Our laboratory is located in the Department of Physics of the University of Basel in Switzerland. Our research is centered around the emerging field of "Quantum sensing", where the use of individual, well-controlled quantum systems as high-performance sensing devices is being explored. We concentrate on implementing various types of such sensors and on applying them to outstanding scientific tasks in mesoscopic physics, nano-science and technology. At the moment, our quantum system of choice for these purposes is the Nitrogen-Vacancy (NV) color center in diamond, whose exceptional quantum-coherent properties allow for high-performance sensing applications (such as single-electron spin detection) even at room temperature.
Magnetic imaging using color centers in diamond through both scanning and wide-field methods offers a combination of unique capabilities for studying superconductivity, for example, enabling accurate vector magnetometry at high temperature or high pressure, with spatial resolution down to the nanometer scale. The paper briefly reviews various experimental modalities in this rapidly developing nascent field and provides an outlook towards possible future directions.
For the first time, we were able to study quantum interference in a three-level quantum system and thereby control the behavior of individual electron spins. To this end, we used a novel nanostructure, in which a quantum system is integrated into a nanoscale mechanical oscillator in form of a diamond cantilever.
Dominik's and Lucas' paper entitled "Real-space probing of the local magnetic response of thin-film superconductors using single spin magnetometry" reports on direct, real-space imaging of the stray magnetic field above a micro-scale disc of a thin film of the high-temperature superconductor YBa2Cu3O7−δ (YBCO) using scanning single spin magnetometry. Our experiments yield a direct measurement of the sample's local London penetration depth and allow for a quantitative reconstruction of the supercurrents flowing in the sample as a result of Meissner screening. These results show the potential of scanning single spin magnetometry for studies of the nanoscale magnetic properties of thin-film superconductors, which could be readily extended to elevated temperatures or magnetic fields.
Patrick's and Brendan's paper entitled "Nanomagnetism of magnetoelectric granular thin-film antiferromagnets" was posted on ArXiv. Since experimental tools to explore antiferromagnetic films on the nanoscale are still sparse, we offer a solution to this technological bottleneck, by addressing the ubiquitous surface magnetisation of magnetoelectic antiferromagnets in a granular thin film sample on the nanoscale using single-spin magnetometry in combination with spin-sensitive transport experiments. Specifically, we quantitatively image the evolution of individual nanoscale antiferromagnetic domains in 200-nm thin-films of Cr2O3 in real space and across the paramagnet-to-antiferromagnet phase transition. These experiments allow us to discern key properties of the Cr2O3 thin film, including the mechanism of domain formation and the strength of exchange coupling between individual grains comprising the film. Our work offers novel insights into Cr2O3's magnetic ordering mechanism and establishes single spin magnetometry as a novel, widely applicable tool for nanoscale addressing of antiferromagnetic thin films.
Patrick Appel and Arne Barfuss successfully defended their PhD thesis. Great job!!!
In collaboration with the group of V. Jacques and the CNRS Thales we were able to demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature and manipulate the cycloid propagation direction by an electric field. These results demonstrate how our material of choice can be used in the design of reconfigurable nanoscale spin textures.
Daniels's paper "Deterministic enhancement of coherent photon generation from a nitrogen-vacancy center in ultrapure diamond" was published in PRX. We couple NV centers to a tunable microcavity and significantly enhance their photonic properties: i.e. we demonstrate an increase of the phonon-free emission--which is required for entanglement swapping schemes--from 4% to close to 50%. By making a step-change in the NV's optical properties in a deterministic way, these results pave the way for much enhanced spin-photon and spin-spin entanglement rates.