D. G. Angelakis

Spectral signatures of many-body localization with interacting photons

  1. P. Roushan,
  2. C. Neill,
  3. J. Tangpanitanon,
  4. V.M. Bastidas,
  5. A. Megrant,
  6. R. Barends,
  7. Y. Chen,
  8. Z. Chen,
  9. B. Chiaro,
  10. A. Dunsworth,
  11. A. Fowler,
  12. B. Foxen,
  13. M. Giustina,
  14. E. Jeffrey,
  15. J. Kelly,
  16. E. Lucero,
  17. J. Mutus,
  18. M. Neeley,
  19. C. Quintana,
  20. D. Sank,
  21. A. Vainsencher,
  22. J. Wenner,
  23. T. White,
  24. H. Neven,
  25. D. G. Angelakis,
  26. and J. Martinis
Statistical mechanics is founded on the assumption that a system can reach thermal equilibrium, regardless of the starting state. Interactions between particles facilitate thermalization,
but, can interacting systems always equilibrate regardless of parameter values\,? The energy spectrum of a system can answer this question and reveal the nature of the underlying phases. However, most experimental techniques only indirectly probe the many-body energy spectrum. Using a chain of nine superconducting qubits, we implement a novel technique for directly resolving the energy levels of interacting photons. We benchmark this method by capturing the intricate energy spectrum predicted for 2D electrons in a magnetic field, the Hofstadter butterfly. By increasing disorder, the spatial extent of energy eigenstates at the edge of the energy band shrink, suggesting the formation of a mobility edge. At strong disorder, the energy levels cease to repel one another and their statistics approaches a Poisson distribution – the hallmark of transition from the thermalized to the many-body localized phase. Our work introduces a new many-body spectroscopy technique to study quantum phases of matter.
arxiv pdf

Beyond mean-field bistability in driven-dissipative lattices: bunching-antibunching transition and quantum simulation

  1. J. J. Mendoza-Arenas,
  2. S. R. Clark,
  3. S. Felicetti,
  4. G. Romero,
  5. E. Solano,
  6. D. G. Angelakis,
  7. and D. Jaksch
In the present work we investigate the existence of multiple nonequilibrium steady states in a coherently-driven XY lattice of dissipative two-level systems. A commonly-used mean-field
ansatz, in which spatial correlations are neglected, predicts a bistable behavior with a sharp shift between low- and high-density states. In contrast one-dimensional matrix product methods reveal these effects to be artifacts of the mean-field approach, with both disappearing once correlations are taken fully into account. Instead a bunching-antibunching transition emerges. This indicates that alternative approaches should be considered for higher spatial dimensions, where classical simulations are currently infeasible. Thus we propose a circuit QED quantum simulator implementable with current technology, to enable an experimental investigation of the model considered.
arxiv pdf