Although abundant research has focused recently on the quantum criticality of itinerant magnets, critical phenomena of insulating magnets in the vicinity of critical endpoints (CEP’s) have rarely been revealed. Here we observe an emergent CEP at 2.05 T and 2.2 K with a suppressed thermal conductivity and concomitant strong critical fluctuations evident via a divergent magnetic susceptibility (e.g., ${\chi }^{\prime \prime }(2.05\mathrm{T},2.2\mathrm{K})/{\chi }^{\prime \prime }(3\mathrm{T},2.2\mathrm{K})\approx 23,500\%$, comparable to the critical opalescence in water) in the hexagonal insulating antiferromagnet ${\mathrm{HoMnO}}_3$.

We demonstrate that pointlike defects in noncollinear magnets give rise to a highly dispersive structure in the magnon scattering, violating a standard paradigm of its momentum independence. For a single impurity spin coupled to a prototypical noncollinear antiferromagnet, we find that the resolvent is dominated by a distinct dispersive structure with its momentum dependence set by the magnon dispersion and shifted by the ordering vector. This feature is a consequence of umklapp scattering off the impurity-induced spin texture, which arises due to the noncollinear ground state of the host system. Detailed results for the staggered and uniform magnetization of this texture as well as the $T$ matrix from numerical linear spin-wave theory are presented.

We present a flexible and effective ab initio scheme to build many-body models for molecular nanomagnets, and to calculate magnetic exchange couplings and zero-field splittings. It is based on using localized Foster-Boys orbitals as a one-electron basis. We apply this scheme to three paradigmatic systems, the antiferromagnetic rings ${\mathrm{Cr}}_8$ and ${\mathrm{Cr}}_7\mathrm{Ni}$, and the single-molecule magnet ${\mathrm{Fe}}_4$. In all cases we identify the essential magnetic interactions and find excellent agreement with experiments.

Hydrophilicity or hydrophobicity is a macroscopic property of the surface, and its atomic scale understanding has not been established. We have studied adsorption of water molecules on the “hydrophobic” carbon nanotube surface at room temperature in water vapor. Based on optical measurements of individual single-walled carbon nanotubes suspended between micropillars in water vapor together with molecular dynamics simulations, we found that water molecules form a stable adsorption layer of 1–2 ML thickness on the nanotube surface and they show rapid adsorption and desorption transition at a critical pressure. This adsorption layer is created by lateral hydrogen bonding of water molecules confined in the weak van der Waals potential of the surface. In spite of hydrophobic hydration, carbon nanotubes exhibit hydrophobicity macroscopically.

Arrhythmias in cardiac tissue are related to irregular electrical wave propagation in the heart. Cardiac tissue is formed by a discrete cell network, which is often heterogeneous. A localized region with a fraction of nonconducting links surrounded by homogeneous conducting tissue can become a source of reentry and ectopic beats. Extensive simulations in a discrete model of cardiac tissue show that a wave crossing a heterogeneous region of cardiac tissue can disintegrate into irregular patterns, provided the fraction of nonconducting links is close to the percolation threshold of the cell network. The dependence of the reentry probability on this fraction, the system size, and the degree of excitability can be inferred from the size distribution of nonconducting clusters near the percolation threshold.

A growing tumor is subjected to intrinsic physical forces, arising from the cellular turnover in a spatially constrained environment. This work demonstrates that such residual solid stresses can provoke a buckling instability in heterogeneous tumor spheroids. The growth rate ratio between the outer shell of proliferative cells and the inner necrotic core is the control parameter of this instability. The buckled morphology is found to depend both on the elastic and the geometric properties of the tumor components, suggesting a key role of residual stresses for promoting tumor invasiveness.

The collective chemosensing of nonexcitable mammalian cells involves a biochemical network that features gap junction communications and heterogeneous single cell activities. To understand the integrated multicellular chemosensing, we study the calcium dynamics of micropatterned fibroblast cell colonies in response to adenosine triphosphate (ATP) stimulation. We find that the cross-correlation function between the responses of individual cells decays with topological distance as a power law for large colonies and much faster for smaller colonies. Furthermore, the strongly correlated cell pairs tend to form clusters and are more likely to exceed the percolation threshold. At a given topological distance, the cross-correlations exhibit characteristics of Poisson distributions, which allows us to estimate the unitary conductance of a single gap junction which is in good agreement with direct experimental measurements.

Bacteria propel themselves with the help of rotating helical flagella. They change their swimming direction during tumbling events in order to increase, for example, their supply of nutrients (chemotaxis). During tumbling a bacterial flagellum assumes different polymorphic states. Based on a continuum model for the motor-flagellum system, we demonstrate that a changing motor torque can initiate these polymorphic transformations. In particular, we investigate the run-and-stop tumble strategy of Rhodobacter sphaeroides which uses a coiled-to-normal transition in its single flagellum. We also show that torque reversal in single-flagellated Escherichia coli generates a normal-to-curly $I$ transition as observed for tumbling E. coli that swim with a bundle of several flagella.

The swimming of Escherichia coli is powered by its multiple flagellar motors. Each motor spins either clockwise or counterclockwise, under the control of an intracellular regulator, CheY-P. There can be two mechanisms (extrinsic and intrinsic) to coordinate the switching of bacterial motors. The extrinsic one arises from the fact that different motors in the same cell sense a common input (CheY-P) which fluctuates near the motors’ response threshold. An alternative, intrinsic mechanism is direct motor-motor coupling which makes synchronized switching energetically favorable. Here, we develop simple models for both mechanisms and uncover their different hallmarks. A quantitative comparison to the recent experiments suggests that the direct coupling mechanism may be accountable for the observed sharp correlation between motors in a single Escherichia coli. Possible origins of this coupling (e.g., hydrodynamic interaction) are discussed.

We describe how to characterize dynamical phase transitions in open quantum systems from a purely dynamical perspective, namely, through the statistical behavior of quantum jump trajectories. This approach goes beyond considering only properties of the steady state. While in small quantum systems dynamical transitions can only occur trivially at limiting values of the controlling parameters, in many-body systems they arise as collective phenomena and within this perspective they are reminiscent of thermodynamic phase transitions. We illustrate this in open models of increasing complexity: a three-level system, the micromaser, and a dissipative version of the quantum Ising model. In these examples dynamical transitions are accompanied by clear changes in static behavior. This is however not always the case, and, in general, dynamical phases need to be uncovered by observables which are strictly dynamical, e.g., dynamical counting fields. We demonstrate this via the example of a class of models of dissipative quantum glasses, whose dynamics can vary widely despite having identical (and trivial) stationary states.

Dimension witnesses allow one to test the dimension of an unknown physical system in a device-independent manner, that is, without placing assumptions about the functioning of the devices used in the experiment. Here we present simple and general dimension witnesses for quantum systems of arbitrary Hilbert space dimension. Our approach is deeply connected to the problem of quantum state discrimination, hence establishing a strong link between these two research topics. Finally, our dimension witnesses can distinguish between classical and quantum systems of the same dimension, making them potentially useful for quantum information processing.

The acceleration of charged particles in magnetized plasmas is considered during turbulent multi-island magnetic reconnection. The particle acceleration model is constructed for an ensemble of islands which produce adiabatic compression of the particles. The model takes into account the statistical fluctuations in the compression rate experienced by the particles during their transport in the acceleration region. The evolution of the particle distribution function is described as a simultaneous first- and second-order Fermi acceleration process. While the efficiency of the first-order process is controlled by the average rate of compression, the second-order process involves the variance in the compression rate. Moreover, the acceleration efficiency associated with the second-order process involves both the Eulerian properties of the compression field and the Lagrangian properties of the particles. The stochastic contribution to the acceleration is nonresonant and can dominate the systematic part in the case of a large variance in the compression rate. The model addresses the role of the second-order process, how the latter can be related to the large-scale turbulent transport of particles, and explains some features of the numerical simulations of particle acceleration by multi-island contraction during magnetic reconnection.

Using density functional molecular dynamics free energy calculations, we show that the body centered cubic (bcc) phase of superionic ice previously believed to be the only phase is, in fact, thermodynamically unstable compared to a novel phase with oxygen positions in face centered cubic lattice sites. The novel phase has a lower proton mobility than the bcc phase and may exhibit a higher melting temperature. We predict a transition between the two phases at a pressure of $1\pm 0.5\mathrm{Mbar}$, with potential consequences for the interiors of ice giants such as Uranus and Neptune.

We show how future gravitational-wave detectors would be able to discriminate between the concordance $\Lambda$ cold dark matter cosmological model and up-to-date competing alternatives, e.g., dynamical dark energy (DE) models or modified gravity (MG) theories. Our method consists of using the weak-lensing magnification effect that affects a standard-siren signal because of its traveling through the Universe’s large scale structure. As a demonstration, we present constraints on DE and MG from proposed gravitational-wave detectors, namely Einstein Telescope and DECI-Hertz Interferometer Gravitational-Wave Observatory and Big-Bang Observer.

A new technique was developed to measure the lifetimes of neutron unbound nuclei in the picosecond range. The decay of ${}^{26}\mathrm{O}\to {}^{24}\mathrm{O}+n+n$ was examined as it had been predicted to have an appreciable lifetime due to the unique structure of the neutron-rich oxygen isotopes. The half-life of ${}^{26}\mathrm{O}$ was extracted as ${4.5}_{-1.5}^{+1.1}(\mathrm{stat})\pm 3(\mathrm{syst})\mathrm{ps}$. This corresponds to ${}^{26}\mathrm{O}$ having a finite lifetime at an 82% confidence level and, thus, suggests the possibility of two-neutron radioactivity.

We create an ultracold-atom-based cavity optomechanical system in which the center-of-mass modes of motion of as many as six distinguishable atomic ensembles are prepared and optically detected near their ground states. We demonstrate that the collective motional state of one atomic ensemble can be selectively addressed while preserving neighboring ensembles near their ground states to better than 95% per excitation quantum. We also show that our system offers nanometer-scale spatial resolution of each atomic ensemble via optomechanical imaging. This technique enables the in situ parallel sensing of potential landscapes, a capability relevant to active research areas of atomic physics and force-field detection in optomechanics.

We use electromagnetically-induced-transparency laser cooling to cool motional modes of a linear ion chain. As a demonstration, we apply electromagnetically-induced-transparency cooling on ${}^{24}\mathrm{Mg}^{+}$ ions to cool the axial modes of a ${}^9\mathrm{Be}^{+}\mathrm{\text{−}}{}^{24}\mathrm{Mg}^{+}$ ion pair and a ${}^9\mathrm{Be}^{+}\mathrm{\text{−}}{}^{24}\mathrm{Mg}^{+}\mathrm{\text{−}}{}^{24}\mathrm{Mg}^{+}\mathrm{\text{−}}{}^9\mathrm{Be}^{+}$ ion chain, thereby sympathetically cooling the ${}^9\mathrm{Be}^{+}$ ions. Compared to previous implementations of conventional Raman sideband cooling, we achieve approximately an order-of-magnitude reduction in the duration required to cool the modes to near the ground state and significant reduction in required laser intensity.

Contrary to conventional wisdom that all dynamics are a result of interference (or “dephasing”) between many (at least two) energy eigenstates, we show that when a continuum of states is present, even a single molecular eigenstate undergoes “steady-state” quantum dynamics. Moreover, this type of dynamics can be initiated by incoherent (e.g., solar) light sources. Continua are invariably involved in molecular systems due to a variety of sources such as the ever present bath modes, spontaneously emitted photons; the detachment of electrons, or the dissociation of chemical bonds. Contrary to a single bound energy eigenfunction which is a real (“standing-waves”) function that carries no flux and, hence, has no dynamics, a single (complex) continuum energy eigenfunction carries “steady-state” flux given by the group velocity of the energetically narrow wave packet it represents. When this energy eigenfunction is a multimode resonance embedded in a continuum via a chain of intramolecular couplings, this dynamics may be initiated by any (light) source, and is controlled, contrary to coherent wave packet dynamics, by the position of the resonance rather than its width.

We use cryogenic helium buffer-gas cooling to form large densities of lithium atoms in a high-density helium gas, from which LiHe molecules form by three-body recombination. These weakly bound van der Waals molecules are detected spectroscopically, and their binding energy is measured from their equilibrium thermodynamic properties.

We demonstrate that, from a $10\mathrm{\text{−}}\mu \mathrm{m}$ metal wire irradiated by a ${10}^{19}\mathrm{W}/{\mathrm{cm}}^2$ laser pulse, fast electrons form a nearly perfect circular beam around the wire and propagate along it. The total charge and diameter of the electron beam are maintained over a propagation distance of 1 m. Moreover, the electron beam can be guided along a slightly bent wire. Numerical simulations suggest that a relatively weak steady electric field, which does not decay for several nanoseconds, is generated around the wire and plays a key role in the long-distance guidance.