Our paper Fabrication of mirror templates in silica with micron-sized radii of curvature was published in Applied Physics Letters. Routinely, we use a laser ablation process to create mirror templates in silica, usually on flat substrates but also on the end facets of optical fibres. For cavity QED applications, the mode volume should be small. We therefore strive to make the radius of curvature as small as possible. However, while the standard process can produce radii down to 5 microns or so, there is a strong correlation between radius and depth – as the radius decreases, the depth increases – such that the smallest radii templates do not support stable cavity modes. In this paper we describe two techniques which allow shallow, small-radius mirror templates to be fabricated. The essential advantage of the laser ablation technique, the creation of super-smooth surfaces, is retained and we demonstrate stable, small-radius microcavity modes with mirror-limited finesse values up to 25,000.
Our paper entitled Decoupling a hole spin qubit from the nuclear spins was published in Nature Materials. An electron spin in a quantum dot interacts with the nuclear spins (via the hyperfine interaction) and this limits the spin dephasing times to quite modest values. What about a hole spin? Theory predicts that a heavy-hole spin decouples from the nuclear spins in an in-plane magnetic field. This is an idealized limit. How does it work out in practice? We have attempted to answer this question with an experiment: we apply an in-plane magnetic field, we measure the hole Zeeman frequency spectroscopically with an ultrahigh resolution technique (“coherent population trapping”, equivalently “dark-state spectroscopy”) and then look for changes in the hole Zeeman frequency as we polarize the nuclear spins. We tried to carry out this experiment several years ago but charge noise defeated us. Now though we have super-quiet hole devices thanks to the efforts of our partners Arne Ludwig and Andreas Wieck in Bochum and the dark-state spectroscopy works really nicely. The result? The hole spin decouples from the nuclear spins, even when we look with 10 neV resolution. The paper was featured in UniNews.