This tool provides scanning cryogenic thermal sensing that is 4 orders of magnitude more sensitive than previous devices allowing the detection of a sub 1 μK temperature difference. Furthermore, it is non-contact and non-invasive and allows thermal imaging of very low intensity, nanoscale energy dissipation down to the fundamental Landauer limit of 40 femtowatts for continuous readout of a single qubit at one gigahertz at 4.2 kelvin.