Optimal free descriptions of many-body theories

• Published in: Nature communications 2017-04, Vol.8 (1), p.14926-14926, Article 14926
• Main Authors: Turner, Christopher J., Meichanetzidis, Konstantinos, Papić, Zlatko, Pachos, Jiannis K.
• Format: Article
• Language: English
• Subjects: 639/766/483/481; 639/766/483/640; Eigenvalues; Electromagnetism; Electrons; Humanities and Social Sciences; multidisciplinary; Physics; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms14926

Interacting bosons or fermions give rise to some of the most fascinating phases of matter, including high-temperature superconductivity, the fractional quantum Hall effect, quantum spin liquids and Mott insulators. Although these systems are promising for technological applications, they also present conceptual challenges, as they require approaches beyond mean-field and perturbation theory. Here we develop a general framework for identifying the free theory that is closest to a given interacting model in terms of their ground-state correlations. Moreover, we quantify the distance between them using the entanglement spectrum. When this interaction distance is small, the optimal free theory provides an effective description of the low-energy physics of the interacting model. Our construction of the optimal free model is non-perturbative in nature; thus, it offers a theoretical framework for investigating strongly correlated systems. Physicists’ understanding of interacting many-body systems often depends on finding an approximate description in terms of non-interacting particles. Here, the authors propose a systematic approach to identify the closest free particle description of a given model.