When passing through an undulator in a free electron laser, dense bunches of relativistic electrons split into microbunches, attaining a periodic space-time structure. We show that the field of such periodically modulated bunches is tremendously influenced by coherence effects, resulting in a novel type of beam-atom interaction. Our results indicate that employing such bunches (alone or in combinations with the radiation they emit) offers a multitude of new opportunities for exploring atomic dynamics on a femtosecond timescale.

We reconsider the footprints of radiation friction in a head-on collision of a bunch of relativistic charged particles with a laser pulse by demonstrating that forward and backward radiation and radiation friction are coherently enhanced in a dense bunch. This opens an avenue to observe radiation friction in laser-matter interactions at much lower energies and laser intensities than previously considered possible. An estimate for the energy losses of the particles in the bunch over the collision due to coherent radiation friction in terms of laser and bunch parameters is derived and validated by comparing with the results of three dimensional particle-in-cell simulations.

We study the phase diagram of a one-dimensional spin quantum breakdown model, which has an exponential $U(1)$ symmetry with charge unit decaying as $2^{-j}$ with site position $j$. By exact diagonalization and density matrix renormalization group, we show that the model with spin $S\ge 2$ exhibits an exponential $U(1)$ spontaneous symmetry-breaking (SSB) phase dubbed a quantum breakdown condensate. It exhibits a bulk gap violating the Goldstone theorem and an edge mode only on the left edge if in open boundary condition. In a length $L$ lattice, the condensate has $\mathcal{O}(2^L)$ number of SSB ground states originating from the $\mathcal{O}(2^L)$ number of exponential $U(1)$ charge sectors, leading to a finite entropy density $\ln 2$. This enforces a first-order SSB phase transition into this phase, as observed numerically and verified in the large $S$ limit on an exactly solvable Rokhsar-Kivelson line. The condensate has an SSB order parameter being the local in-plane spin, which points in angles related by the chaotic Bernoulli (dyadic) map and thus is effectively random. Moreover, we show the condensate exhibits nondecaying local autocorrelations and does not have an off-diagonal long-range order. The quantum breakdown condensate thus behaves as a disorder-free quantum glass and is beyond the existing classifications of phases of matter.

In two-dimensional (2D) van der Waals (vdW) structures, the twist angle between adjacent layers has emerged as a pivotal parameter for engineering electronic band structures. This is vividly exemplified by the discovery of an extensive array of correlated and topological phases in 2D moiré systems. Yet, beyond the twist angle, interlayer separation—a relatively understudied parameter—provides an additional degree of freedom for modulating electronic properties of 2D moiré systems. Here, we demonstrate that in $\text{graphene}/{\mathrm{WSe}}_2$ heterostructures at specific twist angles, reducing the interlayer separation via scanning tunneling microscopy (STM) tip manipulation induces a moiré superlattice with a patent kagomelike arrangement. We show that this structural feature originates from carbon-carbon dimerization within the graphene layer and is driven by an interplay between the moiré superlattice and strong interlayer hybridization between graphene and ${\mathrm{WSe}}_2$. Furthermore, the kagomelike structure induces kagome-type electronic bands, as validated by first principles calculations. Our results establish interlayer hybridization in 2D moiré systems as a powerful and tunable knob for realizing designer quantum phases in vdW materials.

The non-Hermitian skin effect dramatically alters both the spectrum and real-time dynamics of non-Hermitian systems. We investigate the edge dynamics of waves initialized in non-Hermitian lattices, where the non-Hermitian skin effect tends to localize states, leading to behavior beyond the Bloch picture. By focusing on the Lyapunov exponents that quantify wave growth or decay, we show that they are governed by saddle points in the complex momentum space. We introduce an unambiguous criterion based on “Lefschetz thimbles” to identify the dominant saddle point, overcoming the failure of the conventional energy-based criterion. This framework provides a coherent theory for the non-Hermitian edge dynamics, enabling the prediction of observable phenomena such as the non-Bloch boomerang effect—a wave packet round trip across the lattice—and a refined energy threshold for the self-healing of boundary modes.

We show that collective excitations and optical responses of moiré fractional Chern insulators (FCIs) drastically differ from those of standard fractional quantum Hall (FQH) states in a Landau level. By constructing a variational wave function that incorporates the moiré lattice effect, we capture the collective modes in FCIs across a range of crystal momenta including the roton minimum. Interestingly, new collective modes are found in the long wavelength limit ($\mathit{q}\to 0$) at low energy below the excitation continuum, distinct from the FQH case. Some of these modes are optically active and manifest as sharp peaks in optical conductivity at THz frequency. We further show that intraband optical absorption and spectral weight in twisted ${\mathrm{MoTe}}_2$ are highly tunable by the displacement field. Our Letter thus establishes optical spectroscopy as a powerful tool to illuminate the unique collective modes of moiré FCIs.

Strong quantum fluctuations dominate the spin-$1/2$ triangular lattice Heisenberg antiferromagnet, but their survival at spin-1 remains an open question. We address it in ${\mathrm{K}}_2\mathrm{Ni}({\mathrm{SeO}}_3{)}_2$, a nearly ideal spin-1 realization, using inelastic neutron scattering. Below the ordering temperature $T_{\mathrm{N}}$, coherent one-magnon excitations coexist with a broad high-energy continuum. Two complementary approaches, a spectrally consistent $1/\mathrm{S}$-corrected spin-wave theory and a beyond-mean-field Schwinger boson theory, each reproduce distinct facets of the continuum, reflecting multiparticle excitations and the internal structure of confined quasiparticles, respectively. Together they show that substantial quantum fluctuations persist at $S=1$ and are encoded in the spectral distribution of the continuum. Above $T_{\mathrm{N}}$, the continuum bandwidth is conserved while spectral weight redistributes as magnons lose spatial coherence. Bandwidth conservation and the internal organization of continuum spectral weight thus emerge as organizing principles for ordered quantum magnets beyond spin-$1/2$.

Unequal-time correlation functions fundamentally characterize emergent statistical properties in complex systems, yet their direct measurement in experiments is challenging. We report the experimental observation of two-time, ballistic correlations in a photonic platform governed by the focusing nonlinear Schrödinger equation. Using a recirculating optical fiber loop with heterodyne field detection, we acquire the full space-time dynamics of partially coherent optical waves and extract the intensity correlator in stationary states of integrable turbulence. The correlators collapse under ballistic rescaling and quantitatively agree with predictions from generalized hydrodynamics (GHD) evaluated using the density of states obtained via inverse scattering analysis of the recorded fields. Our results provide a direct test (without any fitting parameters) of GHD in an integrable waves system.

Understanding the mechanical response of elastomers requires establishing a direct connection between macroscopic stress and the microscopic conformational statistics of network strands. In this Letter, we develop a unified theoretical framework that quantitatively links macroscopic stress to single-chain mechanics and the conformational statistics of network strands in unentangled elastomers. The framework is validated by extensive molecular dynamics simulations of unentangled elastomers subjected to multiple loading modes, including uniaxial compression, equibiaxial tension, pure shear, and simple shear.

Collective turns in starling flocks propagate linearly with negligible attenuation, indicating the existence of an underdamped sector in the dispersion relation. According to linear response theory, beside granting linear propagation of the phase perturbations, the real part of the frequency should also yield a spin-wave form of the unperturbed correlation function. However, new high-resolution experiments on real flocks show that underdamped traveling waves coexist with an overdamped Lorentzian correlation. Theory and experiments are reconciled once we add to the dynamics a Fermi-Pasta-Ulam-Tsingou term.

Quantum devices featuring midcircuit measurement and reset capabilities, such as quantum computers and dual-species Rydberg quantum simulators, enable the realization of quantum cellular automata. These systems evolve in discrete time following local updates implemented by unitary gates and allow for the realization of both closed and synthetic dissipative dynamics. Here, we focus on quantum cellular automata that implement minimal models of classical and quantum transport. To illustrate our ideas, we focus on a discrete-time totally asymmetric simple exclusion process and investigate how coherent dynamical contributions allow for the emergence of quantum effects and correlations. We find that bipartite entanglement dominates the transient evolution, while stationary states can retain quantum correlations beyond entanglement. Our results suggest viable routes for realizing transport models on quantum devices and characterizing collective quantum correlations in strongly driven systems.

Shannon-Rényi and stabilizer entropies are key diagnostics of structure, “nonstabilizerness,” phase transitions, and universality in quantum many-body states. We establish an exact correspondence for quadratic fermions: for any Gaussian eigenstate, the stabilizer Rényi entropy equals the Shannon-Rényi entropy of a number-conserving free-fermion eigenstate on a doubled system, evaluated in the computational basis. Specializing to the transverse-field Ising (TFI) chain, the TFI ground-state stabilizer entropies map to the Shannon-Rényi entropies of the XX-chain ground state of length $2L$. Building on this correspondence, together with other exact identities we prove, we derive closed expressions for the stabilizer entropy at indices $\alpha =\frac{1}{2},2$, 4 for a broad class of critical closed free-fermion systems. Each of these can be written with respect to the universal functions of the TFI chain. We further derive conformal-field-theory scaling laws for the stabilizer entropy at arbitrary Rényi index under both periodic and open boundary conditions. At $\alpha =4$, these scaling forms display a discontinuity for both open and periodic boundary conditions.

Quantum criticality is a resource for quantum-enhanced metrology, but existing schemes face intrinsic limitations. These arise because using criticality directly in the encoding dynamics restricts the accessible parameters to those explicitly supported by the critical Hamiltonian, and the requirement for critical conditions narrows the effective estimation range. To solve this, we introduce a general framework termed criticality-assisted noncommutative preparation (CANP). In this approach, critical evolution is employed as a state-preparation resource. We establish the underlying algebraic conditions and show that the intrinsic noncommutativity between the preparation and encoding operations leads to a genuine enhancement of the quantum Fisher information (QFI). Remarkably, this enhancement may be achieved at fixed total sensing time and energy cost. The effect is quantified by the Wigner-Yanase skew information, which measures noncommutativity and exhibits the same critical scaling as the QFI. We demonstrate effective use of CANP in the quantum Rabi and Lipkin-Meshkov-Glick models. Our results establish CANP as a robust technique to effectively implement criticality-enhanced quantum metrology.

Entanglement distribution is the overarching purpose of quantum networks. While communication over long distances can use deployed fiber infrastructure, it requires photons in the telecom band. However, advanced quantum network nodes do not operate at such wavelengths. Here we overcome this limitation with two tailor-made low-noise quantum-frequency converters to distribute entanglement between a single atom and a resonant photon over 14 km line of sight via 24 km of a deployed commercial fiber. The photon at wavelength 780 nm is first entangled with the atom, then converted to the telecom S-band, and finally back-converted after propagation through the fiber. This link enables a photon transfer efficiency of 1.7% while affecting the atom-photon entanglement fidelity by less than 1%. This brings integration of atomic quantum nodes with existing long-distance fiber networks into reach, enabling novel applications in quantum information processing.

Using $20.3{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first observation of the semileptonic decays $D^0\to K^{-}\omega e^{+}{\nu }_e$ and $D^{+}\to K_S^0\omega e^{+}{\nu }_e$ with significances of $8.0\sigma$ and $5.8\sigma$, respectively. Their decay branching fractions are measured to be $\mathcal{B}(D^0\to K^{-}\omega e^{+}{\nu }_e)=({9.4}_{-1.8}^{+2.0}\pm 0.6)\times {10}^{-5}$ and $\mathcal{B}(D^{+}\to K_S^0\omega e^{+}{\nu }_e)=({8.0}_{-2.1}^{+2.4}\pm 0.7)\times {10}^{-5}$. Combining these with the latest measurements of $D^{0(+)}\to K^{-}{\pi }^{+}{\pi }^{-(0)}{e}^{+}{\nu }_e$ and assuming ${\overline{K}}_1(1270)$ to be the sole mediating resonance in all processes, the branching ratios are determined to be $\{[\mathrm{\Gamma }(K_1(1270{)}^{-}\to K^{-}{\pi }^{+}{\pi }^{-})]/[\mathrm{\Gamma }(K_1(1270{)}^{-}\to K^{-}\omega )]\}={3.4}_{-0.7}^{+0.8}\pm 0.3$ and $\{[\mathrm{\Gamma }({\overline{K}}_1(1270{)}^0\to K^{-}{\pi }^{+}{\pi }^0)]/[\mathrm{\Gamma }({\overline{K}}_1(1270{)}^0\to {\overline{K}}^0\omega )]\}={7.9}_{-2.1}^{+2.4}\pm 0.7$. The combined branching fraction is determined to be $\mathcal{B}({\overline{K}}_1(1270)\to \overline{K}\omega )=(8.4\pm 1.4\pm 0.5)\%$, which is the most precise measurement from a collider experiment. Furthermore, for the first time based on a single vector-pseudoscalar decay channel, the ${\overline{K}}_1(1270)$ mass is measured to be $(1336\pm 9\pm 2)\mathrm{MeV}/c^2$, providing unique experimental support for the two-pole structure of the ${\overline{K}}_1(1270)$ resonance. The first uncertainties are statistical, and the second are systematic.

The first measurement of the polarization of charm baryons by the LHCb experiment recorded in fixed-target mode is presented. The polarization of ${\mathrm{\Lambda }}_c$ baryons is studied in collisions of protons, at an energy of 2.51 TeV, incident on a gaseous target of neon, at a nucleon-nucleon center-of-mass energy of 68.6 GeV. The world’s first measurement of separate-charge polarizations for ${\mathrm{\Lambda }}_c^{+}$ and ${\overline{\mathrm{\Lambda }}}_c^{-}$ baryons is performed, determining $P_{{\mathrm{\Lambda }}_c^{+}}=(24\pm 9\pm 2)\%$, $P_{{\overline{\mathrm{\Lambda }}}_c^{-}}=(-8\pm 12\pm 3)\%$, where the first uncertainty is statistical and the second systematic. The polarization is also measured in intervals of baryon transverse momentum and the Feynman-$x$ variable.

We present converged ab initio calculations of short-range neutrinoless double-beta ($0\nu \beta \beta$)-decay nuclear matrix elements for the key experimental isotopes ${}^{76}\mathrm{Ge}$, ${}^{82}\mathrm{Se}$, ${}^{130}\mathrm{Te}$, and ${}^{136}\mathrm{Xe}$. Starting from different nuclear forces derived from chiral effective field theory, we apply the in-medium similarity renormalization group to obtain an effective valence-space Hamiltonian along with consistently transformed $0\nu \beta \beta$-decay operators. We then obtain a range of values for the matrix elements that is consistent with, but generally smaller than, those from phenomenology. Finally, we combine our results with current limits from $0\nu \beta \beta$-decay searches to obtain constraints for the sterile-neutrino mixing-mass parameter space when considering the inclusion of a fourth, sterile neutrino.