The temperature dependence of the hydrodynamic boundary condition between a polydimethylsiloxane melt and two different nonattractive surfaces made of either an octadecyltrichlorosilane self-assembled monolayer or a grafted layer of short polydimethylsiloxane chains has been characterized. We observe a slip length proportional to the fluid viscosity. The temperature dependence is deeply influenced by the surfaces. The viscous stress exerted by the polymer liquid on the surface is observed to follow exactly the same temperature dependences as the friction stress of a cross-linked elastomer sliding on the same surfaces. Far above the glass transition temperature, these observations are rationalized in the framework of a molecular model based on activation energies: increase or decrease of the slip length with increasing temperatures can be observed depending on how the activation energy of the bulk viscosity compares to that of the interfacial Navier’s friction coefficient.

We study a swimming undulating sheet in the isotropic phase of an active nematic liquid crystal. Activity changes the effective shear viscosity, reducing it to zero at a critical value of activity. Expanding in the sheet amplitude, we find that the correction to the swimming speed due to activity is inversely proportional to the effective shear viscosity. Our perturbative calculation becomes invalid near the critical value of activity; using numerical methods to probe this regime, we find that activity enhances the swimming speed by an order of magnitude compared to the passive case.

Monopoles are intriguing topological objects, which play a central role in gauge theories and topological states of matter. While conventional monopoles are found in odd-dimensional flat spaces, such as the Dirac monopole in three dimensions and the non-Abelian Yang monopole in five dimensions, more exotic objects were predicted to exist in even dimensions. This is the case of “tensor monopoles,” which are associated with tensor (Kalb-Ramond) gauge fields, and which can be defined in four-dimensional flat spaces. In this work, we investigate the possibility of creating and measuring such a tensor monopole in condensed-matter physics by introducing a realistic three-band model defined over a four-dimensional parameter space. Our probing method is based on the observation that the topological charge of this tensor monopole, which we relate to a generalized Berry curvature, can be directly extracted from the quantum metric. We propose a realistic three-level atomic system, where tensor monopoles could be generated and revealed through quantum-metric measurements.

The last decade has witnessed remarkable progress in our understanding of thermalization in isolated quantum systems. Combining the eigenstate thermalization hypothesis with quantum measurement theory, we extend the framework of quantum thermalization to open many-body systems. A generic many-body system subject to continuous observation is shown to thermalize at a single trajectory level. We show that the nonunitary nature of quantum measurement causes several unique thermalization mechanisms that are unseen in isolated systems. We present numerical evidence for our findings by applying our theory to specific models that can be experimentally realized in atom-cavity systems and with quantum gas microscopy. Our theory provides a general method to determine an effective temperature of quantum many-body systems subject to the Lindblad master equation and thus should be applicable to noisy dynamics or dissipative systems coupled to nonthermal Markovian environments as well as continuously monitored systems. Our work provides yet another insight into why thermodynamics emerges so universally.

We study inclusive processes involving two heavy quarkonia in nonrelativistic QCD (NRQCD) and demonstrate that, in the presence of two $P$-wave Fock states, NRQCD factorization breaks down, leaving uncanceled infrared singularities. As phenomenologically important examples, we consider the decay $\mathrm{\Upsilon }\to {\chi }_{cJ}+X$ via $b\overline{b}({{}^{3}P}_{J_b}^{[8]})\to c\overline{c}({{}^{3}P}_J^{[1]})+gg$ and the production process $e^{+}{e}^{-}\to J/\psi +{\chi }_{cJ}+X$ via $e^{+}{e}^{-}\to c\overline{c}({{}^{3}P}_{J_1}^{[8]})+c\overline{c}({{}^{3}P}_J^{[1]})+g$. We infer that such singularities will appear for double quarkonium hadroproduction at next-to-leading order. As a solution to this problem, we introduce to NRQCD effective field theory new types of operators whose quantum corrections absorb these singularities.

Optical analog signal processing has been gaining significant attention as a way to overcome the speed and energy limitations of digital techniques. Metasurfaces offer a promising avenue towards this goal due to their efficient manipulation of optical signals over deeply subwavelength volumes. To date, metasurfaces have been proposed to transform signals in the spatial domain, e.g., for beam steering, focusing, or holography, for which angular-dependent responses, or nonlocality, are unwanted features that must be avoided or mitigated. Here, we show that the metasurface nonlocality can be engineered to enable signal manipulation in the momentum domain over an ultrathin platform. We explore nonlocal metasurfaces performing basic mathematical operations, paving the way towards fast and power-efficient ultrathin devices for edge detection and optical image processing.

We demonstrated the superradiance-to-polariton crossover of the blue excitons in ${\mathrm{Cu}}_2\mathrm{O}$ by varying the sample thicknesses instead of controlling the cavity quality factor. The crossover behavior was compared with unprecedented calculations based on the nonlocal optical response theory with the inclusion of three exciton resonances. The crossover thickness, found to be $177\pm 2\mathrm{nm}$, was smaller than the predicted value for a single resonance by a factor of 5. The fact that there was much larger longitudinal-transverse splitting ($40\pm 5\mathrm{meV}$) than in the bulk implies a surprisingly fast radiative recombination even without a cavity structure.

A new drift-kinetic theory of the ion response to magnetic islands in tokamak plasmas is presented. Small islands are considered, with widths $w$ much smaller than the plasma radius $r$, but comparable to the trapped ion orbit width ${\rho }_{bi}$. An expansion in $w/r$ reduces the system dimensions from five down to four. In the absence of an electrostatic potential, the ions follow stream lines that map out a drift-island structure that is identical to the magnetic island, but shifted by an amount $\sim$ few ${\rho }_{bi}$. The ion distribution function is flattened across these drift islands, not the magnetic island. For small islands, $w\sim {\rho }_{bi}$, the shifted drift islands result in a pressure gradient being maintained across the magnetic island, explaining previous simulation results [E. Poli et al., Phys. Rev. Lett. 88, 075001 (2002)]. To maintain quasineutrality an electrostatic potential forms, which then supports a pressure gradient in the electrons also. This influence on the electron physics is shown to stabilize small magnetic islands of width a few ion banana widths, providing a new threshold mechanism for neoclassical tearing modes—a key result for the performance of future tokamaks, including ITER.

The complex optical conductivity of the half-Heusler compound GdPtBi is measured in a frequency range from 20 to $22000{\mathrm{cm}}^{-1}$ (2.5 meV–2.73 eV) at temperatures down to 10 K in zero magnetic field. We find the real part of the conductivity, ${\sigma }_1(\omega )$, to be almost perfectly linear in frequency over a broad range from 50 to $800{\mathrm{cm}}^{-1}$ ($\sim 6–100\mathrm{meV}$) for $T\le 50\mathrm{K}$. This linearity strongly suggests the presence of three-dimensional linear electronic bands with band crossings (nodes) near the chemical potential. Band-structure calculations show the presence of triple points, where one doubly degenerate and one nondegenerate band cross each other in close vicinity of the chemical potential. From a comparison of our data with the optical conductivity computed from the band structure, we conclude that the observed nearly linear ${\sigma }_1(\omega )$ originates as a cumulative effect from all the transitions near the triple points.

We report a method to control contributions of bulk and surface states in the topological insulator ${\mathrm{Bi}}_2{\mathrm{Te}}_2\mathrm{Se}$ that allows accessing the spin-polarized transport endowed by topological surface states. An intrinsic surface dominant transport is established when cooling the sample to low temperature or reducing the conduction channel length, both achieved in situ in the transport measurements with a four-probe scanning tunneling microscope without the need of further tailoring the sample. The topological surface states show characteristic transport behaviors with mobility about an order of magnitude higher than reported before, and a spin polarization approaching the theoretically predicted value. Our result demonstrates accessibility to the intrinsic high mobility spin transport of topological surface states, which paves a way to realizing topological spintronic devices.

The Berreman effect (BE) allows one to study the electrodynamics of ultrathin conducting films at the surface of dielectrics by use of grazing-angle infrared spectroscopy and polarized radiation. Here, we first apply the BE to the two-dimensional electron system (2DES) at the interface between a high-purity film of the topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and its sapphire substrate. We determine for the 2DES a charge density $n_s=(8\pm 1)\times {10}^{12}{\mathrm{cm}}^{-2}$, a thickness $d=0.6\pm 0.2\mathrm{nm}$, and a mobility ${\mu }^{\mathrm{IR}}=290\pm 30{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$. Within errors, all of these parameters result in being independent of temperature between 300 and 10 K. These findings consistently indicate that the 2DES is formed by topological surface states, whose infrared response is then directly observed here.

We study Brownian dynamics of colloidal spheres, with planar anchoring conditions, suspended in the nematic phase of the lyotropic chromonic liquid crystal disodium chromoglycate (DSCG). Unlike typical liquid crystals, the unusually small twist elastic modulus of DSCG permits two energetically distinct helical distortions (twisted tails) of the nematic director to “dress” the suspended spheres. Video microscopy is used to characterize the helical distortions versus particle size and to measure particle mean-square displacements. Diffusion coefficients parallel and perpendicular to the far-field director, and their anisotropy ratio, are different for the two twisted tail configurations. Moreover, the crossover from subdiffusive to diffusive behavior is anomalously slow for motion perpendicular to the director ($>100\mathrm{s}$). Simple arguments using Miesowicz viscosities and ideas about twist relaxation are suggested to understand the mean-square displacement observations.

We prove an upper bound on the diffusivity of a dissipative, local, and translation invariant quantum Markovian spin system: $D\le D_0+(\alpha v_{\mathrm{LR}}\tau +\beta \xi )v_C$. Here $v_{\mathrm{LR}}$ is the Lieb-Robinson velocity, $v_C$ is a velocity defined by the current operator, $\tau$ is the decoherence time, $\xi$ is the range of interactions, $D_0$ is a decoherence-induced microscopic diffusivity, and $\alpha$ and $\beta$ are precisely defined dimensionless coefficients. The bound constrains quantum transport by quantities that can either be obtained from the microscopic interactions ($D_0$, $v_{\mathrm{LR}}$, $v_C$, $\xi$) or else determined from independent local nontransport measurements ($\tau$, $\alpha$, $\beta$). We illustrate the general result with the case of a spin-half $XXZ$ chain with on-site dephasing. Our result generalizes the Lieb-Robinson bound to constrain the sub-ballistic diffusion of conserved densities in a dissipative setting.

Future neutron-antineutron ($n\text{−}\overline{n}$) oscillation experiments, such as at the European Spallation Source and the Deep Underground Neutrino Experiment, aim to find first evidence of baryon number violation. We investigate implications of an improved $n\text{−}\overline{n}$ oscillation search for baryogenesis via interactions of $n\text{−}\overline{n}$ mediators, parametrized by an effective field theory (EFT). We find that even in a minimal EFT setup there is overlap between the parameter space probed by $n\text{−}\overline{n}$ oscillation and the region that can realize the observed baryon asymmetry of the Universe. The mass scales of exotic new particles are in the tera-electron-volt–peta-electron-volt regime, inaccessible at the LHC or its envisioned upgrades. Given the innumerable high energy theories that can match, or resemble, the minimal EFT that we discuss, future $n\text{−}\overline{n}$ oscillation experiments could probe many viable theories of baryogenesis beyond the reach of other experiments.

The ${}^{22}\mathrm{Ne}(p,\gamma ){}^{23}\mathrm{Na}$ reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at $E_p=156.2$, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at $E_p=71$ and 105 keV. Here, new ${}^{22}\mathrm{Ne}(p,\gamma ){}^{23}\mathrm{Na}$ data with high statistics and low background are reported. Stringent upper limits of $6\times {10}^{-11}$ and $7\times {10}^{-11}\mathrm{eV}$ (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant $S$ factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the ${}^{22}\mathrm{Ne}(p,\gamma ){}^{23}\mathrm{Na}$ rate is now reduced by 3 orders of magnitude.

We study in a nonperturbative fashion the thermodynamics of a unitary Fermi gas over a wide range of temperatures and spin polarizations. To this end, we use the complex Langevin method, a first principles approach for strongly coupled systems. Specifically, we show results for the density equation of state, the magnetization, and the magnetic susceptibility. At zero polarization, our results agree well with state-of-the-art results for the density equation of state and with experimental data. At finite polarization and low fugacity, our results are in excellent agreement with the third-order virial expansion. In the fully quantum mechanical regime close to the balanced limit, the critical temperature for superfluidity appears to depend only weakly on the spin polarization.

We establish that matter-wave diffraction at near-resonant ultraviolet optical gratings can be used to spatially separate individual conformers of complex molecules. Our calculations show that the conformational purity of the prepared beam can be close to 100% and that all molecules remain in their electronic ground state. The proposed technique is independent of the dipole moment and the spin of the molecule and thus paves the way for structure-sensitive experiments with hydrocarbons and biomolecules, such as neurotransmitters and hormones, which have evaded conformer-pure isolation so far.

We report on a kinematically complete measurement of double ionization of helium by a single 1100 eV circularly polarized photon. By exploiting dipole selection rules in the two-electron continuum state, we observed the angular emission pattern of electrons originating from a pure quadrupole transition. Our fully differential experimental data and companion ab initio nonperturbative theory show the separation of dipole and quadrupole contributions to photo-double-ionization and provide new insight into the nature of the quasifree mechanism.