We discover a transition from extended to localized quasimodes for light in a gas of immobile two-level atoms in a magnetic field. The transition takes place either upon increasing the number density of atoms in a strong field or upon increasing the field at a high enough density. It has many characteristic features of a disorder-driven (Anderson) transition but is strongly influenced by near-field interactions between atoms and the anisotropy of the atomic medium induced by the magnetic field.

We demonstrate in open microcavities with broken chiral symmetry that quasidegenerate pairs of copropagating-wave resonances are transformed by rotation to counterpropagating ones, leading to a striking change of emission directions. The rotation-induced relative change in output intensity increases exponentially with cavity size, in contrast to the linear scaling of the Sagnac effect. By tuning the degree of spatial chirality with cavity shape, we are able to maximize the emission sensitivity to rotation without spoiling the quality factor.

A cone-shaped meniscus of electrified fluids, often called a Taylor cone, is observed in rain drops and lightning and employed in various physical instruments and experimental techniques, but the way it evolves from a rounded shape to a cone is a long-standing puzzle. Earth’s gravity and microgravity measurements on the meniscus whose height is just shy of droplet ejection reveal that field-driven cusp evolution exhibits a universal self-similarity insensitive to the forcing field and scaled by the fluid surface tension and density. Our work paves the way for dynamic control of field-driven phenomena in fluids.

In III-V nanowires the energetic barriers for nucleation in the zinc blende or wurtzite arrangement are typically of a similar order of magnitude. As a result, both arrangements can occur in a single wire. Here, we investigate the evolution of this polytypism in self-catalyzed GaAs nanowires on Si(111) grown by molecular beam epitaxy with time-resolved in situ x-ray diffraction. We interpret our data in the framework of a height dependent Markov model for the stacking in the nanowires. In this way, we extract the mean sizes of faultless wurtzite and zinc blende segments—a key parameter of polytypic nanowires—and their temporal evolution during growth. Thereby, we infer quantitative information on the differences of the nucleation barriers including their evolution without requiring a model of the nucleus.

We investigate the realization of a topological superconductor in a generic bucked honeycomb system equipped with four types of mass-generating terms, where the superconductor gap is introduced by attaching the honeycomb system to an $s$-wave superconductor. Constructing the topological phase diagram, we show that Majorana modes are formed in the phase boundary. In particular, we analyze the honeycomb system with antiferromagnetic order in the presence of perpendicular electric field $E_z$. It becomes topological for $|E_z|>E_z^{\mathrm{cr}}$ and trivial for $|E_z|<E_z^{\mathrm{cr}}$, with $E_z^{\mathrm{cr}}$ a certain critical field. It is possible to create a topological spot in a trivial superconductor by controlling applied electric field. One Majorana zero-energy bound state appears at the phase boundary. We can arbitrarily control the position of the Majorana fermion by moving the spot of applied electric field, which will be made possible by a scanning tunneling microscope probe.

Uniform semiclassical approximations for the number and kinetic-energy densities are derived for many noninteracting fermions in one-dimensional potentials with two turning points. The resulting simple, closed-form expressions contain the leading corrections to Thomas-Fermi theory, involve neither sums nor derivatives, are spatially uniform approximations, and are exceedingly accurate.

The positivity of the probability measure of attractively interacting systems of $2N$-component fermions enables the derivation of an exact convexity property for the ground-state energy of such systems. Using analogous arguments, applied to path-integral expressions for the entanglement entropy derived recently, we prove nonperturbative analytic relations for the Rényi entropies of those systems. These relations are valid for all subsystem sizes, particle numbers, and dimensions, and in arbitrary external trapping potentials.

We show that the heating effect of spontaneous wave-function collapse models implies an experimentally significant increment $\mathrm{\Delta }{T}_{\mathrm{sp}}$ of equilibrium temperature in a mechanical oscillator. The obtained new form $\mathrm{\Delta }{T}_{\mathrm{sp}}$ is linear in the oscillator’s relaxation time $\tau$ and independent of the mass. The oscillator can be in a classical thermal state, also the effect $\mathrm{\Delta }{T}_{\mathrm{sp}}$ is classical for a wide range of frequencies and quality factors. We note that the test of $\mathrm{\Delta }{T}_{\mathrm{sp}}$ does not necessitate quantum state monitoring just tomography. In both the gravity-related and the continuous spontaneous localization models the strong-effect edge of their parameter range can be challenged in existing experiments on classical oscillators. For the continuous spontaneous localization theory, the conjectured highest collapse rate parameter values become immediately constrained by evidences from current experiments on extreme slow-ring-down oscillators.

Constructing a quantum memory for a photonic entanglement is vital for realizing quantum communication and network. Because of the inherent infinite dimension of orbital angular momentum (OAM), the photon’s OAM has the potential for encoding a photon in a high-dimensional space, enabling the realization of high channel capacity communication. Photons entangled in orthogonal polarizations or optical paths had been stored in a different system, but there have been no reports on the storage of a photon pair entangled in OAM space. Here, we report the first experimental realization of storing an entangled OAM state through the Raman protocol in a cold atomic ensemble. We reconstruct the density matrix of an OAM entangled state with a fidelity of $90.3\%\pm 0.8\%$ and obtain the Clauser-Horne-Shimony-Holt inequality parameter $S$ of $2.41\pm 0.06$ after a programed storage time. All results clearly show the preservation of entanglement during the storage.

A sub-GeV dark sector fermion $X$ can have baryon-number-violating interactions induced by high-scale physics, leading to nucleon decay into $X+\text{meson}$ and $\text{neutron}\to X+\text{photon}$. Such processes can mimic standard search modes containing a neutrino, but have different kinematics and may have escaped detection. If a dark force mediated by a light vector $Z_d$ acts on $X$, depending on parameters, $\text{neutron}\to X+Z_d$ can be important. In typical scenarios, $Z_d$ decays into ${\ell }^{+}{\ell }^{-}$, where $\ell =e,\mu$, with an order unity branching fraction. Nucleon decay searches can potentially uncover new dark states that are otherwise inaccessible, due to their negligible coupling to ordinary matter or cosmological abundance.

We present a measurement of the forward-backward asymmetry in the production of $B^{\pm }$ mesons, $A_{\mathrm{FB}}(B^{\pm })$, using $B^{\pm }\to J/\psi K^{\pm }$ decays in $10.4{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the D0 experiment during Run II of the Tevatron collider. A nonzero asymmetry would indicate a preference for a particular flavor, i.e., $b$ quark or $\overline{b}$ antiquark, to be produced in the direction of the proton beam. We extract $A_{\mathrm{FB}}(B^{\pm })$ from a maximum likelihood fit to the difference between the numbers of forward- and backward-produced $B^{\pm }$ mesons. We measure an asymmetry consistent with zero: $A_{\mathrm{FB}}(B^{\pm })=[-0.24\pm 0.41(\mathrm{stat})\pm 0.19(\mathrm{syst})]\%$.

Delocalization error is one of the most fundamental and dominant errors that plagues presently used density functional approximations. It is responsible for a large class of problems in the density functional theory calculations. For an effective and universal alleviation of the delocalization error, we develop a local scaling correction scheme by imposing the Perdew-Parr-Levy- Balduz linearity condition to local regions of a system. Our novel scheme is applicable to various mainstream density functional approximations. It substantially reduces the delocalization error, as exemplified by the significantly improved description of dissociating molecules, transition-state species, and charge-transfer systems. The usefulness of our novel scheme affirms that the explicit treatment of fractional electron distributions is essentially important for reducing the intrinsic delocalization error associated with approximate density functionals.

It is well established that spontaneous parametric down-conversion with induced coherence across two coupled interferometers results in high-visibility single-photon interference. We describe experiments in which additional photon channels are introduced such that “which-path” information is made possible and the fringe visibility in single-photon interference is reduced in accordance with basic notions of complementarity. However, these additional pathways result in nearly perfect visibility when photons are counted in coincidence. A simplified theoretical model accounts for these observations and attributes them directly to the vacuum fields at the different crystals.

We describe generation of stable mode-locked pulse trains from on-chip normal dispersion microresonators. The excitation of hyperparametric oscillation is facilitated by the local dispersion disruptions induced by mode interactions. The system is then driven from hyperparametric oscillation to the mode-locked state with over 200 nm spectral width by controlled pump power and detuning. With the continuous-wave-driven nonlinearity, the pulses sit on a pedestal, akin to a cavity soliton. We identify the importance of pump detuning and wavelength-dependent quality factors in stabilizing and shaping the pulse structure, to achieve a single pulse inside the cavity. We examine the mode-locking dynamics by numerically solving the master equation and provide analytic solutions under appropriate approximations.

Since the demonstration of superlow friction (superlubricity) in graphite at nanoscale, one of the main challenges in the field of nano- and micromechanics was to scale this phenomenon up. A key question to be addressed is to what extent superlubricity could persist, and what mechanisms could lead to its failure. Here, using an edge-driven Frenkel-Kontorova model, we establish a connection between the critical length above which superlubricity disappears and both intrinsic material properties and experimental parameters. A striking boost in dissipated energy with chain length emerges abruptly due to a high-friction stick-slip mechanism caused by deformation of the slider leading to a local commensuration with the substrate lattice. We derived a parameter-free analytical model for the critical length that is in excellent agreement with our numerical simulations. Our results provide a new perspective on friction and nanomanipulation and can serve as a theoretical basis for designing nanodevices with superlow friction, such as carbon nanotubes.

We present a first-principles method for the calculation of the polarization-dependent atomic forces resulting from optical excitation in a solid. We calculate the induced force driving the $E_g$ phonon mode in bismuth immediately after absorption of polarized light. When radiation with polarization perpendicular to the $c$ axis is absorbed, the photoexcited charge density breaks the threefold rotational symmetry, leading to an atomic force component perpendicular to the axis. We calculate the initial excited electronic distribution as a function of photon energy and polarization and find the resulting atomic force components parallel and perpendicular to the axis. The magnitude of the calculated force is in excellent agreement with that derived from recent measurements of the amplitude of $E_g$ atomic motion and the decay time of several femtoseconds for the driving force.

We show that the simplest building blocks of origami-based materials—rigid, degree-four vertices—are generically multistable. The existence of two distinct branches of folding motion emerging from the flat state suggests at least bistability, but we show how nonlinearities in the folding motions allow generic vertex geometries to have as many as five stable states. In special geometries with collinear folds and symmetry, more branches emerge leading to as many as six stable states. Tuning the fold energy parameters, we show how monostability is also possible. Finally, we show how to program the stability features of a single vertex into a periodic fold tessellation. The resulting metasheets provide a previously unanticipated functionality—tunable and switchable shape and size via multistability.