We have achieved large-range frequency tuning of a single-photon emitter, a GaAs quantum dot in a bulk sample. The total tuning range is three orders of magnitude large than the quantum dot’s linewidth, which remains narrow throughout the entire tuning process. Our results are an important step towards building a hybrid system connecting a single-photon emitter to a rubidium quantum memory. You find our work published in Applied Physics Letters

.

We report a radiative Auger process for a trion in a semiconductor quantum dot. The process allows us to measure the quantum mechanical energy separations and the carrier dynamics in the quantum dot. The results have been published in Nature Nanotechnology.

Our work reporting evidence of a first-order magnetic phase transition in a gated two-dimensional semiconductor, monolayer-MoS₂, has been published in Physical Review Letters.

We report cavity-enhanced Raman scattering on diamond, in particular its use in aligning our tunable microcavities.

A coherent exchange of a single energy quantum between an “atom” (in our case a gated InAs quantum dot) and an optical cavity has been reported by our group in Nature. We achieve an atom-cavity Cooperativity of 150, and probe the transitions between singly and doubly excited photon-atom system using photon-statistics spectroscopy.

In our recent paper, we have shown that several optical properties of a quantum dot are correlated with the area of the so-called Voronoi cell surrounding it. In the image below, the Voronoi-diagram is shown in red for a few tens of quantum dots. The quantum dot positions are indicated as black dots.

We have recently shown that InGaAs quantum dots can be grown without conduction band states of the so-called wetting layer. This work is the result of a collaboration with the Ruhr Universität Bochum and the Forschungszentrum Jülich. In the picture below, you see a transmission electron microscopy image of a quantum dot grown with the new technique.

We report a spontaneous polarisation in a gated monolayer of MoS₂: our paper has just appeared in Nature Nanotechnology!

Our paper on imaging single quantum dots has appeared in Nature Photonics. The paper describes how rapid adiabatic passage on a two-level system can be exploited as an on-off switch. This non-linearity enables imaging the quantum dot with a resolution much less than that of a confocal microscope: 30 nm (λ/31) was achieved in this experiment.

Left: image of quantum dots in a semiconductor recorded with a confocal microscope operating close to the diffraction limit. Right: image of the same quantum dots using the switching protocol based on rapid adiabatic passage.

Our paper Narrow optical linewidths and spin pumping on charge-tunable close-to-surface self-assembled quantum dots in an ultrathin diode has been published in Physical Review B. The paper is part of a successful collaboration with our partners at the Ruhr Universität Bochum and the University of Copenhagen. In this work, InGaAs self-assembled quantum dots are embedded into an ultrathin p-i-n-i-n diode structure allowing for the deterministic charging of the quantum dots in the Coulomb blockade regime. The bias voltages, and thus tunnelling currents, can be kept very small, a particular advantage of the p-i-n-i-n diode. These excellent electrical properties allowed us to demonstrate narrow optical linewidths as well as optical spin pumping on single quantum dots in this ultrathin diode structure. The structure is fully compatible with the fabrication of photonic crystals. At least the editor seems to like it: the work was highlighted as an “Editor’s Suggestion”, as was another paper (Indistinguishable and efficient single photons from a quantum dot in a planar nanobeam waveguide) just recently published as part of this collaboration!

The flux of coherent photons emitted by single NV centres in diamond is very low on account of three problems: (i) only a small percentage are emitted into the zero-phonon-line (ZPL); (ii) the extraction efficiency out of the high-index diamond host is small; and (iii) the radiative lifetime is large. All three problems can be solved by embedding a single NV centre into a high-Q-factor, low mode-volume microcavity tuned to the ZPL. In our paper just published in Physical Review X, we show that this concept can be implemented using a tunable, highly-miniaturised microcavity. The ZPL fraction increases from ∼3% to close to 50%.

Schematic of a diamond membrane embedded in a highly miniaturised Fabry-Perot cavity

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.