Title: Controlling Decoherence in Superconducting Qubits

Speaker: Dr. Lara Faoro, Department of Physics and Astronomy, Rutgers University, Department of Physics, Princeton University

Location: Building 980, Room 95 (Sandia NM)

Brief Abstract: Despite remarkable experimental breakthroughs of recent years, the realization of quantum computer using small superconducting circuits containing Josephson junctions remains far away.  Neither of these circuits in fact satisfies the stringent requirements on the amount of allowed decoherence imposed by the fault-tolerant quantum computation.  Thus, it is crucial to identify (and possibly eliminate) the microscopic origin of the noise in these devices.

It is commonly believed that the most important source of noise for superconducting qubits is the motion of charges of unknown origin in the substrate and the insulating barrier that is responsible for both the charge noise and critical current fluctuations. Recent experiments performed on SET and superconducting qubits provide an almost complete characterization of the charge and critical current power spectrum.

The talk consists of two parts. In the first one, I will briefly overview the different superconducting qubits designs and illustrate the experimental status of the art.  In the second part, I will discuss two microscopic mechanisms that might be responsible for the charge noise.  Specifically, first we consider a model of dephasing due to the environment of weakly interacting quantum TLSs and we show that such environment might provide a significant source of dephasing but the detailed characteristics of the noise power spectrum are in a qualitative and quantitative disagreement with the experimental data. Then we propose a novel microscopic mechanism of decoherence based on Kondo-like impurities and argue that within this model we can explain most features observed in the experiments.

CSRI POC: Elebeoba May, (505) 844-9933