A. A. Adamyan

Suppression of 1/f noise in solid state quantum devices by surface spin desorption

  1. S. E. de Graaf,
  2. L. Faoro,
  3. J. Burnett,
  4. A. A. Adamyan,
  5. A. Ya. Tzalenchuk,
  6. S. E. Kubatkin,
  7. T. Lindström,
  8. and A. V. Danilov
Noise and decoherence due to spurious two-level systems (TLS) located at material interfaces is a long-standing issue in solid state quantum technologies. Efforts to mitigate the effects
of TLS have been hampered by a lack of surface analysis tools sensitive enough to identify their chemical and physical nature. Here we measure the dielectric loss, frequency noise and electron spin resonance (ESR) spectrum in superconducting resonators and demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the frequency noise. We provide experimental evidence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and demonstrates their coupling via the electric-field degree of freedom to the resonator, causing dielectric (charge) noise in solid state quantum devices.
arxiv pdf

Direct identification of dilute surface spins on Al2O3: Origin of flux noise in quantum circuits

  1. S. E. de Graaf,
  2. A. A. Adamyan,
  3. T. Lindström,
  4. D. Erts,
  5. S. E. Kubatkin,
  6. A. Ya. Tzalenchuk,
  7. and A. V. Danilov
It is universally accepted that noise and decoherence affecting the performance of superconducting quantum circuits are consistent with the presence of spurious two-level systems (TLS).
In recent years bulk defects have been generally ruled out as the dominant source, and the search has focused on surfaces and interfaces. Despite a wide range of theoretical models and experimental efforts, the origin of these surface TLS still remains largely unknown, making further mitigation of TLS induced decoherence extremely challenging. Here we use a recently developed on-chip electron spin resonance (ESR) technique that allows us to detect spins with a very low surface coverage. We combine this technique with various surface treatments specifically to reveal the nature of native surface spins on Al2O3 — the mainstay of almost all solid state quantum devices. On a large number of samples we resolve three ESR peaks with the measured total paramagnetic spin density n=2.2×1017m−2, which matches the density inferred from the flux noise in SQUIDs. We show that two of these peaks originate from physisorbed atomic hydrogen which appears on the surface as a by-product of water dissociation. We suggest that the third peak is due to molecular oxygen on the Al2O3 surface captured at strong Lewis base defect sites, producing charged O−2. These results provide important information towards the origin of charge and flux noise in quantum circuits. Our findings open up a whole new approach to identification and controlled reduction of paramagnetic sources of noise in solid state quantum devices.
arxiv pdf