While homo sapiens may not be able to detect magnetic fields, as “homo technicus”, human beings make use of a wide variety of technical sensors. Quantum effects are increasingly being exploited to collect information unavailable by conventional means – for example, in order to detect magnetic fields in living organisms or to use such fields for medical imaging purposes.
- Medical imaging: In order to peer inside human beings (without having to cut them open), medicine has developed an arsenal of methods. One way to obtain an image from within is to measure the very weak magnetic fields produced by our brain when thinking – or by our beating heart. Sensors that are highly sensitive to such weak magnetic fields exploit quantum effects such as superconductivity.
- Medical biomarkers: In some cases, medicine must send in “spies” to find out what is happening inside. For example, the path of nanoparticles introduced into a patient’s body can be followed by means of certain particle properties such as magnetism.
- Quantum communication: Highly sensitive magnetic-field sensors can also be used outside of medicine. For example, single photons can be detected by means of these sensors – an important prerequisite for fundamental research as well as for applications of quantum communication.
To detect very weak magnetic fields, superconducting quantum interference devices (SQUIDs) are especially well suited for use as highly sensitive sensors. This special form of quantum technology, together with its requisite cryotechnology, has enjoyed top-caliber development and manufacturing and been used for measurement at PTB for some time now. For example, SQUID magnetometers have been used for several years to measure the tiny magnetic fields generated by the neural activity of the human brain. PTB is an international leader in both the manufacture of such SQUIDs (via superconductor thin-film technology) and the measurement technology based on them. At PTB, SQUID technology is complemented by so-called optically pumped magnetometers (OPMs) for which nuclear spins are “read out” by means of laser light and which – in contrast to SQUIDs – do not require cooling to low temperatures (approximately that of liquid helium).
Magnetic fields in living organisms are so small that the Earth’s magnetic field and the magnetic fields of our electrified world are gigantic by comparison. Therefore, PTB conducts its biomagnetic reference measurements, which are performed before real-life medical applications take place, in a specially shielded room, which is the “magnetically quietest place in the world” (Berlin Magnetically Shielded Room, BMSR). This facility and its associated equipment are also open to external partner institutions from industry and research.