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Published October 3, 2016 | Submitted + Published
Journal Article Open

Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors

Abstract

We present a technique for increasing the internal quality factor of kinetic inductance detectors (KIDs) by nulling ambient magnetic fields with a properly applied magnetic field. The KIDs used in this study are made from thin-film aluminum, they are mounted inside a light-tight package made from bulk aluminum, and they are operated near 150 mK. Since the thin-film aluminum has a slightly elevated critical temperature (T_c = 1.4 K), it therefore transitions before the package (T_c = 1.2 K), which also serves as a magnetic shield. On cooldown, ambient magnetic fields as small as approximately 30 µT can produce vortices in the thin-film aluminum as it transitions because the bulk aluminum package has not yet transitioned and therefore is not yet shielding. These vortices become trapped inside the aluminum package below 1.2 K and ultimately produce low internal quality factors in the thin-film superconducting resonators. We show that by controlling the strength of the magnetic field present when the thin film transitions, we can control the internal quality factor of the resonators. We also compare the noise performance with and without vortices present, and find no evidence for excess noise beyond the increase in amplifier noise, which is expected with increasing loss.

Additional Information

© 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received 31 August 2016 Accepted 20 September 2016 Published online 03 October 2016. R.C. was both an author and the owner of STAR Cryoelectronics, where the devices used in this study were fabricated. H.M. was supported by a NASA Earth and Space Sciences Fellowship. This research was supported, in part, by a grant from the Research Initiatives for Science and Engineering program at Columbia University to B.R.J. We thank the Xilinx University Program for their donation of FPGA hardware and software tools used in the readout system.

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Submitted - 1609.06352v1.pdf

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