  Optical nanofibres are increasingly being used in cold atom experiments due
to their versatility and the clear advantages they have when developing
all-fibred systems for quantum technologies. They provide researchers with a
method of overcoming the Rayleigh range for achieving high intensities in a
focussed beam over a relatively long distance, and can act as a noninvasive
tool for probing cold atoms. In this review article, we will briefly introduce
the theory of mode propagation in an ultrathin optical fibre and highlight some
of the more significant theoretical and experimental progresses to date,
including the early work on atom probing, manipulation and trapping, the study
of atom-dielectric surface interactions, and the more recent observation of
nanofibre-mediated nonlinear optics phenomena in atomic media. The
functionality of optical nanofibres in relation to the realisation of
atom-photon hybrid quantum systems is also becoming more evident as some of the
earlier technical challenges are surpassed and, recently, several schemes to
implement optical memories have been proposed. We also discuss some possible
directions where this research field may head, in particular in relation to the
use of optical nanofibres that can support higher-order modes with an
associated orbital angular momentum.
