500 microkelvin nanoelectronics

Fragile quantum effects such as single electron charging in quantum dots or macroscopic coherent tunneling in superconducting junctions are the basis of modern quantum technologies. These phenomena can only be observed in devices where the characteristic spacing between energy levels exceeds the thermal energy, k(B)T, demanding effective refrigeration techniques for nanoscale electronic devices. Commercially available dilution refrigerators have enabled typical electron temperatures in the 10 to 100 mK regime, however indirect cooling of nanodevices becomes inefficient due to stray radiofrequency heating and weak thermal coupling of electrons to the device substrate. Here, we report on passing the millikelvin barrier for a nanoelectronic device. Using a combination of on-chip and off-chip nuclear refrigeration, we reach an ultimate electron temperature of T-e = 421 35 mu K and a hold time exceeding 85 h below 700 mu K measured by a self-calibrated Coulomb-blockade thermometer. p id=Par Pushing the low temperature limit of refrigerators beyond milli-kelvin regime holds the promise for new discoveries in the nano-electronic devices. Here, Sarsby et al. achieve 500 micro-kelvin electron temperature using combined on-chip and off-chip nuclear refrigeration techniques.