A project of the Theoretical Chemical and Quantum Physics Group
Mr. Tim DuBois, Mr. Martin Cyster, Dr. Nicolas Vogt, A/Prof. Jared Cole, Prof. Salvy Russo
J. Lisenfeld, M. Marthaler, A. Ustinov: Karlsruhe Institute of Technology
C. Müller: University of Queensland
Brief Project Outline
Although superconducting devices are based on the dissipation-less properties of metals below the superconducting transition, they suffer from a fundamental drawback. The quantum effects on which these devices rely stem from Josephson junctions, which are ultra-small, ultra-thin insulating barriers. At present the best method for fabricating these junctions is to take advantage of the native amorphous oxide, which forms on many superconducting metals when exposed to oxygen. This oxide layer in turn contains defects, due to its amorphous nature, which provides a new and dominant dissipation channel. Although much is known about the effects of these defects, very little is known about their precise microscopic origins.
The TCQP group is working on this problem from several directions:
- Developing microscopic models of Josephson junctions themselves to better understand the formation of the junction and their amorphous nature.
- Developing effective models of two-level defects with the aim of comparing to microscopic parameters.
- Working with our experimental collaborators to test theoretical models and design new experiments to more accurately measure junction defects.
T. C. DuBois, S. P. Russo and J. H. Cole, Atomic delocalization as a microscopic origin of two-level defects in Josephson junctions, New Journal of Physics 17 23017 (2015)
J. Lisenfeld, G. Grabovskij, C. Muller, J. H. Cole, G. Weiss and A. V. Ustinov, Observation of directly interacting coherent two-level systems in an amorphous material, Nature Communications 6 6182 (2015)
T. C. DuBois, M. Per, S. P. Russo and J. H. Cole, Delocalized Oxygen as the Origin of Two-Level Defects in Josephson Junctions, Physical Review Letters 110 077002 (2013)
J. H. Cole, C. Müller, P. Bushev, G. J. Grabovskij, J. Lisenfeld, A. Lukashenko, A. V. Ustinov and A. Shnirman, Quantitative evaluation of defect-models in superconducting phase qubits, Appl. Phys. Lett. 97, 252501 (2010)
For more information about this project, please contact Jared Cole.