Controlling electron and phonon heat fluxes in suspended semiconductor-superconductor junctions

For scalable solid-state quantum technologies, there appears to be no alternative to the sub-1 K temperature operation, and it is evident that the required low-temperature infrastructure has been an obstacle for development of... [ view full abstract ]

For scalable solid-state quantum technologies, there appears to be no alternative to the sub-1 K temperature operation, and it is evident that the required low-temperature infrastructure has been an obstacle for development of quantum devices. Although maintenance-free turn-key dry dilution refrigerators are now available, using large refrigerators limits the application only to large facilities such as future quantum data centres.

To solve this problem, we have developed thermoelectrically cooled solid state mK-platform for quantum devices. The platform is a mm-scale silicon sub-chip (Fig. 1) that is suspended by micron scale superconductive tunnel junctions. The interfacial thermal boundary resistance, due to the acoustic phonon mismatch between the superconductor and the sub-chip, provides phonon isolation for the platform. The superconducting energy gap and tunnel barrier enables cooling of the platform by quasi-particle filtering [1]. Here we utilize semiconductor-superconductor (Si-Al) tunnel junction [2] and so far we have demonstrated refrigeration of the platform by 40 % from bath temperature of 170 mK. This novel cooling effect against phonon transmission is in strong contrast to previous works where electronic refrigeration has been limited by electron-phonon coupling of cold finger.    

We have simulated that the platform can be improved by sophisticated material and phonon engineering and multistage cascade structure to enable cooling even from 1.5 K to below 100 mK. This would be a highly cost effective method, both economically and in energy, to reach low temperatures with potential to bring quantum technologies to tabletop pulse tube refrigerators. Furthermore, the platform is a useful test bench for nanoscale heat transport.

References:

[1] J. Muhonen, M. Meschke, J. Pekola, Rep. Progr. Phys. 75, 046501 (2012).

[2] D. Gunnarsson el al., Sci. Rep. 5, 17398 (2015).