Tony X. Zhou

Superconducting Flux Memory for Cryogenic Applications

  1. Tony X. Zhou,
  2. John McFarland,
  3. Aruna N. Ramanayaka,
  4. Brian Sears,
  5. Colin Stack,
  6. Aref Fouladi,
  7. Robert Smith,
  8. Sambarta Rakshit,
  9. Zachary A. Stegen,
  10. Keith D. Hillaire,
  11. Moe Khalil,
  12. Robert M. Young,
  13. David G. Ferguson,
  14. Anthony J. Przybysz,
  15. John X. Pryzbysz,
  16. Mark Covington,
  17. Gregory R Boyd,
  18. Jeremy Clark,
  19. and Aaron Pesetski
We report the development of flux memory for use with superconducting circuits. This technology stores persistent currents in superconducting loops on-chip to be used to provide flux
biasing for superconducting circuits, like qubits. We developed three types of flux memory and draw comparisons among them for circuit design. We demonstrate the utility of flux memory by using an in-situ flux detector and characterize each approach and further demonstrate that once flux is set in a memory cell, benchtop DC control sources can be powered off, leaving the on-chip flux bias in place. We propose that flux memory can be arranged in a two-dimensional configuration to multiplex control signals and reduce how line counts scale (N^2 devices -> 2N control lines), and our experimental results pave the path to the proposed scalability. We demonstrate the use of flux memory to flux bias a transmon qubit and show the tunability of the qubit state to a target frequency which remained stable on-chip for 20 hours.
arxiv pdf

Fast Microwave-free State Preparation and Measurement of Superconducting Qubits

  1. Tony X. Zhou,
  2. and et al
Fast, high-fidelity, scalable state preparation and measurement is critical to the realization of a quantum computing system. The state-of-the-art methods for preparation and readout
of superconducting qubits require finely tuned microwave signals and ~100 ns of measurement time, which are major obstacles to the scalability and performance of superconducting quantum computers. Here, we have demonstrated novel, microwave-free methods for both preparation and readout of superconducting qubits with >99% fidelity in only 10 ns for either operation while maintaining qubit coherence. This technology is compatible with scalable superconducting digital control systems, and using quantum flux parametrons for amplification, we demonstrated full quantum-to-digital conversion in only 15 ns, which is an order of magnitude faster than state-of-the-art microwave-based techniques.
arxiv pdf