What are quantum sensors – and where can they be used?

Munich, 01 October 2024

Tiny, sensitive – and somewhat mysterious: quantum sensors enable high-precision measurements. New applications are becoming possible, for example in the measurement of brain waves to control prostheses or in the measurement of the Earth’s gravitational field to explore mineral resources. At acatech on Tuesday, 24 September, experts discussed with the audience the advantages of quantum sensor technology compared to conventional systems, the state of research in Germany compared to other countries as well as current developments.

acatech member Artur Zrenner from the University of Paderborn stated in his introduction that quantum sensors are already being used in various areas: as sensors for magnetic fields and electric fields, as sensors for motion and for gravity in modern atomic clocks. The advantages of quantum sensors over conventional sensors lie in particular in their maximum precision and sensitivity in the high dynamic range. In addition, quantum sensors are often characterised by their freedom from drift, meaning that the sensor only needs to be calibrated or readjusted once, which is invaluable for many applications. One example is the gyroscope, a device that can measure or maintain rotational movements. According to Artur Zrenner, a researcher at the Centre for Optoelectronics and Photonics and spokesperson for the acatech Nano and Quantum Technologies Network, we are all already benefiting from quantum sensor technology on a daily basis. He cited navigation via GPS and medical imaging diagnostics using MRI (magnetic resonance imaging) as examples.

Overview and application examples of quantum sensors

acatech member Tommaso Calarco, Forschungszentrum Jülich GmbH and Peter Grünberg Institute, began his presentation by describing the first and second ‘quantum revolution’. The first was set in motion over 60 years ago by the invention of the first laser and brought quantum mechanics into real applications – today, telecommunications applications, medical treatments and barcode scanners can no longer do without the achievements of that time. While the first quantum revolution utilised effects that act on a large number of particles, for example in a laser or in a nuclear magnetic resonance tomograph, the second quantum revolution is aimed at manipulating individual quantum particles such as atoms or photons. Here. potential applications can be found in the field of medical imaging, navigation or geodesy. As a concrete example, Tommaso Calarco cited a commercially available quantum gravimeter already in use, which is installed to monitor volcanic activity on Mount Etna and thus enables more precise predictions of possible eruptions.

Possible applications of quantum sensors with laser-cooled atoms

Using the example of gravimeters and acceleration sensors, Tanja E. Mehlstäubler, PTB Braunschweig and Leibniz Universität Hannover, explained how quantum sensors with laser-cooled atoms work. Among other things, gravimeters can measure changes in the groundwater level – which is an important application in view of the increasingly drastic water shortages in various regions of the world. Large-scale measurements by gravimeter-equipped aeroplanes or satellites are a unique method of showing the regional drop in groundwater levels and monitoring the global water balance.

As a second application example, the physicist described atomic clocks based on stored ions, which are already being manufactured industrially. These enable, for example, high-precision satellite-based navigation or high-precision measurement of the earth, which allows the monitoring of minimal geological changes, such as the melting of glaciers and the associated movements of mountain ranges.

Nuclear spin-based quantum gyroscopes for applications in space

Janine Riedrich-Möller, from the Microsensor Systems division at Robert Bosch GmbH, explained the functional principle of the quantum gyroscope developed by her working group, which is based on measuring the frequency of the gyroscopic motion of an atomic nucleus (the so-called nuclear spin). When the sensor is rotated externally, the measured frequency changes. The external rotation can be derived from this change.

As measuring system, Xenon and rubidium atoms are used, which are enclosed in a miniaturised vapour cell manufactured using MEMS technology (‘Micro-Electro-Mechanical Systems’) and magnetically shielded to prevent interference, and are optically excited and read out using a laser.

Applications for these high-precision and drift-free gyroscopes can be found in satellites, for example. To this end, a multi-year research project involving several companies and research institutes is currently being pursued. The project is due to conclude with a test in orbit.