We investigate a recent controversy in ultrafast magnetization dynamics by comparing the demagnetization rates from two frequently used but competing descriptions for finite temperature magnetism, namely a rigid band structure Stoner-like approach and a system of localized spins. The calculations on the localized spin system show a demagnetization rate and time comparable to experimentally obtained values, whereas the rigid band approach yields negligible demagnetization, even when the microscopic spin-flip process is assumed to be instantaneous. This shows that rigid band structure calculations will never be in quantitative agreement with experiments, irrespective of the investigated microscopic scattering mechanism.

Through investigating the spin-dependent charging energy of nanoscale systems, we introduce a new concept of intrinsic molecular magnetocapacitance (MC). In molecules and nanosize quantum dots that undergo a spin state transition, the MC can be as high as 12%. First-principles calculations demonstrate that in a number of nanoscale systems, the quantum capacitance is highly sensitive to the system spin and charge states. In single molecule junctions, one can exploit molecular MC through the Coulomb blockade effect by modulating the bias voltage and applying an external magnetic field, which turns electron conductance on or off. Detailed analysis on molecular nanomagnet ${\mathrm{Mn}}_3\mathrm{O}(\mathrm{sao})_3{}^{-}({\mathrm{O}}_2\mathrm{CMe})({\mathrm{H}}_2\mathrm{O})(\mathrm{py}{)}_3$ shows a 6% MC with a switching field of $\sim 40\mathrm{T}$. Its MC can be further enhanced to 9.6% by placing the molecule above a dielectric surface, opening up new avenues for novel nanoscale materials design. Under current experimental conditions, the predicted molecular MC effect can be probed without substantial difficulties.

Magnetic domains at the surface of a ferroelectric monodomain ${\mathrm{BiFeO}}_3$ single crystal have been imaged by hard x-ray magnetic scattering. Magnetic domains up to several hundred microns in size have been observed, corresponding to cycloidal modulations of the magnetization along the wave vector $\mathit{k}=(\delta ,\delta ,0)$ and symmetry equivalent directions. The rotation direction of the magnetization in all magnetic domains, determined by diffraction of circularly polarized light, was found to be unique and in agreement with predictions of a combined approach based on a spin-model complemented by relativistic density-functional simulations. Imaging of the surface shows that the largest adjacent domains display a 120° vortex structure.

We present a semiclassical theoretical framework on light-wave mixing and scattering with single-component quantum gases. We show that these optical processes originating from elementary excitations with dominant collective atomic recoil motion are stimulated Raman or hyper-Raman in nature. In the forward direction the wave-mixing process, which is the most efficient process in normal gases, is strongly reduced by the condensate structure factor even though the Bogoliubov dispersion relation automatically compensates the optical-wave phase mismatch. In the backward direction, however, the free-particle-like condensate structure factor and Bogoliubov dispersion result in highly efficient light-wave mixing and collective atomic recoil motion that are enhanced by a stimulated hyper-Raman gain and a very narrow two-photon motional state resonance.

We derive reliable entanglement witnesses for coarse-grained measurements on continuous variable systems. These witnesses never return a “false positive” for identification of entanglement, under any degree of coarse graining. We show that even in the case of Gaussian states, entanglement witnesses based on the Shannon entropy can outperform those based on variances. We apply our results to experimental identification of spatial entanglement of photon pairs.

We study the behavior of the Rényi entropies for the toric code subject to a variety of different perturbations, by means of 2D density matrix renormalization group and analytical methods. We find that Rényi entropies of different index $\alpha$ display derivatives with opposite sign, as opposed to typical symmetry breaking states, and can be detected on a very small subsystem regardless of the correlation length. This phenomenon is due to the presence in the phase of a point with flat entanglement spectrum, zero correlation length, and area law for the entanglement entropy. We argue that this kind of splitting is common to all the phases with a certain group theoretic structure, including quantum double models, cluster states, and other quantum spin liquids. The fact that the size of the subsystem does not need to scale with the correlation length makes it possible for this effect to be accessed experimentally.

The Schwarzschild black two-brane in four-dimensional anti–de Sitter space is dual to a finite temperature state in three-dimensional conformal field theory. We show that the solution acquires a nonzero angular momentum density when a gravitational Chern-Simons coupling is turned on in the bulk, even though the solution is not modified. A similar phenomenon is found for the Reissner-Nordström black two-brane with axionic coupling to the gauge field. We discuss interpretation of this phenomenon from the point of view of the boundary three-dimensional conformal field theory.

A search for the decays $B_s^0\to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ is performed using data, corresponding to an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$, collected with the LHCb detector in 2011. The number of candidates observed is consistent with the expected background and, assuming phase-space models of the decays, limits on the branching fractions are set: $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-})<1.6(1.2)\times {10}^{-8}$ and $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-})<6.6(5.3)\times {10}^{-9}$ at 95% (90%) confidence level. In addition, limits are set in the context of a supersymmetric model which allows for the $B_{(s)}^0$ meson to decay into a scalar ($S$) and pseudoscalar particle ($P$), where $S$ and $P$ have masses of $2.5\mathrm{GeV}/c$ and $214.3\mathrm{MeV}/c$, respectively, both resonances decay into ${\mu }^{+}{\mu }^{-}$. The branching fraction limits for these decays are $\mathcal{B}(B_s^0\to SP)<1.6(1.2)\times {10}^{-8}$ and $\mathcal{B}(B^0\to SP)<6.3(5.1)\times {10}^{-9}$ at 95% (90%) confidence level.

Knowing the charge of the parton initiating a light-quark jet could be extremely useful both for testing aspects of the standard model and for characterizing potential beyond-the-standard-model signals. We show that despite the complications of hadronization and out-of-jet radiation such as pileup, a weighted sum of the charges of a jet’s constituents can be used at the LHC to distinguish among jets with different charges. Potential applications include measuring electroweak quantum numbers of hadronically decaying resonances or supersymmetric particles, as well as standard model tests, such as jet charge in dijet events or in hadronically decaying $W$ bosons in $t\overline{t}$ events. We develop a systematically improvable method to calculate moments of these charge distributions by combining multihadron fragmentation functions with perturbative jet functions and pertubative evolution equations. We show that the dependence on energy and jet size for the average and width of the jet charge can be calculated despite the large experimental uncertainty on fragmentation functions. These calculations can provide a validation tool for data independent of Monte Carlo fragmentation models.

The compatibility of neutrino-nucleus deep inelastic scattering data within the universal, factorizable nuclear parton distribution functions has been studied independently by several groups in the past few years. The conclusions are contradictory, ranging from a violation of the universality up to a good agreement, most of the controversy originating from the use of the neutrino-nucleus data from the NuTeV Collaboration. Here, we pay attention to non-negligible differences in the absolute normalization between different neutrino data sets. We find that such variations are large enough to prevent a tensionless fit to all data simultaneously and could therefore misleadingly point towards nonuniversal nuclear effects. We propose a concrete method to deal with the absolute normalization and show that an agreement between independent neutrino data sets is established.

We present a fast and quasideterministic protocol for the production of single ions and electrons from a cloud of laser-cooled atoms. The approach is based on a two-step process where first a single Rydberg atom is photoexcited from a dipole-blockade configuration and subsequently ionized by an electric field pulse. We theoretically describe these excitation-ionization cycles via dynamical quantum maps and observe a rich behavior of the ionization dynamics as a function of laser Rabi frequency, pulse duration, and particle number. Our results show that a fast sequential heralded production of single charged particles is achievable even from an unstructured and fluctuating atomic ensemble.

A method for the spatial separation of $R\mathrm{\text{−}}R$ and $S\mathrm{\text{−}}S$ homodimers from $R\mathrm{\text{−}}S$ heterodimers, where $R$ and $S$ are chiral molecules of opposite handedness (“enantiomers”), is introduced. The separation, achieved by using two spatially inhomogeneous time-delayed laser pulses, is a result of one type of dimer forming a “dark state” and experiencing no light-induced potential, while the other type of dimer, forming a “bright” state, undergoes deflection. The direction of deflection of the two types of chiral dimers may be reversed by reversing the time delay between the laser pulses. We demonstrate the feasibility of the process by simulating the separation of lactic acid dimers.

The laser excitation of Rydberg atoms in ultracold gases is often described assuming that the atomic motion is frozen during the excitation time. We show that this frozen gas approximation can break down for atoms that are held in optical lattices or microtraps. In particular, we show that the excitation dynamics is in general strongly affected by mechanical forces among the Rydberg atoms as well as the spread of the atomic wave packet in the confining potential. This causes decoherence in the excitation dynamics—resulting in a dissipative blockade effect—that renders the Rydberg excitation inefficient even in the antiblockade regime. For a strongly off-resonant laser excitation—usually considered in the context of Rydberg dressing—these motional effects compromise the applicability of the Born-Oppenheimer approximation. In particular, our results indicate that they can also lead to decoherence in the dressing regime.

The $K$ shell excitation of H-like uranium (${\mathrm{U}}^{91+}$) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different $L$ shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.

In recent years quantum correlations have received a lot of attention as a key ingredient in advanced quantum metrology protocols. In this Letter we show that they provide even larger advantages when considering multiple-interferometer setups. In particular, we demonstrate that the use of quantum correlated light beams in coupled interferometers leads to substantial advantages with respect to classical light, up to a noise-free scenario for the ideal lossless case. On the one hand, our results prompt the possibility of testing quantum gravity in experimental configurations affordable in current quantum optics laboratories and strongly improve the precision in “larger size experiments” such as the Fermilab holometer; on the other hand, they pave the way for future applications to high precision measurements and quantum metrology.

We establish a heralded interaction between two remotely trapped single ${}^{40}\mathrm{Ca}^{+}$ ions through the exchange of single photons. In the sender ion, we release single photons with a controlled temporal shape on the $P_{3/2}$ to $D_{5/2}$ transition and transmit them to the distant receiver ion. Individual absorption events in the receiver ion are detected by quantum jumps. For continuously generated photons, the absorption reduces significantly the lifetime of the long-lived $D_{5/2}$ state. For triggered single-photon transmission, we observe a coincidence between the emission at the sender and quantum jump events at the receiver.

We show that, contrary to the common wisdom, surface plasmon poles are not involved in the imaging process in leakage radiation microscopy. Identifying the leakage radiation modes directly from a transverse magnetic potential leads us to reconsider the surface plasmon field and unfold the nonplasmonic contribution to the image formation. While both contributions interfere in the imaging process, our analysis reveals that the reassessed plasmonic field embodies a pole mathematically similar to the usual surface plasmon pole. This removes a long-standing ambiguity associated with plasmonic signals in leakage radiation microscopy.

It is theoretically demonstrated that electron states in semiconductors or graphene can be perfectly transmitted through a complementary material with dual properties, independent of the angle of incidence. It is shown that such complementary material may also provide a strong spatial delocalization of bounded electronic states, changing dramatically the confinement of the wave function, and acting effectively as a lens for the probability wave. The results are the electron analogue of a perfect lens for electromagnetic waves proposed in an earlier work.

We propose a technique to form a single few-cycle attosecond pulse from vacuum ultraviolet or extreme ultraviolet radiation via resonant interaction with hydrogenlike atoms, irradiated by a high-intensity far-off-resonant laser field. The laser field strongly perturbs excited atomic energy levels via the Stark effect and ionizes atoms from the excited states. We show that an isolated attosecond pulse can be formed using either a short incident femtosecond pulse of the resonant radiation or a steep front edge of the laser field. We propose an experimental realization of a single subfemtosecond pulse formation at 121.6 nm in atomic hydrogen and a single sub-100 as pulse formation at 13.5 nm in ${\mathrm{Li}}^{2+}$ plasma.

We characterize statistical properties of the flow field in developed turbulence using concepts from stochastic thermodynamics. On the basis of data from a free air-jet experiment, we demonstrate how the dynamic fluctuations induced by small-scale intermittency generate analogs of entropy-consuming trajectories with sufficient weight to make fluctuation theorems observable at the macroscopic scale. We propose an integral fluctuation theorem for the entropy production associated with the stochastic evolution of velocity increments along the eddy hierarchy and demonstrate its extreme sensitivity to the accurate description of the tails of the velocity distributions.