Nermin Trnjanin

Kerr nonlinearity and three-wave mixing in superconducting resonators hosting Al-InAs weak links

  1. Vittorio Buccheri,
  2. Ivo P. C. Cools,
  3. Nermin Trnjanin,
  4. Ankit Khola,
  5. Oleg Shvetsov,
  6. Thomas Kanne,
  7. Jesper Nygård,
  8. Attila Geresdi,
  9. and Simone Gasparinetti
Nonlinear microwave resonators are a versatile tool in quantum information processing, enabling parametric amplification, continuous variable quantum computing, and engineered mode
interactions. Many of these applications especially benefit from cubic nonlinearities enabling three-wave mixing; at the same time, they are limited by quartic nonlinearities giving rise to undesired Kerr effects. A recurrent challenge is therefore to engineer resonators with a finite cubic nonlinearity while suppressing quartic terms. Here, we investigate a superconducting resonator hosting two weak links fabricated from an aluminum-capped indium arsenide nanowire. We characterize the Kerr nonlinearity as a function of magnetic flux and gate bias, showing that it can be tuned to zero with either control parameter. Furthermore, we experimentally demonstrate three-wave mixing in a semiconductor-superconductor hybrid device, establishing nonzero cubic nonlinearity. An effective model based on Andreev bound states qualitatively captures the observed trends. Our results validate semiconductor-superconductor hybrid devices as a promising platform for tunable nonlinear superconducting circuits, with applications in parametric amplification, quantum control of bosonic modes, and engineering interactions between microwave modes.
arxiv pdf

Electrical post-fabrication tuning of aluminum Josephson junctions at room temperature

  1. Christian Križan,
  2. Maurizio Toselli,
  3. Irshad Ahmad,
  4. Hadi Khaksaran,
  5. Marcus Rommel,
  6. Nermin Trnjanin,
  7. Janka Biznárová,
  8. Mamta Dahiya,
  9. Emil Hogedal,
  10. Halldór Jakobsson,
  11. Andreas Nylander,
  12. Jonas Bylander,
  13. Per Delsing,
  14. and Giovanna Tancredi
Josephson junctions are a key element of superconducting quantum technology, serving as the core building blocks of superconducting qubits. We present an experimental study on room-temperature
electrical tuning of aluminum junctions, showing that voltage pulses can controllably increase their resistance and adjust the Josephson energy while maintaining qubit quality factors above 1 million. We find that the rate of resistance increase scales exponentially with pulse amplitude during manipulation, after which the spontaneous resistance increase scales proportionally to the amount of manipulation. We show that this spontaneous increase halts at cryogenic temperatures, and resumes again at room temperature. Using our stepwise protocol, we achieve up to a 270% increase in junction resistance, corresponding to a reduction of nearly 2 GHz of the qubit transition frequency. These results establish the achievable range, relaxation behavior, and practical limits of electrical tuning, enabling post-fabrication mitigation of frequency crowding in quantum processors.
arxiv pdf