Chi Zhang

Investigation of coherence of niobium-based resonators enabled by a fast-sealing microwave cavity

  1. Chi Zhang,
  2. Richard Germond,
  3. Noah Janzen,
  4. Anne-Marie Valente-Feliciano,
  5. Mustafa Bal,
  6. and Adrian Lupascu
Resonators and qubits with a niobium (Nb) base metal layer achieve some of the highest coherence times in superconducting quantum devices. The performance of such devices is often limited
by loss associated with two-level systems, which are found primarily at material surfaces and interfaces. The metal-air (MA) interface is a major contributor to device loss. In this work, we develop a fast-sealing microwave cavity that enables devices to be placed under vacuum within five minutes of oxide removal, thereby significantly reducing the MA interface loss compared to common device processing and packaging approaches. Using coplanar stripline resonators, we demonstrate that devices sealed in such a cavity exhibit internal quality factors exceeding one million at single-photon power. After re-exposure to air, the devices show downward resonance frequency shifts and quality factor degradations, quantitatively consistent with a model of Nb oxide regrowth. The fast-sealing microwave cavity provides a practical and consistent method to mitigate MA interface loss and sustain high coherence in Nb devices, and establishes a controlled platform for studying metal oxide regrowth kinetics and dielectric properties, the understanding of which is critical to achieving high coherence in superconducting quantum devices.
arxiv pdf

Experimental Implementation of Short-Path Non-adiabatic Geometric Gates in a Superconducting Circuit

  1. Xin-Xin Yang,
  2. Liang-Liang Guo,
  3. Hai-Feng Zhang,
  4. Lei Du,
  5. Chi Zhang,
  6. Hao-Ran Tao,
  7. Yong Chen,
  8. Peng Duan,
  9. Zhi-Long Jia,
  10. Wei-Cheng Kong,
  11. and Guo-Ping Guo
The non-adiabatic geometric quantum computation (NGQC) has attracted a lot of attention for noise-resilient quantum control. However, previous implementations of NGQC require long evolution
paths that make them more vulnerable to incoherent errors than their dynamical this http URL this work, we experimentally realize a universal short-path non-adiabatic geometric gate set (SPNGQC) with a 2-times shorter evolution path on a superconducting quantum processor. Characterizing with both quantum process tomography and randomized benchmarking methods, we report an average single-qubit gate fidelity of 99.86% and a two-qubit gate fidelity of 97.9%. Additionally, we demonstrate superior robustness of single-qubit SP-NGQC gate to Rabi frequency error in some certain parameter space by comparing their performance to those of the dynamical gates and the former NGQC gates.
arxiv pdf