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This Week at Physics

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Event Number 3277

  Thursday, April 3rd, 2014

R. G. Herb Condensed Matter Seminar
Measuring topological transitions in superconducting qubits
Time: 10:00 am
Place: Chamberlin 5310
Speaker: Michael Kolodrubetz, Boston University
Abstract: The field of topological insulators sprung from the realization that in the presence of spin-orbit coupling, non-interacting electrons can have a band structure that non-trivially wraps the first Brillouin zone. From the gauge-invariant Berry curvature that locally defines the geometry of this wrapping, one can define an integer topological invariant – the Chern number – from which all other invariants derive. We investigate the Berry curvature and Chern number of an even simpler case: single and double spin-1/2 systems (qubits) in a rotating magnetic field. We show that these simple systems undergo topological transitions of their Chern number, which for the case of the single qubit can be directly mapped to the topological transitions of the Haldane model of graphene. Furthermore, we experimentally demonstrate such a topological transition in a single superconducting qubit, measuring the Berry curvature as a leading order correction to linear response. We then generalize the methods to two-qubit systems, where we experimentally measure the topological phase diagram and demonstrate interaction-driven topological transitions.
Host: Vavilov
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