Karlsruhe Institute of Technology-Germany
Properties of individual 2-level defects investigated using superconducting qubits
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.  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 . 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.
*Este coloquio se llevará a cabo el jueves 3/11 a las 14 hs en el Aula de Seminarios del Dpto. de Física, 2° piso, pab. 1, Ciudad Universitaria.