Originating from the discovery of the quantum Hall effect in the 1980s, the study of topological phases of matter have received sustained attention in the past few decades. Due to its universal nature, this field has expanded into new and exciting areas, particularly ultracold atomic gases and optics.
The implementation of topological states and their physical parameters in these new areas differ significantly from those in electronic materials explored in the pioneer studies. For instance, the extreme dilution and ultralow temperatures of atomic gases result in much longer timescales for dynamical processes, offering unique experimental opportunities. Current techniques allow researchers to monitor non-equilibrium processes driven by coherent quantum dynamics with exceptionally high temporal resolution and perform rapid parameter switches (quenches) to initiate various dynamical processes. These experimental advantages provide powerful platforms to explore topological dynamics in ultracold atomic gases and optical systems, including topological phase transitions, Floquet topological phases, quantized transport, and nonlinear phenomena. Moreover, these settings enable the creation and study of diverse topological states, such as vortices, vortex solitons, hopfions, skyrmions, and topological insulators, offering insights into their fundamental properties and potential applications.
We expect this special issue will provide a comprehensive overview of the latest achievements and advancements in this field, offering readers high-quality research contributions. We warmly invite theoretical and experimental research groups, as well as individual authors, to submit original research articles and reviews to the special issue. While there are no strict length restrictions for articles, reviews should have a minimum length of 15 pages. Publication fees will be waived for all contributors, and all articles published online will be freely available for download. The submission deadline is October 31, 2025. Authors who require an extension are kindly requested to inform us in advance.
We look forward to receiving your submission.
Sincerely,
Vladimir V. Konotop, University of Lisbon, E-mail: vvkonotop@ciencias.ulisboa.pt
Yongyao Li, Foshan University, E-mail: yongyaoli@gmail.com
Boris Malomed, Tel Aviv University, E-mail: malomed@tauex.tau.ac.il
The Haldane model is the simplest yet most powerful topological lattice model exhibiting various phases, including the Dirac semimetal phase and the anomalous quantum Hall phase (also known as the Chern insulator). Although considered unlikely to be physically directly realizable in condensed matter systems, it has been experimentally demonstrated in other physical settings such as cold atoms, where Hermiticity is usually preserved. Extending this model to the non-Hermitian regime with energy non-conservation can significantly enrich topological phases that lack Hermitian counterparts; however, such exploration remains experimentally challenging due to the lack of suitable physical platforms. Here, based on electric circuits, we report the experimental realization of a genuine non-Hermitian Haldane model with asymmetric next-nearest-neighbor hopping. We observe two previously uncovered phases: a non-Hermitian Chern insulator and a non-Hermitian semimetal phase, both exhibiting boundary-dependent amplifying or dissipative chiral edge states. Our work paves the way for exploring non-Hermiticity-induced unconventional topological phases in the Haldane model.
Hilbert space fragmentation (HSF) is a mechanism for generating quantum many-body scar (QMBS), which provides a route to weakly break ergodicity. Many scarred systems possess an exponentially large number of zero-energy states due to the chiral symmetry induced bipartition of the Hilbert space. In this work, we study the QMBS phenomenology under the interplay between the chiral symmetry and pseudo HSF, where the Hilbert space is approximately fragmented into different blocks. We consider a model of tilted chain of interacting spinless fermions with periodically varying tunneling strength. At small tunneling strength, we analytically derive the resonance conditions under which the system is described by an effective model with chiral symmetry and pseudo HSF. We find that the interplay between the two gives rise to a highly localized zero-energy QMBS when the particle number is even. This zero-energy QMBS induces an unusual scarred dynamical phenomenon. Specifically, the fidelity from a simple initial state oscillates around a finite fixed value without decaying, instead of showing the typical decaying collapse and revival observed when the particle number is odd and in common scarred systems. We show that the signature of the unusual scarred dynamical behaviour can also be detected in the original driven system by measuring local observables. Our findings enrich the scar phenomenon and deepen the understanding of the relation between Hilbert space structure and QMBS.
Recently, the simulation of moiré physics using cold atom platforms has gained significant attention. These platforms provide an opportunity to explore novel aspects of moiré physics that go beyond the limits of traditional condensed matter systems. Building on recent experimental advancements in creating twisted bilayer spin-dependent optical lattices for pseudospin-1/2 Bose gases, we extend this concept to a trilayer optical lattice for spin-1 Bose gases. Unlike conventional moiré patterns, which are typically induced by interlayer tunneling or interspin coupling, the moiré pattern in this trilayer system arises from inter-species atomic interactions. We investigate the ground state of Bose-Einstein condensates loaded in this spin-1 twisted optical lattice under both ferromagnetic and antiferromagnetic interactions. We find that the ground state forms a periodic pattern of distinct phases in the homogeneous case, including ferromagnetic, antiferromagnetic, polar, and broken axial symmetry phases. Additionally, by quenching the optical lattice potential strength, we examine the quench dynamics of the system above the ground state and observe the emergence of topological excitations such as vortex pairs. This study provides a pathway for exploring the rich physics of spin-1 twisted optical lattices and expands our understanding of moiré systems in synthetic quantum platforms.
The persistent flow of superfluids is essential for understanding the fundamental characteristics of superfluidity and shows promise for applications in high-precision metrology and atomtronics. We proposed a protocol for generating persistent flows with significant winding numbers by employing a geometric quench and leveraging two-dimensional (2D) quantum turbulence. By subjecting the trap potential to sudden geometric quenches to drive the system far from equilibrium, we can reveal intriguing nonequilibrium phenomena. Our study demonstrates that transitioning from a single ring-shaped configuration to a double concentric ring-shaped configuration through a geometric quench does not induce a persistent current in Bose−Einstein condensates (BECs). The energy transfer from small to large length scales during the 2D turbulent cascade of vortices can generate persistent flow with a small winding number in toroidal BECs. Nonetheless, the interplay of geometric quench and turbulent cascade can lead to circulation flows that exhibit high stability, uniformity, and are devoid of topological excitations. We showcase the intricate nature of turbulence in our investigation, which is influenced by factors like boundaries and spatial dimensionality. This advancement holds promise for innovative atomtronic designs and provides insights into quantum tunneling and interacting quantum systems under extreme non-equilibrium conditions.
An edge soliton is a localized bound state that arises from the balance between diffraction broadening and nonlinearity-induced self-focusing. It typically resides either at the edge or at the domain wall of a lattice system. To the best of our knowledge, most reported edge solitons have been observed in conservative Hermitian systems; whether stable edge solitons can exist in non-Hermitian systems remains an open question. In this work, we utilize a photonic lattice that naturally exhibits type-II Dirac cones and introduce a domain wall by carefully configuring gains and losses at the three sites within each unit cell. Surprisingly, edge states localized at the domain wall can exhibit entirely real propagation constants. Building on these edge states, we demonstrate the existence of edge solitons that can propagate stably over distances significantly exceeding those in the experimental settings adopted in this study. Although these solitons eventually couple with the bulk states and ultimately collapse, they exhibit remarkable resilience. Our findings establish that a domain wall supporting loss-resistant edge solitons, which can also evade the skin effect, is achievable in non-Hermitian systems. This discovery holds promising potential for the development of compact functional optical devices.