We report on simulations of the degree of polarization entanglement of photon pairs simultaneously emitted from a quantum dot-cavity system that demand revisiting the role of phonons. Since coherence is a fundamental precondition for entanglement and phonons are known to be a major source of decoherence, it seems unavoidable that phonons can only degrade entanglement. In contrast, we demonstrate that phonons can cause a degree of entanglement that even surpasses the corresponding value for the phonon-free case. In particular, we consider the situation of comparatively small biexciton binding energies and either finite exciton or cavity mode splitting. In both cases, combinations of the splitting and the dot-cavity coupling strength are found where the entanglement exhibits a nonmonotonic temperature dependence which enables entanglement above the phonon-free level in a finite parameter range. This unusual behavior can be explained by phonon-induced renormalizations of the dot-cavity coupling $g$ in combination with a nonmonotonic dependence of the entanglement on $g$ that is present already without phonons.

In ferroelectric and relaxor-ferroelectric materials, piezoelectric and dielectric properties are significantly enhanced at the morphotropic phase boundary (MPB), a boundary between different ferroelectric phases with different macroscopic symmetries. By contrast, in relaxor systems, such an MPB does not exist because relaxors of different compositions possess the same macroscopic symmetry. Here, we report the existence of a morphotropic relaxor boundary (MRB) in the single phase relaxor region of a ${\mathrm{K}}_{0.5}{\mathrm{Na}}_{0.5}{\mathrm{NbO}}_3\text{−}x{\mathrm{BaTiO}}_3$ system, which is a composition-induced boundary between two relaxors with different local polar symmetries (tetragonal versus rhombohedral) but with the same macroscopic cubic symmetry. At the MRB the electrostrain increases by $\sim 3$ times and the permittivity increases by $\sim 1.5$ times over a wide temperature range of more than 100 K, as compared with off-MRB compositions. Our Letter demonstrates that the MRB may become an effective mechanism to enhance the dielectric and electrostrictive properties of relaxors.

We report the first measurement of the double-differential and total muon neutrino charged current inclusive cross sections on argon at a mean neutrino energy of 0.8 GeV. Data were collected using the MicroBooNE liquid argon time projection chamber located in the Fermilab Booster neutrino beam and correspond to $1.6\times {10}^{20}$ protons on target of exposure. The measured differential cross sections are presented as a function of muon momentum, using multiple Coulomb scattering as a momentum measurement technique, and the muon angle with respect to the beam direction. We compare the measured cross sections to multiple neutrino event generators and find better agreement with those containing more complete treatment of quasielastic scattering processes at low $Q^2$. The total flux integrated cross section is measured to be $0.693\pm 0.010(\mathrm{stat})\pm 0.165(\mathrm{syst})\times {10}^{-38}{\mathrm{cm}}^2$.

A search for a light charged Higgs boson ($H^{+}$) decaying to a $W$ boson and a $CP$-odd Higgs boson ($A$) in final states with $e\mu \mu$ or $\mu \mu \mu$ is performed using data from $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$. In this search, it is assumed that the $H^{+}$ boson is produced in decays of top quarks, and the $A$ boson decays to two oppositely charged muons. The presence of signals for $H^{+}$ boson masses between 100 and 160 GeV and $A$ boson masses between 15 and 75 GeV is investigated. No evidence for the production of the $H^{+}$ boson is found. Upper limits at 95% confidence level are obtained on the combined branching fraction for the decay chain, $t\to b{H}^{+}\to b{W}^{+}A\to b{W}^{+}{\mu }^{+}{\mu }^{-}$, of $1.9\times {10}^{-6}$ to $8.6\times {10}^{-6}$, depending on the masses of the $H^{+}$ and $A$ bosons. These are the first limits for these decay modes of the $H^{+}$ and $A$ bosons.

In a seminal article, Fano predicts that absorption of light occurs preferably with increase of angular momentum. We generalize Fano’s propensity rule to laser-assisted photoionization, consisting of absorption of an extreme-ultraviolet photon followed by absorption or emission of an infrared photon. The predicted asymmetry between absorption and emission leads to incomplete quantum interference in attosecond photoelectron interferometry. It explains both the angular dependence of the photoionization time delays and the delay dependence of the photoelectron angular distributions. Our theory is verified by experimental results in Ar in the 20–40 eV range.

We present an experimental study of the low-energy stereodynamics of the $\mathrm{Ne}({{}^{3}P}_2)+{\mathrm{N}}_2$ reaction. Supersonic expansions of the two reactants are superposed in a merged beam experiment, where individual velocity control of the two beams allows us to reach average relative velocities of zero, yielding minimum collision energies around 60 mK. We combine the merged beam technique with the orientation of the metastable neon atoms and measure the branching between two reaction channels, Penning ionization and associative ionization, as a function of neon orientation and collision energy, covering the range 0.06–700 K. We find that we lose the ability to orient Ne below $\approx 100\mathrm{K}$ due to dynamic reorientation. Associative ionization products $\mathrm{Ne}\text{−}{\mathrm{N}}_2^{+}$ predissociate with a probability of 30%–60% and that associative ionization is entirely due to reactions of the $\mathrm{\Omega }=2$ state, where the singly occupied $p$ orbital of the ${\mathrm{Ne}}^{*}$ is oriented along the interatomic axis.

We study the breakup of a liquid thread inside another liquid at different surface tensions. In general, the pinch-off of a liquid thread is governed by the dynamics of fluid flow. However, when the interfacial tension is ultralow (2–3 orders lower than normal liquids), we find that the pinch-off dynamics can be governed by bulk diffusion. By studying the velocity and the profile of the pinch-off, we explain why the diffusion-dominated pinch-off takes over the conventional breakup at ultralow surface tensions.

An intense, subpicosecond, relativistic electron beam traversing a dielectric-lined waveguide generates very large amplitude electric fields at terahertz (THz) frequencies through the wakefield mechanism. In recent work employing this technique to accelerate charged particles, the generation of high-power, narrow-band THz radiation was demonstrated. The radiated waves contain fields with measured amplitude exceeding $2\mathrm{GV}/\mathrm{m}$, orders of magnitude greater than those available by other THz generation techniques at a narrow bandwidth. For fields approaching the $\mathrm{GV}/\mathrm{m}$ level, a strong damping has been observed in ${\mathrm{SiO}}_2$. This wave attenuation with an onset near $850\mathrm{MV}/\mathrm{m}$ is consistent with changes to the conductivity of the dielectric lining and is characterized by a distinctive latching mechanism that is reversible on longer timescales. We describe the detailed measurements that serve to clarify the underlying physical mechanisms leading to strong field-induced damping of THz radiation ($h\omega =1.59\mathrm{meV}$, $f=0.38\mathrm{THz}$) in ${\mathrm{SiO}}_2$, a bulk, wide band-gap (8.9 eV) dielectric.

We demonstrate that, in monolayers (MLs) of semiconducting transition metal dichalcogenides, the $s$-type Rydberg series of excitonic states follows a simple energy ladder: ${\epsilon }_n=-{\mathrm{Ry}}^{*}/(n+\delta {)}^2$, $n=1,2,\dots$, in which ${\mathrm{Ry}}^{*}$ is very close to the Rydberg energy scaled by the dielectric constant of the medium surrounding the ML and by the reduced effective electron-hole mass, whereas the ML polarizability is accounted for only by $\delta$. This is justified by the analysis of experimental data on excitonic resonances, as extracted from magneto-optical measurements of a high-quality ${\mathrm{WSe}}_2$ ML encapsulated in hexagonal boron nitride (hBN), and well reproduced with an analytically solvable Schrödinger equation when approximating the electron-hole potential in the form of a modified Kratzer potential. Applying our convention to other ${\mathrm{MoSe}}_2$, ${\mathrm{WS}}_2$, ${\mathrm{MoS}}_2$ MLs encapsulated in hBN, we estimate an apparent magnitude of $\delta$ for each of the studied structures. Intriguingly, $\delta$ is found to be close to zero for ${\mathrm{WSe}}_2$ as well as for ${\mathrm{MoS}}_2$ monolayers, what implies that the energy ladder of excitonic states in these two-dimensional structures resembles that of Rydberg states of a three-dimensional hydrogen atom.

Evidence for Bell’s nonlocality is so far mainly restricted to microscopic systems, where the elements of reality that are negated predetermine results of measurements to within one spin unit. Any observed nonlocal effect (or lack of classical predetermination) is then limited to no more than the difference of a single photon or electron being detected or not (at a given detector). In this paper, we analyze experiments that report the Einstein-Podolsky-Rosen (EPR) steering form of nonlocality for mesoscopic photonic or Bose-Einstein condensate systems. Using an EPR steering parameter, we show how the EPR nonlocalities involved can be quantified for four-mode states, to give evidence of EPR-nonlocal effects corresponding to a two-mode number difference of $10^5$ photons, or of several tens of atoms (at a given site). Applying to experiments, we also show how the variance criterion of Duan, Giedke, Cirac and Zoller for EPR entanglement can be used to determine a lower bound on the number of particles in a pure two-mode EPR-entangled or steerable state.

If an open quantum system is periodically driven with high frequency and the driving commutes with the system-bath coupling operator, it is known that the system approaches a Floquet-Gibbs state, a generalization of Gibbs states to periodically driven systems. Here, we investigate the stationary state of an ac-driven system when the driving and dissipation are noncommutative. Then, the resulting stationary state does not obey the Floquet-Gibbs distribution, and the system dynamics is determined by inelastic scattering processes of the driving field. Based on the Floquet-Redfield formalism, we show that the probability distribution can exhibit population inversion and discontinuities, i.e., jumps, for parameters at which coherent destruction of tunneling takes place. These discontinuities can be observed as intensity jumps in the emission into the bath.

We provide the first example of local quantum energy conditions in quantum field theories that are not Lorentz invariant. We focus on field theories in two dimensions with infinite-dimensional symmetries, like the ones governed by the Bondi–van der Burg–Metzner–Sachs group that appear in the context of flat space holography. Reminiscent of holographic results on the quantum null energy condition, we prove that our new energy conditions saturate for states in the field theory that are dual to vacuum solutions of three-dimensional Einstein gravity with a vanishing cosmological constant.

The exclusive process $e^{+}{e}^{-}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}$, with $\mathrm{\Lambda }\to p{\pi }^{-}$ and $\overline{\mathrm{\Lambda }}\to \overline{p}{\pi }^{+}$, has been studied at $\sqrt{s}=2.396\mathrm{GeV}$ for measurement of the timelike $\mathrm{\Lambda }$ electric and magnetic form factors, $G_E$ and $G_M$. A data sample, corresponding to an integrated luminosity of $66.9{\mathrm{pb}}^{-1}$, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio $R=|G_E/G_M|$ and, for the first time for any baryon, the relative phase $\mathrm{\Delta }\mathrm{\Phi }={\mathrm{\Phi }}_E-{\mathrm{\Phi }}_M$. The resulting values are $R=0.96\pm 0.14(\text{stat})\pm 0.02(\text{syst})$ and $\mathrm{\Delta }\mathrm{\Phi }=37°\pm 12°(\text{stat})\pm 6°(\text{syst})$, respectively. These are obtained using the recently established and most precise value of the asymmetry parameter ${\alpha }_{\mathrm{\Lambda }}=0.750\pm 0.010$ measured by BESIII. In addition, the cross section is measured with unprecedented precision to be $\sigma =118.7\pm 5.3(\text{stat})\pm 5.1(\text{syst})\mathrm{pb}$, which corresponds to an effective form factor of $|G|=0.123\pm 0.003(\text{stat})\pm 0.003(\text{syst})$. The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.

We report on the successful demonstration of a novel scheme for detecting optical transitions in highly charged ions. We applied it to determine the frequency of the dipole-forbidden $2p{{}^{2}P}_{1/2}-{{}^{2}P}_{3/2}$ transition in the fine structure of ${{}^{40}\mathrm{Ar}}^{13+}$ using a single ion stored in the harmonic potential of a Penning trap. Our measurement scheme does not require detection of fluorescence, instead it makes use of the continuous Stern-Gerlach effect. Our value of $679.216464(4{)}_{\mathrm{stat}}(5{)}_{\mathrm{syst}}\mathrm{THz}$ is in reasonable agreement with the current best literature values and improves its uncertainty by a factor of 24.

Quantum simulations of small ${\mathrm{CH}}_5^{+}·{{}^4\mathrm{He}}_n$ complexes disclose significant and antagonistic impact of small-amplitude local vibrational motion vs large-amplitude global fluxional motion within the ${\mathrm{CH}}_5^{+}$ impurity on helium in real and permutation space. While the former significantly enhances bosonic exchange in the surrounding ${}^4\mathrm{He}$ microsolvation shell compared to the rigid-body reference, the latter greatly suppresses long permutation cycles, which is traced back to the different nature of these quantum fluctuations. Therefore, it is expected that the resulting impact on local superfluidity is generic for fluctuating impurities in bosonic environments.

We study photon emission by an ensemble of two-level systems, with strong inhomogeneous broadening and coupled to a cavity mode whose frequency has linear time dependence. The analysis shows that, regardless of the distribution of energy level splittings, a sharp phase transition occurs between the weak and strong cooperative emission phases near a critical photonic frequency sweeping rate. The associated scaling exponent is determined. We suggest that this phase transition can be observed in an ensemble of negatively charged ${\mathrm{NV}}^{-}$ centers in diamond interacting with a microwave half-wavelength cavity mode even in the regime of weak coupling and at strong disorder of two-level splittings.

Extreme events appear in many physics phenomena, whenever the probability distribution has a “heavy tail” differing very much from the equilibrium one. Most unusual are the cases of power-law (Pareto) probability distributions. Among their many manifestations in physics, from “rogue waves” in the ocean to Lévy flights in random walks, Pareto dependences can follow very different power laws. For some outstanding cases, the power exponents are less than 2, leading to indefinite values not only for higher moments but also for the mean. Here we present the first evidence of indefinite-mean Pareto distribution of photon numbers at the output of nonlinear effects pumped by parametrically amplified vacuum noise, known as bright squeezed vacuum (BSV). We observe a Pareto distribution with power exponent 1.31 when BSV is used as a pump for supercontinuum generation, and other heavy-tailed distributions (however, with definite moments) when it pumps optical harmonics generation. Unlike in other fields, we can flexibly control the Pareto exponent by changing the experimental parameters. This extremely fluctuating light is interesting for ghost imaging and for quantum thermodynamics as a resource to produce more efficiently nonequilibrium states by single-photon subtraction, the latter of which we demonstrate experimentally.