## SCL Seminar by Zlatko Papic

SCL seminar of the Center for the Study of Complex Systems, will be held on Thursday, 29 December 2016 at 14:00 in the library reading room “Dr. Dragan Popović" of the Institute of Physics Belgrade. The talk entitled

will be given by Dr. Zlatko Papić (School of Physics and Astronomy, University of Leeds, UK).

Quantum many-body systems are challenging to study because of their exponentially large Hilbert spaces, but at the same time they represent an arena for exciting new physics which results from interactions between particles. For theoretical purposes, it is convenient to know if such systems can be expressed in a "simple" ways in terms of some nearly-free quasiparticles, or more generally if one can construct a large set of operators that approximately commute with the system’s Hamiltonian. In this talk we will discuss two ways of approaching these questions using the "entanglement spectrum". In the first part, we will show that strongly disordered systems in the many-body localized phase have a universal power-law structure in their entanglement spectra. This is a consequence of their local integrability, and distinguishes such states from typical ground states of gapped systems. In the second part, we will introduce a notion of “interaction distance” and show that the entanglement spectrum can be used to quantify “how far” an interacting ground state is from a free (Gaussian) state. We will also discuss some examples of quantum spin chains and outline a few future directions.

[1] M. Serbyn, A. Michailidis, D. Abanin, Z. Papić, arXiv:1605.05737.

[2] C. J. Turner, K. Meichanetzidis, Z. Papić, and J. K. Pachos, arXiv:1607.02679.

**"Quantum integrability from the entanglement spectrum"**will be given by Dr. Zlatko Papić (School of Physics and Astronomy, University of Leeds, UK).

**Abstract of the talk:**Quantum many-body systems are challenging to study because of their exponentially large Hilbert spaces, but at the same time they represent an arena for exciting new physics which results from interactions between particles. For theoretical purposes, it is convenient to know if such systems can be expressed in a "simple" ways in terms of some nearly-free quasiparticles, or more generally if one can construct a large set of operators that approximately commute with the system’s Hamiltonian. In this talk we will discuss two ways of approaching these questions using the "entanglement spectrum". In the first part, we will show that strongly disordered systems in the many-body localized phase have a universal power-law structure in their entanglement spectra. This is a consequence of their local integrability, and distinguishes such states from typical ground states of gapped systems. In the second part, we will introduce a notion of “interaction distance” and show that the entanglement spectrum can be used to quantify “how far” an interacting ground state is from a free (Gaussian) state. We will also discuss some examples of quantum spin chains and outline a few future directions.

[1] M. Serbyn, A. Michailidis, D. Abanin, Z. Papić, arXiv:1605.05737.

[2] C. J. Turner, K. Meichanetzidis, Z. Papić, and J. K. Pachos, arXiv:1607.02679.