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Physics Colloquium Date: Monday, 22 September 2025 Time: 03:30 p.m. Venue: Lecture Hall 6 Elementary excitations, topological defects & emergent universalities in low-temperature physics Sukla Pal NR-INO, Pitaevskii BEC center, Trento, Italy. 22-09-25 Abstract A major part of our current understanding of the low-temperature condensed matter physics is firmly embedded in extremely successful theoretical paradigms which witnessed the development of Landau’s Fermi liquid theory for normal metals, Bogoliubov theory for superfluids, BCS theory for superconductivity and spin-wave theory for magnets. However, there are some systems which exhibit behaviour that falls outside of any of these standard (conventional) paradigms—one such example includes spin liquids. In my talk, I will briefly describe both the scenarios by setting examples of superfluids from the conventional paradigm and frustrated magnets (spin ice) which are of unconventional type. When atoms are cooled to extremely low temperatures, it causes their collective behavior to become governed by quantum mechanical laws, where the individual atoms become indistinguishable and their de Broglie wavelengths overlap which leads to macroscopic quantum phenomena, such as superfluidity (forming a phase coherent Bose-Einstein condensate(BEC) in favourable circumstances) in bosons. The experimental realization of BEC (belongs to the category of compressible quantum fluids) in dilute alkali vapours in 1951 created a landmark at the crossroad of quantum science and atomic physics. Recently, the interface of many-body quantum physics, quantum optics and condensed matter physics, has been one of the tremendously successful and flourishing branches of interdisciplinary physics for understanding the light-matter interaction at In the first part of my talk, I will focus on the theoretical aspects and ground state quantum phases of compressible quantum fluids and their mixtures, considering short-range contact interaction, long-range dipolar interaction and different types of topo- logical defects followed by their elementary excitations based on the Bogoliubov theory of superfluids. I also plan to provide some examples of lattice bosons (bosons in optical lattice) and the role of disorders and geometric frustrations in the ground state phases. In the second half, I will consider statistical aspects of quantum fluids and condensed matter physics capturing few universal aspects of the out of equilibrium dynamics in these systems with special attention to various fixed points and the emergent scalings laws.
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