Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 48: Superconductivity: Tunnelling, Josephson Junctions, SQUIDs 2

TT 48.8: Talk

Wednesday, March 22, 2017, 17:00–17:15, HSZ 201

Finding the Location of Two-Level-Systems within the Josephson Junction of a Superconducting Qubit — •Alexander Bilmes¹, Sebastian Zanker², Andreas Heimes², Michael Marthaler², Gerd Schön², Georg Weiss¹, Alexey V. Ustinov^1,3, and Jürgen Lisenfeld¹ — ¹Physikalisches Institut, KIT, 76131 Karlsruhe, Germany — ²Institut für Theoretische Festkörperphysik, KIT, 76131 Karlsruhe, Germany — ³Russian Quantum Center, MISIS, Moscow 119049, Russia

Superconducting quantum circuits represent the first solid state quantum bits that are close to fulfilling all criteria to realize a quantum processor. However, a severe coherence-limiting factor have been Two-Level-Systems (TLS) that reside in dielectric layers such as surface-oxides and the tunnel barrier of the junction. The strong coupling of junction-hosted TLS by their electrical dipole moment to the qubit enables us to apply resonant microwave pulses to the circuit and to observe the quantum state evolution of individual TLSs, while the qubit serves for TLS-readout. Such experiments reveal microscopic properties of single TLS and offer possible clues to reduce their impact on the qubit's quality. In a recent experiment we showed that TLS couple to evanescent electronic wave-functions leaking from the junction electrodes into the dielectric: Once the superconducting system is brought out of equilibrium, the TLS' energy relaxation is enhanced by inelastic scattering of BCS-quasiparticles. We exploit this interaction scheme to estimate the TLS' position across the tunnel barrier, providing valuable information at which fabrication step TLS preferably emerge.