Design for effective thermalization of junctions for quantum coherence

We present a design for effectively isolating low-dissipation superconducting tunnel junctions without causing excessive heating. In order to obtain a long decoherence time in macroscopic quantum coherence experiments, it will be essential to make high impedance connections to the junction. In our design, the connections are made by thin-film resistors. To prevent excessive heating, we divide the resistors into many short sections, each of which is heat-sunk to small metal banks. We rely on electron diffusion to carry the heat out of the resistors and into the banks. We calculate the resulting temperature profile in the resistors and discuss the effect on the decoherence time of the junction.