GERD SCHOEN - Properties of individual 2-level defects investigated using superconducting qubits

• Coloquios

Gerd Schön.

Karlsruhe Institute of Technology, Germany.

Jueves 3/11/2016, 14 hs. 

Aula Seminario, 2do piso, Pabellón I. 

Recent progress with microfabricated quantum devices has revealed that an ubiquitous source of noise originates from parasitic two-level systems (TLSs). For superconducting qubits, TLSs residing on surfaces or in tunnel junctions account for a major part of dephasing and thus pose a roadblock to the realization of solid-state quantum processors. Recent experiments of Lisenfeld et al. [1] demonstrated that it is possible to utilize a superconducting qubit to explore the quantum state evolution of such high-frequency TLSs. We found that a major source of dephasing of the probed high-frequency TLSs is their interaction with thermal, low-frequency TLSs [2]. The so-called standard model of TLS  is sufficient to quantitatively explain the Ramsey-type experiments. The effect of low-frequency TLSs is efficiently reduced by spin-echo techniques. The remaining dephasing observed in the echo protocol is due to further noise sources with a more white spectrum.

[1] Decoherence spectroscopy with individual two-level tunneling defects. Lisenfeld, A. Bilmes, S. Matityahu, S. Zanker, M. Marthaler, M. Schechter, G. Schön, A. Shnirman , G. Weiss and A.V. Ustinov, Sci. Rep.  6, 23786 (2016).

[2] Decoherence of a quantum two-level system by spectral diffusion. Matityahu, A. Shnirman , G. Schön and M. Schechter, Phys. Rev. B   93, 134208 (2016).