Photolithography-Only Fabrication of Transmons Using Double-Oblique Evaporation

  1. K. Aoyanagi,
  2. S. Abe,
  3. S. Chen,
  4. T. Inada,
  5. C. Kawai,
  6. Y. Mino,
  7. K. Nakamura,
  8. K. Nakazono,
  9. T. Nitta,
  10. and K. Watanabe
We investigate a photolithography-only fabrication process for transmon Josephson junctions using a modified double-oblique evaporation geometry. Using a bilayer resist process and
Al shadow evaporation, we fabricate junction structures and confirm by optical and scanning electron microscopy that the resulting narrowed crossing region reaches a geometrical area on the order of 104 nm2, which lies in the size range relevant to qubit junction fabrication. Room-temperature resistance screening shows that the junction resistance falls within the target range for the present transmon design over a usable process window and exhibits a clear design dependence. We further implement fabricated junctions in transmon devices and evaluate them in a three-dimensional Al cavity at 20mK, where we observe basic transmon qubit operation with f01=4.865 GHz, T1∼9μs, and T∗2∼0.4μs. These results demonstrate the feasibility of realizing functional transmon devices in a photolithography-only process using double-oblique evaporation.

Search for Dark Photon Dark Matter of a Mass around 36.1 μeV Using a Frequency-tunable Cavity Controlled through a Coupled Superconducting Qubit

  1. K. Nakazono,
  2. S. Chen,
  3. H. Fukuda,
  4. Y. Iiyama,
  5. T. Inada,
  6. T. Moroi,
  7. T. Nitta,
  8. A. Noguchi,
  9. R. Sawada,
  10. S. Shirai,
  11. T. Sichanugrist,
  12. K. Terashi,
  13. and K. Watanabe
We report the results of a search for dark photon dark matter using a cavity that employs a transmon qubit as a frequency tuning component. The tuning mechanism utilizes the energy
level shift (Lamb shift) arising from the mode mixing between the qubit and the cavity mode. This method offers several advantages: (i) it does not introduce physical thermal noise from the tuning mechanism itself, (ii) it avoids electromagnetic leakage typically associated with cavity seams, and (iii) its implementation is straightforward. We excluded the dark photon parameter region for a dark photon mass around 36.1 μeVwith a peak sensitivity of χ∼10−12 over the mass range [36.0791,36.1765] μeV, surpassing the existing cosmological bounds.