Superconducting Qubit Quasiparticle Dynamics and Mitigation

My doctoral research investigates nonequilibrium quasiparticles in superconducting quantum devices: how they enter a circuit, how they become trapped or released, how they appear in microwave measurements, and how device design can reduce their contribution to decoherence.

Experimental work

I design, fabricate, package, and measure superconducting resonators and qubit-scale devices in dilution refrigerators. This includes nanobridge-SQUID resonators with features down to 15 nm, custom microwave packages and printed circuit boards, cryogenic RF chains, and automated acquisition and analysis software.

I developed and validated a nanobridge fabrication process that increased functional-device yield from under 2% to over 90%. I also built a hidden-Markov-model pipeline that infers real-time quasiparticle occupation from I/Q measurement trajectories, allowing trapping and release dynamics to be estimated from experimental data.

Current work includes Andreev-bound-state spectroscopy and nanoSQUID-based quasiparticle traps aimed at characterizing and mitigating quasiparticle-induced loss in superconducting circuits.

Publications

Electron-phonon interactions in the Andreev bound states of aluminum nanobridge Josephson junctions, Physical Review B (2023). (Farmer et al., 2023)
Quasiparticle Dynamics in Epitaxial Al-In-As Planar Josephson Junctions, PRX Quantum (2023). (Elfeky et al., 2023)
Related device-design and simulation work appears in SQuADDS.

References

2023

Phys. Rev. B

Electron-phonon interactions in the Andreev bound states of aluminum nanobridge Josephson junctions

James T. Farmer, Azarin Zarassi , Sadman Ahmed Shanto, Darian Hartsell, and Eli M. Levenson-Falk

Phys. Rev. B, Apr 2023

DOI Bib HTML PDF

@article{PhysRevB.107.L140506,
  title = {Electron-phonon interactions in the Andreev bound states of aluminum nanobridge Josephson junctions},
  author = {Farmer, James T. and Zarassi, Azarin and Shanto, Sadman Ahmed and Hartsell, Darian and Levenson-Falk, Eli M.},
  journal = {Phys. Rev. B},
  volume = {107},
  issue = {14},
  pages = {L140506},
  numpages = {7},
  year = {2023},
  month = apr,
  publisher = {American Physical Society},
  doi = {10.1103/PhysRevB.107.L140506},
  url = {https://link.aps.org/doi/10.1103/PhysRevB.107.L140506},
  eprint = {2211.16765},
  archiveprefix = {arXiv},
  primaryclass = {quant-ph},
}

PRX Quantum

Quasiparticle Dynamics in Epitaxial Al-In-As Planar Josephson Junctions

Bassel Heiba Elfeky, William M. Strickland, Jaewoo Lee, James T. Farmer , Sadman Ahmed Shanto, Azarin Zarassi, Dylan Langone, Maxim G. Vavilov, Eli M. Levenson-Falk, and Javad Shabani

PRX Quantum, Sep 2023

DOI Bib HTML PDF

@article{Elfeky2023quasiparticledynamics,
  title = {Quasiparticle Dynamics in Epitaxial Al-In-As Planar Josephson Junctions},
  author = {Elfeky, Bassel Heiba and Strickland, William M. and Lee, Jaewoo and Farmer, James T. and Shanto, Sadman Ahmed and Zarassi, Azarin and Langone, Dylan and Vavilov, Maxim G. and Levenson-Falk, Eli M. and Shabani, Javad},
  journal = {PRX Quantum},
  volume = {4},
  issue = {3},
  pages = {030339},
  numpages = {19},
  year = {2023},
  month = sep,
  publisher = {American Physical Society},
  doi = {10.1103/PRXQuantum.4.030339},
  eprint = {2303.04784},
  archiveprefix = {arXiv},
  primaryclass = {cond-mat.mes-hall},
  url = {https://doi.org/10.1103/PRXQuantum.4.030339},
}