Superconducting electronics at mK temperatures

The interest in superconducting electronics working at millikelvin temperatures has increased during the past few years, and several novel devices and amplifiers utilizing mesoscopic Josephson junctions have been developed. We review the present status of a few of these devices, foremost the inductively-read superconducting Cooper pair transistor and the Bloch oscillating transistor. As a comparison, we review the status of dc SQUID devices which provide the traditional amplifier choice when approaching the standard quantum limit in ultra-sensitive measurements. In addition, we discuss a new type of current pump, the Sluice, in which modulation of Josephson energy is employed to produce large currents at high accuracy. These new developments continue the flourishing “Otaniemi tradition” in ultra-low-temperature physics and SQUID magnetometry for which Academician Olli V. Lounasmaa acted as the primus motor over three decades.