Investigation of a $^{85}$Rb Dark Magneto-Optical Trap using an Optical Nanofibre

TL;DR

This paper demonstrates a dark magneto-optical trap of rubidium-85 atoms using an optical nanofibre, enabling efficient atom detection and providing insights into atom loading dynamics, which advances cold atom research and nanofibre-based sensing.

Contribution

It introduces a novel method of using an optical nanofibre to create and probe a dark MOT of rubidium-85 atoms, with detailed analysis of atom populations and loading rates.

Findings

Fractional population in bright state as low as 0.04

Loading rate dependence on laser intensity studied

Potential for nanofibre-based atomic sensing demonstrated

Abstract

We report here measurements on a dark magneto-optical trap (DMOT) of $^{85}$Rb atoms using an optical nanofibre (ONF) with a waist of $\sim$~1 $\mu$m. The DMOT is created using a doughnut-shaped repump beam along with a depump beam for efficient transfer of cold atoms from the bright hyperfine ground state ($F=3$) into the dark hyperfine ground state ($F=2$). The fluorescence from the cold $^{85}$Rb atoms of the DMOT is detected by coupling it into the fibre-guided modes of the ONF. The measured fractional population of cold atoms in the bright hyperfine ground state ($p$) is as low as $\sim$0.04. The dependence of loading rate of DMOT on cooling laser intensity is investigated and also compared with the loading rate of a bright-MOT (BMOT). This work lays the foundation for the use of an ONF for probing of a small number of atoms in an optically-dense cold atomic cloud.