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Lecture Simon Gustavsson


05 July 2012 FWN-Building 5113.0201, Nijenborgh 4, 9747 AG, Groningen
Speaker: Dr. Simon Gustavsson
Affiliation: Massachusetts Institute of Technology, USA
Title: Noise spectroscopy through dynamical coupling with a superconducting flux qubit
Date: Thu Jul 5, 2012
Start: 11.00
Location: FWN-Building 5113.0201
Host: C.H. van der Wal
Telephone: +31 50 363 4975


We demonstrate dynamical decoupling in a superconducting flux qubit with a long energy-relaxation time, T1 = 12 us. Low-frequency noise acts to dephase the qubit, reducing its transverse coherence time T2. We moderate the dephasing effects of this noise by applying dynamical-decoupling sequences with up to 200 pi pulses. Using the CPMG sequence, we achieve a more than 50-fold enhanced decay time over T2*. We use the filtering property of the pulse sequence to facilitate spectroscopy of the environmental noise and reconstruct its spectral density.

We also implement similar dynamical decoupling techniques to mitigate noise in the coupling between a superconducting flux qubit and a microscopic two-level system, thereby improving the coherence time of the entangled state. The coherence is further enhanced when applying multiple refocusing pulses. The results highlight the potential of decoupling techniques for improving two-qubit gate fidelities, an essential prerequisite for implementing fault-tolerant quantum computing.

Last modified:22 October 2012 2.30 p.m.