Measuring Out-of-Time-Order Correlators with Projected Revivability

Yuan Dong, Shunyao Zhang, Yu Wang +2 more

Quantum many-body scarred systems host special nonthermal eigenstates that support periodic revival dynamics and weakly break the ergodicity. Here, we study the quantum information scrambling dynamics in quantum many-body scarred systems, with a focus on the ``PXP'' model. We use the out-of-time-ordered correlator (OTOC) and Holevo information as measures of the information scrambling and apply an efficient numerical method based on matrix product operators to compute them up to 41 spins. We find that both the OTOC and Holevo information exhibit a linear light cone and periodic oscillations inside the light cone for initial states within the scarred subspace, which is in sharp contrast to thermal or many-body localized systems. The periodic revivals of OTOCs and Holevo information signify unusual breakdown of quantum chaos and are not equivalent to the revival dynamics of state fidelity or local observables studied in the previous literature. To explain the formation of the linear light-cone structure, we provide a perturbation-type calculation based on a phenomenological model. In addition, we demonstrate that the OTOC and Holevo information dynamics of the PXP model can be measured using the Rydberg-atom quantum simulators with current experimental technologies and numerically identify the measurable signatures using experimental parameters.

Adam Smith

Rohit Kumar Shukla, Gautam Kamalakar Naik, S. K. Mishra

Abstract We study the out-of-time-order correlation (OTOC) of the Floquet transverse Ising model and use it to verify the phase diagram of the system. First, we present the exact analytical solution of the transverse magnetization OTOC using the Jorden-Wigner transformation. We calculate the speed of correlation propagation and analyze the behavior of the revival time with the separation between the observables. In order to get the phase structure of the Floquet transverse Ising system, we use the longitudinal magnetization OTOC as it is known to serve as an order parameter of the system. We show the phase structure numerically in the transverse Ising Floquet system by using the long time average of the longitudinal magnetization OTOC. In both the open and the closed chain systems, we find distinct phases out of which two are paramagnetic (0-paramagnetic and π -paramagnetic), and two are ferromagnetic (0-ferromagnetic and π -ferromagnetic) as defined in the literature.

Brian G. Swingle

José Raúl González Alonso, Nicole Yunger Halpern, Justin Dressel

Mykhailo Shushman

We present Hypnos-Q1, an open-weight 4-billion-parameter reasoning language model in whicha single architectural modification couples the model to a superconducting quantum processor.A dedicated special token, <|quantum_sig|>, has its embedding replaced, at every forwardpass, by a learned linear projection of a six-dimensional measurement vector obtained from out-of-time-order correlator (OTOC) experiments on IBM’s ibm_kingston (Heron r2, 156 qubits).