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

Interacting many-body quantum systems show a rich array of physical phenomena and dynamical properties, but are notoriously difficult to study: they are analytically challenging and exponentially hard to simulate on classical computers. Small-scale quantum information processors hold the promise to...

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Bibliographic Details
Published in:	Nature physics 2022-02, Vol.18 (2), p.172-178
Main Authors:	Braumüller, Jochen, Karamlou, Amir H., Yanay, Yariv, Kannan, Bharath, Kim, David, Kjaergaard, Morten, Melville, Alexander, Niedzielski, Bethany M., Sung, Youngkyu, Vepsäläinen, Antti, Winik, Roni, Yoder, Jonilyn L., Orlando, Terry P., Gustavsson, Simon, Tahan, Charles, Oliver, William D.
Format:	Article
Language:	eng
Subjects:	Circuits Correlators Evolution Lattices Localization Many body interactions Propagation Quantum computing Quantum phenomena Quantum theory Qubits (quantum computing) Simulation Thermalization (energy absorption) Time measurement Two dimensional bodies
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Summary:	Interacting many-body quantum systems show a rich array of physical phenomena and dynamical properties, but are notoriously difficult to study: they are analytically challenging and exponentially hard to simulate on classical computers. Small-scale quantum information processors hold the promise to efficiently emulate these systems, but characterizing their dynamics is experimentally difficult, requiring probes beyond simple correlation functions and multi-body tomographic methods. Here we demonstrate the measurement of out-of-time-ordered correlators—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 out-of-time-ordered correlators 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 was achieved with a digital–analogue 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. The complexity of many-body quantum states makes their evolution difficult to simulate with classical computers. Experiments on a 2D nine-qubit device demonstrate that the key properties of quantum lattices can be accessed by measuring out-of-time-ordered correlators.
ISSN:	1745-2473 1745-2481