Speaker: Zlatko Papic (Leeds)
Research Centre: Department of Mathematics
Quantum many-body systems give rise to some of the most remarkable phenomena in nature, such as entanglement and emergent phases of matter, like superconductors, spin liquids or fractional quantum Hall states. Yet, these phenomena are also notoriously difficult to study because of the interactions which cause the Hilbert space to grow exponentially with the number of particles. It is known, however, that in some circumstances these systems may exhibit a much simpler description as a collection of free quasiparticles, such as the well-known Bogoliubov quasiparticles in a superfluid. However, identifying such emergent single-particle degrees of freedom has required a great deal of physical intuition. In this talk I will discuss a general approach to diagnose integrability of a quantum system by studying the entanglement spectrum of its eigenstates. In the first part, I 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, as well as from thermal states. In the second part, I will introduce the notion of “interaction distance” and show that the entanglement spectrum can be used to measure “how far” an interacting ground state is from a free (Gaussian) state. I will discuss some examples of quantum spin chains and outline a few future directions.
 M. Serbyn, A. Michailidis, D. Abanin, Z. Papic, Phys. Rev. Lett. 117, 160601 (2016).
 C. J. Turner, K. Meichanetzidis, Z. Papic, and J. K. Pachos, Nature Communications 8, 14926 (2017).
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When and where
3.00pm - 4.00pmTuesday 14th November 2017