The ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface hosts a two-dimensional electron system that is unusually sensitive to the application of an in-plane magnetic field. Low-temperature experiments have revealed a giant negative magnetoresistance (dropping by 70%), attributed to a magnetic-field induced transition between interacting phases of conduction electrons with Kondo-screened magnetic impurities. Here we report on experiments over a broad temperature range, showing the persistence of the magnetoresistance up to the 20 K range—indicative of a single-particle mechanism. Motivated by a striking correspondence between the temperature and carrier density dependence of our magnetoresistance measurements we propose an alternative explanation. Working in the framework of semiclassical Boltzmann transport theory we demonstrate that the combination of spin-orbit coupling and scattering from finite-range impurities can explain the observed magnitude of the negative magnetoresistance, as well as the temperature and electron density dependence.

We use scanning tunneling spectroscopy to investigate the filled and empty electronic states of superconducting single-unit-cell FeSe deposited on ${\mathrm{SrTiO}}_3(001)$. We map the momentum-space band structure by combining quasiparticle interference imaging with decay length spectroscopy. In addition to quantifying the filled-state bands, we discover a $\mathrm{\Gamma }$-centered electron pocket 75 meV above the Fermi energy. Our density functional theory calculations show the orbital nature of empty states at $\mathrm{\Gamma }$ and explain how the Se height is a key tuning parameter of their energies, with broad implications for electronic properties.

Pump-dependent photoluminescence imaging and second-order photon correlation studies have been performed on individual single-walled carbon nanotubes (SWCNTs) at room temperature. These studies enable the extraction of both the exciton diffusion constant and the Auger recombination coefficient. A linear correlation between these parameters is attributed to the effect of environmental disorder in setting the exciton mean free path and capture-limited Auger recombination at this length scale. A suppression of photon antibunching is attributed to the creation of multiple spatially nonoverlapping excitons in SWCNTs, whose diffusion length is shorter than the laser spot size. We conclude that complete antibunching at room temperature requires an enhancement of the exciton-exciton annihilation rate that may become realizable in SWCNTs allowing for strong exciton localization.

Electromagnetic cavities are used in numerous domains of applied and fundamental physics, from microwave ovens and electromagnetic compatibility to masers, quantum electrodynamics (QED), and quantum chaos. The wave fields established in cavities are statically fixed by their geometry, which are usually modified by using mechanical parts like mode stirrers in reverberation chambers or screws in masers and QED. Nevertheless, thanks to integral theorems, tailoring the cavity boundaries theoretically permits us to design at will the wave fields they support. Here, we show in the microwave domain that it is achievable dynamically simply by using electronically tunable metasurfaces that locally modify the boundaries, switching them in real time from Dirichlet to Neumann conditions. We prove that at a high modal density, counterintuitively, it permits us to create wave patterns presenting hot spots of intense energy. We explain and model the physical mechanism underlying the concept, which allows us to find a criterion ensuring that modifying parts of a cavity’s boundaries turn it into a completely different one. We finally prove that this approach even permits us, in the limiting case where the cavity supports only well-separated resonances, to choose the frequencies at which the latter occur.

Einstein-Podolsky-Rosen (EPR) steering demonstrates that two parties share entanglement even if the measurement devices of one party are untrusted. Here, going beyond this bipartite concept, we develop a novel formalism to explore a large class of EPR steering from generic multipartite quantum systems of arbitrarily high dimensionality and degrees of freedom, such as graph states and hyperentangled systems. All of these quantum characteristics of genuine high-order EPR steering can be efficiently certified with few measurement settings in experiments. We faithfully demonstrate for the first time such generality by experimentally showing genuine four-partite EPR steering and applications to universal one-way quantum computing. Our formalism provides a new insight into the intermediate type of genuine multipartite Bell nonlocality and potential applications to quantum information tasks and experiments in the presence of untrusted measurement devices.

Thermalization of isolated many-body systems is demonstrated by generalizing an approach originally due to von Neumann: For arbitrary initial states with a macroscopically well-defined energy, quantum mechanical expectation values become indistinguishable from the corresponding microcanonical expectation values for the overwhelming majority of all sufficiently late times. As in von Neumann’s work, the eigenvectors of the Hamiltonian and of the considered observable are required to not exhibit any specially tailored (untypical) orientation relative to each other. But all of von Neumann’s further assumptions about the admitted observables are abandoned.

We report the observation of the $X(3823)$ state in the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}X(3823)\to {\pi }^{+}{\pi }^{-}\gamma {\chi }_{c1}$ with a statistical significance of $6.2\sigma$, in data samples at center-of-mass energies $\sqrt{s}=4.230$, 4.260, 4.360, 4.420, and 4.600 GeV collected with the BESIII detector at the BEPCII electron positron collider. The measured mass of the $X(3823)$ state is $(3821.7\pm 1.3\pm 0.7)\mathrm{MeV}/c^2$, where the first error is statistical and the second systematic, and the width is less than 16 MeV at the 90% confidence level. The products of the Born cross sections for $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}X(3823)$ and the branching ratio $\mathcal{B}[X(3823)\to \gamma {\chi }_{c1,c2}]$ are also measured. These measurements are in good agreement with the assignment of the $X(3823)$ state as the $\psi (1\hspace{0.17em}{}^3{D}_2)$ charmonium state.

We report on the observation of half-quantum vortices (HQVs) in the easy-plane polar phase of an antiferromagnetic spinor Bose-Einstein condensate. Using in situ magnetization-sensitive imaging, we observe that pairs of HQVs with opposite core magnetization are generated when singly charged quantum vortices are injected into the condensate. The dynamics of HQV pair formation is characterized by measuring the temporal evolutions of the pair separation distance and the core magnetization, which reveals the short-range nature of the repulsive interactions between the HQVs. We find that spin fluctuations arising from thermal population of transverse magnon excitations do not significantly affect the HQV pair formation dynamics. Our results demonstrate the instability of a singly charged vortex in the antiferromagnetic spinor condensate.

Although Kramers’ theory for diffusive barrier crossing on a 1D free energy profile plays a central role in landscape theory for complex biomolecular processes, it has not yet been rigorously tested by experiment. Here we test this 1D diffusion scenario with single molecule fluorescence measurements of DNA hairpin folding. We find an upper bound of $2.5\mu \mathrm{s}$ for the average transition path time, consistent with the predictions by theory with parameters determined from optical tweezer measurements.

We show that microwave spectroscopy of a dense Rydberg gas trapped on a superconducting atom chip in the dipole blockade regime reveals directly the dipole-dipole many-body interaction energy spectrum. We use this method to investigate the expansion of the Rydberg cloud under the effect of repulsive van der Waals forces and the breakdown of the frozen gas approximation. This study opens a promising route for quantum simulation of many-body systems and quantum information transport in chains of strongly interacting Rydberg atoms.

We demonstrate ground-state cooling of a trapped ion using radio-frequency (rf) radiation. This is a powerful tool for the implementation of quantum operations, where rf or microwave radiation instead of lasers is used for motional quantum state engineering. We measure a mean phonon number of $\overline{n}=0.13(4)$ after sideband cooling, corresponding to a ground-state occupation probability of 88(7)%. After preparing in the vibrational ground state, we demonstrate motional state engineering by driving Rabi oscillations between the $|n=0⟩$ and $|n=1⟩$ Fock states. We also use the ability to ground-state cool to accurately measure the motional heating rate and report a reduction by almost 2 orders of magnitude compared with our previously measured result, which we attribute to carefully eliminating sources of electrical noise in the system.

We present the experimental evidence of the generation of coherent and statistically stable two-color free-electron laser radiation obtained by seeding an electron beam double peaked in energy with a laser pulse single spiked in frequency. The radiation presents two neat spectral lines, with time delay, frequency separation, and relative intensity that can be accurately controlled. The analysis of the emitted radiation shows a temporal coherence and a shot-to-shot regularity in frequency significantly enhanced with respect to the self-amplified spontaneous emission.

We derive that lightning can start if the electric field is 15% of the breakdown field, and if elongated ice particles of 6 cm length and 100 free electrons per ${\mathrm{cm}}^3$ are present. This is one particular example set from a parameter range that we discuss as well. Our simulations include the permittivity $\epsilon (\omega )$ of ice. 100 free electrons per ${\mathrm{cm}}^3$ exist at 5.5 km altitude in air showers created by cosmic particles of at least $5\times {10}^{15}\mathrm{eV}$. If the electric field zone is 3 m high and $0.2{\mathrm{km}}^2$ in the horizontal direction, at least one discharge per minute can be triggered. The size distribution of the ice particles is crucial for our argument; more detailed measurements would be desirable.

On periodic superhydrophobic surfaces the receding contact angle often scales with the surface fraction, as expected from a simple rule of mixture, the Cassie relation. However, it has been argued that energy averaging breaks down owing to line pinning, and that line fraction scaling should apply instead. From experiments and simulations we show that proper inclusion of triple line defects introduce surface fraction scaling in the line depinning threshold. In contrast to the Cassie relation and in agreement with the data, this dependence is strongly nonlinear due to triple line elasticity.

Spatial variations in the distribution of galaxy luminosities, estimated from redshifts as distance proxies, are correlated with the peculiar velocity field. Comparing these variations with the peculiar velocities inferred from galaxy redshift surveys is a powerful test of gravity and dark-energy theories on cosmological scales. Using $\sim 2\times {10}^5$ galaxies from the SDSS Data Release 7, we perform this test in the framework of gravitational instability to estimate the normalized growth rate of density perturbations $f{\sigma }_8=0.37\pm 0.13$ at $z\sim 0.1$, which is in agreement with the cold dark matter model with a cosmological constant. This unique measurement is complementary to those obtained with more traditional methods, including clustering analysis. The estimated accuracy at $z\sim 0.1$ is competitive with other methods when applied to similar data sets.

It is shown that in extensions of the standard model of quarks and leptons where the additive lepton number $L$ is broken by two units, so that $Z_2$ lepton parity, i.e., $(-1{)}^L$ which is either even or odd, remains exactly conserved, there is the possibility of stable dark matter without additional symmetry. This applies to many existing simple models of Majorana neutrino mass with dark matter, including some radiative models. Several well-known examples are discussed. This new insight leads to the construction of a radiative type II seesaw model of neutrino mass with dark matter where the dominant decay of the doubly charged Higgs boson ${\xi }^{++}$ is into $W^{+}{W}^{+}$ instead of the expected $l_i^{+}{l}_j^{+}$ lepton pairs for the well-known tree-level model.