Hi-FrED project

Individual Fellowship in the frame of Marie Skłodowska-Curie Actions founded by the European Commission

Fellow: Dr. Tomasz Jakubczyk

Host: Prof. Dr. Richard J. Warburton, in collaboration with the Quantum Sensing group (prof. Patrick Maletinsky) and the Nano-phononics group (prof. Ilaria Zardo)

Core collaborators: 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.


June 2021
Our paper about low-charge-noise nitrogen-vacancy centers in diamond created using laser writing with a solid-immersion lens is out:

May 2021
Sigurd's paper on https://arxiv.org/pdf/2105.08736.pdf is on arXiv:

April 2020
To create NVs for our project we employed the newly developed femtosecond laser-assisted creation of NV centers (Chen et al. Nat. Photonics11, 77–80) and upgraded it by implementing a solid immersion lens in the process. 

After installation of a new setup and establishing fabrication procedures, we succeeded in fabricating NV centers with unprecedented quality. Their zero-phonon line spectral linewidth, which is the key parameter determining suitability for applications of NV centers as sources of quantum light has a statistical distribution peaking at a record-low value of around 60 MHz. This includes the effect of long-term spectral diffusion induced by a 532 repump laser for charge state stabilization. About 95% of NVs feature a linewidth below 100 MHz, which is an excellent result not only when compared to NVs created with implantation, but also when comparing to all other fabrication methods. The SIL allowed for vacancy formation close to a diamond surface without inducing surface graphitization.

Such high-quality NVs are excellent candidates for practical implementations employing two-photon quantum interference with separate NV centers.  

January 2020
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 here. Among other resutlts described in the paper we observed two narrow (< 250MHz) optical linewidths in the 1.57 µm-thick area of a sample created with this method. 

Confocal scan of laser-written NV centers

Zero-ohonon line optical linewidth statistical distribution in the presence of 532 nm repump laser 

Zero-phonon line power broadening in NV centers

Zero-phonon line power broadening in NV centers

Confocal scan of diamond platelets with binary identification markings

Photoluminescence tomography of laser-written NV centers, with surface and bulk created NVs