The observation of $Z_c(3900)$ by the BESIII Collaboration in the invariant mass spectrum of $J/\psi {\pi }^{\pm }$ in $e^{+}{e}^{-}\to J/\psi {\pi }^{+}{\pi }^{-}$ at the center of mass 4.260 GeV suggests the existence of a charged $\overline{D}{D}^{*}+D{\overline{D}}^{*}$ molecular state with $I(J^P)=1(1^{+})$, which could be an isovector brother of the famous $X(3872)$ and an analogue of $Z_b(10610)$ claimed by the Belle Collaboration. We demonstrate that this observation provides strong evidence that the mysterious $Y(4260)$ is a $\overline{D}{D}_1(2420)+D{\overline{D}}_1(2420)$ molecular state. Especially, we show that the decay of this molecule naturally populates low momentum $\overline{D}{D}^{*}$ pairs and leads unavoidably to a cusp at the $\overline{D}{D}^{*}$ threshold. We discuss the signatures that distinguish such a $\overline{D}{D}^{*}$ cusp from the presence of a true resonance.

A measurement of beam helicity asymmetries in the reaction ${}^3\overrightarrow{\mathrm{He}}(\overrightarrow{e},e^{\prime }n)pp$ is performed at the Mainz Microtron in quasielastic kinematics to determine the electric to magnetic form factor ratio of the neutron $G_E^n/G_M^n$ at a four-momentum transfer $Q^2=1.58{\mathrm{GeV}}^2$. Longitudinally polarized electrons are scattered on a highly polarized ${}^3\mathrm{He}$ gas target. The scattered electrons are detected with a high-resolution magnetic spectrometer, and the ejected neutrons are detected with a dedicated neutron detector composed of scintillator bars. To reduce systematic errors, data are taken for four different target polarization orientations allowing the determination of $G_E^n/G_M^n$ from a double ratio. We find ${\mu }_n{G}_E^n/G_M^n=0.250\pm 0.058(\mathrm{stat})\pm 0.017(\mathrm{syst})$.

The study of the ionization process of molecules in an intense infrared laser field is of paramount interest in strong-field physics and constitutes the foundation of imaging of molecular valence orbitals and attosecond science. We show measurement of alignment-dependent ionization probabilities of the lower-lying orbitals of the molecules by experimentally detecting the alignment dependence of fluorescence emission from tunnel ionized carbon dioxide molecules. The experimental measurements are compared with the theoretical calculations of the strong field approximation and molecular Ammosov-Delone-Krainov models. Our results demonstrate the feasibility of an all-optical approach for probing the ionization dynamics of lower-lying orbitals of molecules, which is until now still difficult to achieve by other techniques. Moreover, the deviation between the experimental and theoretical results indicates the incompleteness of current theoretical models for describing strong field ionization of molecules.

The trapping lasers of a magneto-optical trap have been used to bring Rb atoms into well defined oriented states. Coupled to recoil-ion-momentum spectroscopy, this provided a unique MOTRIMS setup which was able to probe scattering dynamics, including the coherence features, with unprecedented resolution. The technique was applied to the low-energy charge exchange reactions ${\mathrm{Na}}^{+}+\mathrm{Rb}(5p_{\pm 1})\to \mathrm{Na}(3p,4s)+{\mathrm{Rb}}^{+}$. The measurements revealed detailed features of the collisional interaction which were employed to improve the theoretical description. As such, it was possible to ascertain the validity of the intuitive models used to predict the most likely capture transitions.

We propose a scheme to measure the quantized Hall conductivity of an ultracold Fermi gas initially prepared in a topological Chern insulating phase and driven by a constant force. We show that the time evolution of the center of mass, after releasing the cloud, provides a direct and clear signature of the topologically invariant Chern number. We discuss the validity of this scheme, highlighting the importance of driving the system with a sufficiently strong force to displace the cloud over measurable distances while avoiding band-mixing effects. The unusual shapes of the driven atomic cloud are qualitatively discussed in terms of a semiclassical approach.

The deformation of metallic glasses involves two competing processes: a disordering process involving dilatation, free volume accumulation, and softening, and a relaxation process involving diffusional ordering and densification. For metallic glasses at room temperature and under uniaxial loading, disordering usually dominates, and the glass can fail catastrophically as the softening process runs away in a localized mode. Here we demonstrate conditions where the opposite, unexpected, situation occurs: the densifying process dominates, resulting in stable plastic deformation and work hardening at room temperature. We report densification and hardening during deformation in a Zr-based glass under multiaxial loading, in a notched tensile geometry. The effect is driven by stress-enhanced diffusional relaxation, and is attended by a reduction in exothermic heat and hardening signatures similar to those observed in the classical thermal relaxation of glasses. The result is significant, stable, plastic, extensional flow in metallic glasses, which suggest a possibility of designing tough glasses based on their flow properties.

We report that wall slippage can drastically change both steady and dynamic flow characteristics for a wide class of free-surface thin film flows. This is demonstrated by (i) the breakdown of the $2/3$ law and its replacement by a new quadratic law for the deposited film thickness in the Landau-Levich-Bretherton coating, (ii) the departure from de Gennes–Tanner’s cubic law for dynamic contact angles in drop spreading, consequently resulting in much faster spreading than the classical Tanner law, and (iii) the exaggerated capillary instability of an annular film where a fractional amount of wall slip can lead to much more rapid draining and hence make the film more vulnerable to rupture. In (ii), the molecular precursor film is shown to have a length varying like the $-1/2$ power of the spreading speed, producing an anomalous $1/3$ diffusion law governing its spreading dynamics. A variety of existing experimental findings can be well captured by the new scaling laws we derive. All these features are accompanied with no-slip-to-slip transitions, offering alternative means for probing slip boundaries.

We investigate the effect of interactions on shot noise in $\nu =2$ quantum Hall edges, where a repulsive coupling between copropagating edge modes is expected to give rise to charge fractionalization. Using the method of nonequilibrium bosonization, we find that even asymptotically the edge distribution function depends in a sensitive way on the interaction strength between the edge modes. We compute shot noise and the Fano factor from the asymptotic distribution function, and from comparison with a reference model of fractionalized excitations, we find that the Fano factor can be close to the value of the fractionalized charge.

We demonstrate switching behavior and quantized conductance at room temperature in percolating films of nanoparticles. Our experiments and complementary simulations show that switching and quantization result from the formation of atomic-scale wires in the gaps between particles. These effects occur only when tunnel gaps are present in the film, close to the percolation threshold.

We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stückelberg interference structure of a longitudinally driven two-level system. For even stronger drives, we observe a significant change in the Landau-Zener-Stückelberg pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning, and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.

We present an extensive quantum Monte Carlo study of the Néel to valence-bond solid (VBS) phase transition on rectangular- and honeycomb-lattice SU($N$) antiferromagnets in sign-problem-free models. We find that in contrast to the honeycomb lattice and previously studied square-lattice systems, on the rectangular lattice for small $N$, a first-order Néel-VBS transition is realized. On increasing $N\ge 4$, we observe that the transition becomes continuous and with the same universal exponents as found on the honeycomb and square lattices (studied here for $N=5$, 7, 10), providing strong support for a deconfined quantum critical point. Combining our new results with previous numerical and analytical studies, we present a general phase diagram of the stability of ${\mathbb{C}\mathbb{P}}^{N-1}$ fixed points with $q$ monopoles.

Stabilization of the Si(553) surface by Au adsorption results in two different atomically defined chain types, one of Au atoms and one of Si. At low temperature these chains develop two- and threefold periodicity, respectively, previously attributed to Peierls instabilities. Here we report evidence from scanning tunneling microscopy that rules out this interpretation. The $\times 3$ superstructure of the Si chains vanishes for low tunneling bias, i.e., close the Fermi level. In addition, the Au chains remain metallic despite their period doubling. Both observations are inconsistent with a Peierls mechanism. On the contrary, our results are in excellent, detailed agreement with the Si(553)-Au ground state predicted by density-functional theory, where the $\times 2$ periodicity of the Au chain is an inherent structural feature and every third Si atom is spin polarized.

The magnetization process of the orthogonal-dimer antiferromagnet ${\mathrm{SrCu}}_2({\mathrm{BO}}_3{)}_2$ is investigated in high magnetic fields of up to 118 T. A $1/2$ plateau is clearly observed in the field range 84 to 108 T in addition to $1/8$, $1/4$, and $1/3$ plateaus at lower fields. Using a combination of state-of-the-art numerical simulations, the main features of the high-field magnetization, a $1/2$ plateau of width 24 T, a $1/3$ plateau of width 34 T, and no $2/5$ plateau, are shown to agree quantitatively with the Shastry-Sutherland model if the ratio of inter- to intradimer exchange interactions $J^{\prime }/J=0.63$. It is further predicted that the intermediate phase between the $1/3$ and $1/2$ plateaus is not uniform but consists of a $1/3$ supersolid followed by a $2/5$ supersolid and possibly a domain-wall phase, with a reentrance into the $1/3$ supersolid above the $1/2$ plateau.

The space-and time-dependent response of many-body quantum systems is the most informative aspect of their emergent behavior. The dynamical structure factor, experimentally measurable using neutron scattering, can map this response in wave vector and energy with great detail, allowing theories to be quantitatively tested to high accuracy. Here, we present a comparison between neutron scattering measurements on the one-dimensional spin-$1/2$ Heisenberg antiferromagnet ${\mathrm{KCuF}}_3$, and recent state-of-the-art theoretical methods based on integrability and density matrix renormalization group simulations. The unprecedented quantitative agreement shows that precise descriptions of strongly correlated states at all distance, time, and temperature scales are now possible, and highlights the need to apply these novel techniques to other problems in low-dimensional magnetism.

The variation of the optical absorption of carbon nanotubes with their geometry has been a long-standing question at the heart of both metrological and applicative issues, in particular because optical spectroscopy is one of the primary tools for the assessment of the chiral species abundance of samples. Here, we tackle the chirality dependence of the optical absorption with an original method involving ultraefficient energy transfer in porphyrin-nanotube compounds that allows uniform photoexcitation of all chiral species. We measure the absolute absorption cross section of a wide range of semiconducting nanotubes at their $S_{22}$ transition and show that it varies by up to a factor of 2.2 with the chiral angle, with type I nanotubes showing a larger absorption. In contrast, the luminescence quantum yield remains almost constant.

Recent experiments have shown that Landau-Majorana-Stückelberg-Zener (LMSZ) interferometry is a powerful tool for demonstrating and exploiting quantum coherence not only in atomic systems but also in a variety of solid state quantum systems such as spins in quantum dots, superconducting qubits, and nitrogen vacancy centers in diamond. In this Letter, we propose and develop a general (and, in principle, exact) theoretical formalism to identify and characterize the interference resonances that are the hallmark of LMSZ interferometry. Unlike earlier approaches, our scheme does not require any approximations, allowing us to uncover important and previously unknown features of the resonance structure. We also discuss the experimental observability of our results.

Inspired by the Solovay-Kitaev decomposition for approximating unitary operations as a sequence of operations selected from a universal quantum computing gate set, we introduce a method for approximating any single-qubit channel using single-qubit gates and the controlled-not (cnot). Our approach uses the decomposition of the single-qubit channel into a convex combination of “quasiextreme” channels. Previous techniques for simulating general single-qubit channels would require as many as 20 cnot gates, whereas ours only needs one, bringing it within the range of current experiments.

Ramsey theory is a highly active research area in mathematics that studies the emergence of order in large disordered structures. Ramsey numbers mark the threshold at which order first appears and are extremely difficult to calculate due to their explosive rate of growth. Recently, an algorithm that can be implemented using adiabatic quantum evolution has been proposed that calculates the two-color Ramsey numbers $R(m,n)$. Here we present results of an experimental implementation of this algorithm and show that it correctly determines the Ramsey numbers $R(3,3)$ and $R(m,2)$ for $4\le m\le 8$. The $R(8,2)$ computation used 84 qubits of which 28 were computational qubits. This computation is the largest experimental implementation of a scientifically meaningful adiabatic evolution algorithm that has been done to date.

We perform hydrodynamical simulations of neutron-star mergers for a large sample of temperature-dependent nuclear equations of state and determine the threshold mass above which the merger remnant promptly collapses to form a black hole. We find that, depending on the equation of state, the threshold mass is larger than the maximum mass of a nonrotating star in isolation by between 30 and 70 percent. Our simulations also show that the ratio between the threshold mass and maximum mass is tightly correlated with the compactness of the nonrotating maximum-mass configuration. We speculate on how this relation can be used to derive constraints on neutron-star properties from future observations.

In supersymmetric models with minimal particle content and without left-right squark mixing, the conventional wisdom is that the 125.6 GeV Higgs boson mass implies top squark masses of $\mathcal{O}(10)\mathrm{TeV}$, far beyond the reach of colliders. This conclusion is subject to significant theoretical uncertainties, however, and we provide evidence that it may be far too pessimistic. We evaluate the Higgs boson mass, including the dominant three-loop terms at $\mathcal{O}({\alpha }_t{\alpha }_s^2)$, in currently viable models. For multi-TeV top squarks, the three-loop corrections can increase the Higgs boson mass by as much as 3 GeV and lower the required top-squark masses to 3–4 TeV, greatly improving prospects for supersymmetry discovery at the upcoming run of the LHC and its high-luminosity upgrade.