Cyrus F. Hirjibehedin

Demonstration of tunable three-body interactions between superconducting qubits

  1. Tim Menke,
  2. William P. Banner,
  3. Thomas R. Bergamaschi,
  4. Agustin Di Paolo,
  5. Antti Vepsäläinen,
  6. Steven J. Weber,
  7. Roni Winik,
  8. Alexander Melville,
  9. Bethany M. Niedzielski,
  10. Danna Rosenberg,
  11. Kyle Serniak,
  12. Mollie E. Schwartz,
  13. Jonilyn L. Yoder,
  14. Alán Aspuru-Guzik,
  15. Simon Gustavsson,
  16. Jeffrey A. Grover,
  17. Cyrus F. Hirjibehedin,
  18. Andrew J. Kerman,
  19. and William D. Oliver
Nonpairwise multi-qubit interactions present a useful resource for quantum information processors. Their implementation would facilitate more efficient quantum simulations of molecules
and combinatorial optimization problems, and they could simplify error suppression and error correction schemes. Here we present a superconducting circuit architecture in which a coupling module mediates 2-local and 3-local interactions between three flux qubits by design. The system Hamiltonian is estimated via multi-qubit pulse sequences that implement Ramsey-type interferometry between all neighboring excitation manifolds in the system. The 3-local interaction is coherently tunable over several MHz via the coupler flux biases and can be turned off, which is important for applications in quantum annealing, analog quantum simulation, and gate-model quantum computation.
arxiv pdf

Distinguishing multi-spin interactions from lower-order effects

  1. Thomas R. Bergamaschi,
  2. Tim Menke,
  3. William P. Banner,
  4. Agustin Di Paolo,
  5. Steven J. Weber,
  6. Cyrus F. Hirjibehedin,
  7. Andrew J. Kerman,
  8. and William D. Oliver
Multi-spin interactions can be engineered with artificial quantum spins. However, it is challenging to verify such interactions experimentally. Here we describe two methods to characterize
the n-local coupling of n spins. First, we analyze the variation of the transition energy of the static system as a function of local spin fields. Standard measurement techniques are employed to distinguish n-local interactions between up to five spins from lower-order contributions in the presence of noise and spurious fields and couplings. Second, we show a detection technique that relies on time dependent driving of the coupling term. Generalizations to larger system sizes are analyzed for both static and dynamic detection methods, and we find that the dynamic method is asymptotically optimal when increasing the system size. The proposed methods enable robust exploration of multi-spin interactions across a broad range of both coupling strengths and qubit modalities.
arxiv pdf

Characterizing and optimizing qubit coherence based on SQUID geometry

  1. Jochen Braumüller,
  2. Leon Ding,
  3. Antti Vepsäläinen,
  4. Youngkyu Sung,
  5. Morten Kjaergaard,
  6. Tim Menke,
  7. Roni Winik,
  8. David Kim,
  9. Bethany M. Niedzielski,
  10. Alexander Melville,
  11. Jonilyn L. Yoder,
  12. Cyrus F. Hirjibehedin,
  13. Terry P. Orlando,
  14. Simon Gustavsson,
  15. and William D. Oliver
The dominant source of decoherence in contemporary frequency-tunable superconducting qubits is 1/f flux noise. To understand its origin and find ways to minimize its impact, we systematically
study flux noise amplitudes in more than 50 flux qubits with varied SQUID geometry parameters and compare our results to a microscopic model of magnetic spin defects located at the interfaces surrounding the SQUID loops. Our data are in agreement with an extension of the previously proposed model, based on numerical simulations of the current distribution in the investigated SQUIDs. Our results and detailed model provide a guide for minimizing the flux noise susceptibility in future circuits.
arxiv pdf