The quantum Hall effect was originally observed in a two-dimensional electron gas forming Landau levels when exposed to a strong perpendicular magnetic field and was later generalized to Chern insulators without net magnetization. Here, further extending the realm of the quantum Hall effect, we report on the robust occurrence of an integer quantized transverse conductance at the onset of disorder in a microscopic lattice model, all bands of which are topologically trivial (zero Chern number). We attribute this phenomenon to the energetic separation of nonquantized Berry fluxes within those bands. Adding disorder then nudges the system into a quantum Hall phase from an extended critical regime obtained by placing the Fermi energy within a broad window inside a trivial band. This natural integer-rounding mechanism manifests as the mobility-gap-induced quantization of a nonuniversal Hall conductance. Our results are corroborated by numerical transport simulations and the analysis of two complementary topological markers.

We demonstrate single-mode lasing of magnon polaritons in a cavity magnonic system enabled by dissipative coupling between two passive modes, microwave cavity mode and magnon mode in a ferrimagnetic spin ensemble. The cavity mode is partially compensated through a feedback circuit, which reduces its linewidth but retains its dissipative nature. By tuning the compensation strength and dissipative coupling strength, we reach a system cooperativity of unity, marking the lasing threshold and the formation of a zero-linewidth polariton mode. This mode also corresponds to a perfect Friedrich–Wintgen bound state in the continuum. Further increase of the cooperativity drives the system into the strong dissipative coupling regime, where magnon-polariton amplification arises between two real-frequency scattering poles. These results reveal that dissipative coupling cooperativity carries a clear physical meaning and serves as a key parameter for controlling phase transitions. Dissipative coupling offers an alternative paradigm for tailoring light-matter interactions, paving the way for advances in both information processing and quantum technologies.

Urban sprawl reshapes cities, yet its quantitative laws remain elusive. Analyzing built-up expansion in 19 cities (1985–2015) with tools from surface growth physics in radial geometry, we reveal anisotropic, branchlike growth and a piecewise linear scaling between area and population. We uncover a robust local roughness exponent ${\alpha }_{\mathrm{loc}}\approx 0.54$, coexisting with variable $\beta$ and $z$. This unusual coexistence of universal and variable exponents offers a rare empirical test bed for nonequilibrium growth and an empirical basis for modeling urban sprawl.

Double network hydrogels show remarkable mechanical performance, combining high strength and fracture toughness with sufficient stiffness to bear load, despite containing only a low density of cross-linked polymer molecules in water. We introduce a simple mesoscale model of a double network material, detailed enough to resolve the salient microphysics of local plastic bond breakage, yet simple enough to address macroscopic cracking. Load sharing between the networks results in a delocalization of stress such that the double network inherits both the stiffness of its stiff-and-brittle sacrificial network and the ductility of its soft-and-ductile matrix network. The underlying mechanism is a reduction in the Eshelby stress propagator between sacrificial bonds, inhibiting the tendency for the plastic failure of one sacrificial bond to propagate stress to neighboring sacrificial bonds and cause a follow-on cascade of breakages. The mechanism of brittle macroscopic cracking is thereby suppressed, giving instead ductile deformation via diffusely distributed microcracking.

The role of complex quantities in quantum theory has been puzzling physicists since the beginnings. It is, thus, natural to ask whether, in order to describe our experiments, the mathematical structure of the complex Hilbert spaces it is built on is really necessary. Recently, it was shown that this structure is inevitable in network scenarios with independent sources. More precisely, Real Quantum Theory cannot explain the predictions of (Complex) Quantum Theory [Renou et al., Nature (London) 600, 625 (2021).]. Here, we revisit the independence assumption underlying this work. We show that assuming partial independence is sufficient for showing the inadequacy of Real Quantum Theory. We derive a tradeoff between source independence and the Bell value achievable in Real Quantum Theory, which also lower bounds the source correlations required to explain previous experiments by means of real quantum systems. We further show that 1 bit of entanglement is necessary and sufficient for recovering the complex quantum correlations by means of Real Quantum Theory in the scenario from [Renou et al., Nature (London) 600, 625 (2021).]. Finally, building on [McKague et al., Phys. Rev. Lett. 102, 2009], we provide a construction to simulate any complex quantum setup with $m$ independent sources by means of Real Quantum Theory by allowing the sources to share an $m$ real-qubit entangled state in the first round of the experiment.

Understanding the behavior of quantum many-body systems under decoherence is essential for developing robust quantum technologies. Here, we examine the fate of weak ergodicity breaking in systems hosting quantum many-body scars when subject to local pure dephasing—an experimentally relevant form of environmental noise. Focusing on a large class of models with an approximate su(2)-structured scar subspace, we show that scarred eigenmodes of the Liouvillian exhibit a transition reminiscent of spontaneous $\mathbb{PT}$-symmetry breaking as the dephasing strength increases. Unlike previously studied non-Hermitian mechanisms, this transition arises from a distinct quantum jump effect. Remarkably, in platforms such as the XY spin ladder and PXP model of Rydberg atom arrays, the critical dephasing rate shows only weak dependence on the system size, revealing an unexpected robustness of scarred dynamics in noisy environments.

A key challenge in achieving scalable fault tolerance in superconducting quantum processors is readout fidelity, which lags behind one- and two-qubit gate fidelity. A major limitation in improving qubit readout is measurement-induced transitions, also referred to as qubit ionization, caused by multiphoton qubit-resonator excitation occurring at specific photon numbers. Since ionization can involve highly excited states, it has been predicted that in transmons—the most widely used superconducting qubit—the photon number at which measurement-induced transitions occur is gate-charge dependent. This dependence is expected to persist deep in the transmon regime where the qubit frequency is gate-charge insensitive. We experimentally confirm this prediction by characterizing measurement-induced transitions with increasing resonator photon population while actively calibrating the transmon’s gate charge. Furthermore, because highly excited states are involved, achieving quantitative agreement between theory and experiment requires accounting for higher-order harmonics in the transmon Hamiltonian.

We present a comprehensive analysis of the effects of models with very low reheating scenarios [$T_{\mathrm{RH}}\sim \mathcal{O}(\mathrm{MeV})$] on the cosmological observables and derive corresponding bounds on the reheating temperature. With respect to previous work, our Letter includes a more precise computation of neutrino distribution functions, leveraging the latest datasets from cosmological surveys. We perform a joint analysis that combines constraints from big bang nucleosynthesis, the cosmic microwave background, and galaxy surveys, alongside separate investigations of these datasets, carefully assessing the impact of different choices of priors. At the 95% confidence level, we establish a lower bound on the reheating temperature of $T_{\mathrm{RH}}>5.96\mathrm{MeV}$, representing the most stringent constraint to date.

The dark photon is a well-motivated dark matter candidate that appears in many extensions of the standard model. A fundamental mass-range-sensitivity dilemma is always haunting the dark photon search experiments: resonant haloscopes have excellent sensitivity but are narrowband, while nonresonant haloscopes are broadband but not as sensitive as the resonant ones. A scalable architecture integrating numerous resonant haloscopes would be a desirable solution to this dilemma. However, even the concept of a scalable search remains rarely explored due to the size limitation of conventional haloscopes imposed by the dark photon wavelength. Here, we propose and demonstrate a novel architecture using superconducting qubits as subwavelength haloscope units. By virtue of the scalability of superconducting qubits, it is possible to integrate multiple qubits with different frequencies on a chip-scale device. Furthermore, the frequencies of the qubits can be tuned to extend the search mass range. Thus, our scalable architectures allow for sweepable high-sensitivity dark photon searches at multiple frequencies simultaneously. As a proof-of-principle experiment, we designed and fabricated a three-qubit chip and successfully demonstrated a scalable dark-photon search. Our Letter established constraints on dark photons in the mass range of 15.632–15.638, 15.838–15.845, and $16.463–16.468\mathrm{\mu }\mathrm{eV}$, simultaneously, and the constraints are much more stringent than the cosmology constraints. In the future, our Letter can be scaled up to boost the scrutiny of new physics.

Pion scattering amplitudes were recently found to vanish on specific kinematic loci, and to factorize close to these loci into a product of two lower-point amplitudes of an extended theory. We propose a diagrammatic representation of pion amplitudes that makes their vanishing on the loci manifest diagram by diagram. Moreover, we provide evidence that there is a closed-form expression for the amplitudes that generalizes the near-zero factorization in an exact manner, not only close to the loci but for all kinematic configurations. Our approach crucially relies on a novel formulation of the effective field theory of pions, in which tree-level scattering amplitudes are extracted from classical field equations for a set of covariantly conserved currents and emergent composite gauge fields.

Fluorine abundance in stars is a sensitive indicator of the physical conditions and processes occurring within their interiors. Recent extrapolated results on the ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ fluorine destruction cross section suggested an increase of the astrophysical factor by several orders of magnitude at astrophysical energies, with profound implications for our understanding of stellar evolution and nucleosynthesis. We have indirectly measured the ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ cross section using the Trojan horse method, fully covering astrophysical energies with no need of extrapolations. The strength of the 11 keV resonance was extracted and a significant reduction of the reaction rate was determined, compared to previous studies. The analysis of the astrophysical impact suggests that our measurement challenges existing predictions about fluorine and heavier elements’ abundances, reigniting unresolved questions in the field.

We present a method to engineer the Landé $g$ factor of alkali-metal atoms using spin-exchange collisions and nonresonant radio-frequency (rf) magnetic-field dressing. We analyze schemes with both linearly and circularly polarized rf dressing to generate dressed states, allowing the responses to magnetic and nonmagnetic spin-dependent interactions, such as the spin-gravity interaction, to be distinguished in the output signal. Our method provides a complementary approach to conventional comagnetometry in the investigation of exotic spin-dependent interactions and gyroscopes.

Exotic quasiparticle states have been proposed in mixed-valent compounds exhibiting valence transitions. However, clear spectroscopic evidence identifying these states has remained elusive. Using synchrotron-based hard x-ray and extreme ultraviolet photoemission spectroscopy, we have probed the Tm $3d$ and $4f$ emissions in ${\mathrm{TmSe}}_{1-x}{\mathrm{Te}}_x$, where a Te concentration-dependent semimetal–insulator transition occurs alongside the valence transition. Our photoemission results, which are characteristic of the bulk, track this combined transition across the critical concentration ($x_c=0.29$). Notably, our results reveal a noninteger valence for the insulating phase and a novel quasiparticle excitation in the semimetallic phase: a Holstein polaron that extends beyond the standard periodic Anderson model.

In this Letter we consider $D$-dimensional interacting Fermi liquids, and demonstrate that an attractive interaction with a finite range $R_s$ that is much greater than the Fermi wavelength ${\lambda }_F$ breaks the conventional BCS theory of superconductivity. In contrast to the BCS prediction of a finite superconducting gap for all attractive contact interactions, we show that a finite-range interaction does not induce a superconducting gap. Instead, the pair susceptibility develops a power-law singularity at zero momentum and zero frequency signaling quantum critical behavior without long-range ordering. Starting from this, we show that superconductivity can be stabilized by adding a short-range attractive interaction, which is always present in real electronic systems. As an example, we consider a layered quasi-two-dimensional material with attractive electron-electron interactions mediated by optical phonons. We demonstrate a dome shape of the critical temperature $T_c$ versus doping, strongly suppressed isotope effect, and a weak dependence of the optimal doping and maximal $T_c^{*}\sim 0.1E_F$ on the interaction range at $R_s\gg {\lambda }_F$, $E_F$ is the Fermi energy. We believe that these results could be relevant to high-temperature superconductors.

On the kagome lattice, electrons benefit from the simultaneous presence of band topology, flat electronic bands, and Van Hove singularities, forming competing or cooperating orders. Understanding the interrelation between these distinct order parameters remains a significant challenge, leaving much of the associated physics unexplored. In the kagome superconductor ${\mathrm{KV}}_3{\mathrm{Sb}}_5$, which exhibits a charge density wave (CDW) state below $T\simeq 78\mathrm{K}$, we uncover an unpredicted field-induced phase transition below 6 K. The observed transition is marked by a hysteretic anomaly in the resistivity, nonlinear electrical transport, and a change in the symmetry of the electronic response as probed via the angular dependence of the magnetoresistivity. These observations surprisingly suggest the emergence of an unanticipated broken symmetry state coexisting with the original CDW. To understand this experimental observation, we developed a theoretical minimal model for the normal state inside the high-temperature parent CDW phase, where an incommensurate CDW order emerges as an instability subleading to superconductivity. The incommensurate CDW emerges when superconducting fluctuations become fully suppressed by large magnetic fields. Our results suggest that, in kagome superconductors, quantum states can either coexist or are nearly degenerate in energy, indicating that these are rich platforms to expose new correlated phenomena.

The search for fractional quantized Hall phases in the absence of a magnetic field has primarily targeted flat-band systems that mimic the features of a Landau level. In an alternative approach, the fractional excitonic insulator (FEI) has been proposed as a correlated electron-hole fluid that arises near a band inversion between bands of different angular momentum with strong interactions. It remains an interesting challenge to find Hamiltonians with realistic interactions that stabilize this state. Here, we describe composite boson and composite fermion theories that highlight the importance of $(p_x+i{p}_y{)}^m$ excitonic pairing in stabilizing FEIs in a class of band inversion models. We predict a sequence of Jain-like and Laughlin-like FEI states, the simplest of which has the topological order of the bosonic $\nu =1/2$ fractional quantized Hall state. We discuss implications for recent numerical studies on a chiral spin liquid phase in interacting Chern insulator models.