Alessandro Crippa

A gate tunable transmon qubit in planar Ge

  1. Oliver Sagi,
  2. Alessandro Crippa,
  3. Marco Valentini,
  4. Marian Janik,
  5. Levon Baghumyan,
  6. Giorgio Fabris,
  7. Lucky Kapoor,
  8. Farid Hassani,
  9. Johannes Fink,
  10. Stefano Calcaterra,
  11. Daniel Chrastina,
  12. Giovanni Isella,
  13. and Georgios Katsaros
Gate-tunable transmons (gatemons) employing semiconductor Josephson junctions have recently emerged as building blocks for hybrid quantum circuits. In this study, we present a gatemon
fabricated in planar Germanium. We induce superconductivity in a two-dimensional hole gas by evaporating aluminum atop a thin spacer, which separates the superconductor from the Ge quantum well. The Josephson junction is then integrated into an Xmon circuit and capacitively coupled to a transmission line resonator. We showcase the qubit tunability in a broad frequency range with resonator and two-tone spectroscopy. Time-domain characterizations reveal energy relaxation and coherence times up to 75 ns. Our results, combined with the recent advances in the spin qubit field, pave the way towards novel hybrid and protected qubits in a group IV, CMOS-compatible material.
arxiv pdf

Evidence of Josephson coupling in a few-layer black phosphorus planar Josephson junction

  1. Francesca Telesio,
  2. Matteo Carrega,
  3. Giulio Cappelli,
  4. Andrea Iorio,
  5. Alessandro Crippa,
  6. Elia Strambini,
  7. Francesco Giazotto,
  8. Manuel Serrano-Ruiz,
  9. Maurizio Peruzzini,
  10. and Stefan Heun
Setting up strong Josephson coupling in van der Waals materials in close proximity to superconductors offers several opportunities both to inspect fundamental physics and to develop
novel cryogenic quantum technologies. Here we show evidence of Josephson coupling in a planar few-layer black Phosphorus junction. The planar geometry allows us to probe the junction behavior by means of external gates, at different carrier concentrations. Clear signatures of Josephson coupling are demonstrated by measuring supercurrent flow through the junction at milli Kelvin temperatures. Manifestation of Fraunhofer pattern with a transverse magnetic field is also reported, confirming the Josephson coupling. These findings represent the first evidence of proximity Josephson coupling in a planar junction based on a van der Waals material beyond graphene and open the way to new studies, exploiting the peculiar properties of exfoliated black phosphorus thin flakes.
arxiv pdf