Despite the importance of millisecond duration spatial structures [chorus wave nonlinearity or time domain structures (TDS)] to plasma dynamics, there have been no direct observations of the generation and interaction of these waves and TDS with electrons at the millisecond timescale required for their understanding. Through superposition of 0.195 ms Magnetospheric Multiscale Satellite electron measurements inside 37 superposed, millisecond duration electron holes, the first observations of electron spectra and pitch angle distributions on a submillisecond timescale have been obtained. They show that keV electrons inside the superposed electron hole are accelerated by several hundred volts and that the spectrum of electrons inside the electron hole contain several maxima and minima that are explained by a model of electron energy changes on entering the holes. We report the first observation of trapped electrons inside the TDS, in accordance with the theoretical requirement that such electrons must be present in order to form the phase space holes. Mechanisms of electron acceleration by electron holes (through perpendicular energy gain as the TDS moves into a converging magnetic field) and scattering (due to the perpendicular electric field) are discussed.

The spin-coherent-state positive-operator-valued-measure (POVM) is a fundamental measurement in quantum science, with applications including tomography, metrology, teleportation, benchmarking, and measurement of Husimi phase space probabilities. We prove that this POVM is achieved by collectively measuring the spin projection of an ensemble of qubits weakly and isotropically. We apply this in the context of optimal tomography of pure qubits. We show numerically that through a sequence of weak measurements of random directions of the collective spin component, sampled discretely or in a continuous measurement with random controls, one can approach the optimal bound.

Interaction among harmonic oscillators described by a trilinear Hamiltonian $\hslash \xi (a^{†}bc+a{b}^{†}{c}^{†})$ is one of the most fundamental models in quantum optics. By employing the anharmonicity of the Coulomb potential in a linear trapped three-ion crystal, we experimentally implement it among three normal modes of motion in the strong-coupling regime, where the coupling strength is much larger than the decoherence rate of the ion motion. We use it to simulate the interaction of an atom and light as described by the Tavis-Cummings model and the process of nondegenerate parametric down-conversion in the regime of a depleted pump.

We study the superradiant instability of a massive boson around a spinning black hole in full general relativity without assuming spatial symmetries. We focus on the case of a rapidly spinning black hole in the presence of a vector boson with a Compton wavelength comparable to the black hole radius, which is the regime where relativistic effects are maximized. We follow the growth of the boson cloud through superradiance into the nonlinear regime as it spins down the black hole, reaches a maximum energy, and begins to dissipate through the emission of gravitational waves. We find that the superradiant instability can efficiently convert a significant fraction of a black hole’s rotational energy into gravitational radiation.

Quantum gravity in a finite region of spacetime is conjectured to be dual to a conformal field theory (CFT) deformed by the irrelevant operator $T\overline{T}$. We test this conjecture with entanglement entropy, which is sensitive to ultraviolet physics on the boundary, while also probing the bulk geometry. We find that the entanglement entropy for an entangling surface consisting of two antipodal points on a sphere is finite and precisely matches the Ryu-Takayanagi formula applied to a finite region consistent with the conjecture of McGough et al. We also consider a one-parameter family of conical entropies, which are finite and verify a conjecture due to Dong. Since ultraviolet divergences are local, we conclude that the $T\overline{T}$ deformation acts as an ultraviolet cutoff on the entanglement entropy. Our results support the conjecture that the $T\overline{T}$-deformed CFT is the holographic dual of a finite region of spacetime.

The key parameter to discuss the possibility of the pion condensation in nuclear matter, i.e., the so-called Landau-Migdal parameter $g^{\prime }$, was extracted by measuring the double-differential cross sections for the $(p,n)$ reaction at $216\mathrm{MeV}/\mathrm{u}$ on a neutron-rich doubly magic unstable nucleus, ${}^{132}\mathrm{Sn}$ with the quality comparable to data taken with stable nuclei. The extracted strengths for Gamow-Teller (GT) transitions from ${}^{132}\mathrm{Sn}$ leading to ${}^{132}\mathrm{Sb}$ exhibit the GT giant resonance (GTR) at the excitation energy of $16.3\pm 0.4(\mathrm{stat})\pm 0.4(\mathrm{syst})\mathrm{MeV}$ with the width of $\mathrm{\Gamma }=4.7\pm 0.8\mathrm{MeV}$. The integrated GT strength up to $E_x=25\mathrm{MeV}$ is $S_{\mathrm{GT}}^{-}=53\pm {5(\mathrm{stat})}_{-10}^{+11}(\mathrm{syst})$, corresponding to 56% of Ikeda’s sum rule of $3(N-Z)=96$. The present result accurately constrains the Landau-Migdal parameter as $g^{\prime }=0.68\pm 0.07$, thanks to the high sensitivity of the GTR energy to $g^{\prime }$. In combination with previous studies on the GTR for ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$, the result of this work shows the constancy of this parameter in the nuclear chart region with $(N-Z)/A=0.11$ to 0.24 and $A=90$ to 208.

We propose an experimental scheme to construct an optical lattice where the atoms are confined to the surface of a torus. This construction can be realized with spatially shaped laser beams which could be realized with recently developed high resolution imaging techniques. We numerically study the feasibility of this proposal by calculating the tunneling strengths for atoms in the torus lattice. To illustrate the nontrivial role of topology in atomic dynamics on the torus, we study the quantized superfluid currents and fractional quantum Hall (FQH) states on such a structure. For FQH states, we numerically investigate the robustness of the topological degeneracy and propose an experimental way to detect such a degeneracy. Our scheme for torus construction can be generalized to surfaces with higher genus for exploration of richer topological physics.

We demonstrate the scale up of a symmetric three-path contrast interferometer to large momentum separation. The observed phase stability at separation of 112 photon recoil momenta exceeds the performance of earlier free-space interferometers. In addition to the symmetric interferometer geometry and Bose-Einstein condensate source, the robust scalability of our approach relies on the suppression of undesired diffraction phases through a careful choice of atom optics parameters. The interferometer phase evolution is quadratic with number of recoils, reaching a rate as high as $7\times {10}^7\mathrm{rad}/\mathrm{s}$. We discuss the applicability of our method towards a new measurement of the fine-structure constant and a test of QED.

At high energies, single-photon photodetachment of alkali negative ions populates final states where both the ejected electron and the residual valence electron possess high angular momenta. The photodetached electron interacts strongly with the anisotropic core, and thus the partial cross sections for these channels display non-Wigner threshold behavior reflecting these large, and occasionally repulsive, interactions. Our fully quantum-mechanical theoretical study enables a deeper interpretation of these partial cross sections. Comparisons of the behavior in different channels and between different atomic species—sodium, potassium, and cesium—show the critical role of near degeneracies in the energy spectrum and demonstrate that much of the behavior of the partial photodetachment cross sections stems from the permanent, rather than induced, electric dipole moments of these nearly degenerate channels. This provides a concrete example of a system where negative dispersion forces play a decisive role.

We study experimentally and theoretically the interactions among ultrashort optical pulses in the soliton rain multiple-pulse dynamics of a fiber laser. The laser is mode locked by a graphene saturable absorber fabricated using the mechanical transfer technique. Dissipative optical solitons aggregate into pulse bunches that exhibit complex behavior, which includes acceleration and bidirectional motion in the moving reference frame. The drift speed and direction depend on the bunch size and relative location in the cavity, punctuated by abrupt changes under bunch collisions. We model the main effects using the recently proposed noise-mediated pulse interaction mechanism, and obtain a good agreement with experiments. This highlights the major role of long-range Casimir-like interactions over dynamical pattern formations within ultrafast lasers.

The quasibiennial oscillation (QBO) is the nearly periodic reversal of the large scale flow generated by internal waves in the equatorial stratosphere. Using a laboratory model experiment, we study the instability that generates the QBO and investigate its nonlinear regime. We report the first quantitative measurements of the nonlinearly saturated velocity of the flow. We show that the QBO is generated by a bifurcation that is either supercritical or subcritical depending on the dominant dissipative process. This is confirmed by a nonlinear analysis in the vicinity of the instability threshold.

To reach the pressures and densities required for ignition, it may be necessary to develop an approach to design that makes it easier for simulations to guide experiments. Here, we report on a new short-pulse inertial confinement fusion platform that is specifically designed to be more predictable. The platform has demonstrated $99\%+0.5\%$ laser coupling into the hohlraum, high implosion velocity ($411\mathrm{km}/\mathrm{s}$), high hotspot pressure ($220+60\mathrm{Gbar}$), and high cold fuel areal density compression ratio ($>400$), while maintaining controlled implosion symmetry, providing a promising new physics platform to study ignition physics.

Fracture of highly stretched materials challenges our view of how things break. We directly visualize rupture of tough double-network gels at >50% strain. During fracture, crack tip shapes obey a $x\sim y^{1.6}$ power law, in contrast to the parabolic profile observed in low-strain cracks. A new length scale $\ell$ emerges from the power law; we show that $\ell$ scales directly with the stored elastic energy and diverges when the crack velocity approaches the shear wave speed. Our results show that double-network gels undergo brittle fracture and provide a testing ground for large-strain fracture mechanics.

Ferroelectric (FE) size effects against the scaling law were reported recently in ultrathin group-IV monochalcogenides, and extrinsic effects (e.g., defects and lattice strains) were often resorted to. Via first-principles based finite-temperature ($T$) simulations, we reveal that these abnormalities are intrinsic to their unusual symmetry breaking from bulk to thin film. Changes of the electronic structures result in different order parameters characterizing the FE phase transition in bulk and in thin films, and invalidation of the scaling law. Beyond the scaling law $T_c$ limit, this mechanism can help predict materials that are promising for room-$T$ ultrathin FE devices of broad interest.

Transport calculations based on ab initio band structures reveal large interface-generated spin currents at $\mathrm{Co}/\mathrm{Pt}$, $\mathrm{Co}/\mathrm{Cu}$, and $\mathrm{Pt}/\mathrm{Cu}$ interfaces. These spin currents are driven by in-plane electric fields but flow out of plane and can have similar strengths to spin currents generated by the spin Hall effect in bulk Pt. Each interface generates spin currents with polarization along $\widehat{\mathbf{z}}\times \mathbf{E}$, where $\widehat{\mathbf{z}}$ is the interface normal and $\mathbf{E}$ denotes the electric field. The $\mathrm{Co}/\mathrm{Cu}$ and $\mathrm{Co}/\mathrm{Pt}$ interfaces additionally generate spin currents with polarization along $\widehat{\mathbf{m}}\times (\widehat{\mathbf{z}}\times \mathbf{E})$, where $\widehat{\mathbf{m}}$ gives the magnetization direction of Co. The latter spin polarization is controlled by—but not aligned with—the magnetization, providing a novel mechanism for generating spin torques in magnetic trilayers.

The combination of a field-tunable band gap, topological edge states, and valleys in the band structure makes insulating bilayer graphene a unique localized system, where the scaling laws of dimensionless conductance $g$ remain largely unexplored. Here we show that the relative fluctuations in $\ln g$ with the varying chemical potential, in strongly insulating bilayer graphene (BLG), decay nearly logarithmically for a channel length up to $L/\xi \approx 20$, where $\xi$ is the localization length. This “marginal” self-averaging, and the corresponding dependence of $⟨\ln g⟩$ on $L$, suggests that transport in strongly gapped BLG occurs along strictly one-dimensional channels, where $\xi \approx 0.5\pm 0.1\mu \mathrm{m}$ was found to be much longer than that expected from the bulk band gap. Our experiment reveals a nontrivial localization mechanism in gapped BLG, governed by transport along robust edge modes.

Among iron chalcogenide superconductors, FeS can be viewed as a simple, highly compressed relative of FeSe without a nematic phase and with weaker electronic correlations. Under pressure, however, the superconductivity of stoichiometric FeS disappears and reappears, forming two domes. We perform electronic structure and spin fluctuation theory calculations for tetragonal FeS in order to analyze the nature of the superconducting order parameter. In the random phase approximation, we find a gap function with $d$-wave symmetry at ambient pressure, in agreement with several reports of a nodal superconducting order parameter in FeS. Our calculations show that, as a function of pressure, the superconducting pairing strength decreases until a Lifshitz transition takes place at 4.6 GPa. As a hole pocket with a large density of states appears at the Lifshitz transition, the gap symmetry is altered to sign-changing $s$ wave. At the same time, the pairing strength is severely enhanced and increases up to a new maximum at 5.5 GPa. Therefore, our calculations naturally explain the occurrence of two superconducting domes in FeS.

Two ordering states, antiferromagnetism and nematicity, have been observed in most iron-based superconductors (SCs). In contrast to those SCs, the newly discovered SC $\mathrm{CaK}({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x{)}_4{\mathrm{As}}_4$ exhibits an antiferromagnetic (AFM) state, called hedgehog spin-vortex crystal (SVC) structure, without nematic order, providing the opportunity for the investigation into the relationship between spin fluctuations and SC without any effects of nematic fluctuations. Our ${}^{75}\mathrm{As}$ nuclear magnetic resonance studies on $\mathrm{CaK}({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x{)}_4{\mathrm{As}}_4$ ($0\le x\le 0.049$) revealed that ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ is located close to a hidden hedgehog SVC AFM quantum-critical point (QCP). The magnetic QCP without nematicity in $\mathrm{CaK}({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x{)}_4{\mathrm{As}}_4$ highlights the close connection of spin fluctuations and superconductivity in iron-based SCs. The advantage of stoichiometric composition also makes ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ an ideal platform for further detailed investigation of the relationship between magnetic QCP and superconductivity in iron-based SCs without disorder effects.

Electron-hole excitation theory is used to unveil the role of nuclear quantum effects on the x-ray absorption spectral signatures of water, whose structure is computed via path-integral molecular dynamics with the MB-pol intermolecular potential model. Compared to spectra generated from the classically modeled water, quantum nuclei introduce important effects on the spectra in terms of both the energies and line shapes. Fluctuations due to delocalized protons influence the short-range ordering of the hydrogen bond network via changes in the intramolecular covalence, which broaden the preedge spectra. For intermediate-range and long-range ordering, quantum nuclei approach the neighboring oxygen atoms more closely than classical protons, promoting an “icelike” spectral feature with the intensities shifted from the main edge to the postedge. Computed spectra are in nearly quantitative agreement with the available experimental data.

We analyze the properties of strongly coupled excitons and photons in systems made of semiconducting two-dimensional transition-metal dichalcogenides embedded in optical cavities. Through a detailed microscopic analysis of the coupling, we unveil novel, highly tunable features of the spectrum that result in polariton splitting and a breaking of light-matter selection rules. The dynamics of the composite polaritons is influenced by the Berry phase arising both from their constituents and from the confinement-enhanced coupling. We find that light-matter coupling emerges as a mechanism that enhances the Berry phase of polaritons well beyond that of its elementary constituents, paving the way to achieve a polariton anomalous Hall effect.