We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of ${}^{254}\mathrm{No}$ is measured to be $B_{\mathrm{f}}=6.0\pm 0.5\mathrm{MeV}$ at spin $15\hslash$ and, by extrapolation, $B_{\mathrm{f}}=6.6\pm 0.9\mathrm{MeV}$ at spin $0\hslash$. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for ${}^{220}\mathrm{Th}$ and only a lower limit of the fission barrier height can be determined: $B_{\mathrm{f}}(I)>8\mathrm{MeV}$. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.

We demonstrate that the molecular Berry phase and the corresponding nonanalyticity in the electronic Born-Oppenheimer wave function is, in general, not a true topological feature of the exact solution of the full electron-nuclear Schrödinger equation. For a numerically exactly solvable model we show that a nonanalyticity, and the associated geometric phase, only appear in the limit of infinite nuclear mass, while a perfectly smooth behavior is found for any finite nuclear mass.

We present ultrahigh-resolution measurements of state-to-state inelastic differential cross sections for NO-Ne and NO-Ar collisions, obtained by combining the Stark deceleration and velocity map imaging techniques. We show that for counterpropagating crossed beam geometries, the effect of the velocity spreads of the reagent beams on the angular resolution of the images is minimized. Furthermore, the counterpropagating geometry results in images that are symmetric with respect to the relative velocity vector. This allows for the use of inverse Abel transformation methods that enhance the resolution further. State-resolved diffraction oscillations in the differential cross sections are measured with an angular resolution approaching 0.3°. Distinct structures observed in the cross sections gauge the quality of recent ab initio potential energy surfaces for NO–rare-gas atom collisions with unprecedented precision.

Superradiance has been an outstanding problem in quantum optics since Dicke introduced the concept of enhanced directional spontaneous emission by an ensemble of identical two-level atoms. The effect is based on the correlated collective Dicke states which turn out to be highly entangled. Here we show that enhanced directional emission of spontaneous radiation can be produced also with statistically independent incoherent sources, via the measurement of higher-order correlation functions of the emitted radiation. Our analysis is applicable to a wide variety of quantum emitters, like trapped atoms, ions, quantum dots, or nitrogen-vacancy centers, and is also valid for incoherent classical emitters. This is experimentally confirmed with up to eight statistically independent thermal light sources. The arrangement to measure the higher-order correlation functions corresponds to a generalized Hanbury Brown–Twiss setup, demonstrating that the two phenomena, superradiance and the Hanbury Brown–Twiss effect, stem from the same interference phenomenon.

Coherent imaging and communication through or within heavily scattering random media has been considered impossible due to the randomization of the information contained in the scattered electromagnetic field. We report a remarkable result based on speckle correlations over incident field position that demonstrates that the field incident on a heavily scattering random medium can be obtained using a method that is not restricted to weak scatter and is, in principle, independent of the thickness of the scattering medium. Natural motion can be exploited, and the approach can be extended to other geometries. The near-infrared optical results presented indicate that the approach is applicable to other frequency regimes, as well as other wave types. This work presents opportunities to enhance communication channel capacity in the large source and detector number regime, for a new method to view binary stars from Earth, and in biomedical applications.

As lasers become progressively higher in power, optical damage thresholds will become a limiting factor. Using the nonlinear optics of plasma may be a way to circumvent these limits. Here, we present a new self-compression mechanism for high-power, femtosecond laser pulses based on geometrical focusing and three dimensional spatiotemporal reshaping in an ionizing plasma. By propagating tightly focused, 10-mJ femtosecond laser pulses through a $100\text{−}\mu \mathrm{m}$ gas jet, the interplay between ionization gradients, focusing, and diffraction of the light pulse leads to stable and uniform self-compression of the pulse, while maintaining a high-energy throughput and excellent refocusability. Self-compression down to 16 fs from an original 36-fs pulse is measured using second-harmonic-generation frequency-resolved optical gating. Using this mechanism, we are able to maintain a high transmission ($>88\%$) such that the pulse peak power is doubled. Three-dimensional numerical simulations are performed to support our interpretation of the experimental observations.

We propose a class of spectral singularities emerging from the coincidence of two independent singularities with highly directional responses. These spectral singularities result from resonance trapping induced by the interplay between parity-time symmetry and Fano resonances. At these singularities, while the system is reciprocal in terms of a finite transmission, a simultaneous infinite reflection from one side and zero reflection from the opposite side can be realized.

The temporal evolution of mechanical energy and spatially averaged crack speed are both monitored in slowly fracturing artificial rocks. Both signals display an irregular burstlike dynamics, with power-law distributed fluctuations spanning a broad range of scales. Yet, the elastic power released at each time step is proportional to the global velocity all along the process, which enables defining a material-constant fracture energy. We characterize the intermittent dynamics by computing the burst statistics. This latter displays the scale-free features signature of crackling dynamics, in qualitative but not quantitative agreement with the depinning interface models derived for fracture problems. The possible sources of discrepancies are pointed out and discussed.

We report experimental measurements of narrow-band, single-mode excitation, and drive beam energy modulation, in a dielectric wakefield accelerating structure with planar geometry and Bragg-reflector boundaries. A short, relativistic electron beam ($\sim 1\mathrm{ps}$) with moderate charge ($\sim 100\mathrm{pC}$) is used to drive the wakefields in the structure. The fundamental mode of the structure is reinforced by constructive interference in the alternating dielectric layers at the boundary, and is characterized by the spectral analysis of the emitted coherent Cherenkov radiation signal. Data analysis shows a narrow-band peak at 210 GHz corresponding to the fundamental mode of the structure. Simulations in both 2D and 3D provide insight into the propagating fields and reproduction of the electron beams dynamics observables and emitted radiation characteristics.

The performance of accelerators profits from phase-space tailoring by coupling of degrees of freedom. Previously applied techniques swap the emittances among the three degrees but the set of available emittances is fixed. In contrast to these emittance exchange scenarios, the emittance transfer scenario presented here allows for arbitrarily changing the set of emittances as long as the product of the emittances is preserved. This Letter is the first experimental demonstration of transverse emittance transfer along an ion beam line. The amount of transfer is chosen by setting just one single magnetic field value. The envelope functions (beta) and slopes (alpha) of the finally uncorrelated and repartitioned beam at the exit of the transfer line do not depend on the amount of transfer.

In this Letter, we study the effect of quasiparticle interactions in a Bose-Fermi superfluid mixture. We consider the lifetime of a quasiparticle of the Bose superfluid due to its interaction with quasiparticles in the Fermi superfluid. We find that this damping rate, i.e., the inverse of the lifetime, has quite a different threshold behavior at the BCS and the BEC side of the Fermi superfluid. The damping rate is a constant near the threshold momentum in the BCS side, while it increases rapidly in the BEC side. This is because, in the BCS side, the decay process is restricted by the constraint that the fermion quasiparticle is located near the Fermi surface, while such a restriction does not exist in the BEC side where the damping process is dominated by bosonic quasiparticles of the Fermi superfluid. Our results are related to the collective mode experiment in the recently realized Bose-Fermi superfluid mixture.

The Fe-H system has been investigated by combined x-ray diffraction studies and total energy calculations at pressures up to 136 GPa. The experiments involve laser annealing of hydrogen-embedded iron in a diamond anvil cell. Two new ${\mathrm{FeH}}_x$ compounds, with $x\sim 2$ and $x=3$, are discovered at 67 and 86 GPa, respectively. Their crystal structures are identified (unit cell and Fe positional parameters from x-ray diffraction, H positional parameters from ab initio calculations) as tetragonal with space group $I4/mmm$ for ${\mathrm{FeH}}_{\sim 2}$ and as simple cubic with space group $Pm\overline{3}m$ for ${\mathrm{FeH}}_3$. Large metastability regimes are observed that allowed to measure the $P(V)$ equation of state at room temperature of FeH, ${\mathrm{FeH}}_{\sim 2}$, and ${\mathrm{FeH}}_3$.

We perform polarized electronic Raman scattering on ${\mathrm{URu}}_2{\mathrm{Si}}_2$ single crystals at low temperature down to 8 K in the hidden-order state and under a magnetic field up to 10 T. The hidden-order state is characterized by a sharp excitation at 1.7 meV and a gap in the electronic continuum below 6.8 meV. Both Raman signatures are of pure $A_{2g}$ symmetry. By comparing the behavior of the Raman sharp excitation and the neutron resonance at $Q_0=(0,0,1)$, we provide new evidence, constrained by selection rules of the two probes, that the hidden-order state breaks the translational symmetry along the $c$ axis such that $\mathrm{\Gamma }$ and $Z$ points fold on top of each other. The observation of these distinct Raman features with a peculiar $A_{2g}$ symmetry as a signature of the hidden-order phase places strong constraints on current theories of the hidden-order in ${\mathrm{URu}}_2{\mathrm{Si}}_2$.

We report a de Haas–van Alphen (dHvA) oscillation study on ${\mathrm{IrTe}}_2$ single crystals showing complex dimer formations. By comparing the angle dependence of dHvA oscillations with band structure calculations, we show distinct Fermi surface reconstruction induced by a $1/5$-type and a $1/8$-type dimerizations. This verifies that an intriguing quasi-two-dimensional conducting plane across the layers is induced by dimerization in both cases. A phase transition to the $1/8$ phase with higher dimer density reveals that local instabilities associated with intra- and interdimer couplings are the main driving force for complex dimer formations in ${\mathrm{IrTe}}_2$.

Nonlinear continuum generation from diffraction-limited hot spots in rough silver films exhibits striking narrow-band intensity resonances in excitation wavelength. Time-domain Fourier spectroscopy uncovers how these resonances arise due to the formation of a “plasmon staircase”, a discreteness in the fundamental oscillation of the plasmon excitations responsible for generating the white-light continuum. Whereas multiple scattering from discrete antennas can be invoked to explain hot spot formation in random assemblies of isolated particles, hot spots in films of fused nanoparticles are excited by interfering propagating surface plasmons, launched by scattering from individual nanoparticle antennas. For closed films, discrete propagating plasmons interact coherently over distances of tens of microns to pump the hot spot.

What distinguishes trivial superfluids from topological superfluids in interacting many-body systems where the number of particles is conserved? Building on a class of integrable pairing Hamiltonians, we present a number-conserving, interacting variation of the Kitaev model, the Richardson-Gaudin-Kitaev chain, that remains exactly solvable for periodic and antiperiodic boundary conditions. Our model allows us to identify fermion parity switches that distinctively characterize topological superconductivity (fermion superfluidity) in generic interacting many-body systems. Although the Majorana zero modes in this model have only a power-law confinement, we may still define many-body Majorana operators by tuning the flux to a fermion parity switch. We derive a closed-form expression for an interacting topological invariant and show that the transition away from the topological phase is of third order.

We observe the elastic stiffness and ultrasonic absorption of a Skyrmion crystal in the chiral-lattice magnet MnSi. The Skyrmion crystal lattice exhibits a stiffness 3 orders of magnitude smaller than that of the atomic lattice of MnSi, being as soft as the flux line lattice in type-II superconductors. The observed anisotropic elastic responses are consistent with the cylindrical shape of the Skyrmion spin texture. Phenomenological analysis reveals that the spin-orbit coupling is responsible for the emergence of anisotropic elasticity in the Skyrmion lattice.

We show that the spontaneous symmetry breaking in multiferroic hexagonal manganites can be chemically manipulated to yield two complementary ground states: the well-known ferroelectric $P{6}_{3}cm$ and an antipolar $P\overline{3}c$ phase. Both symmetry breakings yield topologically protected vortex defects, with the antipolar vortices dual to those of the ferroelectric. This duality stems from the existence of 12 possible angles of ${\mathrm{MnO}}_5$ tilting, and broad strain-free walls with low energy spontaneously emerge through an intermediate $P3c1$ state, providing a complete unified symmetry description.