Quantum Many-Body Scars

Lead Research Organisation: University of Leeds
Department Name: Physics and Astronomy


In recent years, investigations of out-of-equilibrium phenomena in quantum many-particle
systems have become one of the most active research areas in physics. A recent state-of-theart
experiment at Harvard/MIT [1] has succeeded in assembling large chains of stronglyinteracting
Rydberg atoms, which allowed them to build an impressive 51-atom quantum
simulator. This experiment discovered a new physical phenomenon: when the simulator was
driven away from its equilibrium configuration, the experiment observed enigmatic quantum
oscillations that remained coherent for unusually long times. In our recent work [2] (which was
also featured in Press, see [3, 4]) we provided an explanation of this intriguing phenomenon
by introducing a new concept of quantum many-body scar.
The goal of this PhD project is to develop a deeper understanding of quantum many-body
scars as a new class of systems where ergodicity is weakly broken. One of the pressing
questions is what kind of systems support scars. Currently, it is believed that kinetic
constraints (such as strong nearest-neighbour interactions between the atoms) are essential
to the formation of scars, thus one of the goals of the project would be to investigate more
systematically other types of models with similar constraints. On the other hand, the project
will aim to answer a fundamental question: what is the meaning of a periodic orbit in a
quantum many-body system? Such orbits play a fundamental role in the theory of singleparticle
chaotic billiards, but their meaning for a quantum many-body system is currently an
open problem. Finally, the project will also investigate possible practical applications of
quantum scars. Since the scars effectively "shield" the system from thermal relaxation, this
might allow for new mechanisms of storing and manipulating quantum information.
[1] Probing many-body dynamics on a 51-atom quantum simulator, H. Bernien et al., Nature 551, 579-584
[2] Quantum many-body scars, C. J. Turner, A. A. Michailidis, D. A. Abanin, M. Serbyn, and Z. Papic, Nature
Physics 14, 745 (2018).
[3] https://www.leeds.ac.uk/news/article/4231/insight_into_quantum_chaos_may_be_the_key_to_quantum_comp
[4] https://ist.ac.at/nc/news-media/news/news-detail/article/explanation-for-puzzling-quantum-oscillations-hasbeen-


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R513258/1 30/09/2018 29/09/2023
2282779 Studentship EP/R513258/1 30/09/2019 30/03/2023 Jean-Yves Marc Desaules
Description We have discovered the presence of quantum many-body scarring in other models that are realisable experimentally. As in the original experiment on the Rydberg atom chain, we predict long-lasting oscillations that bring the system back to its initial state when prepared in a few specific states with a simple structure, while we observe fast thermalisation and scrambling of information for any other generic initial state. For one of these models (the Bose-Hubbard model), a collaboration with the Hefei National Laboratory and the Physikalisches Institut in Heidelberg lead to the observation of this phenomenon in an optical lattice. This discovery makes the resource of scarring accessible to a broad class of ultracold-atom experiments beyond Rydberg atoms. [Observation of unconventional many-body scarring in a quantum simulator, G. Su et al., arXiv:2201.00821]

In parallel, in collaboration with the Trinity University in Dublin and the ENS Paris, we established that in many quantum systems with many-body scars these states have an extensive quantum Fisher information. This means that in these scarred states the various atoms have a large multipartite entanglement, which is a precious resource in quantum metrology as it allows to minimise the uncertainty when doing parameter estimation. [Quantum many-body scars have extensive multipartite entanglement, J-Y. Desaules, F. Pietracaprina, Z. Papic, J. Goold, S. Pappalardi, arXiv:2109.09724]
Exploitation Route By making quantum many-body scarring available on a wider range on experimental setups and showing that they have a useful resource in quantum metrology, we have opened the way for these states to be used in parameter estimation in quantum technologies.
Sectors Digital/Communication/Information Technologies (including Software)