Deterministic generation of a 20-qubit two-dimensional photonic cluster state

  1. James O'Sullivan,
  2. Kevin Reuer,
  3. Aleksandr Grigorev,
  4. Xi Dai,
  5. Alonso Hernández-Antón,
  6. Manuel H. Muñoz-Arias,
  7. Christoph Hellings,
  8. Alexander Flasby,
  9. Dante Colao Zanuz,
  10. Jean-Claude Besse,
  11. Alexandre Blais,
  12. Daniel Malz,
  13. Christopher Eichler,
  14. and Andreas Wallraff
Multidimensional cluster states are a key resource for robust quantum communication, measurement-based quantum computing and quantum metrology. Here, we present a device capable of
emitting large-scale entangled microwave photonic states in a two dimensional ladder structure. The device consists of a pair of coupled superconducting transmon qubits which are each tuneably coupled to a common output waveguide. This architecture permits entanglement between each transmon and a deterministically emitted photonic qubit. By interleaving two-qubit gates with controlled photon emission, we generate 2 x n grids of time- and frequency-multiplexed cluster states of itinerant microwave photons. We measure a signature of localizable entanglement across up to 20 photonic qubits. We expect the device architecture to be capable of generating a wide range of other tensor network states such as tree graph states, repeater states or the ground state of the toric code, and to be readily scalable to generate larger and higher dimensional states.

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.