Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 16: Transport: Quantum coherence and quantum information systems - Experiments (TT with HL)

HL 16.8: Vortrag

Montag, 16. März 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).