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TT: Fachverband Tiefe Temperaturen

TT 7: Superconductivity: Cryodetectors

TT 7.8: Topical Talk

Montag, 31. März 2014, 11:30–12:00, HSZ 03

Probing Decoherence in Atomic-Sized Defects Using a Superconducting Qubit — •Jürgen Lisenfeld, Georg Weiss, and Alexey V. Ustinov — Physikalisches Institut, Karlsruhe Institute for Technology (KIT), Karlsruhe, Germany

Advances in nanotechnology lay the ground for a thriving variety of novel devices suitable to explore new realms of quantum phenomena on the mesoscopic scale. Superconducting quantum bits, as an example, have reached very long coherence times by designs that weaken their undesired coupling to environmental degrees of freedom. One particular problem are parasitic Two-level systems (TLS), reported to cause noise in single-photon detectors, SETs, SQUIDs, and microwave- as well as nano-mechanical resonators, although their physical origin remains in dispute.

A particular strong coupling between superconducting qubits and TLS occurs when they reside in the tunnel barrier of Josephson junctions, and this renders qubits ideal tools for the study of single material defects in the coherent regime. Here, we use a phase qubit to directly manipulate and readout the TLS quantum state. We tune TLS properties by the applied mechanical strain and perform high-resolution defect spectroscopy to obtain their distribution and to reveal mutual TLS coupling. By analyzing their coherent dynamics, we utilize single microscopic defects as quantum spectrum analyzers that provide a view into their environment. These new techniques grant multifaceted insights into the TLS nature, which is a prerequisite for avoiding their detrimental effects in nanoscale devices.