Seminar: Morgan Mitchell

How well does quantum mechanics allow us to know the magnetic field?

Precise measurement of magnetic fields is important to many scientific and technical fields, from brain imaging to space science. A great many magnetometer technologies have been developed for these many applications, and a great deal of effort has been put into improving their sensitivity. Curiously, completely different magnetometer technologies arrive to a similar limiting sensitivity, once magnetometer size is taken into account: larger magnetometers are more sensitive, but if you replaced a large magnetometer with many small magnetometers and averaged their signals, you would break even. Still more curiously, it is known for dc-SQUIDs (superconducting devices), rubidium optically-pumped magnetometers, and nitrogen-vacancy centers in diamond, that this limiting sensitivity (in appropriate units) is hbar, the quantum of action. This suggests that there might be some as-yet-undiscovered quantum limit to field sensing. If such a limit exists, it would be a qualitatively different limit from other, better known limits such as the standard quantum limit and the so-called “Heisenberg limit.” I will discuss our hunt for this mysterious limit, as well as our efforts to surpass the hbar limit using a spinor Bose-Einstein condensate as an extreme field sensor.

Colloquium: Quantum limits to the energy resolution of magnetic field sensors

MW Mitchell, SP Alvarez

Reviews of Modern Physics 92 (2), 021001

Single-domain Bose condensate magnetometer achieves energy resolution per bandwidth below hbar

S Palacios Alvarez, P Gomez, S Coop, R Zamora-Zamora, C Mazzinghi, ...

Proceedings of the National Academy of Sciences 119 (6), e2115339119