Kavli Affiliate: Oskar Painter
| First 5 Authors: Cliff Chen, Shahriar Aghaeimeibodi, Yuki Sato, Matthew H. Matheny, Oskar Painter
| Summary:
Two-level systems (TLS) are known to be a dominant source of dissipation and
decoherence in superconducting qubits. Superconducting resonators provide a
convenient way to study TLS-induced loss due to easier design and fabrication
in comparison to devices that include non-linear elements. However, accurately
measuring TLS-induced loss in a resonator in the quantum regime is challenging
due to low signal-to-noise ratio (SNR) and the temporal fluctuations of the
TLS, leading to uncertainties of 30% or more. To address these limitations, we
develop a multi-wave resonator device that extends the resonator length from a
standard quarter-wave $lambda/4$ to $Nlambda/4$ where $N = 37$ at 6GHz. This
design provides two key advantages: the TLS-induced fluctuations are reduced by
a factor of $sqrt{N}$ due to spatial averaging over an increased number of
independent TLS, and the measurement SNR for a given intra-resonator energy
density improves by a factor of $sqrt{N}$. The multi-wave resonator also has
fundamental and harmonic resonances that allow one to study the frequency
dependence of TLS-induced loss. In this work we fabricate both multi-wave and
quarter-wave coplanar waveguide resonators formed from thin-film aluminum on a
silicon substrate, and characterize their TLS properties at both 10mK and
200mK. Our results show that the power-dependent TLS-induced loss measured from
both types of resonators agree well, with the multi-wave resonators achieving a
five-fold reduction in measurement uncertainty due to TLS fluctuations, down to
5%. The $Nlambda/4$ resonator also provides a measure of the fully unsaturated
TLS-induced loss due to the improved measurement SNR at low intra-resonator
energy densities. Finally, measurements across seven harmonic resonances of the
$Nlambda/4$ resonator between 4GHz – 6.5GHz reveals no frequency dependence in
the TLS-induced loss over this range.
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