Metrology for ultra-low magnetic fields

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PTB has a long standing history in the measurement of ultra-low magnetic fields. PTB operates several magnetically shielded rooms and since 2004 the walk-in magnetically shielded room BMSR-2 with worldwide unmatched shielding features. The magnetic sensors that are operated in these rooms are home-built SQUID magnetometers with sensitivity down to the sub-femtotesla range. In addition to their expertise in magnetic metrology, the competence of the PTB staff includes manufacturing of non-magnetic setups and material characterization - an essential requirement for the practical work in ultra-low magnetism. The measurement technique of ultra-low magnetic fields is a well established tool for biosignal registration, in particular for studying brain activity by means of magnetoencephalography (MEG). In addition to this traditional application, metrology for ultra-low magnetic fields has gained increasing importance in a number of other, very different scientific fields. One of them is the characterization, quantification, and visualization of magnetic nanoparticles (MNP): indispensable information when MNP are used as a diagnostic tool in magnetic resonance and magnetic particle imaging, or as a therapeutic tool for focused cancer therapy. Yet another application has emerged by nuclear magnetic resonance in ultra-low fields. In such low fields, precession frequencies of a few Hertz open the window for the investigation of slow molecular dynamics, a domain that up to now was difficult to access for molecular physicists. Even more exciting, the precession of polarized noble gases in ultra-low fields having spin coherence times of more than 100h may serve as a probe for testing fundamental symmetries in nature. In the past, these applications were explored at PTB in collaboration with various external partners. Now the increasing number of external requests for access to our facilities of partners imposes a workload that is difficult to cope with in addition to the metrological mission of PTB. In particular there is the need for a management framework. This includes a regulation concept for managing the access to the core facility, for hands-on technical and scientific support of external scientists, as well as for the dissemination of knowledge. The advancement of magnetic measurement technique and infrastructure is an integral part of this proposal.