Indirect searches for the cosmological dark matter have become ever more competitive during the past years. Here, we report the first full calculation of leading electroweak corrections to the annihilation rate of supersymmetric neutralino dark matter. We find that these corrections can be huge, partially due to contributions that have been overlooked so far. Our results imply a significantly enhanced discovery potential of this well motivated dark matter candidate with current and upcoming cosmic ray experiments, in particular for gamma rays and models with somewhat small annihilation rates at the tree level.

We present a theoretical study of two-color ionization of hydrogen with keV photons at intensities ranging from ${10}^{16}$ to ${10}^{18}\mathrm{W}/{\mathrm{cm}}^2$. We consider the atom in interaction with a superposition of two electromagnetic pulses centered around two frequencies that differ by a few atomic units and we present in detail the case of the frequencies 55 and 50 a.u. We present the electron energy spectra, angular distributions, and ionization rates based on nonperturbative and perturbative calculations. Although the ejected electron energy distribution is dominated by one-photon ionization from each pulse, we are able to identify the contribution of stimulated Compton scattering, a process in which one photon is absorbed while the other is emitted, the photon energy difference being transferred to the electron. This leads to low-energy electrons, and we show in particular that it is of crucial importance to consider the retardation effects on the ionization rates and the electron angular distributions. The relative propagation direction of the two fields also plays an important role; in the case of counterpropagating fields, the ionization by stimulated Compton scattering is dominated by ${\mathbf{A}}^2$ and competes with one-photon ionization at high intensities.

Squeezed vacuum states constitute a particularly useful resource in quantum information as well as in quantum metrology. The frequency conversion of these states is important to provide the bridge between different wavelengths within a sequence of downstream applications and also to provide a way for squeezed-state generation at so-far inaccessible wavelengths. Here we demonstrate the external quantum up-conversion of carrier-light-free squeezed vacuum states for the first time. Our result proves that nondegenerate sum-frequency generation preserves the coherences that are present between photon pairs and higher-order photon pairs of the squeezed input state.

We investigate long-range intensity correlations on both sides of the Anderson transition of classical waves in a three-dimensional disordered material. Our ultrasonic experiments are designed to unambiguously detect a recently predicted infinite-range $C_0$ contribution, due to local density of states fluctuations near the source. We find that these $C_0$ correlations, in addition to $C_2$ and $C_3$ contributions, are significantly enhanced near mobility edges. Separate measurements of the inverse participation ratio reveal a link between $C_0$ and the anomalous dimension ${\mathrm{\Delta }}_2$, implying that $C_0$ may also be used to explore the critical regime of the Anderson transition.

We show that conservation of longitudinal magnetization in a spinor condensate provides a stabilizing mechanism for a coreless vortex phase-imprinted on a polar condensate. The stable vortex can form a composite topological defect with distinct small- and large-distance topology: the inner ferromagnetic coreless vortex continuously deforms toward an outer singular, singly quantized polar vortex. A similar mechanism can also stabilize a nonsingular nematic texture in the polar phase. A weak magnetization is shown to destabilize a coreless vortex in the ferromagnetic phase.

The interaction of coexisting structural instabilities in multiferroic materials gives rise to intriguing coupling phenomena and extraordinarily rich phase diagrams, both in bulk materials and strained thin films. Here we investigate the multiferroic ${\mathrm{BiMnO}}_3$ with its peculiar $6s^2$ electrons and four interacting mechanisms: electric polarity, octahedra tilts, magnetism, and cooperative Jahn-Teller distortion. We have probed structural transitions under high pressure by synchrotron x-ray diffraction and Raman spectroscopy up to 60 GPa. We show that ${\mathrm{BiMnO}}_3$ displays under pressure a rich sequence of five phases with a great variety of structures and properties, including a metallic phase above 53 GPa and, between 37 and 53 GPa, a strongly elongated monoclinic phase that allows ferroelectricity, which contradicts the traditional expectation that ferroelectricity vanishes under pressure. Between 7 and 37 GPa, the $Pnma$ structure remains remarkably stable but shows a reduction of the Jahn-Teller distortion in a way that differs from the behavior observed in the archetypal orthorhombic Jahn-Teller distorted perovskite ${\mathrm{LaMnO}}_3$.

The kinetics associated with the migration of chemisorbed hydrogen on a graphene sheet is studied using density-functional theory. Chemisorbed H atoms interact strongly through the carbon sheet and each chemisorbed H atom must form a pair with a H atom bound on the opposite side of the sheet in order to lower the energy with respect to the free ${\mathrm{H}}_2$ state. The two H atoms in a pair are correlated and migrate cooperatively. Because of the strong C-H bonds, the barrier to H cooperative migration is higher than 2.0 eV. However, when mediated by ${\mathrm{H}}_2\mathrm{O}$ molecules, the barrier can be reduced to less than 0.8 eV. The H pairing up leads to distinctive behavior of graphene hydrogenation, different from H chemisorption on a graphite surface. This study also demonstrates the superior effectiveness of water activation of C-H bonds and uncovers the mystery of fast kinetics of H spillover [Y. W. Li and R. T. Yang, J. Am. Chem. Soc. 128, 8136 (2006)].

We study a hybrid system formed from an optomechanical resonator and a cavity mode strongly coupled to an excitonic transition inside a quantum well. We show that due to the mixing of cavity photon and exciton states, the emergent quasiparticles—polaritons—possess coupling to the mechanical mode of both a dispersive and dissipative nature. We calculate the occupancies of polariton modes and reveal bistable behavior, which deviates from conventional Kerr nonlinearity or dispersive coupling cases due to the dissipative coupling. The described system serves as a good candidate for future polaritonic devices.

We study the properties of a topological Josephson junction made of both edges of a two-dimensional topological insulator. We show that, due to fermion parity pumping across the bulk, the global parity of the junction has a clear signature in the periodicity and critical value of the Josephson current. In particular, we find that the periodicity with the flux changes from $4\pi$ in a junction with an even number of quasiparticles to $2\pi$ in the odd sector. In the case of long junctions, we exhibit a rigorous mathematical connection between the spectrum of Andreev bound states and the fermion parity anomaly, through bosonization. Additionally, we discuss the rather quantitative effects of Coulomb interactions on the Josephson current.

A three-particle spin-$\frac{1}{2}$ fermion problem with on-site repulsion and nearest-neighbor attraction is solved on the two-dimensional square lattice by discretizing a Schrödinger equation in momentum space. Energies of bound complexes (trions) and their binding conditions are obtained. For total spin $S=1/2$, a wide region of trion instability toward decaying into a stable singlet pair plus a free fermion is identified. The instability is attributed to the formation of a wave function node upon addition of the third fermion. In the $S=3/2$ sector, trions are found to form in the absence of bound pairs indicating Borromean binding. In the strong coupling limit the system transitions from an $S=1/2$ ground state to a ferromagnetic $S=3/2$ ground state in agreement with the Nagaoka theorem for a four-site plaquette.

We present for the first time a theoretical model of studying the saturation of the rupture force of a single molecular bond that causes the rupture force to be rate independent under an ultralow loading rate. This saturation will obviously bring challenges to understanding the rupture behavior of the molecular bond using conventional methods. This intriguing feature implies that the molecular bond has a nonzero strength at a vanishing loading rate. We find that the saturation behavior is caused by bond rebinding when the loading rate is lower than a limiting value depending on the loading stiffness.

We propose a class of attacks on quantum key distribution (QKD) systems where an eavesdropper actively engineers new loopholes by using damaging laser illumination to permanently change properties of system components. This can turn a perfect QKD system into a completely insecure system. A proof-of-principle experiment performed on an avalanche photodiode-based detector shows that laser damage can be used to create loopholes. After $\sim 1\mathrm{W}$ illumination, the detectors’ dark count rate reduces 2–5 times, permanently improving single-photon counting performance. After $\sim 1.5\mathrm{W}$, the detectors switch permanently into the linear photodetection mode and become completely insecure for QKD applications.

The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers $A=124$, 128, 132, and 134 in nuclear resonance fluorescence experiments using the $\gamma \mathrm{ELBE}$ bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the $\mathrm{HI}\gamma \mathrm{S}$ facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed $E1$ strengths in the pygmy region for a wide mass range of nuclides.

All-optical switching is a technique in which a gate light pulse changes the transmission of a target light pulse without the detour via electronic signal processing. We take this to the quantum regime, where the incoming gate light pulse contains only one photon on average. The gate pulse is stored as a Rydberg excitation in an ultracold atomic gas using electromagnetically induced transparency. Rydberg blockade suppresses the transmission of the subsequent target pulse. Finally, the stored gate photon can be retrieved. A retrieved photon heralds successful storage. The corresponding postselected subensemble shows an extinction of 0.05. The single-photon switch offers many interesting perspectives ranging from quantum communication to quantum information processing.

Penning ionization initiates the evolution of a dense molecular Rydberg gas to plasma. This process selects for pairs of excited molecules separated by a distance of two Rydberg orbital diameters or less. The deactivated Penning partners predissociate, depleting the leading edge of the distribution of nearest-neighbor distances. For certain density and orbital radii, this sequence of events can form a plasma in which large distances separate a disproportionate fraction of the ions. Experimental results and model calculations suggest that the reduced potential energy of this Penning lattice significantly affects the development of strong coupling in an ultracold plasma.

Hybrid organic-inorganic polaritons are formed by the simultaneous strong coupling of two degenerate excitons and a microcavity photon at room temperature. Wannier-Mott and Frenkel excitons in spatially separated ZnO and 3,4,7,8-napthalene tetracarboxylic dianhydride (NTCDA) layers, respectively, placed in a single Fabry-Perot microcavity contribute to the interaction with the cavity. A Rabi splitting of $(322\pm 8)\mathrm{meV}$ between the upper and middle branches of the three branch polariton energy-momentum dispersion is observed. This is compared to only $(224\pm 22)\mathrm{meV}$ and $(218\pm 8)\mathrm{meV}$ Rabi splittings for NTCDA-only and ZnO-only reference cavities, respectively, and indicates that the excitonic component of the polariton is a Frenkel-Wannier-Mott hybrid. Unlike previous reports of hybrid polaritons, the mixing of the organic and inorganic eigenstates occurs independently of angle due to their energetic degeneracy, and can be tailored by adjusting the optical field distribution within the cavity.

In this Letter we address spin wave dynamics involved in fast and selective vortex core polarity reversal by rotating magnetic field bursts. In a first example we explain the origin of the delayed switching for excitations with short bursts of only one period duration as an interference effect between spin wave modes. Second, when the vortex core is initially no longer at rest but in gyrotropic motion, the magnetization dynamics become more complicated and the interaction of spin waves with the vortex core leads to a variety of nonlinear effects. Our analysis allows us to explain the experimentally observed switching diagram for simultaneous excitation of spin waves and gyrotropic mode.

We report an observation of long-lived spin-singlet states in a ${{}^{13}\mathrm{C}\text{−}{}^1\mathrm{H}}^{}$ spin pair in a zero magnetic field. In ${}^{13}\mathrm{C}$-labeled formic acid, we observe spin-singlet lifetimes as long as 37 s, about a factor of 3 longer than the $T_1$ lifetime of dipole polarization in the triplet state. In contrast to common high-field experiments, the observed coherence is a singlet-triplet coherence with a lifetime $T_2$ longer than the $T_1$ lifetime of dipole polarization in the triplet manifold. Moreover, we demonstrate that heteronuclear singlet states formed between a ${}^1\mathrm{H}$ and a ${}^{13}\mathrm{C}$ nucleus can exhibit longer lifetimes than the respective triplet states even in the presence of additional spins that couple to the spin pair of interest. Although long-lived homonuclear spin-singlet states have been extensively studied, this is the first experimental observation of analogous singlet states in heteronuclear spin pairs.

We describe a method of producing bright atomic solitons of ${}^7\mathrm{Li}$ through efficient radio frequency evaporation in a combined magnetic and optical trap. Solitons released in a magnetic waveguide propagate without dispersion, with lifetimes limited by two-body dipolar relaxation. We show how the method can be used to deterministically produce pairs of solitons.

We investigate the scaling properties of the sources of crackling noise in a fully dynamic numerical model of sedimentary rocks subject to uniaxial compression. The model is initiated by filling a cylindrical container with randomly sized spherical particles that are then connected by breakable beams. Loading at a constant strain rate the cohesive elements fail, and the resulting stress transfer produces sudden bursts of correlated failures, directly analogous to the sources of acoustic emissions in real experiments. The source size, energy, and duration can all be quantified for an individual event, and the population can be analyzed for its scaling properties, including the distribution of waiting times between consecutive events. Despite the nonstationary loading, the results are all characterized by power-law distributions over a broad range of scales in agreement with experiments. As failure is approached, temporal correlation of events emerges accompanied by spatial clustering.