Evgeny Mozgunov

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

Quantum adiabatic theorem for unbounded Hamiltonians, with applications to superconducting circuits

  1. Evgeny Mozgunov,
  2. and Daniel A. Lidar
We present a new quantum adiabatic theorem that allows one to rigorously bound the adiabatic timescale for a variety of systems, including those described by unbounded Hamiltonians.
Our bound is geared towards the qubit approximation of superconducting circuits, and presents a sufficient condition for remaining within the 2n-dimensional qubit subspace of a circuit model of n qubits. The novelty of this adiabatic theorem is that unlike previous rigorous results, it does not contain 2n as a factor in the adiabatic timescale, and it allows one to obtain an expression for the adiabatic timescale independent of the cutoff of the infinite-dimensional Hilbert space of the circuit Hamiltonian. As an application, we present an explicit dependence of this timescale on circuit parameters for a superconducting flux qubit, and demonstrate that leakage out of the qubit subspace is inevitable as the tunneling barrier is raised towards the end of a quantum anneal. We also discuss a method of obtaining a 2n×2n effective Hamiltonian that best approximates the true dynamics induced by slowly changing circuit control parameters.
arxiv pdf