We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.

We present a measurement of the direct $CP$-violating charge asymmetry in $D_s^{+}\to \varphi {\pi }^{\pm }$ decays where the $\varphi$ meson decays to $K^{+}{K}^{-}$, using the full Run II data set with an integrated luminosity of $10.4{\mathrm{fb}}^{-1}$ of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. The normalized difference $A_{CP}$ in the yield of $D_s^{+}$ and $D_s^{-}$ mesons in these decays is measured by fitting the difference between their reconstructed invariant mass distributions. This results in an asymmetry of $A_{CP}=[-0.38\pm 0.27]\%$, which is the most precise measurement of this quantity to date. The result is consistent with the standard model prediction of zero $CP$ asymmetry in this decay.

Excited states in the neutron-rich $N=38$, 36 nuclei ${}^{60}\mathrm{Ti}$ and ${}^{58}\mathrm{Ti}$ were populated in nucleon-removal reactions from ${}^{61}\mathrm{V}$ projectiles at $90\mathrm{MeV}/\text{nucleon}$. The $\gamma$-ray transitions from such states in these Ti isotopes were detected with the advanced $\gamma$-ray tracking array GRETINA and were corrected event by event for large Doppler shifts ($v/c\sim 0.4$) using the $\gamma$-ray interaction points deduced from online signal decomposition. The new data indicate that a steep decrease in quadrupole collectivity occurs when moving from neutron-rich $N=36$, 38 Fe and Cr toward the Ti and Ca isotones. In fact, ${}^{58,60}\mathrm{Ti}$ provide some of the most neutron-rich benchmarks accessible today for calculations attempting to determine the structure of the potentially doubly magic nucleus ${}^{60}\mathrm{Ca}$.

In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic lattice of nuclei immersed in an essentially uniform electron gas. We show that, at densities above that for neutron drip ($\sim 4\times {10}^{11}\mathrm{g}{\mathrm{cm}}^{-3}$ or roughly one-thousandth of nuclear matter density), the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as ${\mathrm{BaTiO}}_3$. As a consequence, the properties of matter in the inner crust are expected to be much richer than previously appreciated, and we mention possible consequences for observable neutron star properties.

We report results of the application of a fully ab initio approach for simulating time-resolved molecular-frame photoelectron angular distributions around conical intersections in ${\mathrm{CS}}_2$. The technique employs wave packet densities obtained with the multiple spawning method in conjunction with geometry- and energy-dependent photoionization matrix elements. The robust agreement of these results with measured molecular-frame photoelectron angular distributions for ${\mathrm{CS}}_2$ demonstrates that this technique can successfully elucidate, and disentangle, the underlying nuclear and photoionization dynamics around conical intersections in polyatomic molecules.

We study the collective response of a dense atomic sample to light essentially exactly using classical-electrodynamics simulations. In a homogeneously broadened atomic sample there is no overt Lorentz-Lorenz local field shift of the resonance, nor a collective Lamb shift. However, the addition of inhomogeneous broadening restores the usual mean-field phenomenology.

Laser-heater systems have been demonstrated to be an important component for the accelerators that drive high gain free electron laser (FEL) facilities. These heater systems suppress longitudinal microbunching instabilities by inducing a small and controllable slice energy spread to the electron beam. For transversely uniform heating, the energy spread augmentation is characterized by a non-Gaussian distribution. In this Letter, we demonstrate experimentally that in addition to suppression of the microbunching instability, the laser heater-induced energy distribution can be preserved to the FEL undulator entrance, significantly impacting the performance of high-gain harmonic generation (HGHG) FELs, especially at soft x-ray wavelengths. In particular, we show that the FEL intensity has several local maxima as a function of the induced heating caused by the non-Gaussian energy distribution together with a strong enhancement of the power at high harmonics relative to that expected for an electron beam with an equivalent Gaussian energy spread at an undulator entrance. These results suggest that a single stage HGHG FEL can produce scientifically interesting power levels at harmonic numbers $m\ge 25$ and with current seed laser technology could reach output photon energies above 100 eV or greater.

We report an experimental test of the photodetection mechanism in a nanowire superconducting single photon detector. Detector tomography allows us to explore the 0.8–8 eV energy range via multiphoton excitations. High accuracy results enable a detailed comparison of the experimental data with theories for the mechanism of photon detection. We show that the temperature dependence of the efficiency of the superconducting single photon detector is determined not by the critical current but by the current associated with vortex unbinding. We find that both quasiparticle diffusion and vortices play a role in the detection event.

By generalizing the quantum weak measurement protocol to the case of quantum fields, we show that weak measurements probe an effective classical background field that describes the average field configuration in the spacetime region between pre- and postselection boundary conditions. The classical field is itself a weak value of the corresponding quantum field operator and satisfies equations of motion that extremize an effective action. Weak measurements perturb this effective action, producing measurable changes to the classical field dynamics. As such, weakly measured effects always correspond to an effective classical field. This general result explains why these effects appear to be robust for pre- and postselected ensembles, and why they can also be measured using classical field techniques that are not weak for individual excitations of the field.

A search for forbidden and exotic $Z$ boson decays in the diphoton mass spectrum is presented for the first time in hadron collisions, based on data corresponding to $10.0{\mathrm{fb}}^{-1}$ of integrated luminosity from proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the CDF experiment. No evidence of signal is observed, and 95% credibility level Bayesian upper limits are set on the branching ratios of decays of the $Z$ boson to a photon and neutral pion (which is detected as a photon), a pair of photons, and a pair of neutral pions. The observed branching ratio limits are $2.01\times {10}^{-5}$ for $Z\to {\pi }^0\gamma$, $1.46\times {10}^{-5}$ for $Z\to \gamma \gamma$, and $1.52\times {10}^{-5}$ for $Z\to {\pi }^0{\pi }^0$. The $Z\to {\pi }^0\gamma$ and $Z\to \gamma \gamma$ limits improve the most stringent results from other experiments by factors of 2.6 and 3.6, respectively. The $Z\to {\pi }^0{\pi }^0$ branching ratio limit is the first experimental result on this decay.

Calcium monofluoride (CaF) is magnetically slowed and trapped using optical pumping. Starting from a collisionally cooled slow beam, CaF with an initial velocity of $\sim 30\mathrm{m}/\mathrm{s}$ is slowed via magnetic forces as it enters a 800 mK deep magnetic trap. Employing two-stage optical pumping, CaF is irreversibly loaded into the trap via two scattered photons. We observe a trap lifetime exceeding 500 ms limited by background collisions. This method paves the way for cooling and magnetic trapping of chemically diverse molecules without closed cycling transitions.

Magnetically tunable Feshbach resonances for polar paramagnetic ground-state diatomics are too narrow to allow for magnetoassociation starting from trapped, ultracold atoms. We show that nonresonant light can be used to engineer the Feshbach resonances in their position and width. For nonresonant field intensities of the order of ${10}^9\mathrm{W}/{\mathrm{cm}}^2$, we find the width to be increased by 3 orders of magnitude, reaching a few Gauss. This opens the way for producing ultracold molecules with sizable electric and magnetic dipole moments and thus for many-body quantum simulations with such particles.

We report observation of oscillations in the dynamics of a microcavity polariton condensate formed under pulsed nonresonant excitation. While oscillations in a condensate have always been attributed to Josephson mechanisms due to a chemical potential unbalance, here we show that under some localization conditions of the condensate, they may arise from relaxation oscillations, a pervasive classical dynamics that repeatedly provokes the sudden decay of a reservoir, shutting off relaxation as the reservoir is replenished. Using nonresonant excitation, it is thus possible to obtain condensate injection pulses with a record frequency of 0.1 THz

The conductance of ballistic graphene at the neutrality point is due to coherent electron tunneling between the leads, the so called pseudodiffusive regime. The conductance scales as a function of the sample dimensions in the same way as in a diffusive metal, despite the difference in the physical mechanisms involved. The electron-electron interaction modifies this regime, and plays a role similar to that of the environment in macroscopic quantum phenomena. We show that interactions can change substantially the transport properties. In the presence of nearby metallic layers, the conductance near the neutrality point can decrease with decreasing temperature, and reach values well below the quantum unit of conductance, as in an insulator.

We report the observation of a Hall effect driven by orbital resonance in the quasi-1-dimensional (q1D) organic conductor ${(\mathrm{TMTSF})}_2{\mathrm{ClO}}_4$. Although a conventional Hall effect is not expected in this class of materials due to their reduced dimensionality, we observed a prominent Hall response at certain orientations of the magnetic field $B$ corresponding to lattice vectors of the constituent molecular chains, known as the magic angles (MAs). We show that this Hall effect can be understood as the response of conducting planes generated by an effective locking of the orbital motion of the charge carriers to the MA driven by an electron-trajectory resonance. This phenomenon supports a class of theories describing the rich behavior of MA phenomena in q1D materials based on altered dimensionality. Furthermore, we observed that the effective carrier density of the conducting planes is exponentially suppressed in large $B$, which indicates possible density wave formation.

In mean-field descriptions of nodal $d$-wave superconductors, generic edges exhibit dispersionless Majorana fermion bands at zero energy. These states give rise to an extensive ground-state degeneracy, and are protected by time-reversal symmetry. We argue that the infinite density of states of these flat bands make them inherently unstable to interactions, and show that repulsive interactions lead to edge ferromagnetism which splits the flat bands. This edge ferromagnetism offers an explanation for the observation of the splitting of zero-bias peaks in edge tunneling in high-$T_c$ cuprate superconductors. We argue that this mechanism for splitting is more likely than previously proposed scenarios and describe its experimental consequences.

A nanoelectromechanical device based on magnetic exchange forces and electron spin flips induced by a weak external magnetic field is suggested. It is shown that this device can operate as a new type of single-electron “shuttle” in the Coulomb blockade regime of electron transport.

Metamaterials—or artificial electromagnetic materials—can create media with properties unattainable in nature, but mitigating dissipation is a key challenge for their further development. Here, we demonstrate a low-loss metamaterial by exploiting dark bound states in dielectric inclusions coupled to the external waves by small nonresonant metallic antennas. We experimentally demonstrate a dispersion-engineered metamaterial based on a meta-atom made from alumina, and we show that its resonance has a much larger quality factor than metal-based meta-atoms. Finally, we show that our dielectric meta-atom can be used to create sheet metamaterials with negative permittivity or permeability.

We find evidence for long-range and short-range ($\zeta =70\AA$ at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (fcc) lattices of the monoclinic double perovskites ${\mathrm{La}}_2{\mathrm{NaRuO}}_6$ and ${\mathrm{La}}_2{\mathrm{NaOsO}}_6$, respectively. Incommensurate magnetic order on the fcc lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbor and next nearest neighbor exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap $\mathrm{\Delta }\sim 2.75\mathrm{meV}$. Magnetic anisotropy is generally minimized in the more familiar octahedrally coordinated $3d^3$ systems, so the large gap observed for ${\mathrm{La}}_2{\mathrm{NaRuO}}_6$ may result from the significantly enhanced value of spin-orbit coupling in this $4d^3$ material.