A single quantum dot as an optical thermometer for mK temperatures
  Resonant laser spectroscopy of a negatively charged self-assembled quantum dot is utilized to measure the temperature of a three dimensional fermionic reservoir down to 100mK. With a magnetic field applied to the quantum dot the single charged ground state is split by the Zeeman energy. As the quantum dot is in tunnel contact with a thermal electron reservoir, a thermal occupation of the quantum dot spin states is enforced by co-tunneling processes. Resonant laser induced fluorescence is used in order to measure the thermal quantum dot spin state population. 
Florian Haupt, Atac Imamoglu, Martin Kroner
cond-mat.mes-hall