Steven M. Disseler

Demonstration of long-range correlations via susceptibility measurements in a one-dimensional superconducting Josephson spin chain

  1. Daniel M. Tennant,
  2. Xi Dai,
  3. Antonio J. Martinez,
  4. Robbyn Trappen,
  5. Denis Melanson,
  6. M. A. Yurtalan,
  7. Yongchao Tang,
  8. Salil Bedkihal,
  9. Rui Yang,
  10. Sergei Novikov,
  11. Jeffery A. Grover,
  12. Steven M. Disseler,
  13. James I. Basham,
  14. Rabindra Das,
  15. David K. Kim,
  16. Alexander J. Melville,
  17. Bethany M. Niedzielski,
  18. Steven J. Weber,
  19. Jonilyn L. Yoder,
  20. Andrew J. Kerman,
  21. Evgeny Mozgunov,
  22. Daniel A. Lidar,
  23. and Adrian Lupascu
Spin chains have long been considered an effective medium for long-range interactions, entanglement generation, and quantum state transfer. In this work, we explore the properties of
a spin chain implemented with superconducting flux circuits, designed to act as a connectivity medium between two superconducting qubits. The susceptibility of the chain is probed and shown to support long-range, cross chain correlations. In addition, interactions between the two end qubits, mediated by the coupler chain, are demonstrated. This work has direct applicability in near term quantum annealing processors as a means of generating long-range, coherent coupling between qubits.
arxiv pdf

Fast, Lifetime-Preserving Readout for High-Coherence Quantum Annealers

  1. Jeffrey A. Grover,
  2. James I. Basham,
  3. Alexander Marakov,
  4. Steven M. Disseler,
  5. Robert T. Hinkey,
  6. Moe Khalil,
  7. Zachary A. Stegen,
  8. Thomas Chamberlin,
  9. Wade DeGottardi,
  10. David J. Clarke,
  11. James R. Medford,
  12. Joel D. Strand,
  13. Micah J. A. Stoutimore,
  14. Sergey Novikov,
  15. David G. Ferguson,
  16. Daniel Lidar,
  17. Kenneth M. Zick,
  18. and Anthony J. Przybysz
We demonstrate, for the first time, that a quantum flux parametron (QFP) is capable of acting as both isolator and amplifier in the readout circuit of a capacitively shunted flux qubit
(CSFQ). By treating the QFP like a tunable coupler and biasing it such that the coupling is off, we show that T1 of the CSFQ is not impacted by Purcell loss from its low-Q readout resonator (Qe=760) despite being detuned by only 40 MHz. When annealed, the QFP amplifies the qubit’s persistent current signal such that it generates a flux qubit-state-dependent frequency shift of 85 MHz in the readout resonator, which is over 9 times its linewidth. The device is shown to read out a flux qubit in the persistent current basis with fidelities surpassing 98.6% with only 80 ns integration, and reaches fidelities of 99.6% when integrated for 1 μs. This combination of speed and isolation is critical to the readout of high-coherence quantum annealers.
arxiv pdf

Anneal-path correction in flux qubits

  1. Mostafa Khezri,
  2. Jeffrey A. Grover,
  3. James I. Basham,
  4. Steven M. Disseler,
  5. Huo Chen,
  6. Sergey Novikov,
  7. Kenneth M. Zick,
  8. and Daniel A. Lidar
Quantum annealers require accurate control and optimized operation schemes to reduce noise levels, in order to eventually demonstrate a computational advantage over classical algorithms.
We study a high coherence four-junction capacitively shunted flux qubit (CSFQ), using dispersive measurements to extract system parameters and model the device. We confirm the multi-level structure of the circuit model of our CSFQ by annealing it through small spectral gaps and observing quantum signatures of energy level crossings. Josephson junction asymmetry inherent to the device causes a deleterious nonlinear cross-talk when annealing the qubit. We implement a nonlinear annealing path to correct the asymmetry in-situ, resulting in a 50% improvement in the qubit performance. Our results demonstrate a low-level quantum control scheme which enhances the success probability of a quantum annealer.
arxiv pdf