Xiaohe Miao

Unraveling the role of disorderness in superconducting materials on qubit coherence

  1. Ran Gao,
  2. Feng Wu,
  3. Hantao Sun,
  4. Jianjun Chen,
  5. Hao Deng,
  6. Xizheng Ma,
  7. Xiaohe Miao,
  8. Zhijun Song,
  9. Xin Wan,
  10. Fei Wang,
  11. Tian Xia,
  12. Make Ying,
  13. Chao Zhang,
  14. Yaoyun Shi,
  15. Hui-Hai Zhao,
  16. and Chunqing Deng
Introducing disorderness in the superconducting materials has been considered promising to enhance the electromagnetic impedance and realize noise-resilient superconducting qubits.
Despite a number of pioneering implementations, the understanding of the correlation between the material disorderness and the qubit coherence is still developing. Here, we demonstrate the first and a systematic characterization of fluxonium qubits with the superinductors made from titanium-aluminum-nitride with varied disorderness. From qubit noise spectroscopy, the flux noise and the dielectric loss are extracted as a measure of the coherence properties. Our results reveal that the 1/f flux noise dominates the qubit decoherence around the flux-frustration point, strongly correlated with the material disorderness; while the dielectric loss remains low under a wide range of material properties. From the flux-noise amplitudes, the areal density (σ) of the phenomenological spin defects and material disorderness are found to be approximately correlated by σ∝ρ3xx, or effectively (kFl)−3. This work has provided new insights on the origin of decoherence channels within superconductors, and could serve as a useful guideline for material design and optimization.
arxiv pdf

Epitaxial titanium nitride microwave resonators: Structural, chemical, electrical, and microwave properties

  1. Ran Gao,
  2. Wenlong Yu,
  3. Hao Deng,
  4. Hsiang-Sheng Ku,
  5. Zhisheng Li,
  6. Minghua Wang,
  7. Xiaohe Miao,
  8. Yue Lin,
  9. and Chunqing Deng
Titanium nitride is an attractive material for a range of superconducting quantum-circuit applications owing to its low microwave losses, high surface inductance, and chemical stability.
The physical properties and device performance, nevertheless, depend strongly on the quality of the materials. Here we focus on the highly crystalline and epitaxial titanium nitride thin films deposited on sapphire substrates using magnetron sputtering at an intermediate temperature (300∘C). We perform a set of systematic and comprehensive material characterization to thoroughly understand the structural, chemical, and transport properties. Microwave losses at low temperatures are studied using patterned microwave resonators, where the best internal quality factor in the single-photon regime is measured to be 3.3×106, and >1.0×107 in the high-power regime. Adjusted with the material filling factor of the resonators, the microwave loss-tangent here compares well with the previously reported best values for superconducting resonators. This work lays the foundation of using epitaxial titanium nitride for low-loss superconducting quantum circuits.
arxiv pdf