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arXiv:2408.14782 · The Journal of Physical Chemistry Letters

Molecular Entanglement Witness by Absorption Spectroscopy in Cavity QED

Weijun Wu, Francesca Fassioli, David A. Huse, Gregory D. Scholes

Published Jul 14, 2025• 2 citations
arXivHTMLPDF

Abstract

Producing and maintaining molecular entanglement at room temperature and detecting multipartite entanglement features of macroscopic molecular systems remain key challenges for understanding intermolecular quantum effects in chemistry. Here, we study the quantum Fisher information, as a multipartite entanglement witness. We generalize the entanglement witness functional related to quantum Fisher information regarding nonidentical local response operators. We demonstrate its effectiveness for intermolecular entanglement in ultrastrong light-matter coupling in cavity quantum electrodynamics, including near the superradiant phase transition. Additionally, we establish a connection between quantum Fisher information and the dipole correlator, indicating that entanglement could be detected through absorption spectroscopy. Our work proposes a general protocol to detect intermolecular entanglement in chemical systems at room temperature.

DOI
10.1021/acs.jpclett.5c01392

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Abstract The detection and certification of entanglement and quantum correlations in materials is of fundamental and far‐reaching importance, and has seen significant recent progress. It impacts both the understanding of the basic science of quantum many‐body phenomena as well as the identification of systems suitable for novel technologies. Frameworks suitable to condensed matter that connect measurements to entanglement and coherence have been developed in the context of quantum information theory. These take the form of entanglement witnesses and quantum correlation measures. The underlying theory of these quantities, their relation to condensed matter experimental techniques, and their application to real materials are comprehensively reviewed. In addition, their usage in, e.g., protocols, the relative advantages and disadvantages of witnesses and measures, and future prospects in, e.g., correlated electrons, entanglement dynamics, and entangled spectroscopic probes, are presented. Consideration is given to the interdisciplinary nature of this emerging research and substantial ongoing progress by providing an accessible and practical treatment from fundamentals to application. Particular emphasis is placed on quantities accessible to collective measurements, including by susceptibility and spectroscopic techniques. This includes the magnetic susceptibility witness, one‐tangle, concurrence and two‐tangle, two‐site quantum discord, and quantum coherence measures such as the quantum Fisher information.
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