M. F. Goffman

FerBo: a noise resilient qubit hybridizing Andreev and fluxonium states

  1. J. J. Caceres,
  2. D. Sanz Marco,
  3. J. Ortuzar,
  4. E. Flurin,
  5. C. Urbina,
  6. H. Pothier,
  7. M. F. Goffman,
  8. F. J. Matute-Cañadas,
  9. and A. Levy Yeyati
We propose a novel superconducting quantum circuit that should be robust against both relaxation and dephasing over a wide and experimentally accessible parameter range. The circuit
consists of a parallel arrangement of a large inductance, a small capacitor, and a well-transmitting Josephson weak link. Protection against relaxation arises from the hybridization between the fermionic degree of freedom associated with Andreev levels in the weak link and the bosonic electromagnetic mode of the LC circuit, hence its name: FerBo. Furthermore, as in the fluxonium qubit, delocalization of the wavefunctions in phase space provides resilience against dephasing.
arxiv pdf

Circuit-QED with phase-biased Josephson weak links

  1. C. Metzger,
  2. Sunghun Park,
  3. L. Tosi,
  4. C. Janvier,
  5. A. A. Reynoso,
  6. M. F. Goffman,
  7. C. Urbina,
  8. A. Levy Yeyati,
  9. and H. Pothier
By coupling a superconducting weak link to a microwave resonator, recent experiments probed the spectrum and achieved the quantum manipulation of Andreev states in various systems.
However, the quantitative understanding of the response of the resonator to changes in the occupancy of the Andreev levels, which are of fermionic nature, is missing. Here, using Bogoliubov-de Gennes formalism to describe the weak link and a general formulation of the coupling to the resonator, we calculate the shift of the resonator frequency as a function of the levels occupancy and describe how transitions are induced by phase or electric field microwave drives. We apply this formalism to analyze recent experimental results obtained using circuit-QED techniques on superconducting atomic contacts and semiconducting nanowire Josephson junctions.
arxiv pdf

From adiabatic to dispersive readout of quantum circuits

  1. Sunghun Park,
  2. C. Metzger,
  3. L. Tosi,
  4. M. F. Goffman,
  5. C. Urbina,
  6. H. Pothier,
  7. and A. Levy Yeyati
Spectral properties of a quantum circuit are efficiently read out by monitoring the resonance frequency shift it induces in a microwave resonator coupled to it. When the two systems
are strongly detuned, theory attributes the shift to an effective resonator capacitance or inductance that depends on the quantum circuit state. At small detuning, the shift arises from the exchange of virtual photons, as described by the Jaynes-Cummings model. Here we present a theory bridging these two limits and illustrate, with several examples, its necessity for a general description of quantum circuits readout.
arxiv pdf