The superconducting single-electron transistor

We report the results of an experimental study of the superconducting single electron transistor (SET) i.e. a small superconducting island weakly coupled through high resistance, low capacitance tunnel junctions to superconducting bias leads, and also capacitively coupled to a gate electrode. Due to the small capacitance of the island, at low temperatures the device behavior is dominated by single electron charging effects.; The superconductivity of both island and leads allows for a number of different charge transport mechanisms: Cooper pair tunneling, quasiparticle tunneling and Andreev reflection. A major current feature in this device is the Josephson quasiparticle (JQP) current cycle, which involves both Cooper pair and quasiparticle tunneling. We studied this current feature for samples with a range of parameters and found our data compared favorably with simulations based on a Lorentzian form for the Cooper pair tunneling rate.; The first experimental observation of Andreev reflection in the all superconducting SET is reported. The combination of Andreev reflection with Cooper pair and quasiparticle tunneling results in a large number of possible current cycles; most of these cycles were observed in our data, and confirmed by simulation. At low bias voltages in our devices, we measured many smaller current features due to higher order processes such as thermally activated and parity-effect quasiparticle tunneling, and simultaneous tunneling of a Cooper pair and quasiparticle tunneling at the two different junctions. The behavior of the superconducting SET depends on both the Josephson and charging energies. We observe experimentally that as the ratio of the Josephson energy to the charging energy increases, the effective size of the Coulomb blockade modulation in the device decreases.; Finally we describe the design and construction of a cryogenic amplifier that allows high frequency operation of the SET. This amplifier operates inside a dilution refrigerator, just centimeters from the SET. Additionally this amplifier had to have low-noise with significant gain, be broadband to time-resolve signals, and have a low output impedance. With this amplifier we were able to operate our SET at frequencies up to 1 MHz, with a charge sensitivity of ∼1.3 x 10-5 e/ Hz 100 kHz.