μΩ-resistance tunnel junctions investigated by weak localization

We have established a method for measuring the tunneling rates between two-electron systems. This is achieved in a sandwich of two thin Mg films separated by an insulating Sb layer. The tunneling through the Sb junction couples the dephasing rates of the electrons in the Mg layers. This rate is determined by means of weak localization. One observes a splitting of the dephasing rates in analogy to the energy splitting of coupled quantum systems. Tunnel junctions with a resistance of less than 1 μΩ/${\mathrm{mm}}^2$ can be investigated by this method.