Experimental implementation of an NMR NOON state thermometer

Abstract

Utilizing the highly correlated quantum NOON states of spins, we have implemented a proof-of-principle quantum thermometer using the NMR technique for measuring the variation of local magnetic field with the temperature. The system used was the star topology system of hexafluorophosphate molecules, and the thermometer showed a sensitivity of $$85\,\mathrm{nT}/^\circ $$ C. Using the hexafluorophosphate and the trimethylphosphite spin systems, we have quantified the advantage of the quantum protocol over the classical one for measuring magnetic field. The quantum protocol showed the best performance for the sensing time of $$T_\mathrm{max} = 20\,$$ ms, where the errors in the measurement scaled as the Heisenberg limit 1 / N. The thermometer implementation provided measurements in the temperature with errors scaling approximately with the Heisenberg limit, more precisely $$N^{-0.94}$$ .