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.

Figures (7)

• Figure 1: Geometry of the cold atomic fountain measurement. The cold atoms transported by the optical dipole trap as the moving beam are launched upward with an initial velocity $v_0$ by switching off the trap beam. When light undergoes total internal reflection at the dielectric interface, it generates an evanescent field at the dielectric interface that interacts with the launched cold atoms. After traversing the evanescent region, the atoms are recaptured by the optical dipole trap, now functioning as the recapturing beam. This recaptured beam, when reflected at the dielectric surface, forms a standing wave that facilitates efficient recapture.
• Figure 2: Experimental geometry of the velocity-controlled system for cold atoms using an optical dipole trap. The position of the lens, mounted on a motorized translation stage, is adjusted horizontally to control the vertical position of cold atoms confined by the moving beam. After being transported by the moving beam, the cold atoms are released and subsequently recaptured by the recapturing beam by turning on the identical beam following a designated flight time.
• Figure 3: Flight time dependence of the recaptured number of atoms. Experimental results (symbols) are compared with calculations using $C_3 = 5.6\times 10^{-49}$ Jm$^3$ (solid line) and $C_3 = 0$ (dashed line).
• Figure 4: Flight time dependence of the recaptured number of atoms. Experimental results (symbols) are compared with the calculations using $C_3 = 5.6\times 10^{-49}$ Jm$^3$ (solid line) and $C_3 = 0$ (dashed line); (a) frequency detuning $\delta = \pm 3.4$ MHz, (b) $\delta = \pm 6.7$ MHz, (c) $\delta = \pm 10.1$ MHz, and (d) $\delta = \pm 20.2$ MHz of the evanescent light.
• Figure 5: Least square errors between experiments and calculations with $C_3$. The dashed line is determined using experimental and systematic errors.