Regensburg 2016 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 8: Transport: Quantum Coherence and Quantum Information Systems - Experiment (Joint session of HL, MA and TT, organized by TT)
HL 8.3: Vortrag
Montag, 7. März 2016, 10:15–10:30, H22
Quasiparticle-Induced Decoherence of Microscopic Two-Level-Systems in Superconducting Qubits — •Alexander Bilmes1, Jürgen Lisenfeld1, Sebastian Zanker1, Michael Marthaler2, Gerd Schön2, Georg Weiss1, and Alexey V. Ustinov1 — 1PHI, KIT, 76131 Karlsruhe, Germany — 2TFP, KIT, 76131 Karlsruhe, Germany
Parasitic Two-Level-Systems (TLS) are one of the main sources of decoherence in superconducting nano-scale devices such as SQUIDs, resonators and quantum bits (qubits), although the TLS’ microscopic nature remains unclear. We use a superconducting phase qubit to detect TLS contained within the tunnel barrier of the qubit’s Al/AlOx/Al Josephson junction. If the TLS transition frequency lies within the 6−10 GHz range, we can coherently drive it by resonant microwave pulses and access its quantum state by utilizing the strong coupling to the qubit. Our previous measurements of TLS coherence in dependence of the temperature indicate that quasiparticles (QPs), which diffuse from the superconducting Al electrodes into the oxide layer, may give rise to TLS energy loss and dephasing [1]. Here, we probe the TLS-QP interaction using a reliable method of in-situ QP injection via an on-chip dc-SQUID that is pulse-biased beyond its switching current. The QP density is calibrated by measuring associated characteristic changes to the qubit’s energy relaxation rate. We will present experimental data which show the QP-induced TLS decoherence in good agreement to theoretical predictions.
J. Lisenfeld et al., PRL 105, 230504 (2010)