We report measurements of discrete excitation-induced frequency shifts on the ${}^{7}F_0\to {}^{5}D_0$ transition of the ${\mathrm{Eu}}^{3+}$ center in $\mathrm{La}\mathrm{\text{:}}\mathrm{Lu}\mathrm{\text{:}}{\mathrm{EuCl}}_3·6{\mathrm{D}}_2\mathrm{O}$ resulting from the optical excitation of neighboring ${\mathrm{Eu}}^{3+}$ ions. Shifts of up to $46.081\pm 0.005\mathrm{MHz}$ were observed. The magnitude of the interaction between neighboring ions was found to be significantly larger than expected from the electric dipole-dipole mechanism often observed in rare earth systems. We show that a large network of interacting and individually addressable centers can be created by lightly doping crystals otherwise stoichiometric in the optically active rare earth ion, and that this network could be used to implement a quantum processor with more than ten qubits.

We introduce the concept of embedding quantum simulators, a paradigm allowing the efficient quantum computation of a class of bipartite and multipartite entanglement monotones. It consists in the suitable encoding of a simulated quantum dynamics in the enlarged Hilbert space of an embedding quantum simulator. In this manner, entanglement monotones are conveniently mapped onto physical observables, overcoming the necessity of full tomography and reducing drastically the experimental requirements. Furthermore, this method is directly applicable to pure states and, assisted by classical algorithms, to the mixed-state case. Finally, we expect that the proposed embedding framework paves the way for a general theory of enhanced one-to-one quantum simulators.

We study the statistics of near-extreme events of Brownian motion (BM) on the time interval $[0,t]$. We focus on the density of states near the maximum, $\rho (r,t)$, which is the amount of time spent by the process at a distance $r$ from the maximum. We develop a path integral approach to study functionals of the maximum of BM, which allows us to study the full probability density function of $\rho (r,t)$ and obtain an explicit expression for the moments $⟨[\rho (r,t){]}^k⟩$ for arbitrary integer $k$. We also study near extremes of constrained BM, like the Brownian bridge. Finally we also present numerical simulations to check our analytical results.

In situ observations of the solar wind frequently show the temperature of $\alpha$ particles (fully ionized helium) $T_{\alpha }$ to significantly differ from that of protons (ionized hydrogen) $T_p$. Many heating processes in the plasma act preferentially on $\alpha$ particles, even as collisions among ions act to gradually establish thermal equilibrium. Measurements from the Wind spacecraft’s Faraday cups reveal that, at $r=1.0\mathrm{AU}$ from the Sun, the observed values of the $\alpha$-proton temperature ratio, ${\theta }_{\alpha p}\equiv T_{\alpha }/T_p$, has a complex, bimodal distribution. This study applied a simple model for the radial evolution of ${\theta }_{\alpha p}$ to these data to compute expected values of ${\theta }_{\alpha p}$ at $r=0.1\mathrm{AU}$. These inferred ${\theta }_{\alpha p}$ values have no trace of the bimodality seen in the ${\theta }_{\alpha p}$ values measured at $r=1.0\mathrm{AU}$ but are instead consistent with the actions of the known mechanisms for $\alpha$-particle preferential heating. This result underscores the importance of collisional processes in the dynamics of the solar wind and suggests that similar mechanisms may lead to preferential $\alpha$-particle heating in both slow and fast wind.

The existence of a positive linear functional acting on the space of (differences between) conformal blocks has been shown to rule out regions in the parameter space of conformal field theories (CFTs). We argue that at the boundary of the allowed region the extremal functional contains, in principle, enough information to determine the dimensions and operator product expansion (OPE) coefficients of an infinite number of operators appearing in the correlator under analysis. Based on this idea we develop the extremal functional method (EFM), a numerical procedure for deriving the spectrum and OPE coefficients of CFTs lying on the boundary (of solution space). We test the EFM by using it to rederive the low lying spectrum and OPE coefficients of the two-dimensional Ising model based solely on the dimension of a single scalar quasiprimary—no Virasoro algebra required. Our work serves as a benchmark for applications to more interesting, less known CFTs in the near future.

The coupling between bound quantum states and those in the continuum is of high theoretical interest. Experimental studies of bound drip-line nuclei provide ideal testing grounds for such investigations since they, due to the feeble binding energy of their valence particles, are easy to excite into the continuum. In this Letter, continuum states in the heaviest particle-stable Be isotope, ${}^{14}\mathrm{Be}$, are studied by employing the method of inelastic proton scattering in inverse kinematics. New continuum states are found at excitation energies $E^{*}=3.54(16)\mathrm{MeV}$ and $E^{*}=5.25(19)\mathrm{MeV}$. The structure of the earlier known $2_1^{+}$ state at 1.54(13) MeV was confirmed with a predominantly $(0d_{5/2}{)}^2$ configuration while there is very clear evidence that the $2_2^{+}$ state has a predominant ($1s_{1/2}$, $0d_{5/2}$) structure with a preferential three-body decay mechanism. The region at about 7 MeV excitation shows distinct features of sequential neutron decay via intermediate states in ${}^{13}\mathrm{Be}$. This demonstrates that the increasing availability of energetic beams of exotic nuclei opens up new vistas for experiments leading towards a new understanding of the interplay between bound and continuum states.

Neutron star (NS) merger ejecta offer a viable site for the production of heavy $r$-process elements with nuclear mass numbers $A\gtrsim 140$. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of $110\lesssim A\lesssim 170$ nuclei. Here, we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant $A\simeq 278$ mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations, we show that this specific FFD leads to a production of the $A\simeq 165$ rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of $r$ nuclei with $A\gtrsim 140$.

Relativistic and QED corrections are calculated for a hyperfine splitting of the $2S_{1/2}$ ground state in ${}^{6,7}\mathrm{Li}$ atoms with a numerically exact account for electronic correlations. The resulting theoretical predictions achieve such a precision level that, by comparison with experimental values, they enable determination of the nuclear properties. In particular, the obtained results show that the ${}^7\mathrm{Li}$ nucleus, having a charge radius smaller than ${}^6\mathrm{Li}$, has about a 40% larger Zemach radius. Together with known differences in the electric quadrupole and magnetic dipole moments, this calls for a deeper understanding of the Li nuclear structure.

Angle-resolved electron spectroscopy in coincidence with high-resolution mass spectroscopy has been applied to study two-color resonant photoionization in atomic xenon. Separation of different isotopes enabled us to extract results for the electronic dynamics free from depolarization effects, which are generally introduced by the coupling of the electronic and nuclear angular momenta. The concerted experimental and theoretical analysis of the photoelectron angular distributions in the region of an autoionizing resonance emphasizes the strong sensitivity of the observed structures to the fine details of the treatment of the underlying dynamics.

Anomalously large linear and quadratic Zeeman shifts are measured for weakly bound ultracold ${}^{88}\mathrm{Sr}_2$ molecules near the intercombination-line asymptote. Nonadiabatic Coriolis coupling and the nature of long-range molecular potentials explain how this effect arises and scales roughly cubically with the size of the molecule. The linear shifts yield nonadiabatic mixing angles of the molecular states. The quadratic shifts are sensitive to nearby opposite $f$-parity states and exhibit fourth-order corrections, providing a stringent test of a state-of-the-art ab initio model.

Optical quantum memories are vital for the scalability of future quantum technologies, enabling long-distance secure communication and local synchronization of quantum components. We demonstrate a THz-bandwidth memory for light using the optical phonon modes of a room temperature diamond. This large bandwidth makes the memory compatible with down-conversion-type photon sources. We demonstrate that four-wave mixing noise in this system is suppressed by material dispersion. The resulting noise floor is just $7\times {10}^{-3}$ photons per pulse, which establishes that the memory is capable of storing single quanta. We investigate the principle sources of noise in this system and demonstrate that high material dispersion can be used to suppress four-wave mixing noise in $\Lambda$-type systems.

The time and space resolved dynamics of a qubit with an Ohmic coupling to propagating 1D photons is studied, from weak coupling to the ultrastrong coupling regime. A nonperturbative study based on matrix product states shows the following results, (i) The ground state of the combined systems contains excitations of both the qubit and the surrounding bosonic field. (ii) An initially excited qubit equilibrates through spontaneous emission to a state, which under certain conditions is locally close to that ground state, both in the qubit and the field. (iii) The resonances of the combined qubit-photon system match those of the spontaneous emission process and also the predictions of the adiabatic renormalization [A. J. Leggett et al., Rev. Mod. Phys. 59, 1 (1987)]. Finally, nonperturbative ab initio calculations show that this physics can be studied using a flux qubit galvanically coupled to a superconducting transmission line.

Multiple scatterings occurring in a turbid medium attenuate the intensity of propagating waves. Here, we propose a method to efficiently deliver light energy to the desired target depth in a scattering medium. We measure the time-resolved reflection matrix of a scattering medium using coherent time-gated detection. From this matrix, we derive and experimentally implement an incident wave pattern that optimizes the detected signal corresponding to a specific arrival time. This leads to enhanced light delivery at the target depth. The proposed method will lay a foundation for efficient phototherapy and deep-tissue in vivo imaging in the near future.

A surface electromagnetic wave called the Dyakonov-Tamm wave has been theoretically predicted to exist at the interface of two dielectric materials at least one of which is both anisotropic and periodically nonhomogeneous. For experimental confirmation, a prism-coupled configuration was used to excite Dyakonov-Tamm waves guided by the interface of a dense thin film of magnesium fluoride and a chiral sculptured thin film of zinc selenide. The excitation was indicated by a reflection dip (with respect to the angle of incidence in the prism-coupled configuration) that is independent of the polarization state of the incident light as well as the thicknesses of both partnering materials beyond some thresholds. Applications to optical sensing and long-range on-chip communication are expected.

We show that the interaction of relativistic-intensity, picosecond laser pulses with solid targets is affected by the reflected light through the strong currents and ${10}^4\mathrm{T}$ magnetic fields it produces. Three-dimensional particle-in-cell simulations, with the axisymmetry broken by a small angle of incidence, show that these magnetic fields deflect the laser-accelerated electrons away from the incident laser axis. This directly impacts the interpretation of electron divergence and directionality in applications such as laser-driven ion acceleration or fast-ignition inertial fusion.

Perpendicular collisionless shocks propagating into partially ionized plasmas are investigated by two-dimensional hybrid particle simulations. It is shown that some neutral particles leak into the upstream region from the downstream region, the leaking neutral particles become pickup ions in the upstream region and modify the shock structure, the pickup ions are preferentially accelerated, and plasma instabilities are excited by the pickup ions in the upstream and downstream regions.

Spin-polarized transport of photoelectrons in bulk, $p$-type GaAs is investigated in the Pauli blockade regime. In contrast to usual spin diffusion processes in which the spin polarization decreases with distance traveled due to spin relaxation, images of the polarized photoluminescence reveal a spin-filter effect in which the spin polarization increases during transport over the first $2\mu \mathrm{m}$ from 26% to 38%. This is shown to be a direct consequence of the Pauli principle and the associated quantum degeneracy pressure which results in a spin-dependent increase in the minority carrier diffusion constants and mobilities. The central role played by the quantum degeneracy pressure is confirmed via the observation of a spin-dependent increase in the photoelectron volume and a spin-charge coupling description of this is presented.

Current induced spin-orbit torques have been studied in ferromagnetic nanowires made of 20 nm thick Co/Pd multilayers with perpendicular magnetic anisotropy. Using Hall voltage and lock-in measurements, it is found that upon injection of an electric current both in-plane (Slonczewski-like) and perpendicular (fieldlike) torques build up in the nanowire. The torque efficiencies are found to be as large as 1.17 and 5 kOe at ${10}^8\mathrm{A}/{\mathrm{cm}}^2$ for the in-plane and perpendicular components, respectively, which is surprisingly comparable to previous studies in ultrathin ($\sim 1\mathrm{nm}$) magnetic bilayers. We show that this result cannot be explained solely by spin Hall effect induced torque at the outer interfaces, indicating a probable contribution of the bulk of the Co/Pd multilayer.

By combining density functional theory, nonequilibrium Green’s function formulism and effective-Hamiltonian approaches, we demonstrate strain-engineered surface transport in Si(001), with the complete isolation of the Si surface states from the bulk bands. Our results show that sufficient tensile strain can effectively remove the overlap between the surface valence state and the bulk valence band, because of the drastically different deformation potentials. Isolation of the surface valence state is possible with a tensile strain of $\sim 1.5\%$, a value that is accessible experimentally. Quantum transport simulations of a chemical sensing device based on strained Si(001) surface confirm the dominating surface conductance, giving rise to an enhanced molecular sensitivity. Our results show promise for using strain engineering to further our ability to manipulate surface states for quantum information processing and surface state–based devices.

We propose a scheme for the deterministic generation of steady-state entanglement between the two nuclear spin ensembles in an electrically defined double quantum dot. Because of quantum interference in the collective coupling to the electronic degrees of freedom, the nuclear system is actively driven into a two-mode squeezedlike target state. The entanglement buildup is accompanied by a self-polarization of the nuclear spins towards large Overhauser field gradients. Moreover, the feedback between the electronic and nuclear dynamics leads to multistability and criticality in the steady-state solutions.