Spins under control
Extremely sensitive quantum sensors have great potential to revolutionize medical imaging, navigation and information technology. An international researcher team led by scientists from the Cluster of Excellence ct.qmat has made a breakthrough that could shorten the path to this goal greatly: The researchers have shown that spin states of atomic defects in boron nitride can be controlled at room temperature.
Boron nitride is a technologically interesting material because it forms a two-dimensional crystalline structure - similar to the “wonder material” graphene, which is used in the laboratories of quantum physicists. Boron nitride therefore opens up pathways to electronic components with completely new properties. About a year ago, the researchers of the Cluster of Excellence ct.qmat–Complexity and Topology in Quantum Matter succeeded for the first time in creating and identifying experimentally spin states in an extremely flat crystal layer of boron nitride. This time, the researchers took a next important step: they succeeded in controlling individual spin states of atomic defects in boron nitride–and that even at room temperature, without any extensive cooling. In physics, spin refers to an intrinsic angular momentum of particles.
Artificial defects in atomic lattice
Every material consists of an atomic lattice. The special feature of boron nitride is that quantum physicists can artificially create defects on the underlying atomic lattice of this material. It is these atomic "defects" that make spin states possible and which can now be manipulated under everyday conditions. Up to now, these states in boron nitride have only been controllable under ultra-low temperatures. As a basic prerequisite for cutting-edge quantum technologies, controllable spin states promise novel technical applications.
A gyroscope that rotates around its axis
“Imagine a gyroscope that rotates around its axis. We have succeeded in proving that such mini gyroscopes exist in a layer of boron nitride. And now we have shown how to control the gyroscope, i.e., for example, to deflect it by any angle without even touching it, and above all, to control this state,” Andreas Gottscholl, lead author on the paper, explains the principle of controllable spin states. “We achieved this contactless manipulation of the gyroscope through purely optical control with a pulsed alternating electromagnetic field.” The research findings were reported in the journal Science Advances. Research groups from the University of Technology Sydney in Australia and Trent University in Canada were also involved into this research.
Measuring local electromagnetic fields even more precisely
“We expect that materials with controllable spin defects will allow more precise measurements of local electromagnetic fields once they are used in a sensor", explains the head scientist from Würzburg, Prof. Vladimir Dyakonov. Conceivable areas of application are imaging in medicine, navigation, or in information technology. A magnetic resonance tomograph, for example, could scan the body much more precisely if nanoscale quantum sensors were used, Dyakonov adds.
Electronic devices with spin decorated boron nitride layers
The research team's next goal: The scientists want to realize an artificially stacked two-dimensional crystal made of different materials and electronic components. The essential building blocks for this purpose are atomically thin boron nitride layers containing optically active defects with an accessible spin state. “What is particularly appealing in our next project is to also control the spin states in the devices via electric current instead of just optically. This is completely new territory,” Dyakonov says.
Date & Facts
13 Apr 2021
Sponsors of the work
The work was funded by the German Research Foundation DFG and the Alexander von Humboldt Foundation. Vladimir Dyakonov is a Principle Investigator in the Würzburg-Dresden Cluster of Excellence ct.qmat, whose topics include the control of spin-photon interfaces in topological material systems.
Gottscholl et al., Room Temperature Coherent Control of Spin Defects in hexagonal Boron Nitride, Science Advances 2021, 7, eabf3630, DOI: 10.1126/sciadv.abf3630
Prof. Dr. Vladimir Dyakonov, Chair of Experimental Physics VI, University of Würzburg, T +49 931 31-83111, email@example.com
Image lines f.l.t.r.
Schematic representation of the coherent control of a spin defect (red) in an atomic layer of boron nitride. Boron nitride consists of boron (yellow spheres) and nitrogen (blue spheres) and lies on a stripline. The spin defect is excited by a laser and its state is read out via photoluminescence. The qubit can be manipulated both by microwave pulses (light blue) of the stripline and also by a magnetic field. (Image: Andreas Gottscholl / University of Wuerzburg)
The researchers plan to realize such a stacked structure. It consists of metallic graphene (bottom), insulating boron nitride (middle) and semiconducting molybdenum disulfide (top). The red dot symbolizes the single spin defect in one of the boron nitride layers. The defect can serve as a local probe in the stack. (Image: Andreas Gottscholl / University of Wuerzburg)