Abstract
A quantum spin- chain with an axial symmetry is normally described by quasiparticles associated with the spins oriented along the axis of rotation. Kinetic constraints can enrich such a description by setting apart different species of quasiparticles, which can get stuck at high enough density, realizing the quantum analog of jamming. We identify a family of interactions satisfying simple kinetic constraints and consider generic translationally invariant models built up from them. We study dynamics following a local unjamming perturbation in a jammed state. We show that they can be mapped into dynamics of ordinary unconstrained systems, but the nonlocality of the mapping changes the scales at which the phenomena manifest themselves. Scattering of quasiparticles, formation of bound states, and eigenstate localization become all visible at macroscopic scales. Depending on whether a symmetry is present or not, the microscopic details of the jammed state turn out to have either a marginal or a strong effect. In the former case or when the initial state is almost homogeneous, we show that even a product state is turned into a macroscopic quantum state.
- Received 1 September 2023
- Revised 20 January 2024
- Accepted 11 March 2024
DOI:https://doi.org/10.1103/PhysRevX.14.021015
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
In the presence of kinetic constraints, quasiparticles describing the behavior of an ordered arrangement of quantum spins can get “stuck” as their density increases. Because of its similarity to the formation of amorphous solids, this situation can be interpreted as the quantum analog of jamming. Jammed states are intrinsically unstable and small perturbations produce unusual nonequilibrium dynamics. Here, we show that quantum jamming is a mechanism to make microscopic phenomena visible at a macroscopic scale: A single impurity produces a permanent change in the state, and a few impurities leave an imprint of their scattering properties and bound states.
In this study, we set out to understand what phenomenology should be expected close to quantum jamming when the system is perturbed out of unstable equilibrium rather than driven from or to thermodynamic equilibrium. Aiming at both generality and simplicity, we focus on a class of quantum spin-1/2 chains, and we propose a model of kinetic constraints that would trigger jamming in such a system. We find that a single measurement of a local observable in a jammed separable state realizes a macroscopic entangled state, much like the cat in Schrödinger’s famous thought experiment. This entanglement becomes macroscopic independently of the probability of the outcome.
The stability of the phenomenology under imperfections of the system is still an open question, which could determine the feasibility of experimental implementation. Such experiments could in turn open the door to exploiting kinetic constraints as tools for probing microscopic quantum properties.
