arXiv subjects

Danny O'Shea

Publications and source records attributed to Danny O'Shea.

3 recordsLinked to original sources

arXiv2014

All-optical coherent population trapping with defect spin ensembles in silicon carbide

Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions, with properties that are similar to the nitrogen-vacancy defect in diamond. We report experiments on 4H-SiC that investigate all-optical addressing of spin states with the zero-phonon-line transitions. Our magneto-spectroscopy results identify the spin $S=1$ structure of the ground and excited state, and a role for decay via intersystem crossing. We use these results for demonstrating coherent population trapping of spin states with divacancy ensembles that have particular orientations in the SiC crystal.

cond-mat.mes-hall↗

arXiv2013

Fiber-optical switch controlled by a single atom

We demonstrate highly efficient switching of optical signals between two optical fibers controlled by a single atom. The key element of our experiment is a whispering-gallery mode bottle microresonator, which is coupled to a single atom and interfaced by two tapered fiber couplers. Even in the presence of the coupling fibers, the atom--resonator system reaches the strong coupling regime of cavity quantum electrodynamics (CQED), leading to a vacuum Rabi splitting in the excitation spectrum. We systematically investigate the switching efficiency of our system, i.e., the probability that the CQED fiber-optical switch redirects the light into the desired output. We obtain a large redirection efficiency reaching a raw fidelity of more than 60% without post-selection.

quant-ph↗

arXiv2013

Strong coupling between single atoms and non-transversal photons

We investigate the interaction between single quantum emitters and non-transversally polarised photons for which the electric field vector amplitude has a significant component in the direction of propagation. Even though this situation seems to be at odds with the description of light as a transverse wave, it regularly occurs when interfacing or manipulating emitters with non-paraxial, guided, or evanescent light. Here, we couple single rubidium atoms to single photons which are confined in an optical microresonator by continuous total internal reflection. We experimentally show that the non-transversal polarisation decisively alters the physics of strong light--matter interaction. This effect has far-reaching and highly advantageous implications, which, e.g., significantly advance the field of cavity quantum electrodynamics with whispering-gallery-mode resonators. In particular, our finding allows us to experimentally realise a paradigmatic quantum system, which is ideally suited for basic studies and technological applications.

quant-ph↗