Description:

Anya Abraham, Kovachy Research Group

“Progress Toward Narrow-Line Cooling of Strontium"

Atom interferometers are natural extensions of optical interferometers, and exploit the wave-nature of matter to split, redirect, and recombine atomic wavefunctions using laser pulses. They have proven to be useful tools in probing fundamental physics and making extremely precise measurements of gravitational and inertial forces. To perform these measurements more precisely and to increase coherence times, we require our atoms (88Sr) to be trapped and cooled down to uK temperatures. MOTs (Magneto-Optical Traps) help us achieve this goal, and have become a standard technique for cooling and trapping neutral atoms. Our apparatus has already implemented cooling on the broad 1S0-1P1 transition at 461nm (the “blue MOT”), bringing our atoms down to ~mK temperatures. In this talk, I will present the basic theory of atom interferometry as well as the working principle behind MOTs. I will then outline the progress on our journey to colder atoms, and our efforts to implement a “red MOT” on the narrow dipole-forbidden 1S0-3P1 transition at 689nm.

Saptarshi Biswas, Goswami Research Group

“Topological PhaseTransition in a Variant of the LMG (Lipkin-Meshkov-Glick) Model"

Originally proposed as an effective description of closed-shell nuclei and (in principle) solvable model of interacting particles, the LMG model has since found relevance in several scenarios such as in quantum optics for generating multiparticle entangled states, nitrogen-vacancy (NV) center based spin-mechanical system for matter wave interferometry, Bose-Einstein condensates in different traps and many others. Essentially, it is a non-linear spin model with large spin (S). Semiclassical analysis in the S -> infinity limit, using spin coherent state trial wave function has revealed different phase transitions in the model, which manifest as non-analyticity in the classical energy surface, ground state energy, observable dynamics, order-parameter / change from single-particle to collective nature of eigen-function. However, phase transition in the finite-S model where quantum effects should be most prominent, is less understood. Recently, efforts are made to study markers of quantum phase transitions using the quantum geometric tensor and quantum complexity while incorporating 1/S corrections within linear spin wave theory, but it suffers from discrepancies between analytic and numeric results. In a separate class of studies, the finite-S LMG model, as well as a modified version of it to realize certain molecular magnets, are found to undergo precise ground (and excited) state level crossings that persist even upto small values of S, which signifies non-analyticity in the eigenfunctions. We argue that these can be associated with a topological phase transition, revealing a precise relation with quantum geometry as well as a quantification of the level crossings using the total change in topological quantum number.