[quantum-info] IQC/Physics special Seminar Thursday Feb 27 1:00 pm

Matthew Fries mfries at uwaterloo.ca
Wed Feb 26 14:30:13 EST 2014


Seminar

Institute for Quantum Computing/Physics

Thursday, 27 February 2014 at 1:00PM

QNC 1102

Quasiparticle effects in superconducting qubits

Gianluigi Catelani

Peter Grünberg Institute, Germany

Superconducting qubits based on Josephson junctions are a promising platform for quantum computation, reaching quality factors of over one million. Such high quality factors enable the investigation of decoherence mechanisms with high accuracy. An intrinsic decoherence process originates from the coupling between the qubit degree of freedom and the quasiparticles that tunnel across Josephson junctions. In this talk I will review the general theory of quasiparticle effects, valid both for equilibrium and non-equilibrium quasiparticles [1-3]. In a transmon qubit, tunnelling of a single quasiparticle is associated with a change in parity; I will discuss the theory of the parity switching rate in single-junction transmons [4], compare it with recent measurements [5], and comment on the implications for the dephasing rate. In qubits that can be tuned by magnetic flux, such as the ³split² transmon and the fluxonium, the quasiparticle-induced decoherence rate depends on the flux; as experimentally shown in fluxonium [6], this provides a way to differentiate quasiparticle tunnelling from other sources of decoherence.
[1] G. Catelani, J. Koch, L. Frunzio, R. J. Schoelkopf, M. H. Devoret, and L. I. Glazman, Phys. Rev. Lett. 106, 077002 (2011) [2] G. Catelani, R. J. Schoelkopf, M. H. Devoret, and L. I. Glazman, Phys. Rev. B 84, 064517 (2011) [3] G. Catelani, S. E. Nigg, S. M. Girvin, R. J. Schoelkopf, and L. I. Glazman, Phys. Rev. B 86, 184514 (2012) [4] G. Catelani (unpublished, arXiv:1401.5575) [5] D. Ristè, C. C. Bultnik, M. J. Tiggelman, R. N. Schouten, K. W. Lehnert, and L. DiCarlo, Nature Communications 4, 1913 (2013) [6] I. M. Pop, K. Geerlings, G. Catelani, R. J. Schoelkopf, L. I. Glazman, and M. H. Devoret (Nature, to appear)



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