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Low-temperature defects in quantum-regime superconducting devices

May 9, 2011 - 12:30pm
Speaker: 
Kevin Osborn
Institution: 
Laboratory for Physical Sciences

Amorphous dielectrics have long been known to have low-temperature properties dictated by two-level system (TLS) defects which can be inferred from a tunneling-system model. These defects lead to absorption and dispersion of electromagnetic and acoustic waves. Modern superconducting resonators used for single-photon detection in astronomy and superconducting qubits and resonators in quantum computing are at milli-Kelvin temperatures and operate at multi-GHz photon frequencies, such that they can operate in the quantum regime. These devices exhibit deleterious phenomena which are very often attributed to TLS defects, and here I will present two new experiments which study relevant defects. In the first experiment, the defects of amorphous silicon nitride are studied and are found to differ from those described by a standard TLS model. In particular, we see evidence for TLS-TLS interactions which lower the loss at below 70 mK due to interactions. By turning on a dc electric field of up to 300 mV /nm, we see temporal changes in these interactions. In the second experiment, TLS defects within the aluminum oxide barrier of a Josephson junction are observed with a new frequency-tunable resonator circuit. This device is a convenient strong-coupling probe of TLS defects in Josephson junctions and will allow for rapid testing of new Josephson junction barrier materials for qubits in the near future.

1201 Physics Building
College Park, MD 20742

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