Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 35: Postersession Transport: Nanoelectronics, Quantum Coherence and Quantum Information, Fluctuations and Noise

TT 35.28: Poster

Wednesday, March 25, 2009, 14:00–18:00, P1A

Noise Measurements of Cryogenic Amplifiers for Qubit Experiments — •Christian Schwemmer¹, Tobias Wirth¹, Alexander Lukashenko¹, Jürgen Lisenfeld¹, Michael Mück², and Alexey Ustinov¹ — ¹Physikalisches Institut, Universität Karlsruhe (TH), Germany — ²Institut für Angewandte Physik der Justus-Liebig Universität Giessen, Germany

Ultra-low noise cryogenic amplifiers are a prerequisite for a variety of readout schemes of qubits based on Josephson junctions. Evaluation of the noise temperature of cryogenic amplifiers is an essential task for achieving high sensitivity and lowest back action. We developed a cryogenic noise source based on a 50 Ohm load located in vacuum with variable temperature between 8 K and 60 K. By measuring the output power of a cryogenic low noise HEMT-amplifier at different temperatures of the load using a standard spectrum analyzer we determine the amplification and the noise temperature of the amplifier. The advantage of our method compared to the conventional noise diode switching technique is that in our approach the noise source is heated up continuously providing many data points and thus offering better resolution. In our ongoing measurements we are using this approach to measure the noise temperature and amplification of microstrip SQUID amplifiers operated at 4.2 K.