Many-Body Theory of Correlated Fermion Systems

C.H. Harzer, H. Muether, Markus Stauf +1 more

Steffen Backes, Jae-Hoon Sim, Silke Biermann

Motivated by the intriguing physics of quasi-two-dimensional fermionic systems, such as high-temperature superconducting oxides, layered transition metal chalcogenides, or surface or interface systems, the development of many-body computational methods geared at including both local and nonlocal electronic correlations has become a rapidly evolving field. It has been realized, however, that the success of such methods can be hampered by the emergence of noncausal features in the effective or observable quantities involved. Here, we present an approach wherein local many-body techniques such as dynamical mean-field theory (DMFT) are extended to nonlocal correlations and interactions, which preserves causality and has a physically intuitive interpretation. Our strategy has implications for the general class of DMFT-inspired many-body methods and can be adapted to cluster, dual boson, or dual fermion techniques with minimal effort.

Masatoshi Imada

Barnali Chakrabarti, Arnaldo Gammal, N. D. Chavda +1 more

We study the dynamical fermionization of strongly interacting one-dimensional bosons in Tonks-Girardeau limit by solving the time-dependent many-boson Schr\"odinger equation numerically exactly. We establish that the one-body momentum distribution approaches the ideal Fermi gas distribution at the time of dynamical fermionization. The analysis is further complemented by the measures on the two-body level. The dynamical fermionization in the two-body level should be inferred as the presence of a distinct correlation hole along the diagonal of two-body correlation. Investigation of two-body momentum distribution for the strongly interacting bosons clearly exhibits a pattern along the diagonal which is not extinguished at the time of fermionization. Two-body local and nonlocal correlation also clearly distinguish the fermionized bosons from noninteracting fermions. The magnitude of distinguishablity between the two systems is further discussed employing suitable measures of information theory, i.e., the well-known Kullback-Leibler relative entropy and the Jensen-Shannon divergence entropy. We also observe very rich structure in the higher-body density for strongly correlated bosons, whereas noninteracting fermions do not possess any higher-order correlation beyond two-body.

T. V. Ramakrishnan, B. Sriram Shastry

Aksak, Çağan

Quantum correlations are crucial features in both quantum information theory and many-body physics. Characterization and quantification of quantum correlations have delivered a rich body of work and helped to understand some quantum phenomena. Entanglement is a unique quantum correlation for which it is a resource in many quantum information tasks. Developed for quantification of entanglement, entanglement witness formalism is a remarkable tool in the quantum information toolkit. It can be deployed beyond the entanglement theory to quantify quantum correlations in many-body systems. For many-body systems, the particle statistics and indistinguishability are essential. The relation between indistinguishability and entanglement has to be studied carefully. In this thesis, first, a class of witness operators for pairing correlations in both fermionic and bosonic systems have been proposed and the necessary and sufficient conditions for being a witness operator are found. Then, a Clauser-Horne-Shimony-Holt type test and its bounds for fermions have been demonstrated.