We probe the density-wave transition of the trilayer nickelate ${\mathrm{La}}_4{\text{Ni}}_3{\mathrm{O}}_{10}$ with polarization-resolved infrared spectroscopy. The low-energy electrodynamics is strongly anisotropic, with metallic in-plane and insulating out-of-plane character. In the ordered phase, the anisotropy grows more than an order of magnitude as the out-of-plane conductivity is sharply suppressed. We interpret this enhancement as an effective electronic decoupling of the Ni-O layers driven by a spin-density-wave-induced redistribution of $\mathrm{Ni}\text{−}{d}_{z^2}$ occupation within the trilayers. This electronic response is accompanied by clearly shifting and splitting out-of-plane phonons, compatible with a density-wave instability of electronic origin.

We provide a theoretical framework to describe the nonequilibrium temporal dynamics of correlated electron systems for realistic system parameters and the consequent, often exponentially long timescales. It is based on an entirely integrodifferential formulation of time-dependent dynamical mean-field theory, the noncrossing approximation, and the quantum representation of a driving electromagnetic field. For heavy-fermion systems, we identify two key nonequilibrium mechanisms governing their time evolution after a single-cycle terahertz excitation: transient, instantaneous shift from the Kondo toward the mixed-valence regime by an enhanced, photo-assisted hybridization, and slow recovery of the heavy-fermion state due to the long Kondo coherence time. This explains recent time-resolved terahertz spectroscopy experiments microscopically and establishes the latter as a technique for direct experimental access to the Kondo coherence time and to the heavy-fermion quasiparticle weight, central for the classification of heavy-fermion quantum phase transitions.

In quantum science applications, ranging from many-body physics to quantum metrology, dipolar interactions in spin ensembles are often controlled via Floquet engineering. However, this technique typically reduces the interaction strength between spins and effectively weakens the coupling to a target sensing field, limiting the metrological sensitivity. In this Letter, we develop and demonstrate an alternative method that directly tunes the native dipolar interaction in an ensemble of nitrogen-vacancy (NV) centers in diamond, thereby overcoming these limitations inherent to Floquet engineering. Our approach utilizes dressed-state qubit encoding under a bias magnetic field applied perpendicular to the crystal lattice orientation. This method leads to a $3.2\times$ enhancement of the dimensionless coherence parameter $J{T}_2$ compared to state-of-the-art Floquet engineering and a $2.6\times$ (8.3 dB) enhanced sensitivity in ac magnetometry. Our results provide a powerful Hamiltonian engineering tool for future studies with NV ensembles and other interacting higher-spin ($S>\frac{1}{2}$) systems.

Quantum interference can produce pivotal effective photon-photon interactions, enabling the exploration of various quantum information technologies that are beyond the possibilities of classical physics. While this effective interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, loss-induced nonunitary operations provide an alternative degree of freedom to control quantum interference. Here, we propose and experimentally demonstrate a concise yet powerful tool to unravel the essential features of quantum interference based on the phase change material vanadium dioxide. Since the insulator-metal transition in an elaborate vanadium dioxide thin film can create any desired particle exchange phase response, harnessing its phase transition would allow the dynamical control of photon-photon interaction such that the conventional coalescence and the anomalous anti-coalescence of photons can be continuously tuned. These results highlight an alternative approach for investigating quantum light-matter interactions, and facilitate nonunitary quantum interference for various quantum information processing tasks.

The newly discovered family of nonmagnetic kagome metals ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ ($\mathrm{A}=\mathrm{K}$, Rb, or Cs) provides a unique platform for exploring the interplay between charge-density wave (CDW) order, superconductivity, nontrivial topology, and spontaneous time-reversal symmetry breaking. Although characterizing the CDW phase is essential for understanding and modeling these exotic phenomena, its nature remains unresolved. In this Letter, we employ first-principles free-energy calculations, accounting for both ionic kinetic energy and anharmonic effects, to resolve the atomistic phase diagram of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ and its charge ordering structure. Our results uncover that the CDW ground state is formed by reconstructed vanadium kagome layers in a triangular-hexagonal pattern, featuring energetically degenerate different stacking orders. This accounts for the various out-of-plane modulations observed experimentally and supports the coexistence of multiple domains. The discovered symmetry-broken ground state is consistent with the absence of any electronic anisotropy in transport experiments. By combining anharmonic phonons with the calculation of electron-phonon matrix elements, we predict a superconducting critical temperature for the CDW phase in agreement with experiments showing that superconductivity is phonon mediated. These findings not only resolve a long-standing structural puzzle, but also clarify the impact of the CDW in superconductivity, highlighting its fundamental importance in shaping the low-temperature quantum phase diagram of kagome metals.

The search for multiferroicity in two-dimensional (2D) systems has predominantly focused on spin-driven mechanisms, leaving the distinct physics of coupled spin-orbital orders largely unexplored. Here, we propose a theoretical mechanism for orbital multiferroicity on 2D triangular lattices, arising from the intrinsic interplay between ferro-orbital and magnetic orders. Through symmetry analysis and effective model derivation, we reveal that the orbital order imposes a strong interaction on the magnetic sector, activating robust orbiton-magnon hybridization. Using density-functional theory calculations, we substantiate this mechanism in monolayer ${\mathrm{FeH}}_2$, where cooperative orbital and spin interactions stabilize an antiferro-orbital antiferromagnetic ground state. Remarkably, mechanical strain efficiently tunes these interactions, enabling reversible phase transitions between the antiferro-orbital and ferro-orbital states. Crucially, the elementary excitation spectrum exhibits hybridization gaps, serving as a definitive fingerprint of the formed entangled magnon-orbiton modes. Our Letter thus establishes a novel paradigm for exploring orbital multiferroicity in 2D systems.

Achieving all-to-all coherent networks is critical for the advancement of large-scale coherent computing and communication protocols. By exploiting the resonant dipole-dipole interaction between distant spin ensembles coupled to a one-dimensional coplanar waveguide (CPW) terminated by a mirror, we successfully demonstrate an on-demand all-to-all coherent network enabling selective coupling and decoupling between four spin ensembles. Furthermore, by repositioning the spin ensembles along the CPW, we achieve collective coupling and demonstrate coherent energy exchange between multiple spin ensembles in the time domain. These results strongly indicate the potential of this device as a medium-scale all-to-all network structure, which is poised to advance the exploration of many-body physics and enhance coherent information processing capabilities.

Luminescent solar concentrators (LSCs) are highly transparent, cost-effective photovoltaic devices that convert sunlight into fluorescence, which is then concentrated on peripheral solar cells via total internal reflection (TIR). In this Letter, we systematically analyzed the influence of directional emission on the efficiency of LSCs, revealing that directional emission not only enhances TIR efficiency but also mitigates light propagation losses. To validate this, we utilized highly bright and polarized emitting CdSe/CdZnS quantum rods (QRs) as the emitter. By developing an electrically aligned photopolymerization technique, we successfully induced and fixed the orientation of the QRs within a polymer matrix, thereby preventing the aggregation-induced quenching. Further characterization demonstrated a 1.23-fold efficiency improvement for the directionally emitting LSC device compared to its isotropic counterpart. Ultimately, the $3.5\times 3.5\times 0.85{\mathrm{cm}}^3$ laminated-glass device achieved an extremely high power conversion efficiency of $\sim 4.92\%$. By adjusting QRs concentration, a light utilization efficiency of $\sim 2.39\%$ with over 60% transmittance was obtained, rivaling state-of-the-art transparent photovoltaic devices.

GW231123, the heaviest binary black hole merger detected by the LIGO-Virgo-KAGRA Collaboration to date, lies in the pair-instability mass gap and exhibits unusually high component spins. In this Letter, we show that both merging black holes may have a primordial origin with smaller initial masses. The observed masses and, crucially, the spins of GW231123 are naturally accommodated within the most vanilla primordial black hole framework, once cosmological accretion is taken into account. Interestingly, the parameter space needed to explain the inferred GW231123 rate is at the edge of the exclusion region from x-ray and CMB observations, suggesting that this interpretation can be either confirmed or ruled out. The upcoming O5 observing run by the collaboration should detect $\mathcal{O}(20)$ similar events, testing their mass-spin correlation, while next-generation detectors would be capable of observing high-redshift events, as predicted in this scenario.

The activation of ${\mathrm{O}}_2$ on Au surfaces is a fundamental step for heterogeneous catalysis and surface oxidation. Although Au is widely recognized for its selectivity in various oxidation reactions, its limited ability to dissociate ${\mathrm{O}}_2$ remains a challenge for Au-based catalysis. In this Letter, we show that the surface reconstructions that Au(110) and Au(100) display contribute significantly to their inertness. By studying a series of Au surfaces with different surface geometries, we show that in general hexagonal Au surface structures exhibit a high ${\mathrm{O}}_2$ dissociation barrier, while rectangular or square surfaces show a significantly lower barrier. Thus, the reconstruction of the Au(110) and Au(100) surfaces to quasihexagonal structures slows ${\mathrm{O}}_2$ dissociation by many orders of magnitude, and Au would likely oxidize quickly under ambient conditions if these surfaces did not reconstruct. This provides new understanding as to why Au is so inert toward ${\mathrm{O}}_2$ and suggests that creating surfaces with square or rectangular structures may significantly improve catalytic activity for oxidation reactions on Au.

Chiral phonons, lattice vibrations carrying finite angular momentum, are at the forefront of a fast-developing field for exploring and controlling quantum materials in captivating ways. Phonon chirality originating from topological phonon bands is physically interesting but generally small and limited to a few material classes. Here, we report the observation of significant phonon chirality in the triangular-lattice rare-earth compound ${\mathrm{KNdSe}}_2$. We find that the chirality is activated by a distinct local mechanism—crystalline electric field (CEF) excitations—rather than by a global topology. Using helicity-resolved magneto-Raman spectroscopy, we observe a clear splitting ($\sim 3{\mathrm{cm}}^{-1}$ under 9 T, or equivalently $\sim 0.4{\mu }_B$) of the degenerate $E_g$ phonon mode that exhibits perfect circular polarization selection rules—the unambiguous fingerprint of chirality. The magnitude, field dependence, and thermal evolution of the splitting are quantitatively reproduced by a microscopic theory of CEF-phonon coupling, which we solve by employing the Dyson equation formalism and incorporating a careful analysis of symmetry and angular momentum conservation. Our findings demonstrate a deterministic, CEF-activated mechanism for realizing phononic chirality and identify the rare-earth chalcogenides as a highly tunable playground for investigating the rich physics of coupled electronic and vibrational quasiparticles.

We present a model for strongly interacting fermions with internal O(3) symmetry on the fuzzy sphere that (i) preserves the rotational symmetry of the fuzzy sphere and (ii) undergoes a quantum phase transition in the ($2+1$)-dimensional O(3) Wilson-Fisher universality class. Using exact diagonalization and density matrix renormalization group, we locate the quantum critical point via conformal perturbation theory and obtain scaling dimensions from finite-size spectra. We identify 24 primary operators and determine some of their operator product expansion coefficients through first-order conformal perturbation theory. The results are benchmarked against conformal bootstrap and large quantum-number expansions and reveal a weakly irrelevant operator that plays a role in dimerized antiferromagnets. Our Letter provides a general framework for quantitatively accessing conformal data for $O(N)$ Wilson-Fisher conformal field theories.

Non-Hermitian extensions of the Aubry-André-Harper (AAH) model reveal a rich variety of phase transitions arising from the interplay of quasiperiodicity and nonhermiticity. Despite their theoretical significance, experimental explorations remain challenging due to intricacies in realizing controlled nonhermiticity. Here, we present the first experimental realization of the unitary almost-Mathieu operator that simulates the AAH model by employing single-photon quantum walks. We systematically observe a phase transition between localized and delocalized regimes in the Hermitian limit. Subsequently, by introducing a nonreciprocal hopping, we experimentally probe the parity-time symmetry-breaking transition that is characterized by the emergence of complex quasienergies. Moreover, we identify a novel spectral transition exclusive to discrete-time settings, beyond which the real parts of all quasienergies vanish. These results clarify the interplay between localization, symmetry breaking, and topology in non-Hermitian quasicrystals, thereby paving the way for future exploration of synthetic quantum matter.

Two-dimensional (2D) magnetism, particularly 2D altermagnetism (AM), has attracted considerable interest due to its exceptional physical properties and broad application potential. However, the classification of AM undergoes a fundamental paradigm shift when transitioning from three-dimensional (3D) to 2D symmetry-enforced fully compensated collinear magnetism—a shift that has remained largely overlooked. Here, by extending unconventional magnetism to 2D collinear systems, we identify the symmetry conditions and electronic band characteristics of a distinct magnetic phase: type-IV magnetism. This new class lies beyond the established descriptions of ferromagnetism, conventional antiferromagnetism, and AM. Type-IV magnetism supports the successive emergence of both nonrelativistic spin-degenerate and relativistic spin-splitting phenomena, belonging strictly to neither conventional antiferromagnetism nor standard AM. We further establish a universal symmetry classification framework for 2D type-IV magnets via a mapping from the collinear spin layer group to the magnetic layer group. Monolayer ${\text{MgCr}}_2{\mathrm{O}}_4$ and monolayer ${\mathrm{BaMn}}_2{\mathrm{Ch}}_3$ ($\mathrm{Ch}=\mathrm{Se}$, Te) are showcased as representative materials, exhibiting gate-tunable reversible spin textures and the quantum electric Hall effect, respectively. Our Letter underscores the rich functional prospects of type-IV magnets, offering a new route toward spin manipulation and anomalous transport that promises innovative designs for high-performance spintronic devices.