Tiantian Wang

Selective-Area-Grown PbTe-Pb Planar Josephson Junctions for Quantum Devices

  1. Ruidong Li,
  2. Wenyu Song,
  3. Wentao Miao,
  4. Zehao Yu,
  5. Zhaoyu Wang,
  6. Shuai Yang,
  7. Yichun Gao,
  8. Yuhao Wang,
  9. Fangting Chen,
  10. Zuhan Geng,
  11. Lining Yang,
  12. Jiaye Xu,
  13. Xiao Feng,
  14. Tiantian Wang,
  15. Yunyi Zang,
  16. Lin Li,
  17. Runan Shang,
  18. Qi-Kun Xue,
  19. Ke He,
  20. and Hao Zhang
Planar Josephson junctions are predicted to host Majorana zero modes. The material platforms in previous studies are two dimensional electron gases (InAs, InSb, InAsSb and HgTe) coupled
to a superconductor such as Al or Nb. Here, we introduce a new material platform for planar JJs, the PbTe-Pb hybrid. The semiconductor, PbTe, was grown as a thin film via selective area epitaxy. The Josephson junction was defined by a shadow wall during the deposition of the superconductor Pb. Scanning transmission electron microscopy reveals a sharp semiconductor-superconductor interface. Gate-tunable supercurrent and multiple Andreev reflections are observed. A perpendicular magnetic field causes interference patterns of the switching current, exhibiting Fraunhofer-like and SQUID-like behaviors. We further demonstrate a prototype device for Majorana detection, wherein phase bias and tunneling spectroscopy are applicable.
arxiv pdf

Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas

  1. Lucas Casparis,
  2. Malcolm R. Connolly,
  3. Morten Kjaergaard,
  4. Natalie J. Pearson,
  5. Anders Kringhøj,
  6. Thorvald W. Larsen,
  7. Ferdinand Kuemmeth,
  8. Tiantian Wang,
  9. Candice Thomas,
  10. Sergei Gronin,
  11. Geoffrey C. Gardner,
  12. Michael J. Manfra,
  13. Charles M. Marcus,
  14. and Karl D. Petersson
The coherent tunnelling of Cooper pairs across Josephson junctions (JJs) generates a nonlinear inductance that is used extensively in quantum information processors based on superconducting
circuits, from setting qubit transition frequencies and interqubit coupling strengths, to the gain of parametric amplifiers for quantum-limited readout. The inductance is either set by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by parallelizing multiple JJs in superconducting quantum interference devices (SQUIDs) with local current-biased flux lines. JJs based on superconductor-semiconductor hybrids represent a tantalizing all-electric alternative. The gatemon is a recently developed transmon variant which employs locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control. Here, we go beyond proof-of-concept and demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a suitable platform for building a scalable gatemon-based quantum computer. We show 2DEG gatemons meet the requirements by performing voltage-controlled single qubit rotations and two-qubit swap operations. We measure qubit coherence times up to ~2 us, limited by dielectric loss in the 2DEG host substrate.
arxiv pdf