Quantum physics: Information on heat
In the past 20 years, physicists have learnt a tremendous amount about the transport of matter and energy through devices small enough for quantum effects to come into play. One surprising fact that has emerged is that the rates of transport in such devices, expressed for example by their electronic or thermal conductance, have simple quantum-mechanical limits. On page 187 of this issue, Meschke et al. extend this principle to heat conduction by photons. Although the result will certainly have practical ramifications for the engineering of ultra-sensitive detectors, sensors and microelectronic refrigerators, the physics behind it hints at more fundamental truths.