A persistent-supercurrent atom chip is a quantum device designed with a view to transcending the limits of conventional technologies by employing some of the significant properties of quantum mechanics.We have applied this novel technique to achieve an atomic gas in a macroscopic quantum state in the vicinity of a solid-state surface.In this article, we review a technique for making an extremely stable Bose-Einstein condensate above a chip surface and describe our attempts to overcome several unpredicted problems introduced by superconductivity.
The ability to generate and tune quantized persistent supercurrents is crucial for building superconducting or atomtronic devices with novel functionalities. In ultracold atoms, previous methods for generating quantized supercurrents are generally based on dynamical processes to prepare atoms in metastable excited states. Here, we show that arbitrary quantized circulation states can be adiabatically prepared and tuned as the ground state of a ring-shaped Bose-Einstein condensate by utilizing spin--orbital-angular-momentum (SOAM) coupling and an external potential. There exists superfluid hysteresis for tuning supercurrents between different quantization values with nonlinear atomic interactions, which is explained by developing a nonlinear Landau-Zener theory. Our work will provide a powerful platform for studying SOAM-coupled ultracold atomic gases and building atomtronic circuits.
We study the metastability and decay of multiply charged superflow in a ring-shaped atomic Bose-Einstein condensate. Supercurrent corresponding to a giant vortex with topological charge up to
q=10 is phase imprinted optically and detected both interferometrically and kinematically. We observe
q=3 superflow persisting for up to a minute and clearly resolve a cascade of quantized steps in its decay. These stochastic decay events, associated with vortex-induced $2\ensuremath{\pi}$ phase slips, correspond to collective jumps of atoms between discrete
q values. We demonstrate the ability to detect quantized rotational states with $>
99%$ fidelity, which allows a detailed quantitative study of time-resolved phase-slip dynamics. We find that the supercurrent decays rapidly if the superflow speed exceeds a critical velocity in good agreement with numerical simulations, and we also observe rare stochastic phase slips for superflow speeds below the critical velocity.