Dresden 2020 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 16: Poster Session Superconductivity, Cryogenic Particle Detectors, Cryotechnique

TT 16.41: Poster

Monday, March 16, 2020, 15:00–19:00, P2/EG

Investigating the Non-equilibrium Dynamics of two-level systems at Low Temperatures — •Marcel Haas, Andreas Reiser, Andreas Fleischmann, and Christian Enss — Kirchhoff Institute for Physics, Heidelberg University, 69120 Heidelberg

The dielectric loss of amorphous materials along with noise and decoherence is the major limiting factor in many applications like superconducting circuits, Josephson junctions and quantum computing. It is mainly determined by atomic tunneling systems described by quantum mechanical two-level systems (TLS) leading to a broad distribution of low-energy excitations in the sample. The spontaneous phonon emission of an excited TLS gives rise to a relaxation time T₁ and the interaction between TLSs with their thermally excited surrounding induces a dephasing timescale T₂. These effects mainly determine the measurable dielectric loss in the observed material, which we ascertain by measuring the quality factor of a bridge type superconducting LC-resonator. The dielectric medium in between the capacitor plates is a sputter deposited a-SiO₂ film. A variation of the Rabi-frequency through the electric field strength of the drive can thereby change the transition probability of the TLSs and thus the influence of loss generating effects. The experimental setup additionally allows the application of a DC to AC electric bias field across the capacitance. This enables us to manipulate the occupation difference of the TLSs by shoving new unexcited TLSs through resonance which restores the influence of decoherence. We present first measurements at a frequency of 1 GHz performed with a microfabricated superconducting resonator.