Connor D. Shelly

Electron-beam annealing of Josephson junctions for frequency tuning of quantum processors

  1. Yashwanth Balaji,
  2. Narendra Acharya,
  3. Robert Armstrong,
  4. Kevin G. Crawford,
  5. Sergey Danilin,
  6. Thomas Dixon,
  7. Oscar W. Kennedy,
  8. Renuka Devi Pothuraju,
  9. Kowsar Shahbazi,
  10. and Connor D. Shelly
Superconducting qubits are a promising route to achieving large-scale quantum computers. A key challenge in realising large-scale superconducting quantum processors involves mitigating
frequency collisions. In this paper, we present an approach to tuning fixed-frequency qubits with the use of an electron beam to locally anneal the Josephson junction. We demonstrate the ability to both increase and decrease the junction barrier resistance. The technique shows an improvement in wafer scale frequency targetting by assessing the frequency collisions in our qubit architecture. Coherence measurements are also done to evaluate the performance before and after tuning. The tuning process utilises a standard electron beam lithography system, ensuring reproducibility and implementation by any group capable of fabricating these Josephson junctions. This technique has the potential to significantly improve the performance of large-scale quantum computing systems, thereby paving the way for the future of quantum computing.
arxiv pdf

Capturing Complex Behaviour in Josephson Travelling Wave Parametric Amplifiers

  1. Tom Dixon,
  2. Jacob W. Dunstan,
  3. George B. Long,
  4. Jonathan M. Williams,
  5. Phil J. Meeson,
  6. and Connor D. Shelly
We present an analysis of wave-mixing in recently developed Josephson Travelling Wave Parametric Amplifiers (JTWPAs). Circuit simulations performed using WRspice show the full behaviour
of the JTWPA allowing propagation of all tones. The Coupled Mode Equations (CMEs) containing only pump, signal, and idler propagation are shown to be insufficient to completely capture complex mixing behaviour in the JTWPA. Extension of the CMEs through additional state vectors in the analytic solutions allows closer agreement with WRspice. We consider an ordered framework for the systematic inclusion of extended eigenmodes and make a qualitative comparison with WRspice at each step. The agreement between the two methods validates both approaches and provides insight into the operation of the JTWPA. We show that care should be taken when using the CMEs and propose that WRspice should be used as a design tool for non-linear superconducting circuits such as the JTWPA.
arxiv pdf