“Our aim is to further increase the sensitivity of magnetic-field quantum sensors in order to measure smallest magnetic fields emitted by our brain. In the future, such sensors could make it possible to control exoskeletons more precisely using neural activity. The novel principle of laser threshold magnetometry with nitrogen-vacancy centers in diamond promises a significant improvement in the sensitivity of those sensors,” summarizes Hahl the aim of his research. Currently, he is continuing his work at Fraunhofer IAF in the Dr. Jan Jeske’s group Quantum Sensing.
In the final round, five candidates each presented their master’s or doctoral theses. It took place on November 24, 2023 at the Federal Ministry of Education and Research (BMBF) in Berlin and was broadcasted online via livestream. As the first-place winner in the jury ranking, Hahl will receive a study trip worth €6,000. The Audience Award is associated with a further training opportunity in the field of science communication.
First demonstration of diamond-based laser threshold magnetometry
Hahl wrote his thesis entitled “Cavity-enhanced magnetic-field sensing via stimulated emission from nitrogen-vacancy centers in diamond” (DOI: 10.6094/UNIFR/232328) between 2018 and 2022 as a doctoral student at Fraunhofer IAF. He received his doctorate from the University of Freiburg. In his work, Hahl experimentally demonstrated the principle of diamond-based laser threshold magnetometry for the first time. The approach enables highly sensitive quantum sensors that can measure the smallest magnetic fields.
The special feature compared to other approaches such as SQUIDs (superconducting quantum interference devices) and OPMs (optically pumped magnetometers) is that these sensitivities could be achieved without cryogenic cooling to -270 °C and without shielding from background magnetic fields. This promises significant savings in resources and greater suitability for everyday use.
The technology is based on nitrogen-vacancy centers (NV centers) in diamond, which is used as the laser medium in laser threshold magnetometry. NV centers absorb green light and emit red light, whereby the luminosity depends on the strength of the external magnetic field. Hahl achieved a world record: he achieved a contrast of approx. 33 % by magnetic field-dependent stimulated emission compared to 16 % with spontaneous emission.
Laser threshold magnetometer for brain-computer interfaces
One potential application that Hahl explained in his pitch is in brain-computer interfaces (BCIs). Laser threshold magnetometers are theoretically sensitive enough to measure the tiny magnetic fields that arise during brain activity. With their help, paralyzed people could gain more freedom of movement as they control exoskeletons more precisely using BCIs — even in everyday environments thanks to the specific advantages of diamond-based sensors.
Hahl is currently working in the project NeuroQ — Laser threshold magnetometer for neuronal communication interfaces, which is led by Dr. Jan Jeske at Fraunhofer IAF. Together with Charité — Universitätsmedizin Berlin, the research teams involved are working on the further development and clinical testing of laser threshold magnetometers on humans.
About the Quantum Future Award
The Quantum Future Award is presented once a year by the BMBF in the categories of master’s and doctoral theses. Theses from all areas of the natural sciences, engineering and information sciences can be submitted. They must deal with the technical exploitation of controlled quantum states (so-called second-generation quantum technologies) and must have been completed at a German university in the last four years.