Arne Barfuss

Strain coupling of a nitrogen-vacancy center spin to a diamond mechanical oscillator.

We report on single electronic spins coupled to the motion of mechanical resonators by a novel mechanism based on crystal strain. Our device consists of single-crystalline diamond cantilevers with embedded Nitrogen-Vacancy center spins. Using optically detected electron spin resonance, we determine the unknown spin-strain coupling constants and demonstrate that our system resides well within the resolved sideband regime. We realize coupling strengths exceeding ten MHz under mechanical driving and show that our system has the potential to reach strong coupling. Our novel hybrid system forms a resource for future experiments on spin-based cantilever cooling and coherent spin-oscillator coupling.

Strong mechanical driving of a single electron spin

The efficient and robust manipulation of single spins is an essential requirement for successful quantum devices. The manipulation of a single nitrogen–vacancy spin centre is now demonstrated by means of a mechanical resonator approach.

Elemental topological insulator with tunable Fermi level: strained α-Sn on InSb(001).

We report on the epitaxial fabrication and electronic properties of a topological phase in strained α-Sn on InSb. The topological surface state forms in the presence of an unusual band order not based on direct spin-orbit coupling, as shown in density functional and GW slab-layer calculations. Angle-resolved photoemission including spin detection probes experimentally how the topological spin-polarized state emerges from the second bulk valence band. Moreover, we demonstrate the precise control of the Fermi level by dopants.

Fabrication of all diamond scanning probes for nanoscale magnetometry

The electronic spin of the nitrogen vacancy (NV) center in diamond forms an atomically sized, highly sensitive sensor for magnetic fields. To harness the full potential of individual NV centers for sensing with high sensitivity and nanoscale spatial resolution, NV centers have to be incorporated into scanning probe structures enabling controlled scanning in close proximity to the sample surface. Here, we present an optimized procedure to fabricate single-crystal, all-diamond scanning probes starting from commercially available diamond and show a highly efficient and robust approach for integrating these devices in a generic atomic force microscope. Our scanning probes consisting of a scanning nanopillar (200 nm diameter, 1-2 μm length) on a thin (<1 μm) cantilever structure enable efficient light extraction from diamond in combination with a high magnetic field sensitivity (ηAC≈50±20nT/Hz). As a first application of our scanning probes, we image the magnetic stray field of a single Ni nanorod. We show that this stray field can be approximated by a single dipole and estimate the NV-to-sample distance to a few tens of nanometer, which sets the achievable resolution of our scanning probes.

Phase-controlled coherent dynamics of a single spin under closed-contour interaction

In three-level quantum systems, interference between two simultaneously driven excitation pathways can give rise to effects such as coherent population trapping1,2 and electromagnetically induced transparency3. The possibility to exploit these effects has made three-level systems a cornerstone of quantum optics. Coherent driving of the third available transition forms a closed-contour interaction (CCI), which yields fundamentally new phenomena, including phase-controlled coherent population trapping4,5 and phase-controlled coherent population dynamics6. Despite attractive prospects, prevalent dephasing in experimental systems suitable for CCI driving has made its observation elusive7–10. Here, we exploit recently developed methods for coherent manipulation of nitrogen–vacancy electronic spins to implement and study highly coherent CCI driving of a single spin. Our experiments reveal phase-controlled quantum interference, reminiscent of electron dynamics on a closed loop threaded by a magnetic flux, which we synthesize from the driving-field phase11. Owing to the nature of the dressed states created under CCI, we achieve nearly two orders of magnitude improvement of the dephasing times, even for moderate drive strengths. CCI driving constitutes a novel approach to coherent control of few-level systems, with potential for applications in quantum sensing or quantum information processing.Coherent driving of all transitions of a three-level system generates a closed-contour interaction, which is here shown to create efficient manipulation methods for electronic spins in nitrogen–vacancy centres in diamond.

Advanced Fabrication of Single-Crystal Diamond Membranes for Quantum Technologies

Many promising applications of single crystal diamond and its color centers as sensor platform and in photonics require free-standing membranes with a thickness ranging from several micrometers to the few 100 nm range. In this work, we present an approach to conveniently fabricate such thin membranes with up to about one millimeter in size. We use commercially available diamond plates (thickness 50 μm) in an inductively coupled reactive ion etching process which is based on argon, oxygen and SF6. We thus avoid using toxic, corrosive feed gases and add an alternative to previously presented recipes involving chlorine-based etching steps. Our membranes are smooth (RMS roughness <1 nm) and show moderate thickness variation (central part: <1 μm over ≈200 × 200 μm2). Due to an improved etch mask geometry, our membranes stay reliably attached to the diamond plate in our chlorine-based as well as SF6-based processes. Our results thus open the route towards higher reliability in diamond device fabrication and up-scaling.