Cold-atom fountain for atom-surface interaction measurements mediated by a near-resonant evanescent light field

Abstract

Cold atomic ensembles offer precise tools for probing near-field interactions, yet experimental data linking atom dynamics to surface-induced forces remains limited. This study investigated the interaction between atoms and a dielectric surface using an atomic fountain measurement technique, in which cold rubidium atoms were released from a moving optical dipole trap. The launched cold atoms were irradiated with an evanescent light detuned from the D$_2$ transition by $-$20.2 to $+$20.2 MHz, after which they were recaptured by reactivating the optical dipole trap. Our measurements revealed that the number of recaptured atoms decreased with increasing flight time, and the decay was suppressed under blue-detuned conditions. We modeled the motion dynamics of the cold atomic ensemble, incorporating Casimir-Polder interactions between the dielectric surface and cold atoms, and observed that the rate of decrease in the number of residual atoms depended on the value of the van der Waals potential coefficient $C_3$. The calculation results demonstrated good agreement with the experimental results, allowing us to estimate $C_3 = 5.6^{+2.4}_{-1.9} \times 10^{-49}$ Jm$^3$ by comparing simulations with the experimental results across various $C_3$ values, accounting for experimental errors.