  Motivated by the recent development of fast and ultra-sensitive thermometry
in nanoscale systems, we investigate quantum calorimetric detection of
individual heat pulses in the sub-meV energy range. We propose a hybrid
superconducting injector-calorimeter set-up, with the energy of injected pulses
carried by tunneling electrons. Treating all heat transfer events
microscopically, we analyse the statistics of the calorimeter temperature
fluctuations and derive conditions for an accurate measurement of the heat
pulse energies. Our results pave the way for novel, fundamental quantum
thermodynamics experiments, including calorimetric detection of single
microwave photons.
