Michele Piscitelli

Characterization of Nanostructural Imperfections in Superconducting Quantum Circuits

  1. Mohammed Alghadeer,
  2. Simone D. Fasciati,
  3. Shuxiang Cao,
  4. Michele Piscitelli,
  5. Susannah C Speller,
  6. Peter J. Leek,
  7. and Mustafa Bakr
Decoherence in superconducting quantum circuits, caused by loss mechanisms like material imperfections and two-level system (TLS) defects, remains a major obstacle to improving the
performance of quantum devices. In this work, we present atomic-level characterization of cross-sections of a Josephson junction and a spiral resonator to assess the quality of critical interfaces. Employing scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) and electron-energy loss spectroscopy (EELS), we identify structural imperfections associated with oxide layer formation and carbon-based contamination, and correlate these imperfections to the pattering and etching steps in the fabrication process and environmental exposure. These results help to understand that TLS imperfections at critical interfaces play a key role in limiting device performance, emphasizing the need for an improved fabrication process.
arxiv pdf

Multiplexed Readout of Superconducting Qubits Using a 3D Re-entrant Cavity Filter

  1. Mustafa Bakr,
  2. Simone D. Fasciati,
  3. Shuxiang Cao,
  4. Giulio Campanaro,
  5. James Wills,
  6. Mohammed Alghadeer,
  7. Michele Piscitelli,
  8. Boris Shteynas,
  9. Vivek Chidambaram,
  10. and Peter J. Leek
Hardware efficient methods for high fidelity quantum state measurements are crucial for superconducting qubit experiments, as qubit numbers grow and feedback and state reset begin to
be employed for quantum error correction. We present a 3D re-entrant cavity filter designed for frequency-multiplexed readout of superconducting qubits. The cavity filter is situated out of the plane of the qubit circuit and capacitively couples to an array of on-chip readout resonators in a manner that can scale to large qubit arrays. The re-entrant cavity functions as a large-linewidth bandpass filter with intrinsic Purcell filtering. We demonstrate the concept with a four-qubit multiplexed device.
arxiv pdf