Interaction-assisted quantum tunneling of a Bose-Einstein condensate out of a single trapping well

We experimentally study tunneling of Bose-condensed ${}^{87}$Rb atoms prepared in a quasi-bound state and observe a non-exponential decay caused by interatomic interactions. A combination of a magnetic quadrupole trap and a thin $1.3\mu \mathrm{m}$ barrier created using a blue-detuned sheet of light is used to tailor traps with controllable depth and tunneling rate. The escape dynamics strongly depend on the mean-field energy, which gives rise to three distinct regimes— classical spilling over the barrier, quantum tunneling, and decay dominated by background losses. We show that the tunneling rate depends exponentially on the chemical potential. Our results show good agreement with numerical solutions of the 3D Gross-Pitaevskii equation.