Kinetically constrained spin systems are toy models of supercooled liquids and amorphous solids. In this perspective, we revisit the prototypical Fredrickson-Andersen (FA) kinetically constrained model from the viewpoint of $K$-core combinatorial optimization. Each kinetic cluster of the FA system, containing all the mutually visitable microscopic occupation configurations, is exactly the solution space of a specific instance of the $K$-core attack problem. The whole set of different jammed occupation patterns of the FA system is the configuration space of an equilibrium $K$-core problem. Based on recent theoretical results achieved on the $K$-core attack and equilibrium $K$-core problems, we discuss the thermodynamic spin glass phase transitions and the maximum occupation density of the fully unfrozen FA kinetic cluster, and the minimum occupation density and extreme vulnerability of the partially frozen (jammed) kinetic clusters. The equivalence between $K$-core attack and the fully unfrozen FA kinetic cluster also implies a new way of sampling $K$-core attack solutions.

Exploring the realms of physics that extend beyond thermal equilibrium has emerged as a crucial branch of condensed matter physics research. It aims to unravel the intricate processes involving the excitations, interactions, and annihilations of quasi- and many-body particles, and ultimately to achieve the manipulation and engineering of exotic non-equilibrium quantum phases on the ultrasmall and ultrafast spatiotemporal scales. Given the inherent complexities arising from many-body dynamics, it therefore seeks a technique that has efficient and diverse detection degrees of freedom to study the underlying physics. By combining high-power femtosecond lasers with real- or momentum-space photoemission electron microscopy (PEEM), imaging excited state phenomena from multiple perspectives, including time, real space, energy, momentum, and spin, can be conveniently achieved, making it a unique technique in studying physics out of equilibrium. In this context, we overview the working principle and technical advances of the PEEM apparatus and the related laser systems, and survey key excited-state phenomena probed through this surface-sensitive methodology, including the ultrafast dynamics of electrons, excitons, plasmons, spins, etc., in materials ranging from bulk and nano-structured metals and semiconductors to low-dimensional quantum materials. Through this review, one can further envision that time-resolved PEEM will open new avenues for investigating a variety of classical and quantum phenomena in a multidimensional parameter space, offering unprecedented and comprehensive insights into important questions in the field of condensed matter physics.

Electronic processes within atoms and molecules reside on the timescale of attoseconds. Recent advances in the laser-based pump-probe interrogation techniques have made possible the temporal resolution of ultrafast electronic processes on the attosecond timescale, including photoionization and tunneling ionization. These interrogation techniques include the attosecond streak camera, the reconstruction of attosecond beating by interference of two-photon transitions, and the attoclock. While the former two are usually employed to study photoionization processes, the latter is typically used to investigate tunneling ionization. In this review, we briefly overview these timing techniques towards an attosecond temporal resolution of ionization processes in atoms and molecules under intense laser fields. In particular, we review the backpropagation method, which is a novel hybrid quantum-classical approach towards the full characterization of tunneling ionization dynamics. Continued advances in the interrogation techniques promise to pave the pathway towards the exploration of ever faster dynamical processes on an ever shorter timescale.

Metal-organic frameworks (MOFs), which are self-assembled porous coordination materials, have garnered considerable attention in the fields of optoelectronics, photovoltaic, photochemistry, and photocatalysis due to their diverse structures and excellent tunability. However, the performance of MOF-based optoelectronic applications currently falls short of the industry benchmark. To enhance the performance of MOF materials, it is imperative to undertake comprehensive investigations aimed at gaining a deeper understanding of photophysics and sequentially optimizing properties related to photocarrier transport, recombination, interaction, and transfer. By utilizing femtosecond laser pulses to excite MOFs, time-resolved optical spectroscopy offers a means to observe and characterize these ultrafast microscopic processes. This approach adds the time coordinate as a novel dimension for comprehending the interaction between light and MOFs. Accordingly, this review provides a comprehensive overview of the recent advancements in the photophysics of MOFs and additionally outlines potential avenues for exploring the time domain in the investigation of MOFs.

Dynamic topological photonics is a novel research field, combining the time-domain optics and topological physics. In this review, the recent progress and realization platforms of dynamic topological photonics have been well introduced. The definition, measurement methods and the evolution process of the dynamic topological photonics are demonstrated to better understand the physical diagram. This review is meant to bring the readers a different perspective on topological photonics, grasp the advanced progress of dynamic topology, and inspire ideas about future prospects.

Ultrafast transmission electron microscope (UTEM) with the multimodality of time-resolved diffraction, imaging, and spectroscopy provides a unique platform to reveal the fundamental features associated with the interaction between free electrons and matter. In this review, we summarize the principles, instrumentation, and recent developments of the UTEM and its applications in capturing dynamic processes and non-equilibrium transient states. The combination of the transmission electron microscope with a femtosecond laser via the pump—probe method guarantees the high spatiotemporal resolution, allowing the investigation of the transient process in real, reciprocal and energy spaces. Ultrafast structural dynamics can be studied by diffraction and imaging methods, revealing the coherent acoustic phonon generation and photo-induced phase transition process. In the energy dimension, time-resolved electron energy-loss spectroscopy enables the examination of the intrinsic electronic dynamics of materials, while the photon-induced near-field electron microscopy extends the application of the UTEM to the imaging of optical near fields with high real-space resolution. It is noted that light—free-electron interactions have the ability to shape electron wave packets in both longitudinal and transverse directions, showing the potential application in the generation of attosecond electron pulses and vortex electron beams.