
Chair: David Luitz (MaxPlanckInstitut für Physik komplexer Systeme)

09:30  10:00

Alexey Gorshkov
(University of Maryland)
Confined dynamics in longrange interacting quantum spin chains

10:00  10:30

Michael Knap
(Technische Universität München)
Dynamical Phase Transition in a 2D Quantum Dimer Model
We consider the quench dynamics of a twodimensional (2D) constrained quantum dimer model and determine its rich dynamical phase diagram. By means of exact diagonalization on systems of sizes up to 8x8 we show that properly defined order parameters relax to their thermal expectation values. This allows us to study the underlying equilibrium phase transitions in a dynamical context: a BKTtransition between a columnar ordered valence bond solid (VBS) and a valence bond liquid (VBL), as well as a first order transition between a staggered VBS and the VBL. For quenches across the BKT transition, the Loschmidt rate develops conventional nonanalyticities at the zerocrossings of the order parameter, fixed by microscopic parameters. By contrast, the relaxation time across the first order transition scales linearly with the correlation length of the initial state, preventing the formation of sharp kinks. Within the staggered VBS, some local observables even fail to thermalize as a result of the kinematic constraints of the quantum dimer model.

10:30  11:00

Coffee break

11:00  11:30

Discussions


Chair: David Luitz (MaxPlanckInstitut für Physik komplexer Systeme)

11:30  12:00

Juan P. Garrahan
(University of Nottingham)
Slow dynamics due to kinetic constraints, from classical to quantum

12:00  13:00

Lunch

13:00  14:00

Discussions


Chair: Alexander Chernyshev (University of California, Irvine)

14:00  14:30

Maksym Serbyn
(Institute of Science and Technology Austria)
Weak ergodicity breaking from quantum manybody scars
The statistical mechanics description of manyparticle systems rests on the assumption of ergodicity, the ability of a system to explore all allowed configurations in the phase space. For quantum manybody systems statistical mechanics predicts the equilibration of highly excited nonequilibrium state towards a featureless thermal state. Hence, it is highly desirable to explore possible ways to avoid ergodicity in quantum systems. Manybody localization presents one generic mechanism for a strong violation of ergodicity relying on the presence of quenched disorder. In my talk I will discuss a different mechanism of the weak ergodicity breaking relevant for the experimentally realized Rydbergatom quantum simulator [1]. This mechanism arises from the presence of special eigenstates in the manybody spectrum that are reminiscent of quantum scars in chaotic noninteracting systems [2]. In the singleparticle case, quantum scars correspond to wave functions concentrated in the vicinity of unstable periodic classical trajectories. I will demonstrate that manybody scars appear in the Fibonacci chain, a model with a constrained local Hilbert space which can be realized by a Rydberg chain. The quantum scarred eigenstates are embedded throughout the otherwise thermalizing manybody spectrum but lead to direct experimental signatures, as I show for periodic recurrences that reproduce those observed in the experiment [1]. Finally, I will construct the weak deformation of the Rydberg chain Hamiltonian that makes revivals virtually perfect [3]. I will conclude with discussing a new opportunities for the creation of novel states with longlived coherence in systems that are now experimentally realizable and possible generalizations of these results. \\
[1] Bernien, H. et al., Nature 551, 579–584 (2017), arXiv:1707.04344 \\
[2] C. J. Turner, A. A. Michailidis, D. A. Abanin, M. Serbyn, Z. Papić, Nature Physics (May 2018), arXiv:1711.03528 and Phys. Rev. B 98, 155134 (2018) arXiv:1806.10933 \\
[3] S. Choi, C. J. Turner, et al. arXiv:1812.05561

14:30  15:00

Michael Pretko
(University of Colorado at Boulder)
Localization and ManyBody Scars in Fracton Systems
Fractons are a special type of emergent particle which obey not only conservation of charge, but also of higher charge moments, such as the dipole moment. In this talk, based on work in collaboration with Shriya Pai and Rahul Nandkishore, I will describe how the conservation of dipole moment leads to severe restrictions on the dynamics of fractons and can prevent the system from reaching thermal equilibrium. Specifically, we study onedimensional fracton systems evolving under random unitary dynamics, subject only to the conservation of charge and dipole moment. We show that, when initialized with a single charge, the system forever remembers the initial position of the fracton, failing to reach thermal equilibrium. When the system is initialized with multiple fractons, all charges agglomerate to form a single density peak at their collective center of mass. We also study onedimensional fracton systems undergoing periodic time evolution. In such Floquet systems, we can study the eigenstates of the time evolution operator and their entanglement spectra. We find that a Floquet fracton system hosts a small number of nonthermalizing eigenstates, obeying semiPoisson statistics in their entanglement spectra, while the majority of the spectrum is thermal, obeying WignerDyson statistics. We argue that the nonthermalizing states provide an example of quantum manybody scars.

15:00  15:30

Olexei Motrunich
(CALTECH  California Institute of Technology)
Exact Quantum Manybody Scar States in the Rydbergblockaded Atom Chain
A recent experiment in the Rydberg atom chain observed unusual oscillatory quench dynamics with a charge density wave initial state, and theoretical works identified a set of manybody ``scar states'' showing nonthermal behavior in the Hamiltonian as potentially responsible for the atypical dynamics.
In the same nonintegrable Hamiltonian, we discover several eigenstates at \emph{infinite temperature} that can be represented exactly as matrix product states with \emph{finite} bond dimension, for both periodic boundary conditions (two exact $E = 0$ states) and open boundary conditions (two $E = 0$ states and one each $E = \pm \sqrt{2}$). This discovery explicitly demonstrates violation of strong eigenstate thermalization hypothesis in this model and uncovers exact quantum manybody scar states. These states show signatures of translational symmetry breaking with period2 bondcentered pattern, despite being in 1d at infinite temperature. We show that the nearby manybody scar states can be well approximated as ``quasiparticle excitations" on top of our exact $E = 0$ scar states, and propose a quasiparticle explanation of the strong oscillations observed in experiments.

15:30  16:00

Coffee break

16:00  16:30

Discussions


Chair: Alexander Chernyshev (University of California, Irvine)

16:30  17:00

Elsa Lhotel
(CNRS  Institut Néel)
Magnetic monopole dynamics in spin ice
Among the original magnetic states which emerge from frustrated magnetic systems, spin ice has aroused a strong interest because beyond its macroscopically degenerate ground state, the excitations can be described as magnetic charges, called magnetic monopoles.
At very low temperature, below 200 mK, spin ice dynamics is governed by these monopoles. By performing thermal quenches in spin ice compounds down to these temperatures, through a specific protocol called "avalanche quench" [1], we are able to prepare samples with a very large outofequilibrium density of metastable magnetic monopoles. We used this method to study the monopole dynamics in the spin ice compounds Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$, and could measure the monopole current as a function of magnetic field [2].
In this talk, I will present some of our recent results which show that even below 200 mK, there is a fast recombination of magnetic monopoles. The comparison between magnetic relaxation measurements performed on several samples with different isotopes gives insights on the quantum tunneling mechanism governing the hopping of monopoles on the lattice, and shows the role of the dynamic coupling between the hyperfine fields and the electronic spins associated with magnetic monopoles.
[1] C. Paulsen et al., Nature Physics 10, 135 (2014)
[2] C. Paulsen et al., Nature Physics 12, 661 (2016)

17:00  17:30

Santiago Grigera
(The University of St Andrews)
Phases and dynamics using machine learning

17:30  18:30

Discussions

18:30  21:00

Workshop dinner (MPIPKS cafeteria)
