We found that GaAs surface passivation is key to minimize losses in a gated semiconductor microcavity and thus increase its quality factor by almost two orders of magnitude. The procedure not only eliminates a Franz-Keldysh-like surface loss inherent to gated semiconductor microcavities, but also mitigates the effect of surface scattering due to roughness. We elucidate these findings in our open-access publication at Physical Review Applied.
Nadine Leisgang was featured by NCCR (National Centres of Competence in Research) in their new campaign #NCCRWomen. In the video, Nadine explains a bit about her work as a physicist at the University of Basel and her motivation to do science. Congratulations!
Video here: https://www.youtube.com/watch?v=3eaSz3fry84
In our recent publication in Nature Nanotechnology we present the results of our record-breaking single photon source. The source, based on InAs quantum dots coupled in a carefully designed open-access microcavity, is able to emit up to 1 billion single photons per second with an end-to-end efficiency of 57%. Furthermore, photons present high single-photon purity (98%) and preserve high coherence (HOM visibility = 97%) in timescales of up to 1.5us. This result allows for significant improvement in quantum processing with photons. More information can be found at UniNews.
We have realized electrical tuning of the energy and the charge-state of GaAs quantum dots in AlGaAs. In contrast to previous work on the same system, the quantum dots do not suffer from a fluctuating charge-state. At the same time, we achieve linewidths that are just a few percent broader than the lifetime-limit. Our results are an important step towards connecting a quantum dot as a single-photon emitter to a rubidium memory in which quantum information can be stored. You can find our results in the open-access journal Nature Communications.
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
In our recent paper, we have shown that interlayer excitons in bilayer MoS2 exhibit both a high oscillator strength and highly tunable energies in an applied electric field. Owing to this very large tunability, we were able to optically probe the interaction between intra- and interlayer excitons as they were energetically tuned into resonance. These results have been published in Nature Nanotechnology. More details can also be read at UniNews.
Daniel Najer was one of the 5 young scientists to win the Swiss Nanotechnology PhD award. The prize is awarded by the company Bühler for Daniel’s publication on an efficient light-matter interface, coupling a semiconductor QD strongly to an optical microcavity. Congratulations!
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!
We report at AIP Advances the observation of optical Second Harmonic Generation (SHG) in Single-Layer Indium Selenide (InSe) and demonstrate that the SHG technique can also be applied to encapsulated samples to probe their crystal orientation.
Daniel Riedel has won the Swiss Nanotechnology PhD Award 2018, an award sponsored by the Hightech Zentrum Aargau. He received the award for his publication in Physical Review X on improving the quality of the photons emitted by NV centres in diamond.
Our Post-doctoral research, Tomek, has been awarded a Marie-Skłdowska-Curie Individual Fellowship!
Tomek’s project, entitled “High-Frequency Spin Entanglement Generation in Diamond” (Hi-FrED) aims at establishing the Nitrogen-Vacancy center in diamond not only as spin-coherent, but also as an optically-coherent efficient emitter of single photons.
More details about the project, starting in September 2019, can be found here.
Host: Prof. Dr. Richard J. Warburton, in collaboration with the Quantum Sensing group (prof. Patrick Maletinsky) and the Nano-phononics group (prof. Ilaria Zardo)
Fellow: Dr. Tomasz Jakubczyk
Core participants: Viktoria Yurgens, Sigurd Flågan, Brendan Shields
The ultimate goal of the project is to achieve high-frequency generation of spin-spin entanglement in spatially separated nitrogen vacancy (NV) centers in diamond. While current photon collection efficiencies (few percent) and entanglement rates (approx. one entanglement event per minute) may be sufficient for proof-of-principle experiments, they need to be greatly improved for the implementation in practical quantum networks.
The project exploits deterministic cavity-assisted enhancement of the coherent photon emission rate of NV centers embedded in a micrometer-thin diamond sample. The increase of the decay rate results in enhanced radiative efficiency and makes the emission robust against dephasing, enhancing the photon indistinguishability and boosting the photon extraction efficiency. This work helps in establishing the NV center as not only spin- but also optically- coherent.
The main experimental challenge is to eliminate the optical linewidth broadening resulting from necessary processing of the diamond crystal, even though the processing remains at a minimal level in the selected open cavity scheme. We’re examining the suitability of novel NV fabrication methods to tackle this issue. In parallel, we are examining sources of optical losses in our open cavity design and trying to eliminate them to push the performance to a new level.
In the long term, the project aims at enabling new ways of studying phenomena resulting from the enhanced light-matter coupling of the NV center and other quantum emitters. Success of this project may provide a route to the realisation of scalable quantum computers based on optical networks of electronic and nuclear spins.
-We examined the effect of a novel approach of creating NV centers in thin diamond samples, where the nitrogen is implanted after all etching processes have been completed. Results of our studies are described in Ref. .
-We achieved pulsed laser-induced and solid-immersion lens (SIL)-assisted generation of low-noise NV centers in diamond. The NV center ensemble features a distribution of zero-phonon-lines with a mean of 58 MHz and standard deviation of 19 MHz. This includes the effect of long-term spectral diffusion caused by a necessary green repump laser for charge stabilization. Such high-quality NVs are excellent candidates for practical implementations employing two-photon quantum interference with separate NV centers. We are currently working on implementing these NVs in our open microcavities.
Publications: Kasperczyk, M., Zuber, J. A., Kölbl, J., Yurgens, V., Flågan, S., Jakubczyk, T., … Warburton, R. & Maletinsky, P. (2020). Statistically Modeling Optical Linewidths of Nitrogen Vacancy Centers in Post-Implanted Nanostructures. arXiv preprint arXiv:2005.03666.
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.
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!