Probing quantum information propagation with out-of-time-ordered correlators

  1. Jochen Braumüller,
  2. Amir H. Karamlou,
  3. Yariv Yanay,
  4. Bharath Kannan,
  5. David Kim,
  6. Morten Kjaergaard,
  7. Alexander Melville,
  8. Bethany M. Niedzielski,
  9. Youngkyu Sung,
  10. Antti Vepsäläinen,
  11. Roni Winik,
  12. Jonilyn L. Yoder,
  13. Terry P. Orlando,
  14. Simon Gustavsson,
  15. Charles Tahan,
  16. and William D. Oliver
Interacting many-body quantum systems show a rich array of physical phenomena and dynamical properties, but are notoriously difficult to study: they are challenging analytically and exponentially difficult to simulate on classical computers. Small-scale quantum information processors hold the promise to efficiently emulate these systems, but characterizing their dynamics is experimentally challenging, requiring probes beyond simple correlation functions and multi-body tomographic methods. Here, we demonstrate the measurement of out-of-time-ordered correlators (OTOCs), one of the most effective tools for studying quantum system evolution and processes like quantum thermalization. We implement a 3×3 two-dimensional hard-core Bose-Hubbard lattice with a superconducting circuit, study its time-reversibility by performing a Loschmidt echo, and measure OTOCs that enable us to observe the propagation of quantum information. A central requirement for our experiments is the ability to coherently reverse time evolution, which we achieve with a digital-analog simulation scheme. In the presence of frequency disorder, we observe that localization can partially be overcome with more particles present, a possible signature of many-body localization in two dimensions.
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