We present the first evidence of the direct influence of gas turbulence on the shear instability of a planar air-water mixing layer. We show with two different experiments that increasing the level of velocity fluctuations in the gas phase continuously increases the frequency of the instability, up to a doubling of frequency for the largest turbulence intensity investigated. A modified spatiotemporal stability analysis taking turbulence into account via a simple Reynolds stress closure provides the right trend and magnitude for this effect.

When the background density in a bounded plasma is modulated in time, discrete modes become coupled. Interestingly, for appropriately chosen modulations, the average plasmon energy might be made to grow in a ladderlike manner, achieving upconversion or downconversion of the plasmon energy. This reversible process is identified as a classical analog of the effect known as quantum ladder climbing, so that the efficiency and the rate of this process can be written immediately by analogy to a quantum particle in a box. In the limit of a densely spaced spectrum, ladder climbing transforms into continuous autoresonance; plasmons may then be manipulated by chirped background modulations much like electrons are autoresonantly manipulated by chirped fields. By formulating the wave dynamics within a universal Lagrangian framework, similar ladder climbing and autoresonance effects are predicted to be achievable with general linear waves in both plasma and other media.

We study the quantum phase diagram of a three dimensional noninteracting Dirac semimetal in the presence of either quenched axial or scalar potential disorder, by calculating the average and the typical density of states as well as the inverse participation ratio using numerically exact methods. We show that as a function of the disorder strength a half-filled (i.e., undoped) Dirac semimetal displays three distinct ground states, namely an incompressible semimetal, a compressible diffusive metal, and a localized Anderson insulator, in stark contrast to a conventional dirty metal that only supports the latter two phases. We establish the existence of two distinct quantum critical points, which respectively govern the semimetal-metal and the metal-insulator quantum phase transitions and also reveal their underlying multifractal nature. Away from half-filling the (doped) system behaves as a diffusive metal that can undergo Anderson localization only, which is shown by determining the mobility edge and the phase diagram in terms of energy and disorder.

Quantum spin liquids, which are spin versions of quantum matter, have been sought after in systems with geometrical frustration. We show that disorder drives a classical magnet into a quantum spin liquid through conducting NMR experiments on an organic Mott insulator, $\kappa \text{−}({\mathrm{ET})}_2\mathrm{Cu}[\mathrm{N}({\mathrm{CN})}_2]\mathrm{Cl}$. Antiferromagnetic ordering in the pristine crystal, when irradiated by x rays, disappears. Spin freezing, spin gap, and critical slowing down are not observed, but gapless spin excitations emerge, suggesting a novel role of disorder that brings forth a quantum spin liquid from a classical ordered state.

We present a method for estimating the probabilities of outcomes of a quantum circuit using Monte Carlo sampling techniques applied to a quasiprobability representation. Our estimate converges to the true quantum probability at a rate determined by the total negativity in the circuit, using a measure of negativity based on the 1-norm of the quasiprobability. If the negativity grows at most polynomially in the size of the circuit, our estimator converges efficiently. These results highlight the role of negativity as a measure of nonclassical resources in quantum computation.

We propose a new method to obtain kinetic properties of infrequent events from molecular dynamics simulation. The procedure employs a recently introduced variational approach [Valsson and Parrinello, Phys. Rev. Lett. 113, 090601 (2014)] to construct a bias potential as a function of several collective variables that is designed to flood the associated free energy surface up to a predefined level. The resulting bias potential effectively accelerates transitions between metastable free energy minima while ensuring bias-free transition states, thus allowing accurate kinetic rates to be obtained. We test the method on a few illustrative systems for which we obtain an order of magnitude improvement in efficiency relative to previous approaches and several orders of magnitude relative to unbiased molecular dynamics. We expect an even larger improvement in more complex systems. This and the ability of the variational approach to deal efficiently with a large number of collective variables will greatly enhance the scope of these calculations. This work is a vindication of the potential that the variational principle has if applied in innovative ways.

We present a novel quantum-classical approach to nonadiabatic dynamics, deduced from the coupled electronic and nuclear equations in the framework of the exact factorization of the electron-nuclear wave function. The method is based on the quasiclassical interpretation of the nuclear wave function, whose phase is related to the classical momentum and whose density is represented in terms of classical trajectories. In this approximation, electronic decoherence is naturally induced as an effect of the coupling to the nuclei and correctly reproduces the expected quantum behavior. Moreover, the splitting of the nuclear wave packet is captured as a consequence of the correct approximation of the time-dependent potential of the theory. This new approach offers a clear improvement over Ehrenfest-like dynamics. The theoretical derivation presented in this Letter is supported by numerical results that are compared to quantum mechanical calculations.

The low temperature behavior of a Fermi liquid can be described in terms of quasiparticle excitations that are in 1-1 correspondence with those of the noninteracting system. Because of adiabatic continuity, the Landau parameters, which describe the interactions between the quasiparticles, must evolve continuously as the interactions are turned on and be described by a set of flow equations. For strongly correlated electron systems it is not possible to follow this flow in perturbation theory when the interactions become strong. We explore the idea here of overcoming this problem by renormalizing the quasiparticles in this flow using a renormalized perturbation theory. This approach is tested in the case of a single impurity Anderson model. Analytic flow equations are derived which give excellent results for the Landau parameters in the strong correlation regime.

We describe three analytic classes of infinitely many ${\mathrm{AdS}}_d$ supersymmetric solutions of massive IIA supergravity, for $d=7,5,4$. The three classes are related by simple universal maps. For example, the ${\mathrm{AdS}}_7\times M_3$ solutions (where $M_3$ is topologically $S^3$) are mapped to ${\mathrm{AdS}}_5\times {\mathrm{\Sigma }}_2\times M_3^{\prime }$, where ${\mathrm{\Sigma }}_2$ is a Riemann surface of genus $g\ge 2$ and the metric on $M_3^{\prime }$ is obtained by distorting $M_3$ in a certain way. The solutions can have localized D6 or O6 sources, as well as an arbitrary number of D8-branes. The ${\mathrm{AdS}}_7$ case (previously known only numerically) is conjecturally dual to an NS5-D6-D8 system. The field theories in three and four dimensions are not known, but their number of degrees of freedom can be computed in the supergravity approximation. The ${\mathrm{AdS}}_4$ solutions have numerical “attractor” generalizations that might be useful for flux compactification purposes.

We present the complete calculation of $W$-boson production in association with a jet in hadronic collisions through next-to-next-to-leading order (NNLO) in perturbative QCD. To cancel infrared divergences, we discuss a new subtraction method that exploits the fact that the $N$-jettiness event-shape variable fully captures the singularity structure of QCD amplitudes with final-state partons. This method holds for processes with an arbitrary number of jets and is easily implemented into existing frameworks for higher-order calculations. We present initial phenomenological results for $W+\text{jet}$ production at the LHC. The NNLO corrections are small and lead to a significantly reduced theoretical error, opening the door to precision measurements in the $W+\text{jet}$ channel at the LHC.

The exciton is one of the most crucial physical entities in the performance of optoelectronic and photonic devices, and widely varying exciton binding energies have been reported in different classes of materials. Using first-principles calculations within the $GW$–Bethe-Salpeter equation approach, here we investigate the excitonic properties of two recently discovered layered materials: phosphorene and graphene fluoride. We first confirm large exciton binding energies of, respectively, 0.85 and 2.03 eV in these systems. Next, by comparing these systems with several other representative two-dimensional materials, we discover a striking linear relationship between the exciton binding energy and the band gap and interpret the existence of the linear scaling law within a simple hydrogenic picture. The broad applicability of this novel scaling law is further demonstrated by using strained graphene fluoride. These findings are expected to stimulate related studies in higher and lower dimensions, potentially resulting in a deeper understanding of excitonic effects in materials of all dimensionalities.

The dynamics of magnetic vortex cores is of great interest because the gyrotropic mode has applications in spin torque driven magnetic microwave oscillators, and also provides a means to flip the direction of the core for use in magnetic storage devices. Here, we propose a new means of stimulating magnetization reversal of the vortex core by applying a time-varying strain gradient to planar structures of the magnetostrictive material ${\mathrm{Fe}}_{\mathbf{8}\mathbf{1}}{\mathrm{Ga}}_{\mathbf{1}\mathbf{9}}$ (Galfenol), coupled to an underlying piezoelectric layer. Using micromagnetic simulations we have shown that the vortex core state can be deterministically reversed by electric field control of the time-dependent strain-induced anisotropy.

Propagation of light in a medium is dictated by equifrequency surfaces (EFSs), which play a similar role as Fermi surfaces for electrons in crystals. Engineering the equifrequency surface of light through structuring a photonic medium enables superior control over light propagation that goes beyond natural materials. In this Letter, we show that a bulk metamaterial with a suitably designed bianisotropy can exhibit line degeneracy in its EFSs that consist of two ellipsoids of opposite helicity states intersecting with each other. Very interestingly, light propagating along the direction of the line degeneracy experiences strong spin-dependent photon deflection, or optical spin Hall effect, which may lead to applications in optical signal processing and spin-optical manipulations. We provide a realistic metamaterial design to show that the required bianisotropy can be readily obtained.

The precision of the $CP$ phases $2\beta$ and $2{\beta }_s$ determined from the mixing-induced $CP$ asymmetries in $B_d\to J/\psi K_S$ and $B_s\to J/\psi \varphi$, respectively, is limited by the unknown long-distance contribution of a penguin diagram involving up quarks. The penguin contribution is expected to be comparable in size to the precision of the LHCb and Belle II experiments and, therefore, limits the sensitivity of the measured quantities to new physics. We analyze the infrared QCD structure of this contribution and find that all soft and collinear divergences either cancel between different diagrams or factorize into matrix elements of local four-quark operators up to terms suppressed by ${\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{\psi }$, where $m_{\psi }$ denotes the $J/\psi$ mass. Our results, which are based on an operator product expansion, allow us to calculate the penguin-to-tree ratio $P/T$ in terms of the matrix elements of these operators and to constrain the penguin contribution to the phase $2\beta$ as $|\mathrm{\Delta }{\varphi }_d|\le 0.68°$. The penguin contribution to $2{\beta }_s$ is bounded as $|\mathrm{\Delta }{\varphi }_s^0|\le 0.97°$, $|\mathrm{\Delta }{\varphi }_s^{\parallel }|\le 1.22°$, and $|\mathrm{\Delta }{\varphi }_s^{\perp }|\le 0.99°$ for the case of longitudinal, parallel, and perpendicular $\varphi$ and $J/\psi$ polarizations, respectively. Further, we place bounds on $|\mathrm{\Delta }{\varphi }_d|$ for $B_d\to \psi (2S)K_S$ and the polarization amplitudes in $B_d\to J/\psi K^{*}$. In our approach, it is further possible to constrain $P/T$ for decays in which $P/T$ is Cabibbo unsuppressed, and we derive upper limits on the penguin contribution to the mixing-induced $CP$ asymmetries in $B_d\to J/\psi {\pi }^0$, $B_d\to J/\psi {\rho }^0$, $B_s\to J/\psi K_S$, and $B_s\to J/\psi K^{*}$. For all studied decay modes, we also constrain the sizes of the direct $CP$ asymmetries.

Total absorption spectroscopy is used to investigate the $\beta$-decay intensity to states above the neutron separation energy followed by $\gamma$-ray emission in ${}^{87,88}\mathrm{Br}$ and ${}^{94}\mathrm{Rb}$. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large $\gamma$ intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The $\gamma$ branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For ${}^{87}\mathrm{Br}$ and ${}^{88}\mathrm{Br}$ the $\gamma$ branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich ${}^{94}\mathrm{Rb}$ the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled by introducing an enhancement of 1 order of magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proves to be correct, leads to a similar increase in the ($\mathit{n},\gamma$) cross section that would have an impact on $r$ process abundance calculations.