Quantifying fermionic interactions from the violation of Wick’s theorem

Jiannis K. Pachos1 and Chrysoula Vlachou2,3

1School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
2Instituto de Telecomunicações, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
3Departamento de Matemática, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal

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In contrast to interacting systems, the ground state of free systems has a highly ordered pattern of quantum correlations, as witnessed by Wick's decomposition. Here, we quantify the effect of interactions by measuring the violation they cause on Wick's decomposition. In particular, we express this violation in terms of the low entanglement spectrum of fermionic systems. Moreover, we establish a relation between the Wick's theorem violation and the interaction distance, the smallest distance between the reduced density matrix of the system and that of the optimal free model closest to the interacting one. Our work provides the means to quantify the effect of interactions in physical systems though measurable quantum correlations.

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Cited by

[1] Aydin Deger, Aiden Daniel, Zlatko Papić, and Jiannis K. Pachos, "Persistent Non-Gaussian Correlations in Out-of-Equilibrium Rydberg Atom Arrays", PRX Quantum 4 4, 040339 (2023).

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