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arXiv · 1203.4431

A Josephson junction defect spectrometer for measuring two-level systems

M. J. A. Stoutimore·M. S. Khalil·C. J. Lobb·K. D. Osborn
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Abstract

We have fabricated and measured Josephson junction defect spectrometers (JJDSs), which are frequency-tunable, nearly-harmonic oscillators that probe strongly-coupled two-level systems (TLSs) in the barrier of a Josephson junction (JJ). The JJDSs accommodate a wide range of junction inductances, $L_{J}$, while maintaining a resonance frequency, $f_{0}$, in the range of 4-8 GHz. By applying a magnetic flux bias to tune $f_{0}$, we detect strongly-coupled TLSs in the junction barrier as splittings in the device spectrum. JJDSs fabricated with a via-style Al/thermal AlOx/Al junction and measured at 30 mK with single-photon excitation levels show a density of TLSs in the range $σ_{TLS}h = 0.4-0.5 /GHz μm^2$, and a junction loss tangent of $\tan δ_{J} = 2.9x10^{-3}$.

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M. J. A. Stoutimore, M. S. Khalil, C. J. Lobb, K. D. Osborn. 2012-03-20. A Josephson junction defect spectrometer for measuring two-level systems. https://doi.org/10.1063/1.4744901

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