Probing the density of states of two-level tunneling systems in silicon oxide films using superconducting lumped element resonators

• Published in: Applied physics letters 2015-01, Vol.106 (2)
• Main Authors: Skacel, S. T., Kaiser, Ch, Wuensch, S., Rotzinger, H., Lukashenko, A., Jerger, M., Weiss, G., Siegel, M., Ustinov, A. V.
• Format: Article
• Language: English
• Subjects: Amorphous silicon; AMPLIFIERS; Applied physics; Broadband; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DENSITY OF STATES; Dielectric loss; DIELECTRIC MATERIALS; ENERGY DEPENDENCE; MICROWAVE RADIATION; NOISE; OPERATION; Oxide coatings; Power combiners; PROBES; Quantum theory; QUBITS; RESONATORS; SILICON OXIDES; SUPERCONDUCTIVITY; THIN FILMS; TUNNEL EFFECT
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4905149

We have investigated dielectric losses in amorphous silicon oxide (a-SiO) thin films under operating conditions of superconducting qubits (mK temperatures and low microwave powers). For this purpose, we have developed a broadband measurement setup employing multiplexed lumped element resonators using a broadband power combiner and a low-noise amplifier. The measured temperature and power dependences of the dielectric losses are in good agreement with those predicted for atomic two-level tunneling systems (TLS). By measuring the losses at different frequencies, we found that the TLS density of states is energy dependent. This had not been seen previously in loss measurements. These results contribute to a better understanding of decoherence effects in superconducting qubits and suggest a possibility to minimize TLS-related decoherence by reducing the qubit operation frequency.