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Resonant effects in a SQUID qubit subjected to nonadiabatic changes

  • Autori: Chiarello, F.; Spilla, S.; Castellano, M.; Cosmelli, C.; Messina, A.; Migliore, R.; Napoli, A.; Torrioli, G.
  • Anno di pubblicazione: 2014
  • Tipologia: Articolo in rivista (Articolo in rivista)
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By quickly modifying the shape of the effective potential of a double SQUID flux qubit from a single well to a double well condition, we experimentally observe an anomalous behavior, namely an alternance of resonance peaks, in the probability to find the qubit in a given flux state. The occurrence of Landau-Zener transitions as well as resonant tunneling between degenerate levels in the two wells may be invoked to partially justify the experimental results. A quantum simulation of the time evolution of the system indeed suggests that the observed anomalous behavior can be imputable to quantum coherence effects. The interplay among all these mechanisms has a practical implication for quantum computing purposes, giving a direct measurement of the limits on the sweeping rates possible for a correct manipulation of the qubit state by means of fast flux pulses, avoiding transitions to non-computational states.