This Letter presents the observation and measurement of electroweak production of a same-sign $W$ boson pair in association with two jets using $36.1{\mathrm{fb}}^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$ by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of $69\pm 7$ events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial signal cross section is ${\sigma }^{\text{fid}}={2.89}_{-0.48}^{+0.51}(\text{stat}{)}_{-0.28}^{+0.29}(\text{syst})\mathrm{fb}$.

We use $R$-matrix with time-dependence theory, with spin-orbit effects included, to study krypton irradiated by two time-delayed extreme ultraviolet ultrashort pulses. The first pulse excites the atom to $4s^{2}4p^{5}5s$. The second pulse then excites $4s4p^{6}5s$ autoionizing levels, whose population can be observed through their subsequent decay. By varying the time delay between the two pulses, we are able to control the excitation pathway to the autoionizing states. The use of cross-polarized light pulses allows us to isolate the two-photon pathway, with one photon taken from each pulse.

When the feature size of photonic structures becomes comparable or even smaller than the wavelength of light, the fabrication imperfections inevitably introduce disorder that may eliminate many functionalities of subwavelength photonic devices. Here we suggest a novel concept to achieve a robust band gap which can endure disorder beyond 30% as a result of the transition from photonic crystals to Mie-resonant metamaterials. By utilizing Mie-resonant metamaterials with high refractive index, we demonstrate photonic waveguides and cavities with strong robustness to position disorder, thus providing a novel approach to the band-gap-based nanophotonic devices with new properties and functionalities.

We use the theory of isostable reduction to incorporate higher order effects that are lost in the first order phase reduction of coupled oscillators. We apply this theory to weakly coupled complex Ginzburg-Landau equations, a pair of conductance-based neural models, and finally to a short derivation of the Kuramoto-Sivashinsky equations. Numerical and analytical examples illustrate bifurcations occurring in coupled oscillator networks that can cause standard phase-reduction methods to fail.

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit setup.

We propose a new mechanism for the thermal Hall effect in exchange spin-wave systems, which is induced by the magnon-phonon interaction. Using symmetry arguments, we first show that this effect is quite general, and exists whenever the mirror symmetry in the direction of the magnetization is broken. We then demonstrate our result in a collinear ferromagnet on a square lattice, with perpendicular easy-axis anisotropy and Dzyaloshinskii-Moriya interaction from mirror symmetry breaking. We show that the thermal Hall conductivity is controlled by the resonant contribution from the anticrossing points between the magnon and phonon branches, and estimate its size to be comparable to that of the magnon-mediated thermal Hall effect.

Transport properties of a hard-sphere colloidal fluid are investigated by Brownian dynamics simulations. We implement a novel algorithm for the time-dependent velocity-autocorrelation function (VACF) essentially eliminating the noise of the bare random motion. The measured VACF reveals persistent anti-correlations manifested by a negative algebraic power-law tail $t^{-5/2}$ at all densities. At small packing fractions the simulations fully agree with the analytic low-density prediction, yet the amplitude of the tail becomes dramatically suppressed as the packing fraction is increased. The mode-coupling theory of the glass transition provides a qualitative explanation for the strong variation in terms of the static compressibility as well as the slowing down of the structural relaxation.

Photonic entanglement swapping, the procedure of entangling photons without any direct interaction, is a fundamental test of quantum mechanics and an essential resource to the realization of quantum networks. Probabilistic sources of nonclassical light were used for seminal demonstration of entanglement swapping, but applications in quantum technologies demand push-button operation requiring single quantum emitters. This, however, turned out to be an extraordinary challenge due to the stringent prerequisites on the efficiency and purity of the generation of entangled states. Here we show a proof-of-concept demonstration of all-photonic entanglement swapping with pairs of polarization-entangled photons generated on demand by a GaAs quantum dot without spectral and temporal filtering. Moreover, we develop a theoretical model that quantitatively reproduces the experimental data and provides insights on the critical figures of merit for the performance of the swapping operation. Our theoretical analysis also indicates how to improve state-of-the-art entangled-photon sources to meet the requirements needed for implementation of quantum dots in long-distance quantum communication protocols.

Transferring entangled states between photon pairs is essential in quantum communication. Semiconductor quantum dots are the leading candidate for generating polarization-entangled photons deterministically. Here we show for the first time swapping of entangled states between two pairs of photons emitted by a single dot. A joint Bell measurement heralds the successful generation of the Bell state ${\mathrm{\Psi }}^{+}$, yielding a fidelity of $0.81\pm 0.04$ and violating the CHSH and Bell inequalities. Our photon source matches atomic quantum memory frequencies, facilitating implementation of hybrid quantum repeaters.

We investigate the subadditivity of the bipartite entanglement entropy (EE) of many-particle states, represented by Slater determinants, with respect to single particle excitations. In this setting, subadditivity can be phrased as erasure of EE, i.e., as a relative decrease in EE when adding excitations to the quantum state. We identify sets of single particle states that yield zero EE if jointly excited. Such states we dub entanglement erasing partner states (EEPS). These EEPS reveal a mechanism that describes how to disentangle two subspaces of a Hilbert space by exciting additional states. We demonstrate this general finding in Anderson and many-body localized models. The studied concept of entanglement erasure further enables us to derive the EE of Slater determinants in the free tight binding model. Here, our analytical findings show surprisingly good agreement with numerical results of the interacting $XXX$ chain. The described EEPS further impose a universal, i.e., model independent, erasure of EE for randomly excited Slater determinants. This feature allows us to compute many-particle EE by means of the associated single particle states and the filling ratio. This novel finding can be employed to drastically reduce the computational effort in free models.

Continuous weak measurement allows localizing open quantum systems in state space and tracing out their quantum trajectory as they evolve in time. Efficient quantum measurement schemes have previously enabled recording quantum trajectories of microwave photon and qubit states. We apply these concepts to a macroscopic mechanical resonator, and we follow the quantum trajectory of its motional state conditioned on a continuous optical measurement record. Starting with a thermal mixture, we eventually obtain coherent states of 78% purity—comparable to a displaced thermal state of occupation 0.14. We introduce a retrodictive measurement protocol to directly verify state purity along the trajectory, and we furthermore observe state collapse and decoherence. This opens the door to measurement-based creation of advanced quantum states, as well as potential tests of gravitational decoherence models.

Temporal multiplexing provides an efficient and scalable approach to realize a quantum random walk with photons that can exhibit topological properties. But two-dimensional time-multiplexed topological quantum walks studied so far have relied on generalizations of the Su-Shreiffer-Heeger model with no synthetic gauge field. In this work, we demonstrate a two-dimensional topological quantum random walk where the nontrivial topology is due to the presence of a synthetic gauge field. We show that the synthetic gauge field leads to the appearance of multiple band gaps and, consequently, a spatial confinement of the quantum walk distribution. Moreover, we demonstrate topological edge states at an interface between domains with opposite synthetic fields. Our results expand the range of Hamiltonians that can be simulated using photonic quantum walks.

Loop-tree duality (LTD) offers a promising avenue to numerically integrate multiloop integrals directly in momentum space. It is well established at one loop, but there have been only sparse numerical results at two loops. We provide a formal derivation for a novel multiloop LTD expression and study its threshold singularity structure. We apply our findings numerically to a diverse set of up to four-loop finite topologies with kinematics for which no contour deformation is needed. We also lay down the ground work for constructing such a deformation. Our results serve as an important stepping stone towards a generalized and efficient numerical implementation of LTD, which is applicable to the computation of virtual corrections.

The NOvA experiment has seen a $4.4\sigma$ signal of ${\overline{\nu }}_e$ appearance in a 2 GeV ${\overline{\nu }}_{\mu }$ beam at a distance of 810 km. Using $12.33\times {10}^{20}$ protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ candidates with a background of 10.3 and 102 ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_{\mu }$ candidates. This new antineutrino data are combined with neutrino data to measure the parameters $|\mathrm{\Delta }{m}_{32}^2|=2.48_{-0.06}^{+0.11}\times {10}^{-3}{\mathrm{eV}}^2/c^4$ and ${\sin }^2{\theta }_{23}$ in the ranges from (0.53–0.60) and (0.45–0.48) in the normal neutrino mass hierarchy. The data exclude most values near ${\delta }_{CP}=\pi /2$ for the inverted mass hierarchy by more than $3\sigma$ and favor the normal neutrino mass hierarchy by $1.9\sigma$ and ${\theta }_{23}$ values in the upper octant by $1.6\sigma$.

We report the observation of a new structure in the ${\mathrm{\Lambda }}_b^0{\pi }^{+}{\pi }^{-}$ spectrum using the full LHCb data set of $pp$ collisions, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$, collected at $\sqrt{s}=7$, 8, and 13 TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be $m_{{\mathrm{\Lambda }}_b{(6146)}^0}=6146.17\pm 0.33\pm 0.22\pm 0.16\mathrm{MeV},m_{{\mathrm{\Lambda }}_b{(6152)}^0}=6152.51\pm 0.26\pm 0.22\pm 0.16\mathrm{MeV},{\mathrm{\Gamma }}_{{\mathrm{\Lambda }}_b{(6146)}^0}=2.9\pm 1.3\pm 0.3\mathrm{MeV},{\mathrm{\Gamma }}_{{\mathrm{\Lambda }}_b{(6152)}^0}=2.1\pm 0.8\pm 0.3\mathrm{MeV},$with a mass splitting of $\mathrm{\Delta }m=6.34\pm 0.32\pm 0.02\mathrm{MeV}$, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the ${\mathrm{\Lambda }}_b^0$ baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of ${\mathrm{\Lambda }}_b{(1D)}^0$ states.