Experiments within a cryogenic 22-pole ion trap have revealed an interesting reaction dynamic phenomenon, where rovibrational excitation of an ionic molecule slows down a reaction with a neutral partner. This is demonstrated for the low-temperature hydrogen abstraction reaction $\mathrm{c}\text{−}{\mathrm{C}}_3{{\mathrm{H}}_2}^{+}+{\mathrm{H}}_2$, where excitation of the ion into the ${\nu }_7$ antisymmetric C-H stretching mode decreased the reaction rate coefficient toward the products $\mathrm{c}\text{−}{\mathrm{C}}_3{{\mathrm{H}}_3}^{+}+\mathrm{H}$. Supported by high-level quantum-chemical calculations, this observation is explained by the reaction proceeding through a $\mathrm{c}\text{−}{\mathrm{C}}_3{{\mathrm{H}}_2}^{+}-{\mathrm{H}}_2$ collision complex in the entrance channel, in which the hydrogen molecule is loosely bound to the hydrogen atom of the $\mathrm{c}\text{−}{\mathrm{C}}_3{{\mathrm{H}}_2}^{+}$ ion. This discovery enables high-resolution vibrational action spectroscopy for $\mathrm{c}\text{−}{\mathrm{C}}_3{{\mathrm{H}}_2}^{+}$ and other molecular ions with similar reaction pathways. Moreover, a detailed kinetic model relating the extent of the observed product depletion signal to the rate coefficients of inelastic collisions reveals that rotational relaxation of the vibrationally excited ions is significantly faster than the rovibrational relaxation, allowing for a large fraction of the ions to be vibrationally excited. This result provides fundamental insight into the mechanism for an important class of chemical reactions, and is capable of probing the inelastic collisional dynamics of molecular ions.

Efficient detection of spin-charge conversion is crucial for advancing our understanding of emergent phenomena in spin-orbit-coupled nanostructures. Here, we provide a proof of principle of an electrical detection scheme of spin-charge conversion that enables full disentanglement of competing spin-orbit coupling (SOC) transport phenomena in diffusive lateral channels, i.e., the inverse spin Hall effect and the spin galvanic effect. A suitable geometry in an applied oblique magnetic field is shown to provide direct access to SOC transport coefficients through a symmetry analysis of the output nonlocal resistance. The scheme is robust against tilting of the spin-injector magnetization, disorder, and spurious non-spin-related contributions to the nonlocal signal and can be used to probe spin-charge conversion effects in both spin-valve and hybrid optospintronic devices.

Recent observations of selective emergence (suppression) of superconductivity in the uncollapsed (collapsed) tetragonal phase of ${\mathrm{LaFe}}_2{\mathrm{As}}_2$ has rekindled interest in understanding what features of the band structure control the superconducting $T_c$. We show that the proximity of the narrow $\mathrm{Fe}\text{−}{d}_{xy}$ state to the Fermi energy emerges as the primary factor. In the uncollapsed phase this state is at the Fermi energy, and is most strongly correlated and a source of enhanced scattering in both single and two particle channels. The resulting intense and broad low energy spin fluctuations suppress magnetic ordering and simultaneously provide glue for Cooper pair formation. In the collapsed tetragonal phase, the $d_{xy}$ state is driven far below the Fermi energy, which suppresses the low-energy scattering and blocks superconductivity. A similar source of broad spin excitation appears in uncollapsed and collapsed phases of ${\mathrm{CaFe}}_2{\mathrm{As}}_2$. This suggests controlling coherence provides a way to engineer $T_c$ in unconventional superconductors primarily mediated through spin fluctuations.

A central result in the foundations of quantum mechanics is the Kochen-Specker theorem. In short, it states that quantum mechanics cannot be reconciled with classical models that are noncontextual for ideal measurements. The first explicit derivation by Kochen and Specker was rather complex, but considerable simplifications have been achieved thereafter. We propose a systematic approach to find minimal Hardy-type and Greenberger-Horne-Zeilinger-type (GHZ-type) proofs of the Kochen-Specker theorem, these are characterized by the fact that the predictions of classical models are opposite to the predictions of quantum mechanics. Based on our results, we show that the Kochen-Specker set with 18 vectors from Cabello et al. [Phys. Lett. A 212, 183 (1996)] is the minimal set for any dimension, verifying a longstanding conjecture by Peres. Our results allow to identify minimal contextuality scenarios and to study their usefulness for information processing.

Analog quantum simulation is widely considered a step on the path to fault tolerant quantum computation. With current noisy hardware, the accuracy of an analog simulator will degrade after just a few time steps, especially when simulating complex systems likely to exhibit quantum chaos. Here we describe a quantum simulator based on the combined electron-nuclear spins of individual Cs atoms, and its use to run high fidelity simulations of three different model Hamiltonians for $>100$ time steps. While not scalable to exponentially large Hilbert spaces, it provides the accuracy and programmability required to explore the interplay between dynamics, imperfections, and accuracy in quantum simulation.

By analyzing a data sample corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the $D^{+}\to \eta {\mu }^{+}{\nu }_{\mu }$ decay to be ${\mathcal{B}}_{D^{+}\to \eta {\mu }^{+}{\nu }_{\mu }}=(10.4\pm 1.0_{\mathrm{stat}}\pm 0.5_{\mathrm{syst}})\times {10}^{-4}$. Using the world averaged value of ${\mathcal{B}}_{D^{+}\to \eta e^{+}{\nu }_e}$, the ratio of the two branching fractions is determined to be ${\mathcal{B}}_{D^{+}\to \eta {\mu }^{+}{\nu }_{\mu }}/{\mathcal{B}}_{D^{+}\to \eta e^{+}{\nu }_e}=0.91\pm {0.13}_{(\mathrm{stat}+\mathrm{syst})}$, which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor $f_{+}^{\eta }(0)$ and the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ to be $f_{+}^{\eta }(0)|V_{cd}|=0.087\pm 0.008_{\mathrm{stat}}\pm 0.002_{\mathrm{syst}}$. Taking the input of $|V_{cd}|$ from the global fit in the standard model, we determine $f_{+}^{\eta }(0)=0.39\pm 0.04_{\mathrm{stat}}\pm 0.01_{\mathrm{syst}}$. On the other hand, using the value of $f_{+}^{\eta }(0)$ calculated in theory, we find $|V_{cd}|=0.242\pm 0.022_{\mathrm{stat}}\pm 0.006_{\mathrm{syst}}\pm 0.033_{\text{theory}}$.

The elastic properties of three-dimensional (3D) crystalline mechanical metamaterials, unlike those of amorphous structures, are generally strongly anisotropic—even in the long-wavelength limit and for highly symmetric crystals. Aiming at isotropic linear elastic wave propagation, we therefore study 3D periodic approximants of 3D icosahedral quasicrystalline mechanical metamaterials consisting of uniaxial chiral metarods. Considering the increasing order of the approximants, we approach nearly isotropic effective speeds of sound and isotropic acoustical activity. The latter is directly connected to circularly polarized 3D metamaterial chiral acoustic phonons—for all propagation directions in three dimensions.

We show that dirty quantum Hall systems exhibit large hydrodynamic fluctuations at their edge that lead to anomalously damped charge excitations in the Kardar-Parisi-Zhang universality class $\omega \simeq ck-i\mathcal{D}{k}^{3/2}$. The dissipative optical conductivity of the edge is singular at low frequencies $\sigma (\omega )\sim 1/{\omega }^{1/3}$. These results are direct consequences of the charge continuity relation, the chiral anomaly, and thermalization on the edge—in particular translation invariance is not assumed. Diffusion of heat similarly breaks down, with a universality class that depends on whether the bulk thermal Hall conductivity vanishes. We further establish the theory of fluctuating hydrodynamics for surface chiral metals, where charge fluctuations give logarithmic corrections to transport.

Using the recently introduced molecular dynamics lattice gas approach, we test fluctuations of coarse-grained quantities. We show that as soon as the system can no longer be considered an ideal gas fluctuations fail to diminish upon coarse graining as is usually expected. These results suggest that current approaches to simulating fluctuating hydrodynamics may have to be augmented to achieve quantitative results for systems with a nonideal equation of state. The molecular dynamics lattice gas method gives a guidance to the exact nature of the fluctuation in such systems.

High pressure structural transformations are typically characterized by the thermodynamic state (pressure-volume-temperature) of the material. We present in situ x-ray diffraction measurements on laser-shock compressed silver and platinum to determine the role of deformation-induced lattice defects on high pressure phase transformations in noble metals. Results for shocked Ag show a copious increase in stacking faults (SFs) before transformation to the body-centered-cubic (bcc) structure at 144–158 GPa. In contrast, shock compressed Pt remains largely free of SFs and retains the fcc structure to over 380 GPa. These findings, along with recent results for shock compressed gold, show that SF formation promotes high pressure structural transformations in shocked noble metals that are not observed under static compression. Potential SF-related mechanisms for fcc-bcc transformations are discussed.

We perform friction experiments between a compliant gel and a rigid cylinder at sliding velocities comparable to the Rayleigh wave or secondary wave velocity of the gel. We find that, when the sliding velocity exceeds the wave velocities, the contact state transitions from Hertzian like to flat punch like, resulting in the breakdown of the lubricating oil film and the abrupt increase in the friction coefficient. We succeed in deriving theoretical solutions for the contact pressure distributions and the deformation profiles in the presence of friction, which are consistent with our experimental observations.

Certain scalar-tensor theories of gravity provide negative-energy, tachyonic modes to a fundamental scalar inside matter, giving rise to nonperturbative phenomena around compact stars. Studies of this and other tachyonic instabilities always average over local matter properties. We use elementary, flat space models to understand possible collective effects and the accuracy of the averaging procedure. In particular, we consider bodies made of elementary constituents which do not, in isolation, scalarize because their compactness $\mathcal{C}$ is too small, $\mathcal{C}\lesssim {\mathcal{C}}_{\mathrm{crit}}$. We show that when the individual constituents have compactness smaller but close to the threshold, one is able to scalarize composite bodies through collective effects, and the compactness of the composite body can be made arbitrarily small. On the other hand, our results suggest that when the fundamental building blocks have very low compactness, then scalarization of the composite body requires a global compactness ${\mathcal{C}}_{\text{global}}\gtrsim {\mathcal{C}}_{\mathrm{crit}}$. Thus, our results rule out scalarization of dilute bodies via collective effects.

The ground-state-to-ground-state $\beta$-decay $Q$ value of ${}^{135}\mathrm{Cs}(7/2^{+})\to {}^{135}\mathrm{Ba}(3/2^{+})$ has been directly measured for the first time. The measurement was done utilizing both the phase-imaging ion-cyclotron resonance technique and the time-of-flight ion-cyclotron resonance technique at the JYFLTRAP Penning-trap setup and yielded a mass difference of 268.66(30) keV between ${}^{135}\mathrm{Cs}(7/2^{+})$ and ${}^{135}\mathrm{Ba}(3/2^{+})$. With this very small uncertainty, this measurement is a factor of 3 more precise than the currently adopted $Q$ value in the Atomic Mass Evaluation 2016. The measurement confirms that the first-forbidden unique ${\beta }^{-}$-decay transition ${}^{135}\mathrm{Cs}(7/2^{+})\to {}^{135}\mathrm{Ba}(11/2^{-})$ is a candidate for antineutrino mass measurements with an ultralow $Q$ value of 0.44(31) keV. This $Q$ value is almost an order of magnitude smaller than those of nuclides presently used in running or planned direct (anti)neutrino mass experiment.

We report the measurement of reaction cross sections (${\sigma }_R^{\mathrm{ex}}$) of ${}^{27,29}\mathrm{F}$ with a carbon target at RIKEN. The unexpectedly large ${\sigma }_R^{\mathrm{ex}}$ and derived matter radius identify ${}^{29}\mathrm{F}$ as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the $2p_{3/2}$ orbital, thereby vanishing the shell closure associated with the neutron number $N=20$. The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of ${}^{27}\mathrm{F}$ but are challenged for ${}^{29}\mathrm{F}$.