  Colloidal Quantum dots (CQDs) are nowadays one of the cornerstones of modern
photonics as they have led to the emergence of new optoelectronic and
biomedical technologies. However, the full characterization of these quantum
emitters is currently restricted to the visible wavelengths and it remains a
key challenge to optically probe single CQDs operating in the infrared spectral
domain which is targeted by a growing number of applications. Here, we report
the first experimental detection and imaging at room temperature of single
infrared CQDs operating at telecommunication wavelengths. Imaging was done with
a doubly resonant bowtie nano-aperture antenna (BNA) written at the end of a
fiber nanoprobe, whose resonances spectrally fit the CQD absorption and
emission wavelengths. Direct near-field characterization of PbS CQDs reveal
individual nanocrystals with a spatial resolution of 75 nm (lambda/20) together
with their intrinsic 2D dipolar free-space emission properties and exciton
dynamics (blinking phenomenon). Because the doubly resonant BNA is strongly
transmissive at both the CQD absorption and emission wavelengths, we are able
to perform all-fiber nano-imaging with a standard 20 % efficiency InGaAs
avalanche photodiode (APD). Detection efficiency is predicted to be 3000 fold
larger than with a conventional circular aperture tip of the same transmission
area. Double resonance BNA fiber probes thus offer the possibility of exploring
extreme light-matter interaction in low band gap CQDs with current
plug-and-play detection techniques, opening up new avenues in the fields of
infrared light emitting devices, photodetectors, telecommunications,
bio-imaging and quantum information technology.
