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A current measuring system capable of detecting single ions is described. The detector operates at a frequency of nominally 900 kHz and utilizes a superconducting inductor with high Q(Q≊8500) and a cryogenic GaAs field-effect transistor (FET) amplifier with noise temperature less than 0.3 K. Noise measurements of the FET are presented along with details of the construction of the superconducting inductor.
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Jefferts et al. (1993) studied this question.
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