Laser writing of low-charge-noise nitrogen-vacancy centers in diamond

In our recent publication in ACS Photonics, we report on the pulsed-laser-induced generation of high-quality nitrogen-vacancy (NV) centers in diamond facilitated by a solid-immersion lens (SIL). The SIL enables laser writing at energies as low as 5.8 nJ per pulse and allows vacancies to be formed close to a diamond surface without inducing surface graphitization. We present samples in which NV center arrays were laser-written across the full diamond thickness, all presenting narrow optical linewidth distributions with means down to 62.1 MHz. The linewidths include the effect of long-term spectral diffusion induced by a 532 nm repump laser for charge-state stabilization, underlining the extremely low charge-noise environment of the created color centers.

Laser writing of low-charge-noise nitrogen-vacancy centers in diamond

Tuning the polarization splitting of a microcavity with stress

In our recent open-access publication at Physical Review Applied we report a technique to control the frequency splitting of two orthogonal polarization modes in an open semiconductor microcavity. We employ the photoelastic effect by stressing uniaxially the sample and controlling the birefringence of the semiconductor crystal. The semiconductor mirror is mounted on a strain piezo, and the amount of stress is gauged by observing the emission spectrum shift of quantum dots embedded in the sample. We achieve up to 11 GHz tuning at the center of the stopband.

Tuning the polarization splitting of a microcavity with stress

Natasha Tomm wins the QCQT Excellence Award!

Natasha Tomm was one of the 3 PhD students from the QCQT PhD school to be awarded with the QCQT Excellence award. The prize is awarded by the Basel Center for Quantum Computing and Quantum Coherence in recognition of her outstanding work “A bright and fast source of coherent single photons“. Congratulations!

Read more here: https://www.quantum.unibas.ch/qcqt-phd-school/awards-support/

Natasha Tomm wins the QCQT Excellence Award!

Surface passivation of GaAs mitigates surface-related losses in a microcavity

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.

Surface passivation of GaAs mitigates surface-related losses in a microcavity

QSIT features Nadine Leisgang in #NCCRWomen 2021 campaign

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!

Read more here: https://nccr-qsit.ethz.ch/equal-opportunity/NCCRWomen_campaign.html

Video here: https://www.youtube.com/watch?v=3eaSz3fry84

 

QSIT features Nadine Leisgang in #NCCRWomen 2021 campaign

Silicon quantum dots with a self-aligned gates

In our recent publication at Applied Physics Letters we present our work on silicon-finFET quantum dots with perfectly self-aligned 2nd gate layer and gate lengths down to 15 nm. The fabrication is industry compatible and scalable and gives very high-quality devices. We observe Pauli spin blockade and extract the hole g-factor and strong spin-orbit coupling with spin-orbit length of ~50 nm, thus paving the way for scalable silicon spin qubits with fast, all-electrical control. Device fabrication and measurements were done in collaboration between IBM Zürich and University of Basel team.

Silicon quantum dots with a self-aligned gates

A record-breaking single photon source

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.

A record-breaking single photon source

Low-Noise GaAs Quantum Dots for Quantum Photonics

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.

Low-Noise GaAs Quantum Dots for Quantum Photonics

Interlayer excitons in bilayer MoS2

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.

Interlayer excitons in bilayer MoS2

Daniel Najer wins the Swiss Nanotechnology PhD award!

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!

Read more here: https://nanoscience.ch/en/2020/07/15/five-awards-for-young-scientists/ 

Daniel Najer wins the Swiss Nanotechnology PhD award!

Daniel Riedel wins PhD prize!

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.

Christian Schönenberger, Daniel Riedel and Martin Bopp (Director of the Hightech Zentrum Aargau) during the award ceremony of the Swiss Nanotechnology PhD Award (Image: Edward Byrne).

Daniel Riedel wins PhD prize!

Tomek secures Marie-Skłodowska-Curie Fellowship

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.

Tomek secures Marie-Skłodowska-Curie Fellowship

Hi-FRED Project

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.

 

 

News:

-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. [1].

-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:

[1] 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.

 

 

Hi-FRED Project

Immo secures Marie-Skłodowska-Curie Fellowship

With great pleasure we announce that Dr. Immo Söllner, postdoctoral researcher in the Nano-Photonics Group, has been awarded a Marie-Skłodowska-Curie Individual Fellowship for the project “Emitter-mediated Photon-Phonon InteraCtion (EPPIC)”. The project will focus on engineering the interaction of single seminconductor quantum dots with the phononic environment. Immo will work closely with PhDs and postdoctoral researchers at the University of Basel to carry out this project and will profit greatly from a close collaboration with European partners in Germany and Denmark. We thank the European Union for the generous support and hope that our work will help exploit the potential of quantum science!

Immo secures Marie-Skłodowska-Curie Fellowship

Andreas Kuhlmann leaves for IBM

Andreas Kuhlmann starts today at IBM, Rüshlikon in the team of Andreas Fuhrer. Andreas was RJW’s first PhD student in Basel, subsequently a post-doc in the group. We shall miss him but wish him well with his new job, incidentally a QSIT-funded project.

Andreas Kuhlmann leaves for IBM