New paradigms of order amidst quantum many-body chaos

Summary

A perennial mystery of nature is how order can exist amidst chaos. Familiar systems such as the clock pendulum exhibit regular periodic motion. This ordered behaviour, however, is fragile. For example, interactions between particles rapidly lead to chaos, forcing the system to thermalise and forget its initial state. This can be visualised as an ice cream that melts away and never finds its way back to the frozen state. Quantum scars refer to the surprising behaviour that defies such common intuition: for special initial states, the ice cream periodically melts away and then freezes up again. Recent experiments on ultracold Rydberg atoms have found evidence of similar behaviour where the atoms were able to return to their initial state many times during the measurement. This project seeks to develop an understanding of quantum scars in systems of ultra cold atoms in optical lattices, with the goal of predicting future experiments that may unlock a range of applications in the emerging quantum technologies.

Recent experiments on quantum simulators built from Rydberg atoms [H. Bernien et al., Nature 551, 579 (2017)] have discovered a remarkable dynamical phenomenon that challenged the conventional notion of how quantum systems reach thermal equilibrium. We have recently proposed the first theoretical explanation for this phenomenon and named it "quantum many-body scars" [Nature Physics 14, 745 (2018]. Following the surge of international interest in this topic, including popular articles such as https://www.quantamagazine.org/quantum-scarring-appears-to-defy-universes-push-for-disorder-20190320/, this project will contribute to the on-going quest to understand the origins of quantum many-body scars and their physical realisations. This will be achieved by developing new computational techniques for simulating non-ergodic many-body dynamics and phases of matter, and exploring the potential of scars for applications in quantum technology.

The initial phase of the project will focus on: (i) learning about quantum dynamics, thermalisation, and related phenomena (integrability, many-body localisation), and (ii) learning how to numerically simulate quantum many-body systems (e.g., using Python, Julia, C++, or any preferred language). In particular, you will learn how to apply quantum information concepts, such as matrix product states and tensor networks, to characterise dynamics and thermalisation.

Desired student background: We seek talented and highly-motivated physics students to pursue this project in the general area of quantum many-body physics, which intersects with the fields of quantum information and condensed matter physics. A significant component of the project is numerical modelling of quantum many-body systems via exact diagonalisation and tensor network methods, so the project is particularly suitable for those with strong interest in computational physics and numerical simulations.

For an accessible introduction to the field of quantum many-body scars, see our recent review article: https://arxiv.org/abs/2011.09486

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