We report the experimental measurement of bipartite quantum correlations of an unknown two-qubit state. Using a liquid state Nuclear Magnetic Resonance setup and employing geometric discord, we evaluate the quantum correlations of a state without resorting to prior knowledge of its density matrix. The method is applicable to any $2\otimes d$ system and provides, in terms of number of measurements required, an advantage over full state tomography scaling with the dimension $d$ of the unmeasured subsystem. The negativity of quantumness is measured as well for reference. We also observe the phenomenon of sudden transition of quantum correlations when local phase and amplitude damping channels are applied to the state.

A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on $6.8\times {10}^6$ positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to $\sim 250\mathrm{GeV}$, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.

We show that in the presence of a rapidly modulated dielectric permittivity with a large modulation depth (Kapitza medium) a novel and robust regime of diffractionless electromagnetic propagation occurs. This happens when the mean value to depth ratio of the dielectric profile is comparable to the small ratio between the modulation period and the wavelength. We show that the standard effective medium theory is inadequate to describe the proposed regime and that its occurrence is not substantially hampered by medium losses. We check the feasibility of the proposed regime by means of a large modulation depth metal-dielectric layered medium whose electromagnetic behavior is analytically investigated.

We demonstrate the existence of the spectral phase shift a pulse experiences when it is subjected to spectral focusing. This $\frac{\pi }{2}$ phase shift is the spectral analog of the Gouy phase shift a 2D beam experiences when it crosses its focal plane. This spectral Gouy phase shift is measured using spectral interference between a reference pulse and a negatively chirped parabolic pulse experiencing spectral focusing in a nonlinear photonic crystal fiber. To avoid inherent phase instability in the measurement, both reference and parabolic pulses are generated with a $4\mathrm{\text{−}}f$ pulse shaper and copropagate in the same fiber. We measure a spectral phase shift of $\frac{\pi }{2}$, reaffirming its generality as a consequence of wave confinement in the spatial, temporal and spectral domains.

A new method to drive a system of neutral dipolar fermions into the lowest Landau level regime is proposed. By employing adiabatic spin-flip processes in combination with a diabatic transfer, the fermions are pumped to higher orbital angular momentum states in a repeated scheme that allows for the precise control over the final angular momentum. A simple analytical model is derived to quantify the transfer and compare the approach to rapidly rotating systems. Numerical simulations of the transfer process have been performed for small, interacting systems.

We study a multiorbital model for the alkaline iron selenides ${\mathrm{K}}_{1-x}{\mathrm{Fe}}_{2-y}{\mathrm{Se}}_2$ using a slave-spin method. With or without ordered vacancies, we identify a metal-to-Mott-insulator transition at the commensurate filling of six $3d$ electrons per iron ion. For Hund’s couplings beyond a threshold value, this occurs via an intermediate orbital-selective Mott phase, in which the $3d$ $xy$ orbital is Mott localized while the other $3d$ orbitals remain itinerant. This phase is still stabilized over a range of carrier dopings. Our results lead to an overall phase diagram for the alkaline iron selenides, which provides a unified framework to understand the interplay between the strength of the vacancy order and carrier doping. In this phase diagram, the orbital-selective Mott phase provides a natural link between the superconducting ${\mathrm{K}}_{1-x}{\mathrm{Fe}}_{2-y}{\mathrm{Se}}_2$ and its Mott-insulating parent compound.

For the paradigmatic case of ${\mathrm{H}}_2$ dissociation, we compare state-of-the-art many-body perturbation theory in the $GW$ approximation and density-functional theory in the exact-exchange plus random-phase approximation (RPA) for the correlation energy. For an unbiased comparison and to prevent spurious starting point effects, both approaches are iterated to full self-consistency (i.e., sc-RPA and sc-$GW$). The exchange-correlation diagrams in both approaches are topologically identical, but in sc-RPA they are evaluated with noninteracting and in sc-$GW$ with interacting Green functions. This has a profound consequence for the dissociation region, where sc-RPA is superior to sc-$GW$. We argue that for a given diagrammatic expansion, sc-RPA outperforms sc-$GW$ when it comes to bond breaking. We attribute this to the difference in the correlation energy rather than the treatment of the kinetic energy.

Exciton bound states in solids between electrons and holes are predicted to form a superfluid at high temperatures. We show that by employing atomically thin crystals such as a pair of adjacent bilayer graphene sheets, equilibrium superfluidity of electron-hole pairs should be achievable for the first time. The transition temperatures are well above liquid helium temperatures. Because the sample parameters needed for the device have already been attained in similar graphene devices, our work suggests a new route toward realizing high-temperature superfluidity in existing quality graphene samples.

We investigate the high-energy magnetic excitation spectrum of the high-$T_c$ cuprate superconductor ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ (Bi-2212) using Cu $L_3$ edge resonant inelastic x-ray scattering. Broad, dispersive magnetic excitations are observed, with a zone boundary energy of $\sim 300\mathrm{meV}$ and a weak dependence on doping. These excitations are strikingly similar to the bosons proposed to explain the high-energy “kink” observed in photoemission. A phenomenological calculation of the spin response, based on a parametrization of the the angle-resolved photoemission spectroscopy derived electronic structure and Yang-Rice-Zhang quasiparticles, provides a reasonable prediction of the energy dispersion of the observed magnetic excitations. These results indicate a possible unified framework to reconcile the magnetic and electronic properties of the cuprates and we discuss the advantages and disadvantages of such an approach.

A single-domain nanomagnet is a basic example of a system where relaxation from high to low energy is probabilistic in nature even when thermal fluctuations are neglected. The reason is the presence of multiple stable states combined with extreme sensitivity to initial conditions. It is demonstrated that for this system the probability of relaxing from high energies to one of the stable magnetization orientations can be tuned to any desired value between 0 and 1 by applying a small transverse magnetic field of appropriate amplitude. In particular, exact analytical predictions are derived for the conditions under which the probability of reaching one of the stable states becomes exactly 0 or 1. Under these conditions, magnetization relaxation is totally insensitive to initial conditions, and the final state can be predicted with certainty, a feature that could be exploited to devise novel magnetization switching strategies or novel methods for the measurement of the magnetization damping constant.

Anomalous trends in nanoparticle correlation and motion are reported in soft nanoparticle suspensions using static and dynamic x-ray scattering measurements. Contrary to normal expectations, we find that particle-particle correlations decrease and particle dynamics become faster as volume fraction rises above a critical particle loading associated with overlap. Our observations bear many similarities to the cascade of structural and transport anomalies reported for complex, network forming molecular fluids such as water, and are argued to share similar physical origins.

We study a relativistic $O(N)$ model near the quantum critical point in $2+1$ dimensions for $N=2$ and $N=3$. The scalar susceptibility is evaluated by Monte Carlo simulation. We show that the spectrum contains a well-defined peak associated with the Higgs mode arbitrarily close to the critical point. The peak fidelity and the amplitude ratio between the critical energy scales on both sides of the transition are determined.

In this Letter we report an observation of interference effects in Compton scattering in the experiment held on the VEPP-2000 collider. Infrared laser radiation was scattered head-on the 990 MeV electrons inside the dipole magnet, where an electron orbit radius is about 140 cm. It was observed that the energy spectrum of backscattered photons, measured by a HPGe detector, differs from that defined by the Klein-Nishina cross section and scattering kinematics of free electrons. The explanation of the effect, proposed in terms of classical electrodynamics, is in agreement with QED calculations.

We demonstrate teleportation of quantum bits between two single atoms in distant laboratories. Using a time-resolved photonic Bell-state measurement, we achieve a teleportation fidelity of $(88.0\pm 1.5)\%$, largely determined by our entanglement fidelity. The low photon collection efficiency in free space is overcome by trapping each atom in an optical cavity. The resulting success probability of 0.1% is almost 5 orders of magnitude larger than in previous experiments with remote material qubits. It is mainly limited by photon propagation and detection losses and can be enhanced with a cavity-based deterministic Bell-state measurement.

Using extensive molecular dynamics simulations we explore the fine-grained phase space structure of systems with long-range interactions. We find that if the initial phase space particle distribution has no holes, the final stationary distribution will also contain a compact simply connected region. The microscopic holes created by the filamentation of the initial distribution function are always restricted to the outer regions of the phase space. In general, for complex multilevel distributions it is very difficult to a priori predict the final stationary state without solving the full dynamical evolution. However, we show that, for multilevel initial distributions satisfying a generalized virial condition, it is possible to predict the particle distribution in the final stationary state using Casimir invariants of the Vlasov dynamics.

Understanding the mesoscopic behavior of dynamical systems described by Langevin equations with colored noise is a fundamental challenge in a variety of fields. We propose a new approach to derive closed-form equations for joint and marginal probability density functions of state variables. This approach is based on a so-called large-eddy-diffusivity closure and can be used to model a wide class of non-Markovian processes described by the noise with an arbitrary correlation function. We demonstrate the accuracy of the proposed probability density function method for several linear and nonlinear Langevin equations.

Recent experiments on blinking quantum dots, weak turbulence in liquid crystals, and nanoelectrodes reveal the fundamental connection between $1/f$ noise and power law intermittency. The nonstationarity of the process implies that the power spectrum is random—a manifestation of weak ergodicity breaking. Here, we obtain the universal distribution of the power spectrum, which can be used to identify intermittency as the source of the noise. We solve in this case an outstanding paradox on the nonintegrability of $1/f$ noise and the violation of Parseval’s theorem. We explain why there is no physical low-frequency cutoff and therefore why it cannot be found in experiments.

A late epoch cosmic acceleration may be naturally entangled with cosmic coincidence—the observation that at the onset of acceleration the vacuum energy density fraction nearly coincides with the matter density fraction. In this Letter we show that this is indeed the case with the cosmology of a Friedmann-Lamaître-Robertson-Walker (FLRW) 3-brane in a five-dimensional anti–de Sitter spacetime. We derive the four-dimensional effective action on a FLRW 3-brane, from which we obtain a mass-reduction formula, namely, $M_P^2={\rho }_b/|{\Lambda }_5|$, where $M_P$ is the effective (normalized) Planck mass, ${\Lambda }_5$ is the five-dimensional cosmological constant, and ${\rho }_b$ is the sum of the 3-brane tension $V$ and the matter density $\rho$. Although the range of variation in ${\rho }_b$ is strongly constrained, the big bang nucleosynthesis bound on the time variation of the effective Newton constant $G_N=(8\pi M_P^2{)}^{-1}$ is satisfied when the ratio $V/\rho \gtrsim O({10}^2)$ on cosmological scales. The same bound leads to an effective equation of state close to $-1$ at late epochs in accordance with astrophysical and cosmological observations.

We provide a first derivation of the Bekenstein-Hawking entropy of 3D flat cosmological horizons in terms of the counting of states in a dual field theory. These horizons appear in the flat limit of nonextremal rotating Banados-Teitleboim-Zanelli black holes and are remnants of the inner horizons. They also satisfy the first law of thermodynamics. We study flat holography as a limit of ${\mathrm{AdS}}_3/{\mathrm{CFT}}_2$ to semiclassically compute the density of states in the dual theory, which is given by a contraction of a 2D conformal field theory, exactly reproducing the bulk entropy in the limit of large charges. We comment on how the dual theory reproduces the bulk first law and how cosmological bulk excitations are matched with boundary quantum numbers.

The degenerate top squark next-to-lightest supersymmetric particle (NLSP) and neutralino (LSP) scenario is well motivated but hard to detect in the collider experiments. We propose a novel signature for detection of this scenario at the Large Hadron Collider and demonstrate its feasibility. In the constrained minimal supersymmetric standard model and top squark NLSP, gluinos are in general much heavier than the lighter top squark and, thus, it decays dominantly to high transverse momentum ($p_T$) top-quark–top-squark pairs. We consider gluino pair production and study two high-$p_T$ top jets and missing energy as the signature of this scenario.