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Over the years, the coherence of superconducting qubits has been significantly improved, so that at present they reach quality factors in excess of 10^6. Further improvements in coherence would help reducing the overhead necessary for implementing quantum error correction algorithms; therefore, despite the past successes, it is still necessary to investigate decoherence processes and to devise ways to suppress them. Since the early years of superconducting qubits, quasiparticles have been recognized as a possible source of decoherence. I will briefly review the history of quasiparticle effects in qubits, both in theory and experiments. Interestingly, the qubit sensitivity to quasiparticles makes it possible to measure their dynamics. I will discuss ways to control this dynamics, so that the detrimental effects of quasiparticles can be minimized. Finally, I will discuss some recent findings hinting at possible origins of quasiparticles.

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Gianluigi Catelani, FZ Juelich
Seminar Room of the Institute of theoretical Physics (old building)
Contact: Y. Ando