S. Wuensch

Hybrid quantum circuit with implanted erbium ions

  1. S. Probst,
  2. N. Kukharchyk,
  3. H. Rotzinger,
  4. A. Tkalcec,
  5. S. Wünsch,
  6. A. D. Wieck,
  7. M. Siegel,
  8. A. V. Ustinov,
  9. and P. A. Bushev
We report on hybrid circuit QED experiments with focused ion beam implanted Er3+ ions in Y2SiO5 coupled to an array of superconducting lumped element microwave resonators. The Y2SiO5
crystal is divided into several areas with distinct erbium doping concentrations, each coupled to a separate resonator. The coupling strength is varied from 5 MHz to 18.7 MHz, while the linewidth ranges between 50 MHz and 130 MHz. We confirm the paramagnetic properties of the implanted spin ensemble by evaluating the temperature dependence of the coupling. The efficiency of the implantation process is analyzed and the results are compared to a bulk doped Er:Y2SiO5 sample. We demonstrate the successful integration of these engineered erbium spin ensembles with superconducting circuits.
arxiv pdf

Probing the TLS Density of States in SiO Films using Superconducting Lumped Element Resonators

  1. S. T. Skacel,
  2. Ch. Kaiser,
  3. S. Wuensch,
  4. H. Rotzinger,
  5. A. Lukashenko,
  6. M. Jerger,
  7. G. Weiss,
  8. M. Siegel,
  9. and A. V. Ustinov
We have investigated dielectric losses in amorphous SiO thin films under operating conditions of superconducting qubits (mK temperatures and low microwave powers). For this purpose,
we have developed a broadband measurement setup employing multiplexed lumped element resonators using a broadband power combiner and a low-noise amplifier. The measured temperature and power dependences of the dielectric losses are in good agreement with those predicted for atomic two-level tunneling systems (TLS). By measuring the losses at different frequencies, we found that the TLS density of states is energy dependent. This had not been seen previously in loss measurements. These results contribute to a better understanding of decoherence effects in superconducting qubits and suggest a possibility to minimize TLS-related decoherence by reducing the qubit operation frequency.
arxiv pdf