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arXiv · 1702.08240

Revealing the nonlinear response of a tunneling two-level system ensemble using coupled modes

Naftali Kirsh·Elisha Svetitsky·Alexander L. Burin·Moshe Schechter·Nadav Katz
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Abstract

Atomic sized two-level systems (TLSs) in amorphous dielectrics are known as a major source of loss in superconducting devices. In addition, individual TLS are known to induce large frequency shifts due to strong coupling to the devices. However, in the presence of a broad ensemble of TLSs these shifts are symmetrically canceled out and not observed in a typical single-tone spectroscopy experiment. We introduce a two-tone spectroscopy on the normal modes of a pair of coupled superconducting coplanar waveguide resonators to reveal this effect. Together with an appropriate saturation model this enables us to extract the average single-photon Rabi frequency of dominant TLSs to be $Ω_0/2π\approx 79 $ kHz. At high photon numbers we observe an enhanced frequency shift due to nonlinear kinetic inductance when using the two-tone method and estimate the value of the nonlinear coefficient as $K/2π\approx -1\times 10^{-4}$ Hz/photon. Furthermore, the life-time of each resonance can be controlled (increased) by pumping of the other mode as demonstrated both experimentally and theoretically.

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Naftali Kirsh, Elisha Svetitsky, Alexander L. Burin, Moshe Schechter, Nadav Katz. 2017-07-02. Revealing the nonlinear response of a tunneling two-level system ensemble using coupled modes. https://doi.org/10.1103/physrevmaterials.1.012601

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