Scaleinvariant spin dynamics and the quantum limits of field sensing
Abstract
We describe quantum limits to field sensing that relate noise, geometry and measurement duration to fundamental constants, with no reference to particle number. We cast the Tesche and Clarke (TC) bound on dcSQUID sensitivity as such a limit, and find analogous limits for volumetric spinprecession magnetometers. We describe how randomlyarrayed spins, coupled to an external magnetic field of interest and to each other by the magnetic dipoledipole interaction, execute a spin dynamics that depolarizes the spin ensemble even in the absence of coupling to an external reservoir. We show the resulting spin dynamics are scale invariant, with a depolarization rate proportional to spin number density and thus a numberindependent quantum limit on the energy resolution per bandwidth E_{R}. Numerically, we find E_{R} ⩾ αℏ, α ∼ 1, in agreement with the TC limit, for paradigmatic spinbased measurements of static and oscillating magnetic fields.
 Publication:

New Journal of Physics
 Pub Date:
 May 2020
 DOI:
 10.1088/13672630/ab81b8
 arXiv:
 arXiv:1904.01528
 Bibcode:
 2020NJPh...22e3041M
 Keywords:

 quantum sensing;
 quantum limits of measurement;
 magnetometry;
 spin precession;
 Quantum Physics
 EPrint:
 14 pages, 4 figures, 56 references