Abstract
Non-Hermitian descriptions of quantum matter have seen impressive progress recently, with major advances in understanding central aspects such as their topological properties or the physics of exceptional points, the non-Hermitian counterpart of critical points. Here, we use single-photon interferometry to reconstruct the non-Hermitian Kibble-Zurek mechanism and its distinct scaling behavior for exceptional points, by simulating the defect production upon performing slow parameter ramps. We report progress along two axes. First, we realize parameter ramps across higher-order exceptional points, providing experimental access to their theoretically predicted characteristic Kibble-Zurek scaling behavior in the defect production. Second, we extend the scaling properties to the defect fluctuations, which enables us to extract the correlation length and dynamical exponents of the underlying the exceptional point (EP) and therefore to gain direct experimental information about the universality class of the EPs. Our work represents a step toward increasing the experimental complexity of non-Hermitian quantum time evolution, as part of the quest to move the frontier from single-particle physics toward increasingly complex settings.
1 More- Received 3 December 2020
- Accepted 5 April 2021
DOI:https://doi.org/10.1103/PRXQuantum.2.020313
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
While the thermodynamics of phase transitions, such as the one when water turns into ice, is as fundamental as it is well studied, the real-time dynamics through phase transitions are relatively much more recent. Crucial universal aspects of this behavior are captured by the Kibble-Zurek theory, which plays a pivotal role in quantum and statistical mechanics, cosmology, and condensed-matter physics. Parallel to these developments, there is a recent surge of interest in understanding and analyzing non-Hermitian quantum dynamics, which is an extension of conventional quantum mechanics to settings in which a system interacts with the outside world. In this setting, the concept of an exceptional point replaces the idea of a critical point. Here, we generalize and experimentally verify the Kibble-Zurek theory for various exceptional points and protocols, and demonstrate that not only the defect density but also its fluctuations obey a universal scaling form.
By using a highly controllable single-photon interferometry setup, we simulate the time evolution of exotic multiband structures and incrementally augment their complexity, thus realizing higher-order exceptional points and determining their characteristic properties experimentally. Borrowing ideas from scaling, we theoretically demonstrate and experimentally confirm that the defect density and its fluctuations follow universal scaling. This allows us to extract the correlation length and dynamical exponents of the underlying exceptional point and therefore to gain direct experimental information of its universality class.
As a key consequence, we identify a platform for realizing non-Hermitian dynamics of increasing complexity as a route toward further study of the dynamics in many-body systems.