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A. Bhattacharyya, L. K. Joshi, B. Sundar Quantum Information Scrambling: From Holography to Quantum Simulators,
Eur. Phys. J. C 82 458 (2022-05-19),
http://dx.doi.org/10.1140/epjc/s10052-022-10377-y doi:10.1140/epjc/s10052-022-10377-y (ID: 720700)
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In this review, we present the ongoing developments in bridging the gap between holography and experiments. To this end, we discuss information scrambling and models of quantum teleportation via Gao-Jafferis-Wall wormhole teleportation. We review the essential basics and summarize some of the recent works that have so far been obtained in quantum simulators towards a goal of realizing analogous models of holography in a lab.
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A. M. Green, A. Elben, C. Huerta Alderete, L. K. Joshi, N. H. Nguyen, T. Zache, Y. Zhu, B. Sundar, N. M. Linke Experimental measurement of out-of-time-ordered correlators at finite temperature,
Phys. Rev. Lett. 128 (2022-04-06),
http://dx.doi.org/10.1103/PhysRevLett.128.140601 doi:10.1103/PhysRevLett.128.140601 (ID: 720746)
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Out-of-time-ordered correlators (OTOCs) are a key observable in a wide range of interconnected fields including many-body physics, quantum information science, and quantum gravity. The ability to measure OTOCs using near-term quantum simulators will extend our ability to explore fundamental aspects of these fields and the subtle connections between them. Here, we demonstrate the first experimental measurement of OTOCs at finite temperatures and study their temperature dependence. These measurements are performed on a digital quantum computer running a simulation of the transverse field Ising model. Our flexible method, based on the creation of a thermofield double state, can be extended to other models and enables us to probe the OTOC's temperature-dependent decay rate. Measuring this decay rate opens up the possibility of testing the fundamental temperature-dependent bounds on quantum information scrambling.
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B. Sundar, A. Elben, L. K. Joshi, T. Zache Proposal for measuring out-of-time-ordered correlators at finite temperature with coupled spin chains,
New J. Phys. 24 23037 (2022-02-25),
http://dx.doi.org/10.1088/1367-2630/ac5002 doi:10.1088/1367-2630/ac5002 (ID: 720675)
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Information scrambling, which is the spread of local information through a system's many-body degrees of freedom, is an intrinsic feature of many-body dynamics. In quantum systems, the out-of-time-ordered correlator (OTOC) quantifies information scrambling. Motivated by experiments that have measured the OTOC at infinite temperature and a theory proposal to measure the OTOC at finite temperature using the thermofield double state, we describe a protocol to measure the OTOC in a finite temperature spin chain that is realized approximately as one half of the ground state of two moderately-sized coupled spin chains. We consider a spin Hamiltonian with particle-hole symmetry, for which we show that the OTOC can be measured without needing sign-reversal of the Hamiltonian. We describe a protocol to mitigate errors in the estimated OTOC, arising from the finite approximation of the system to the thermofield double state. We show that our protocol is also robust to main sources of decoherence in experiments.
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L. K. Joshi, A. Elben, A. Vikram, B. Vermersch, V. Galitski, P. Zoller Probing many-body quantum chaos with quantum simulators,
Phys. Rev. X (2022-01-27),
http://dx.doi.org/10.1103/PhysRevX.12.011018 doi:10.1103/PhysRevX.12.011018 (ID: 720665)
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The spectral form factor (SFF), characterizing statistics of energy eigenvalues, is a key diagnostic of many-body quantum chaos. In addition, partial spectral form factors (pSFFs) can be defined which refer to subsystems of the many-body system. They provide unique insights into energy eigenstate statistics of many-body systems, as we show in an analysis on the basis of random matrix theory and of the eigenstate thermalization hypothesis. We propose a protocol which allows the measurement of SFF and pSFFs in quantum many-body spin models, within the framework of randomized measurements. Aimed to probe dynamical properties of quantum many-body systems, our scheme employs statistical correlations of local random operations which are applied at different times in a single experiment. Our protocol provides a unified testbed to probe many-body quantum chaotic behavior, thermalization and many-body localization in closed quantum systems which we illustrate with simulations for Hamiltonian and Floquet many-body spin-systems.