Z. Pagel

Mitigating coherent leakage of superconducting qubits in a large-scale quantum socket

  1. T.G. McConkey,
  2. J.H. Béjanin,
  3. C.T. Earnest,
  4. C.R.H. McRae,
  5. Z. Pagel,
  6. J.R. Rinehart,
  7. and M. Mariantoni
A practical quantum computer requires quantum bit (qubit) operations with low error rates in extensible architectures. We study a packaging method that makes it possible to address
hundreds of superconducting qubits by means of three-dimensional wires: The large-scale quantum socket. A qubit chip is housed in a superconducting box, where both box and chip dimensions lead to unwanted modes that can interfere with qubit operations. We theoretically analyze these interference effects in the context of qubit coherent leakage. We propose two methods to mitigate the resulting errors by detuning the resonance frequency of the modes from the qubit frequency. We perform detailed electromagnetic field simulations indicating that the resonance frequency of the modes increases with the number of installed three-dimensional wires and can be engineered to be significantly higher than the highest qubit frequency. Finally, we show preliminary experimental results towards the implementation of a large-scale quantum socket.
arxiv pdf

Thermocompression Bonding Technology for Multilayer Superconducting Quantum Circuits

  1. C.R.H. McRae,
  2. J.H. Béjanin,
  3. Z. Pagel,
  4. A. O. Abdallah,
  5. T.G. McConkey,
  6. C.T. Earnest,
  7. J.R. Rinehart,
  8. and M. Mariantoni
Extensible quantum computing architectures require a large array of quantum devices operating with low error rates. A quantum processor based on superconducting quantum bits can be
scaled up by stacking microchips that each perform different computational functions. In this article, we experimentally demonstrate a thermocompression bonding technology that utilizes indium films as a welding agent to attach pairs of lithographically-patterned chips. We perform chip-to-chip indium bonding in vacuum at 190∘C with indium film thicknesses of 150nm. We characterize the dc and microwave performance of bonded devices at room and cryogenic temperatures. At 10mK, we find a dc bond resistance of 515nΩmm2. Additionally, we show minimal microwave reflections and good transmission up to 6.8GHz in a tunnel-capped, bonded device as compared to a similar uncapped device. As a proof of concept, we fabricate and measure a set of tunnel-capped superconducting resonators, demonstrating that our bonding technology can be used in quantum computing applications.
arxiv pdf