A. Di Paolo

Nanowire Superinductance Fluxonium Qubit

  1. T. M. Hazard,
  2. A. Gyenis,
  3. A. Di Paolo,
  4. A. T. Asfaw,
  5. S. A. Lyon,
  6. A. Blais,
  7. and A. A. Houck
Disordered superconducting materials provide a new capability to implement novel circuit designs due to their high kinetic inductance. Here, we realize a fluxonium qubit in which a
long NbTiN nanowire shunts a single Josephson junction. We explain the measured fluxonium energy spectrum with a nonperturbative theory accounting for the multimode structure of the device in a large frequency range. Making use of multiphoton Raman spectroscopy, we address forbidden fluxonium transitions and observe multilevel Autler-Townes splitting. Finally, we measure lifetimes of several excited states ranging from T1=620 ns to T1=20 μs, by applying consecutive π-pulses between multiple fluxonium levels. Our measurements demonstrate that NbTiN is a suitable material for novel superconducting qubit designs.
arxiv pdf

Coherence properties of the 0-π qubit

  1. Peter Groszkowski,
  2. A. Di Paolo,
  3. A. L. Grimsmo,
  4. A. Blais,
  5. D.I. Schuster,
  6. A. A. Houck,
  7. and Jens Koch
Superconducting circuits rank among the most interesting architectures for the implementation of quantum information processing devices. The recently proposed 0-π qubit [Brooks et
al., Phys. Rev. A 87, 52306 (2013)] promises increased protection from spontaneous relaxation and dephasing. In practice, this ideal behavior is only realized if the parameter dispersion among nominally identical circuit elements vanishes. In this paper we present a theoretical study of the more realistic scenario of slight variations in circuit elements. We discuss how the coupling to a spurious, low-energy mode affects the coherence properties of the 0-π device, investigate the relevant decoherence channels, and present estimates for achievable coherence times in multiple parameter regimes.
arxiv pdf