We perform an experimental study of granular impact, where intruders strike 2D beds of photoelastic disks from above. High-speed video captures the intruder dynamics and the local granular force response, allowing investigation of grain-scale mechanisms in this process. We observe rich acoustic behavior at the leading edge of the intruder, strongly fluctuating in space and time, and we show that this acoustic activity controls the intruder deceleration, including large force fluctuations at short time scales. The average intruder dynamics match previous studies using empirical force laws, suggesting a new microscopic picture, where acoustic energy is carried away and dissipated.

We report the first evidence for the ${\eta }_b(2S)$ using the $h_b(2P)\to {\eta }_b(2S)\gamma$ transition and the first observation of the $h_b(1P)\to {\eta }_b(1S)\gamma$ and $h_b(2P)\to {\eta }_b(1S)\gamma$ transitions. The mass and width of the ${\eta }_b(1S)$ and ${\eta }_b(2S)$ are measured to be $m_{{\eta }_b(1S)}=(9402.4\pm 1.5\pm 1.8)\mathrm{MeV}/c^2$, $m_{{\eta }_b(2S)}=(9999.0\pm {3.5}_{-1.9}^{+2.8})\mathrm{MeV}/c^2$, and ${\Gamma }_{{\eta }_b(1S)}=({10.8}_{-3.7-2.0}^{+4.0+4.5})\mathrm{MeV}$. We also update the $h_b(1P)$ and $h_b(2P)$ mass measurements. We use a $133.4{\mathrm{fb}}^{-1}$ data sample collected at energies near the ${\rm Y}(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

We propose to use subwavelength confinement of light associated with the near field of plasmonic systems to create nanoscale optical lattices for ultracold atoms. Our approach combines the unique coherence properties of isolated atoms with the subwavelength manipulation and strong light-matter interaction associated with nanoplasmonic systems. It allows one to considerably increase the energy scales in the realization of Hubbard models and to engineer effective long-range interactions in coherent and dissipative many-body dynamics. Realistic imperfections and potential applications are discussed.

We investigate the Casimir effect between two-dimensional electron systems driven to the quantum Hall regime by a strong perpendicular magnetic field. In the large-separation ($d$) limit where retardation effects are essential, we find (i) that the Casimir force is quantized in units of $3\hslash c{\alpha }^2/8{\pi }^2{d}^4$ and (ii) that the force is repulsive for mirrors with the same type of carrier and attractive for mirrors with opposite types of carrier. The sign of the Casimir force is therefore electrically tunable in ambipolar materials such as graphene. The Casimir force is suppressed when one mirror is a charge-neutral graphene system in a filling factor $\nu =0$ quantum Hall state.

We study the superconducting-gap anisotropy of the $\Gamma$-centered hole Fermi surface in optimally doped ${\mathrm{FeTe}}_{0.6}{\mathrm{Se}}_{0.4}$ ($T_c=14.5\mathrm{K}$), using laser-excited angle-resolved photoemission spectroscopy. We observe sharp superconducting (SC) coherence peaks at $T=2.5\mathrm{K}$. In contrast to earlier angle-resolved photoemission spectroscopy studies but consistent with thermodynamic results, the momentum dependence shows a $\cos (4\phi )$ modulation of the SC-gap anisotropy. The observed SC-gap anisotropy strongly indicates that the pairing interaction is not a conventional phonon-mediated isotropic one. Instead, the results suggest the importance of second-nearest-neighbor electronic interactions between the iron sites in the framework of $s_{\pm }$-wave superconductivity.

Polarized inelastic neutron scattering under a magnetic field is used to get a microscopic insight into the spin resonance of the heavy fermion superconductor ${\mathrm{CeCoIn}}_5$. The resonance line shape is found to depend on the neutron polarization: Some of the spectral weight is common to the two polarization channels while the remaining part is distributed equally between them. This is evidence for the spin resonance being a degenerate mode with three fluctuation channels: A Zeeman split contribution and an additional longitudinal mode.

Artificial nanowalkers are inspired by biomolecular counterparts from living cells, but remain far from comparable to the latter in design principles. The walkers reported to date mostly rely on chemical mechanisms to gain a direction; they all produce chemical wastes. Here we report a light-powered DNA bipedal walker based on a design principle derived from cellular walkers. The walker has two identical feet and the track has equal binding sites; yet the walker gains a direction by pure physical mechanisms that autonomously amplify an intrasite asymmetry into a ratchet effect. The nanowalker is free of any chemical waste. It has a distinct thermodynamic feature that it possesses the same equilibrium before and after operation, but generates a truly nonequilibrium distribution during operation. The demonstrated design principle exploits mechanical effects and is adaptable for use in other nanomachines.

The number of four-body states known to behave universally is small. This work adds a new class of four-body states to this relatively short list. We predict the existence of a universal four-body bound state for heavy-light mixtures consisting of three identical heavy fermions and a fourth distinguishable lighter particle with a mass ratio $\kappa \gtrsim 9.5$ and short-range interspecies interaction characterized by a positive $s$-wave scattering length. The structural properties of these universal states are discussed, and finite-range effects are analyzed. The bound states can be experimentally realized and probed by utilizing ultracold atom mixtures.

A model is proposed that describes the evolution of a mixed state of a quantum system for which gain and loss of energy or amplitude are present. Properties of the model are worked out in detail. In particular, invariant subspaces of the space of density matrices corresponding to the fixed points of the dynamics are identified, and the existence of a transition between the phase in which gain and loss are balanced and the phase in which this balance is lost is illustrated in terms of the time average of observables. The model is extended to include a noise term that results from a uniform random perturbation generated by white noise. Numerical studies of example systems show the emergence of equilibrium states that suppress the phase transition.

Blind quantum computation is a secure delegated quantum computing protocol where Alice, who does not have sufficient quantum technology at her disposal, delegates her computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice’s input, output, and algorithm. Protocols of blind quantum computation have been proposed for several qudit measurement-based computation models, such as the graph state model, the Affleck-Kennedy-Lieb-Tasaki model, and the Raussendorf-Harrington-Goyal topological model. Here, we consider blind quantum computation for the continuous-variable measurement-based model. We show that blind quantum computation is possible for the infinite squeezing case. We also show that the finite squeezing causes no additional problem in the blind setup apart from the one inherent to the continuous-variable measurement-based quantum computation.

Many-particle optical lattice clocks have the potential for unprecedented measurement precision and stability due to their low quantum projection noise. However, this potential has so far never been realized because clock stability has been limited by frequency noise of optical local oscillators. By synchronously probing two ${}^{87}\mathrm{Sr}$ lattice systems using a laser with a thermal noise floor of $1\times {10}^{-15}$, we remove classically correlated laser noise from the intercomparison, but this does not demonstrate independent clock performance. With an improved optical oscillator that has a $1\times {10}^{-16}$ thermal noise floor, we demonstrate an order of magnitude improvement over the best reported stability of any independent clock, achieving a fractional instability of $1\times {10}^{-17}$ in 1000 s of averaging time for synchronous or asynchronous comparisons. This result is within a factor of 2 of the combined quantum projection noise limit for a 160 ms probe time with $\sim {10}^3$ atoms in each clock. We further demonstrate that even at this high precision, the overall systematic uncertainty of our clock is not limited by atomic interactions. For the second Sr clock, which has a cavity-enhanced lattice, the atomic-density-dependent frequency shift is evaluated to be $-3.11\times {10}^{-17}$ with an uncertainty of $8.2\times {10}^{-19}$.

We evaluated the $C_6$ coefficients of Yb-Yb, Yb-alkali, and Yb-group II van der Waals interactions with 2% uncertainty. The only existing experimental result for such quantities is for the Yb-Yb dimer. Our value, $C_6=1929(39)\mathrm{a}.\mathrm{u}.$, is in excellent agreement with the recent experimental determination of 1932(35) a.u. We have also developed a new approach for the calculation of the dynamic correction to the blackbody radiation shift. We have calculated this quantity for the Yb $6s^2{}^{1}S_0-6s6p{}^{3}P_0^o$ clock transition with 3.5% uncertainty. This reduces the fractional uncertainty due to the blackbody radiation shift in the Yb optical clock at 300 K to the ${10}^{-18}$ level.

We study the interface between a fractional topological insulator and an ordinary insulator, both described using holography. By turning on a chemical potential we induce a finite density of matter localized at the interface. These are gapless surface excitations which are expected to have a fermionic character. We study the thermodynamics of the system, finding a symmetry preserving compressible state at low temperatures, whose excitations exhibit hyperscaling violation. These results are consistent with the expectation of gapless fermionic excitations forming a Fermi surface at finite density.

Measurements of $B_c^{+}$ production and mass are performed with the decay mode $B_c^{+}\to J/\psi {\pi }^{+}$ using $0.37{\mathrm{fb}}^{-1}$ of data collected in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ by the LHCb experiment. The ratio of the production cross section times branching fraction between the $B_c^{+}\to J/\psi {\pi }^{+}$ and the $B^{+}\to J/\psi K^{+}$ decays is measured to be $\mathbf{(}0.68\pm 0.10(\mathrm{stat})\pm 0.03(\mathrm{syst})\pm 0.05(\mathrm{\text{lifetime}})\mathbf{)}\%$ for $B_c^{+}$ and $B^{+}$ mesons with transverse momenta $p_{\mathrm{T}}>4\mathrm{GeV}/c$ and pseudorapidities $2.5<\eta <4.5$. The $B_c^{+}$ mass is directly measured to be $6273.7\pm 1.3(\mathrm{stat})\pm 1.6(\mathrm{syst})\mathrm{MeV}/c^2$, and the measured mass difference with respect to the $B^{+}$ meson is $M(B_c^{+})-M(B^{+})=994.6\pm 1.3(\mathrm{stat})\pm 0.6(\mathrm{syst})\mathrm{MeV}/c^2$.

The phenomenon of core excitation in the breakup of a two-body halo nucleus is investigated. We show that this effect plays a significant role in the reaction dynamics and, furthermore, its interference with the valence excitation mechanism has sizable and measurable effects on the breakup angular distributions. These effects have been studied in the resonant breakup of ${}^{11}\mathrm{Be}$ on a carbon target, populating the resonances at 1.78 MeV ($5/2^{+}$) and 3.41 MeV ($3/2^{+}$). The calculations have been performed using a recent extension of the distorted-wave Born approximation method, which takes into account the effect of core excitation in both the structure of the halo nucleus and in the reaction mechanism. The calculated angular distributions have been compared with the available data [Fukuda et al., Phys. Rev. C 70, 054606 (2004).]. Although each of these resonances is dominated by one of the two considered mechanisms, the angular patterns of these resonances depend in a very delicate way on the interference between them. This is the first clear evidence of this effect but the phenomenon is likely to occur in other similar reactions.

We investigate the possibility of the existence of the exotic torus configuration in the high-spin excited states of ${}^{40}\mathrm{Ca}$. We here consider the spin alignments about the symmetry axis. To this end, we use a three-dimensional cranked Skyrme Hartree-Fock method and search for stable single-particle configurations. We find one stable state with the torus configuration at the total angular momentum $J=60\hslash$ and an excitation energy of about 170 MeV in all calculations using various Skyrme interactions. The total angular momentum $J=60\hslash$ consists of aligned 12 nucleons with the orbital angular momenta $\Lambda =+4$, $+5$, and $+6$ for spin-up or -down neutrons and protons. The obtained results strongly suggest that a macroscopic amount of circulating current breaking the time-reversal symmetry emerges in the high-spin excited state of ${}^{40}\mathrm{Ca}$.

Recently, using midinfrared laser-induced electron diffraction (LIED), snapshots of a vibrating diatomic molecule on a femtosecond time scale have been captured [C. I. Blaga et al., Nature (London) 483, 194 (2012)]. In this Letter, a comprehensive treatment for the atomic LIED response is reported, a critical step in generalizing this imaging method. Electron-ion differential cross sections (DCSs) of rare gas atoms are extracted from measured angular-resolved, high-energy electron momentum distributions generated by intense midinfrared lasers. Following strong-field ionization, the high-energy electrons result from elastic rescattering of a field-driven wave packet with the parent ion. For recollision energies $\ge 100\mathrm{eV}$, the measured DCSs are indistinguishable for the neutral atoms and ions, illustrating the close collision nature of this interaction. The extracted DCSs are found to be independent of laser parameters, in agreement with theory. This study establishes the key ingredients for applying LIED to femtosecond molecular imaging.

We show that in a gas of ultracold atoms distance selective two-body loss can be engineered via the resonant laser excitation of atom pairs to interacting electronic states. In an optical lattice this leads to a dissipative master equation dynamics with Lindblad jump operators that annihilate atom pairs with a specific interparticle distance. In conjunction with coherent hopping between lattice sites this unusual dissipation mechanism leads to the formation of coherent long-lived complexes that can even exhibit an internal level structure which is strongly coupled to their external motion. We analyze this counterintuitive phenomenon in detail in a system of hard-core bosons. While current research has established that dissipation in general can lead to the emergence of coherent features in many-body systems our work shows that strong nonlocal dissipation can effectuate a binding mechanism for particles.

We report on three-dimensional optical trapping of single ions in a one-dimensional optical lattice formed by two counterpropagating laser beams. We characterize the trapping parameters of the standing-wave using the ion as a sensor stored in a hybrid trap consisting of a radio-frequency (rf), a dc, and the optical potential. When loading ions directly from the rf into the standing-wave trap, we observe a dominant heating rate. Monte Carlo simulations confirm rf-induced parametric excitations within the deep optical lattice as the main source. We demonstrate a way around this effect by an alternative transfer protocol which involves an intermediate step of optical confinement in a single-beam trap avoiding the temporal overlap of the standing-wave and the rf field. Implications arise for hybrid (rf-optical) and pure optical traps as platforms for ultracold chemistry experiments exploring atom-ion collisions or quantum simulation experiments with ions, or combinations of ions and atoms.

We report one-dimensional pinning of a single ion by an optical lattice. A standing-wave cavity produces the lattice potential along the rf-field-free axis of a linear Paul trap. The ion’s localization is detected by measuring its fluorescence when excited by standing-wave fields with the same period, but different spatial phases. The experiments agree with an analytical model of the localization process, which we test against numerical simulations. For the best localization achieved, the ion’s average coupling to the cavity field is enhanced from 50% to 81(3)% of its maximum possible value, and we infer that the ion is bound in a lattice well with over 97% probability.