William Livingston

Implementation of scalable suspended superinductors

  1. Christian Jünger,
  2. Trevor Chistolini,
  3. Long B. Nguyen,
  4. Hyunseong Kim,
  5. Larry Chen,
  6. Thomas Ersevim,
  7. William Livingston,
  8. Gerwin Koolstra,
  9. David I. Santiago,
  10. and Irfan Siddiqi
Superinductors have become a crucial component in the superconducting circuit toolbox, playing a key role in the development of more robust qubits. Enhancing the performance of these
devices can be achieved by suspending the superinductors from the substrate, thereby reducing stray capacitance. Here, we present a fabrication framework for constructing superconducting circuits with suspended superinductors in planar architectures. To validate the effectiveness of this process, we systematically characterize both resonators and qubits with suspended arrays of Josephson junctions, ultimately confirming the high quality of the superinductive elements. In addition, this process is broadly compatible with other types of superinductors and circuit designs. Our results not only pave the way for scalable novel superconducting architectures but also provide the primitive for future investigation of loss mechanisms associated with the device substrate.
arxiv pdf

Optimization of infrared and magnetic shielding of superconducting TiN and Al coplanar microwave resonators

  1. John Mark Kreikebaum,
  2. Allison Dove,
  3. William Livingston,
  4. Eunseong Kim,
  5. and Irfan Siddiqi
We present a systematic study of the effects of shielding on the internal quality factors (Qi) of Al and TiN microwave resonators designed for use in quantum coherent circuits. Measurements
were performed in an adiabatic demagnetization refrigerator, where typical magnetic fields of 200 {\mu}T are present at the unshielded sample stage. Radiation shielding consisted of 100 mK and 500 mK Cu cans coated with infrared absorbing epoxy. Magnetic shields consisted of Cryoperm 10 and Sn plating of the Cu cans. A 2.7 K radiation can and coaxial thermalization filters were present in all measurements. TiN samples with Qi = 1.3∗106 at 100 mK exhibited no significant variation in quality factor when tested with limited shielding. In contrast, Al resonators showed improved Qi with successive shielding, with the largest gains obtained from the addition of the first radiation and magnetic shields and saturating before the addition of Sn plating infrared absorbing epoxy.
arxiv pdf