Daniel M. Tennant

Simulating noise on a quantum processor: interactions between a qubit and resonant two-level system bath

  1. Yujin Cho,
  2. Dipti Jasrasaria,
  3. Keith G. Ray,
  4. Daniel M. Tennant,
  5. Vincenzo Lordi,
  6. Jonathan L DuBois,
  7. and Yaniv J. Rosen
Material defects fundamentally limit the coherence times of superconducting qubits, and manufacturing completely defect-free devices is not yet possible. Therefore, understanding the
interactions between defects and a qubit in a real quantum processor design is essential. We build a model that incorporates the standard tunneling model, the electric field distributions in the qubit, and open quantum system dynamics and draw from the current understanding of two-level system (TLS) theory. Specifically, we start with one million TLSs distributed on the surface of a qubit and pick the 200 highest coupling systems. We then perform a full Lindbladian simulation that explicitly includes the coherent coupling between the qubit and the TLS bath to model the time dependent density matrix of resonant TLS defects and the qubit. We find that the 200 most strongly coupled TLSs can accurately describe the qubit energy relaxation time. This work confirms that resonant TLSs located in areas where the electric field is strong can significantly affect the qubit relaxation time, even if they are located far from the Josephson junction. Similarly, a strongly-coupled resonant TLS located in the Josephson junction does not guarantee a reduced qubit relaxation time if a more strongly coupled TLS is far from the Josephson junction. In addition to the coupling strengths between TLSs and the qubit, the model predicts that the geometry of the device and the TLS relaxation time play a significant role in qubit dynamics. Our work can provide guidance for future quantum processor designs with improved qubit coherence times.
arxiv pdf

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

Low frequency correlated charge noise measurements across multiple energy transitions in a tantalum transmon

  1. Daniel M. Tennant,
  2. Luis A. Martinez,
  3. Chris D. Wilen,
  4. Robert McDermott,
  5. Jonathan L DuBois,
  6. and Yaniv J. Rosen
Transmon qubits fabricated with tantalum metal have been shown to possess energy relaxation times greater than 300 μs and, as such, present an attractive platform for high precision,
correlated noise studies across multiple higher energy transitions. Tracking the multi-level fluctuating qudit frequencies over the course of hours and even days, with a precision enabled by the high coherence of the device, allows us to extract the underlying charge offset and quasi-particle dynamics. We observe qualitatively different charge offset dynamics in the tantalum device than those measured in previous low frequency charge noise studies. In particular, we find the charge offset dynamics dominated by rare, discrete charge offset jumps between a finite number of quasi-stationary charge configurations, a previously unobserved charge noise process in superconducting qubits.
arxiv pdf