Magnetic Resonance Force Microscopy of paramagnetic electron spins at millikelvin temperatures

摘要

Magnetic Resonance Force Microscopy (MRFM) is a powerful technique to detecta small number of spins that relies on force-detection by an ultrasoftmagnetically tipped cantilever and selective magnetic resonance manipulation ofthe spins. MRFM would greatly benefit from ultralow temperature operation,because of lower thermomechanical noise and increased thermal spinpolarization. Here, we demonstrate MRFM operation at temperatures as low as 30mK, thanks to a recently developed SQUID-based cantilever detection techniquewhich avoids cantilever overheating. In our experiment, we detect dangling bondparamagnetic centers on a silicon surface down to millikelvin temperatures.Fluctuations of such kind of defects are supposedly linked to 1/f magneticnoise and decoherence in SQUIDs as well as in several superconducting andsingle spin qubits. We find evidence that spin diffusion plays a key role inthe low temperature spin dynamics.