Sub-Kelvin optical thermometry of an electron reservoir coupled to a   self-assembled InGaAs quantum dot
  We show how resonant laser spectroscopy of the trion optical transitions in a self-assembled quantum dot can be used to determine the temperature of a nearby electron reservoir. At finite magnetic field the spin-state occupation of the Zeeman-split quantum dot electron ground states is governed by thermalization with the electron reservoir via co-tunneling. With resonant spectroscopy of the corresponding excited trion states we map out the spin occupation as a function of magnetic field to establish optical thermometry for the electron reservoir. We demonstrate the implementation of the technique in the sub-Kelvin temperature range where it is most sensitive, and where the electron temperature is not necessarily given by the cryostat base temperature. 
F. Seilmeier, M. Hauck, E. Schubert, G. J. Schinner, S. E. Beavan and   A. H\"ogele
cond-mat.mes-hall physics.optics