J. Martinis

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

Chiral groundstate currents of interacting photons in a synthetic magnetic field

  1. P. Roushan,
  2. C. Neill,
  3. A. Megrant,
  4. Y. Chen,
  5. R. Babbush,
  6. R. Barends,
  7. B. Campbell,
  8. Z. Chen,
  9. B. Chiaro,
  10. A. Dunsworth,
  11. A. Fowler,
  12. E. Jeffrey,
  13. J. Kelly,
  14. E. Lucero,
  15. J. Mutus,
  16. P. J. J. O'Malley,
  17. M. Neeley,
  18. C. Quintana,
  19. D. Sank,
  20. A. Vainsencher,
  21. J. Wenner,
  22. T. White,
  23. E. Kapit,
  24. and J. Martinis
The intriguing many-body phases of quantum matter arise from the interplay of particle interactions, spatial symmetries, and external fields. Generating these phases in an engineered
system could provide deeper insight into their nature and the potential for harnessing their unique properties. However, concurrently bringing together the main ingredients for realizing many-body phenomena in a single experimental platform is a major challenge. Using superconducting qubits, we simultaneously realize synthetic magnetic fields and strong particle interactions, which are among the essential elements for studying quantum magnetism and fractional quantum Hall (FQH) phenomena. The artificial magnetic fields are synthesized by sinusoidally modulating the qubit couplings. In a closed loop formed by the three qubits, we observe the directional circulation of photons, a signature of broken time-reversal symmetry. We demonstrate strong interactions via the creation of photon-vacancies, or „holes“, which circulate in the opposite direction. The combination of these key elements results in chiral groundstate currents, the first direct measurement of persistent currents in low-lying eigenstates of strongly interacting bosons. The observation of chiral currents at such a small scale is interesting and suggests that the rich many-body physics could survive to smaller scales. We also motivate the feasibility of creating FQH states with near future superconducting technologies. Our work introduces an experimental platform for engineering quantum phases of strongly interacting photons and highlight a path toward realization of bosonic FQH states.
arxiv pdf