Thang Pham

Materials for Quantum Information Science: Roles in the Quantum Evolution 2.0

  1. Thang Pham,
  2. Vsevolod Ivanov,
  3. Dominic P. Goronzy,
  4. Abhiram Devata,
  5. Joshua Feldon,
  6. David Barton,
  7. and You Zhou
Quantum information science is entering a second phase, the Quantum Evolution 2.0, in which the challenge has shifted from demonstrating coherent control of individual quantum states
to building scalable multi-qubit processors and networks. This transition places materials science at the center of the field. Across superconducting circuits, quantum defects, quantum photonic devices, and emerging materials platforms, including two-dimensional materials and heterostructures, performance is now limited less by device design than by poorly controlled surfaces, buried interfaces, and defects whose atomic identities remain incompletely known. This review surveys the materials challenges of these quantum platforms together with the characterization methods needed to resolve them. For each platform we identify the dominant decoherence mechanisms, the current state of materials understanding, and the most pressing open materials problems. A cross-platform comparison then reveals a shared structure-coherence problem. The implicated material chemistry recurs across platforms, involving light elements in disordered or buried environments, yet no platform can quantitatively connect a specific atomic-scale structure to a measured change in coherence. We close by identifying three needs, mechanistic understanding of decoherence at the atomistic level, high-throughput proxy metrics predictive of device performance, and characterization tools built for quantum materials, whose resolution would advance coherence, scalability, and integration across all platforms.
arxiv pdf

Enhanced Superconducting Qubit Performance Through Ammonium Fluoride Etch

  1. Cameron J. Kopas,
  2. Dominic P. Goronzy,
  3. Thang Pham,
  4. Carlos G. Torres-Castanedo,
  5. Matthew Cheng,
  6. Rory Cochrane,
  7. Patrick Nast,
  8. Ella Lachman,
  9. Nikolay Z. Zhelev,
  10. Andre Vallieres,
  11. Akshay A. Murthy,
  12. Jin-su Oh,
  13. Lin Zhou,
  14. Matthew J. Kramer,
  15. Hilal Cansizoglu,
  16. Michael J. Bedzyk,
  17. Vinayak P. Dravid,
  18. Alexander Romanenko,
  19. Anna Grassellino,
  20. Josh Y. Mutus,
  21. Mark C. Hersam,
  22. and Kameshwar Yadavalli
The performance of superconducting qubits is often limited by dissipation and two-level systems (TLS) losses. The dominant sources of these losses are believed to originate from amorphous
materials and defects at interfaces and surfaces, likely as a result of fabrication processes or ambient exposure. Here, we explore a novel wet chemical surface treatment at the Josephson junction-substrate and the substrate-air interfaces by replacing a buffered oxide etch (BOE) cleaning process with one that uses hydrofluoric acid followed by aqueous ammonium fluoride. We show that the ammonium fluoride etch process results in a statistically significant improvement in median T1 by ∼22% (p=0.002), and a reduction in the number of strongly-coupled TLS in the tunable frequency range. Microwave resonator measurements on samples treated with the ammonium fluoride etch prior to niobium deposition also show ∼33% lower TLS-induced loss tangent compared to the BOE treated samples. As the chemical treatment primarily modifies the Josephson junction-substrate interface and substrate-air interface, we perform targeted chemical and structural characterizations to examine materials‘ differences at these interfaces and identify multiple microscopic changes that could contribute to decreased TLS.
arxiv pdf