We investigate the splitting probability of a monitored continuous-time quantum walk with two targets and show that, in stark contrast to a classical random walk, it exhibits a nonanalytic, phase-transition-like behavior controlled by the sampling time at the targets. For large systems and sampling times smaller than a critical value ${\tau }_c=2\pi /\mathrm{\Delta }E$, where $\mathrm{\Delta }E$ is the energy bandwidth, the splitting probability is universal and equal to $1/2$, independent of the initial condition and the sampling time. Above the critical sampling time, a nonuniversal regime emerges in which the splitting probability deviates from $1/2$ and develops a fluctuating pattern of pronounced peaks and dips dependent on both the sampling time and the initial condition. These results follow from a nontrivial mapping of the splitting problem onto a pair of single-target detection problems enabled by the superposition principle.

The dynamical preparation of exotic many-body quantum states is a persistent goal of analog quantum simulation, often limited by experimental coherence times. Recently, it was shown that fast, nonadiabatic Hamiltonian parameter sweeps can create finite-size “lakes” of quantum order in certain settings, independent of what is present in the ground state phase diagram. Here, we show that going further out of equilibrium via external driving can substantially accelerate the preparation of these quantum lakes. Concretely, when lakes can be prepared, existing counterdiabatic driving techniques—originally designed to target the ground state—instead naturally target the lakes state. We demonstrate this both for an illustrative single qutrit and a model of a ${\mathbb{Z}}_2$ Rydberg quantum spin liquid. In the latter case, we construct experimental drive sequences that accelerate preparation by almost an order of magnitude at fixed laser power. We conclude by using a Landau-Ginzburg model to provide a semiclassical picture for how our method accelerates state preparation.

We report a $3.3\sigma$ measurement of coherent elastic neutrino-nucleus scattering from solar ${}^8\mathrm{B}$ neutrinos using a $6.77\mathrm{t}\times \mathrm{yr}$ exposure from the XENONnT experiment, inferring a solar ${}^8\mathrm{B}$ neutrino flux of $(5_{-2}^{+3})\times {10}^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, consistent with previous measurements. In the presence of the ${}^8\mathrm{B}$ “neutrino fog,” we find no evidence for light dark matter, and observe diminishing returns in sensitivity with increasing exposure. A 93% increase in exposure from the previous search improves the median sensitivity to the nucleon scattering cross section for a $5\mathrm{GeV}/c^2$ spin-independent weakly interacting massive particle by 10%. The dataset was also used to measure the weak mixing angle at $\sim 0.02\mathrm{GeV}/c$ momentum transfer and constrain physics beyond the Standard Model.

Bound states in the continuum (BICs) are nonradiative modes embedded in the radiation continuum, offering powerful opportunities for wave manipulation in open systems. Although BICs themselves cannot be assigned a well-defined polarization state in the far field, the surrounding polarization field encodes essential topological information. In conventional BIC systems, the polarization trajectory surrounding a BIC typically forms a loop near or parallel to the equator of the Poincaré sphere and encircles the $S_3$ axis, resulting in a nonzero topological charge. Here, we show that such $S_3$-axis winding is not a prerequisite for the existence of a BIC. By introducing structural shear deformation, the polarization trajectory evolves from an equatorial loop to a tilted orbit, undergoes pole crossings, and eventually becomes nearly perpendicular to the equator. During this process, an isolated BIC remains intact while its topological charge continuously evolves from $-1$ to 0 and $+1$ without conventional singularity creation, annihilation, or merging. Furthermore, we generalize the formation mechanism of BICs beyond conventional orthogonal polarization states and establish a semianalytical geometric approach that predicts the polarization winding directly from the nodal-line configuration. Our results reveal a new route for momentum-space polarization engineering and extend the topological understanding of BICs.

Using an extension of the fermionic functional renormalization group for systems where strong correlations give rise to projected Hilbert spaces, we calculate the phase diagram and the electronic spectral function of the Hubbard model at infinite on-site repulsion. For a square lattice with nearest-neighbor hopping we find that the ground state evolves from a paramagnetic Fermi liquid at low densities via a state with antiferromagnetic stripe order at intermediate densities to an extended Nagaoka ferromagnet at high densities. The single-particle spectral function of the Nagaoka ferromagnet exhibits a flat but rather broad band characteristic for an incoherent non-Fermi liquid. We identify two distinct ferromagnetic regimes separated by a Lifshitz transition.

Tunneling spectroscopy cannot be used as an unambiguous detection tool for Majorana zero modes (MZMs) in conventional partial-shell nanowires. The presence of smooth confinement at the end of the hybrid wire (among other sources of disorder) can create exponentially pinned zero-energy states, called quasi-MZMs, that mimic all local signatures of MZMs but lack topological protection. We find that this ambiguity in MZM detection does not occur in full-shell hybrid nanowires, an alternative nanowire design where a superconducting shell fully surrounds the semiconductor core. Acting as a synthetic vortex, a full-shell hybrid nanowire hosts Caroli–de Gennes–Matricon state analogs. In the presence of smooth confinement, these states create a topologically trivial skin at the wire’s end that prevents the local probe from detecting quasi-MZMs. In this way, the same mechanism that creates MZM impostors makes them invisible in tunneling spectroscopy, avoiding false positives produced by smooth disorder.

The concept of morphotropic phase boundary has recently been employed to enhance the piezoelectric response in polymeric ferroelectrics, substantially improving the $d_{33}$ coefficient through engineered phase boundaries between $\beta$ and $3/1$-helical phases in polyvinylidene fluoride-based systems. However, this strategy has so far been effective primarily for the converse piezoelectric effect, with negligible impact on the direct piezoelectric response. This is a critical limitation as most practical applications of ferroelectric polymers rely on direct piezoelectricity (e.g., sensing, energy harvesting). Here, we reveal that during dipole reorientation from the $3/1$-helical to the $\beta$ conformation, the pronounced disparity between weak interchain van der Waals cohesion and strong intrachain covalent rigidity triggers an unexpected lateral expansion of the interchain spacing. This intermediate expansion raises the energy barrier for dipole reorientation under compressive stress, the very condition central to direct piezoelectric operation. To overcome this barrier, we apply a bias electric field combined with constant tensile stress along the $c$ axis, deliberately inducing a moderate interchain lattice expansion in advance. This preexpansion effectively lowers the energy barrier for subsequent dipole rotation under compression, thereby facilitating polarization switching and significantly enhancing the direct piezoelectric response. Using this approach, we achieve a giant direct piezoelectric coefficient of $d_{33}\approx -271\mathrm{pC}/\mathrm{N}$ in relaxor ferroelectric polymers. This work uncovers the structural origin of the inefficacy of morphotropic phase boundary for enhancing direct $d_{33}$ in polyvinylidene fluoride-based polymers and demonstrates that substantial potential remains for improving their direct piezoelectric performance.

Circular dichroism (CD) and other chiroptical responses are key probes of both chirality and momentum-space geometry in solids, but first-principles calculations are still challenging in periodic systems with strong exciton effects. Here, we develop a gauge-invariant first-principles framework for CD including exciton effects based on full minimal coupling (FMC) within the GW plus Bethe-Salpeter equation (GW-BSE) formalism. In contrast to standard multipole expansion and sum-over-states (SOS) approaches, which require careful gauge fixing, converge slowly, and suffer from origin ambiguities, FMC evaluates optical matrix elements directly at finite photon wave vector, naturally including intraband and near-degenerate transitions while placing electric dipole (ED), magnetic dipole (MD), and electric quadrupole (EQ) contributions on equal footing. Applied to two prototypical two-dimensional chiral hybrid perovskites, ${(\mathrm{S}\text{−}\mathrm{NEA})}_2{\mathrm{PbBr}}_4$ and ${(\text{S-MBA})}_2{\mathrm{PbI}}_4$, our calculations reveal that MD and EQ channels both contribute to the CD signal. Crucially, intraband and quasidegenerate transitions captured only within FMC can significantly modify CD spectra, especially in systems with dense band degeneracies. The FMC framework, therefore, offers a computationally efficient and numerically robust way for predicting chiral optoelectronic phenomena in complex solids.

The fermion sign problem poses a formidable challenge to the use of Monte Carlo methods for lattice gauge theories with dynamical fermionic matter fields. A meron-cluster algorithm recently formulated for gauge fields represented as spin-$1/2$ quantum links coupled to a single flavor of staggered fermions samples only two of the exponentially many Gauss law (GL) sectors at low temperatures, allowing the simulation of those two GL sectors at zero temperature in polynomial time. In this Letter, we analytically identify GL sectors which can be simulated without encountering the fermion sign problem in arbitrary spatial dimensions. Using large-scale exact diagonalization and cluster Monte Carlo methods, we explore the nature of phases in the GL sectors dominating at zero temperature. The ground state lives in a superselection sector free of the sign problem and maps to the quantum dimer model with mobile monomers. The usual zero-charge GL sector suffers from the fermion sign problem and maps to the fully packed loop model with mobile monomers. The role of the magnetic energy in causing transitions between GL sectors is outlined. We expect our results to be valid for truncated Kogut-Susskind gauge theories, beyond quantum link models.

The $\mathrm{\Lambda }$ cold dark matter cosmological model faces increasingly significant and robust tensions among independent cosmological probes, prompting renewed scrutiny of its foundational assumptions. While general relativity and the nature of darkenergy are now routinely tested with cosmological surveys, less progress has been made testing the spacetime geometry at the largest scales, and in particular testing the assumption that observables (distances, redshifts, expansion of space, etc.) on the largest scales are described by a single Friedmann-Lemaître-Robertson-Walker (FLRW) metric. In order to enable such tests, we introduce a model-independent framework that combines successive derivatives of the angular diameter distance, $d_A(z)$, with the line-of-sight expansion rate, $\mathcal{H}(z)$, to expose the physical content of well-known FLRW consistency relations. This allows us to perform diagnostic tests of the large-scale geometry that are free of assumptions about dark energy and the theory of gravity on large scales. In addition, we derive a new nonparametric estimator for the cosmic density field that is independent of the Friedmann equations. This enables qualitatively new, observationally accessible tests of the FLRW framework and provides a stringent, model-independent diagnostic for departures from standard cosmology using current and forthcoming distance and expansion rate measurements.

Using $20.3{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data taken at the center-of-mass energy of $\sqrt{s}=3.773\mathrm{GeV}$, we report the first experimental constraint on the scalar current in the $D^{0(+)}\to \overline{K}{\ell }^{+}{\nu }_{\ell }$ transitions, based on a simultaneous fit to the first measured forward-backward asymmetries and precisely determined partial decay rates. The parameters of the scalar current are determined to be $\mathrm{Re}(c_S^{\mu })=0.017\pm 0.008_{\mathrm{stat}}\pm 0.006_{\mathrm{syst}}$ and $\mathrm{Im}(c_S^{\mu })=\pm (0.077\pm 0.011_{\mathrm{stat}}\pm 0.009_{\mathrm{syst}})$, which deviates from the standard model by a significance of $2.3\sigma$. The branching fractions of $D^{0(+)}\to \overline{K}{\ell }^{+}{\nu }_{\ell }$, the hadronic form factor $f_{+}(0)$, and the modulus of the $c\to s$ Cabibbo-Kobayahsi-Maskawa matrix element $|V_{cs}|$ are also determined with improved precision. In addition, lepton flavor universality is tested via the ratios of the decay rates between semimuonic and semielectronic decays in the full momentum transfer range and in subranges.

This Letter presents the first evidence of the simultaneous production of two $Z$ bosons and one photon with the ATLAS detector at the Large Hadron Collider. The measurement is performed using the full Run-2 dataset, recorded from 2015 to 2018, of proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $140{\mathrm{fb}}^{-1}$. The fully leptonic final state with four leptons and one photon is analyzed, $pp\to ZZ\gamma \to {\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}\gamma$ with $\ell ,{\ell }^{\prime }=e$ or $\mu$. This final state is measured in a fiducial region where photon final-state radiation is minimized, and the photon has a transverse momentum of $p_{\mathrm{T}}^{\gamma }>20\mathrm{GeV}$. Eight events are selected, with a background estimate of $0.92\pm 0.15$. This results in an observed (expected) significance of the $ZZ\gamma$ final state of $4.4\sigma$ ($4.0\sigma$). The measured cross section for $pp\to ZZ\gamma \to {\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}\gamma$ in the fiducial region is ${\sigma }_{ZZ\gamma }=0.144_{-0.051}^{+0.065}{(\mathrm{stat})}_{-0.004}^{+0.008}(\mathrm{syst})\mathrm{fb}$, in agreement with the standard model prediction of ${\sigma }_{\mathrm{fid}}^{\mathrm{SM}}=0.130\pm 0.006\mathrm{fb}$.

Evidence of the production of two $Z$ bosons and a photon in proton-proton collisions is reported for the first time in CMS. The analysis uses data collected by the CMS experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. Evidence for the process $pp\to ZZ\gamma \to 4\ell \gamma$ ($\ell =e$, $\mu$), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by $p_{\mathrm{T}}^{\gamma }>20\mathrm{GeV}$, $|{\eta }^{\gamma }|<2.4$, $\mathrm{\Delta }R(\ell ,\gamma )>0.5$, $m_Z$ between 60 and 120 GeV, and the invariant mass of either of the two $Z$ bosons combined with the photon ($m_{Z_{\gamma }}$) larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is ${60}_{-22}^{+27}\mathrm{ab}$ ($47.56\pm 0.04\mathrm{ab}$). Additionally, the inclusive production of $pp\to 4\ell \gamma$ is studied by removing the $m_{Z_{\gamma }}$ requirement to include final state radiation where one $Z$ boson decays to $2\ell \gamma$, yielding an observed (expected) significance of 5.0 (4.2) standard deviations and a measured (predicted) fiducial cross section of ${156}_{-35}^{+39}\mathrm{ab}$ ($99.97\pm 0.09\mathrm{ab}$).

We apply continuous normalizing flows trained with the flow matching method to the problem of phase-space sampling in Monte Carlo event generation for high-energy collider physics. Focusing on lepton-pair and top-quark pair production with multiple jets, the two computationally most expensive processes at the Large Hadron Collider, we train helicity-conditioned continuous normalizing flows to remap the random numbers used in matrix element evaluation. Compared to standard methods, we achieve unweighting efficiency improvements by factors of up to 184 and 25 for the two processes at their respective highest jet number, at the cost of an increased evaluation time. When combining the advantages of continuous normalizing flows with the fast evaluation times of coupling-layer-based flows, using the RegFlow approach, we find parton-level unweighted event generation walltime gains of about a factor of 10 at the highest jet numbers. These substantial gains highlight the promise of samplers based on machine learning for next-generation collider experiments.

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.