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TT: Fachverband Tiefe Temperaturen
TT 16: Transport: Quantum Coherence and Quantum Information Systems – Experiments (jointly with HL, MA)
TT 16.8: Talk
Monday, March 16, 2015, 16:45–17:00, H 0110
Probing the Interaction of Microscopic Material Defects with Quasiparticles using a Superconducting Qubit — •Alexander Bilmes1, Jürgen Lisenfeld1, Andreas Heimes2, Sebastian Zanker2, Gerd Schön2, Georg Weiß1, and Alexey V. Ustinov1 — 1PI, Fakultät für Physik, KIT, Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany — 2TFP, Fakultät für Physik, KIT, Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
Two-Level-Systems (TLS) are one of the main sources of decoherence in superconducting nano-scale devices such as SQUIDs, photon detectors, 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 Josephson junction. We coherently operate individual TLS by resonant microwave pulses and access their quantum state by utilizing their strong coupling to the qubit. Our previous measurements of TLS coherence in dependence of the temperature indicate that quasiparticles may give rise to TLS energy loss and dephasing. Here, we probe the TLS-quasiparticle interaction using a reliable method of in-situ quasiparticle injection via an on-chip dc-SQUID that is pulse-biased beyond its critical current. The quasiparticle density is calibrated by measuring associated characteristic changes to the qubit’s resonance frequency and energy relaxation rate [1]. We will present experimental data that clearly show the influence of quasiparticles on TLS coherence.
[1] M. Lenander et al., Phys.Rev. B 84, 024501 (2011).