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Physics Seminar Date: Monday, 23 September 2024 Time: 11.45 AM Venue: Lecture Hall 1 Correlations and entanglement in quantum many-body systems: detection, computation and applications Roopayan Ghosh University College London, UK. 23-09-24 Abstract In this talk, I will explore various aspects of quantum correlations and quantum entanglement within the context of quantum many-body systems. In the first part of my presentation, I will address the challenges associated with detecting and measuring entanglement in generic quantum many-body states, particularly in mixed states. I will then demonstrate how, under specific conditions, these challenges can be significantly simplified[1]. Following this, I will discuss how quantum entanglement might be used to quantify quantum causality through a quantity known as quantum Liang information, which offers a natural extension of classical ideas[2]. In the second part, I will delve into the computation of well-known entanglement measures, such as entanglement entropy and negativity, for quantum many-body systems. I will focus on the simplifications that can be achieved for Gaussian systems, which allow for the study of exact entanglement dynamics in large systems governed by quadratic Hamiltonians. I will also discuss an intriguing phenomenon that emerges using this method[3]. Additionally, I will briefly describe the generalization of this technique to quadratic action, using the Mott insulator-superfluid transition in the Bose-Hubbard model as an example[4]. In the final part of my talk, I will discuss how the application of concepts from quantum entanglement can enhance our understanding of quantum many-body systems. I will begin by discussing many-body localized (MBL) systems, where a quantity known as number entropy has sparked debate in the community regarding the validity of the MBL phase due to observations of its slow increase. I will explain the reasons behind this slow increase and demonstrate how it can be accounted for within the framework of MBL[5]. Next, I will explore open localized systems and resolve a longstanding debate concerning the relaxation of imbalance with the addition of dephasing, using a range of analytical and numerical tools[6]. Finally, I will conclude by illustrating how quantum entanglement presents a fundamental bottleneck in adiabatic quantum annealing and discuss a recent proposal we have presented to mitigate this effect.[7,8]
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