title: SQUID-based current sensing noise thermometry for quantum resistors at dilution refrigerator temperatures.
abstract: We present a dc Superconducting QUantum Interference Device (SQUID)-based current amplifier with an estimated input referred noise of only 2.3 fA/Hz. Because of such a low amplifier noise, the circuit is useful for Johnson noise thermometry of quantum resistors in the kΩ range down to mK temperatures. In particular, we demonstrate that our circuit does not contribute appreciable noise to the Johnson noise of a 3.25 kΩ resistor down to 16 mK. Our circuit is a useful alternative to the commonly used High Electron Mobility Transistor-based amplifiers, but in contrast to the latter, it offers a much reduced 1/f noise. In comparison to SQUIDs interfaced with cryogenic current comparators, our circuit has similar low noise levels, but it is easier to build and to shield from magnetic pickup.
authors.affiliation: Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Ethan
authors.initials: E
authors.lastname: Kleinbaum
authors.affiliation: Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Vidhi
authors.identifier: 0000000294971857
authors.initials: V
authors.lastname: Shingla
authors.affiliation: Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Csáthy