Adiabatic preparation of ultracold lattice bosons across the low-entropy Mott transition

The three-dimensional Superfluid-to-Mott transition has been extensively studied with ultracold atoms since its first realization two decades ago [1]. However, the critical regime close to the quantum critical point has hardly been investigated so far. By combining measurements of the 3D momentum-space density ρ(k) of lattice bosons with ab-initio Quantum Monte-Carlo (QMC) calculations of the same quantity [2], we first certify that equilibrium states of the Bose-Hubbard model – including those in the quantum-critical regime above the zero-temperature Mott transition – can be adiabatically prepared (at a constant entropy per particle of S/N = 0.8(1)k_B in our experiment) [3]. Upon varying the ratio between the interaction U and the tunnelling energy J across the superfluid transition, we then observe that ρ(k=0) exhibits a sharp transition at a value of U/J consistent with the bulk prediction from quantum Monte Carlo. Finally, the variation of ρ(k=0) with U/J exhibits a critical behavior consistent with the expected 3D XY universality class, showing that the momentum distribution of ultracold bosons can reveal traits of the critical behavior of the superfluid transition even in an inhomogeneous trapped system [4].

[1] Greiner, M., Mandel, O., Esslinger, T. et al., Nature 415, 39–44 (2002)

[2] H. Cayla et al., Phys. Rev. A 97, 061609(R) (2018)

[3] C. Carcy et al., Phys. Rev. Lett. 126, 045301 (2021)

[4] G. Hercé et al., arxiv :2103.03007 (2021)