Electrical noise is the ultimate limiting factor in many sensitive measurements and applications. Our magnetic sensors measure magnetic flux and consequently are affected by magnetic flux noise. This flux noise appears to be universal and affects the ultimate sensitivity of our sensors, the dephasing rates of donor atoms in silicon, and the coherence time of quantum computers. We find that the origin of this noise may be magnetic spins on the surface of metallic and insulating thin films. Measurements with our scanning SQUID show a paramagnetic response with a temperature dependence that indicates unpaired spins are the origin, and that these spins are even more ubiquitous than previously thought.

The top image shows and scanning electron micrograph of gold structures. The bottom image shows the magnetic response of the same region where brighter color represents a stronger magnetic signal.

Hendrik Bluhm, Julie A. Bert, Nicholas C. Koshnick, Martin E. Huber, and Kathryn A. Moler, Physical Review Letters 103 026805 (2009). Full Text