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Lower bounds on entanglement entropy without twin copy
Journal article   Open access   Peer reviewed

Lower bounds on entanglement entropy without twin copy

Yannick Meurice
Physical review research, Vol.7(2), L022023
04/01/2025
DOI: 10.1103/PhysRevResearch.7.L022023
url
https://doi.org/10.1103/PhysRevResearch.7.L022023View
Published (Version of record) Open Access

Abstract

We discuss the possibility of estimating experimentally the von Neumann entanglement entropy S_{A}^{vN} of a symmetric bipartite quantum system AB by using the basic measurement counts (bitstrings) for a single copy of a prepared state. Using exact diagonalization and analog simulations performed with the publicly available QuEra facilities for chains and ladders of Rydberg atoms, we calculate the Shannon entropy S_{AB}^{X} associated with the bitstrings of adiabatically prepared ground states and the reduced entropies S_{A}^{X} and S_{B}^{X} obtained from the marginal probabilities in A and B. We then calculate the classical mutual information I_{AB}^{X}=S_{A}^{X}+S_{B}^{X}−S_{AB}^{X}, which is a lower bound on S_{A}^{vN}. We show that for a broad range of lattice spacing and detuning, I_{AB}^{X} is typically 20% below S_{A}^{vN} in regions where S_{A}^{vN} is large and a less close bound in regions where S_{A}^{vN} is low. We argue that this use of the easily available bitstrings provides a robust and efficient way to explore empirically the phase diagram of qubit-based quantum simulators and identify critical regions.

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