Transmission-line resonators for the study of individual two-level tunneling systems

Abstract

Parasitic two-level tunneling systems (TLS) emerge in amorphous dielectrics and constitute a serious nuisance for various microfabricated devices, where they act as a source of noise and decoherence. Here, we demonstrate a new test bed for the study of TLS in various materials which provides access to properties of individual TLS as well as their ensemble response. We terminate a superconducting transmission-line resonator with a capacitor that hosts TLS in its dielectric. By tuning TLS via applied mechanical strain, we observe the signatures of individual TLS strongly coupled to the resonator in its transmission characteristics and extract the coupling components of their dipole moments and energy relaxation rates. The strong and well-defined coupling to the TLS bath results in pronounced resonator frequency fluctuations and excess phase noise, through which we can study TLS ensemble effects such as spectral diffusion, and probe theoretical models of TLS interaction.

Fast Tunable High- Q -Factor Superconducting Microwave Resonators

“…We attribute these fluctuations in Q int to the interaction with an ensemble of charged two-level systems (TLSs), as previously reported in Ref. [37]. At high temperature or high excitation powers, the TLSs are saturated and the observed ripples are smeared.…”

Towards understanding two-level-systems in amorphous solids: insights from quantum circuits

“…This mechanism is similar to the one proposed to be responsible for qubit dissipation at elevated sample temperatures, where quasiparticles that are tunneling across a JJ can absorb energy from the qubit . The interaction of quasiparticles with single TLS in the tunnel barrier of a phase qubit was studied theoretically by Zanker et al (2016) with experiments performed by Bilmes et al (2017) as described in more detail in Sec. V.…”

“…This technique was used by Lisenfeld et al (2010a) to probe the temperature dependence of TLS energy relaxation and dephasing rates, which at elevated temperatures were found to exceed the rates due to TLS-phonon coupling. The responsible mechanism was identified by Bilmes et al (2017) to originate in the interaction of TLS with BCS quasiparticles, where TLS couple to the evanescent electronic wave function that leaks from the junction electrodes into the tunnel barrier. This work also showed that one may obtain information about the location of TLS across the tunnel barrier by injecting quasiparticles either into the junction's top or bottom electrodes, which can provide clues about the fabrication step in which TLS predominantly emerge.…”

Dynamical decoupling of quantum two-level systems by coherent multiple Landau–Zener transitions

“…In addition, our setup allows for mechanical TLS tuning by controlling the strain in the sample material with a piezo actuator [14]. Each chip contains 8 slightly different resonators that are coupled to a common transmission line, and is installed in a well-shielded and heavily filtered cryogenic setup that allows for measurements in the single-photon regime at sample temperatures of 30 mK [42]. All capacitors contain a 25-nm thick layer of amorphous AlO x that is deposited in a Plassys system by eBeam-evaporation of aluminum in a low-pressure oxygen atmosphere.…”