freedom are introduced due to the Z₂ gauge field, which is incorporated into the Bose-Hubbard model by placing spins on links between neighboring sites. In the case where spin fluctuations are negligible, this model exhibits the structural phase transition with the translational symmetry breaking[1]. By using the density-matrix renormalization method in matrix-product state form [2], we elucidate the effect of spin fluctuations on the phase diagram of the Z₂ Bose Hubbard model. We investigate the phase diagram that includes the diabatic regimes in which spin fluctuations cannot be ignored, and study the effect of spin fluctuations on ground states. 

References

[1] González-Cuadra, D., Grzybowski, P. R., Dauphin, A. & Lewenstein, M. Strongly Correlated Bosons on a Dynamical Lattice. Phys. Rev. Lett. 121, 090402 (2018). 

[2] Schollwöck, U. The density-matrix renormalization group in the age of matrix product states. Ann. Phys.-New York 326, 96–192 (2011).