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Ask Me About My Scar (States)

Isabel Martinez-Robles

Published Jul 31, 2026• 0 citations
OpenAlex

Abstract

Isolated quantum systems are anticipated to obey the eigenstate thermalization hypothesis by coming to thermal equilibrium. In our experiments, ultracold Rydberg atoms thermalize when they exchange energy via two-body interactions, but not three-body interactions. We believe this to be the result of a specially tuned initial state that maps onto quantum many body scar states. We propose an experiment in which we modify the initial state and measure the degree to which the system thermalizes. We present experimental and simulation data to support this.

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arXiv:2410.14613•SciPost Physics•Feb 9, 2026•1 citation
Isolated quantum systems are anticipated to obey the eigenstate thermalization hypothesis by coming to thermal equilibrium. In our experiments, ultracold Rydberg atoms thermalize when they exchange energy via two-body interactions, but not three-body interactions. We believe this to be the result of a specially tuned initial state that maps onto quantum many body scar states. We propose an experiment in which we modify the initial state and measure the degree to which the system thermalizes. We present experimental and simulation data to support this.
An explanation of the thermalization of closed quantum systems is the eigenstate thermalization hypothesis, which states that all eigenstates are thermal. Quantum many-body scars are a relatively newly discovered phenomenon, which describe a band of nonthermal eigenstates that have high overlap with the initial state. These states impede the thermalization of systems. This paper looks at a system of ultracold Rubidium Rydberg atoms that interact via dipole-dipole interactions. This system has apparently normal thermalization when the dipole interactions are primarily two-body interactions, however when they are primarily three-body interaction the system thermalizes slower than expected. Simulations results are presented which suggest that scars states affect the time evolution of the system.
Isolated quantum systems are typically observed to come to thermal equilibrium. The weak Eigenstate Thermalization Hypothesis (wETH) states that the vast majority of eigenvectors are thermal. This implies that most initial states should thermalize. Studying the rare cases in which they fail to thermalize could reveal insight into quantum dynamics. In our experiment, we excite Rydberg atoms and allow them to exchange energy via dipole-dipole interactions. We find that they do not thermalize. We present numerical and theoretical results that show that our experimental initial state is not typical.
We simulate the dynamics of Rydberg atoms resonantly exchanging energy via two-, three-, and four-body dipole-dipole interactions in a one-dimensional array. Using simplified models of a realistic experimental system, we study the initial-state survival probability, mean level spacing, spread of entanglement, and properties of the energy eigenstates. By exploring a range of disorders and interaction strengths, we find regions in parameter space where the three- and four-body dynamics either fail to thermalize or do so slowly. The interplay between the stronger hopping and weaker field-tuned interactions gives rise to quantum many-body scar states, which play a critical role in slowing the dynamics of the three- and four-body interactions. Published by the American Physical Society 2024
Systems are known to thermalize, or reach equilibrium, with the passing of time. However, when this does not occur, the quantum states of the system may be localized. Localized states carry information of the system’s initial state that is typically lost during the process of thermalization. We aim to study thermalization and localization in systems of rubidium Rydberg atoms, and to further understand these phenomena via simulation while we are developing a more refined experiment. These atoms exchange energy via tuned resonances while contained within a magneto optical trap. This process can be categorized as either a two, three, or four body interaction; localization is only expected to occur in the latter two. As the atoms transfer energy via dipole-dipole interactions, the population of atoms occupying different states shifts. Some atoms are shifted to a measurable state, and each trial of the experiment lasts for only several microseconds as data is collected. The energy transport within the system is simulated on a supercomputer in order to produce a model for the experimental data, while also allowing us to closely analyze parameters that are not accessible through experiment. From the model, we hope to learn whether the system thermalizes or localizes. We present initial simulation results exploring the energy exchange dynamics in a Rubidium many-body system.
The ongoing quest for understanding nonequilibrium dynamics of complex quantum systems underpins the foundation of statistical physics as well as the development of quantum technology. Quantum many-body scarring has recently opened a window into novel mechanisms for delaying the onset of thermalization by preparing the system in special initial states, such as the Z2{\mathbb{Z}}_{2}Z2​ state in a Rydberg atom system. Here we realize many-body scarring in a Bose-Hubbard quantum simulator from previously unknown initial conditions such as the unit-filling state. We develop a quantum-interference protocol for measuring the entanglement entropy and demonstrate that scarring traps the many-body system in a low-entropy subspace. Our work makes the resource of scarring accessible to a broad class of ultracold-atom experiments, and it allows one to explore the relation of scarring to constrained dynamics in lattice gauge theories, Hilbert space fragmentation, and disorder-free localization.
Quantum many-body scars are energy eigenstates which fail to reproduce thermal expectation values of local observables, in systems where the rest of the many-body spectrum fulfils eigenstate thermalization. Experimental observation of quantum many-body scars has so far been limited to models with multiple scar states evenly spaced in energy. It is thus an interesting question whether even single isolated scars, which theoretically embody the weakest possibile violation of eigenstate thermalization and may be thought to have no detectable impact in experiments, can leave a trace in measurable quantities. Moreover, single scars offer an interesting scenario for exploring the connection between quantum many-body scars and the original notion of scarring in quantum dynamical systems theory. Here we propose protocols to observe single scars in architectures of fixed-frequency, fixed-coupling superconducting qubits. We first adapt known models possessing the desired features into a form particularly suited for the experimental platform. We develop protocols for the implementation of these models, through trotterized sequences of two-qubit cross-resonance interactions, and verify the existence of the approximate scar state in the stroboscopic effective Hamiltonian. Since a single scar cannot be detected from coherent revivals in the dynamics, differently from towers of scar states, we propose and numerically investigate alternative and experimentally-accessible signatures. These include the dynamical response of the scar to local state deformations, to controlled noise, and to the resolution of the Lie-Suzuki-Trotter digitization.