Lawsonhart5963

We demonstrate the Rydberg series of dark excitons, known as paraexcitons, up to the principal quantum number n=6 for the yellow exciton series in Cu_2O, using second harmonic generation. Each of these states is optically inactive to all orders, but their observation becomes possible by application of a magnetic field which leads to mixing with the quadrupole-allowed bright excitons, called orthoexcitons, of the same n. The dark parastates are generally located below the bright orthostates, whose energies are increased by the electron-hole exchange interaction, except for n=2, where this order is reversed. This inversion occurs due to band mixing, namely, of the 2S_y,o orthoexciton of the yellow series with the 1S_g,o orthoexciton of the green exciton series.In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized until both types of magnetic orders disappear abruptly and a narrow SC dome develops. With further increasing pressure characteristics of a Kondo-lattice system become more and more apparent in the electrical resistivity. This suggests a connection of the emergence of superconductivity with the extinction of the magnetic order and the onset of Kondo screening of the Ce-4f moments.Mitigating crosstalk errors, whether classical or quantum mechanical, is critically important for achieving high-fidelity entangling gates in multiqubit circuits. For weakly anharmonic superconducting qubits, unwanted ZZ interactions can be suppressed by combining qubits with opposite anharmonicity. We present experimental measurements and theoretical modeling of two-qubit gate error for gates based on the cross resonance interaction between a capacitively shunted flux qubit and a transmon, and demonstrate the elimination of the ZZ interaction.Entanglement plays a central role in quantum information processing and quantum physics. see more However, few effective ways are known to detect the amount of entanglement of an unknown quantum state. Here, we propose a scheme to estimate the entanglement negativity for any bipartition of a composite system. The proposed scheme is based on the random unitary evolution and local measurements on a single-copy quantum state, which is more practical compared to former methods based on collective measurements on many copies of the identical state. Meanwhile, we generalize the scheme to quantify the total correlation. We demonstrate the efficiency of the scheme with statistical analyses and numerical simulations. Our scheme is quite suitable for state-of-the-art quantum platforms, which can serve as a useful benchmarking tool to advance quantum technologies and a probe to study fundamental quantum physics like entanglement dynamics.Pair distribution function measurement of SiO_2 glass up to 120 GPa reveals changes in the first-, second-, and third-neighbor distances associated with an increase in Si coordination number C_Si to >6 above 95 GPa. Packing fractions of Si and O determined from the first- and second-neighbor distances show marked changes accompanied with the structural evolution from C_Si=6 to >6. Structural constraints in terms of ionic radius ratio of Si and O, and ratio of nonbonded radius to bonded Si─O distance support the structural evolution of SiO_2 glass with C_Si>6 at high pressures.We investigate theoretically and experimentally stochastic resonance in a quantum dot coupled to electron source and drain via time-dependent tunnel barriers. A central finding is a transition visible in the current noise spectrum as a bifurcation of a dip originally at zero frequency. The transition occurs close to the stochastic resonance working point and relates to quantized pumping. For the evaluation of power spectra from measured waiting times, we generalize a result from renewal theory to the ac-driven case. Moreover, we develop a master equation method to obtain phase-averaged current noise spectra for driven quantum transport.The independent measurement of the Hubble constant with gravitational-wave standard sirens will potentially shed light on the tension between the local distance ladders and Planck experiments. Therefore, thorough understanding of the sources of systematic uncertainty for the standard siren method is crucial. In this Letter, we focus on two scenarios that will potentially dominate the systematic uncertainty of standard sirens. First, simulations of electromagnetic counterparts of binary neutron star mergers suggest aspherical emissions, so the binaries available for the standard siren method can be selected by their viewing angles. This selection effect can lead to ≳2% bias in Hubble constant measurement even with mild selection. Second, if the binary viewing angles are constrained by the electromagnetic counterpart observations but the bias of the constraints is not controlled under ∼10°, the resulting systematic uncertainty in the Hubble constant will be >3%. In addition, we find that both of the systematics cannot be properly removed by the viewing angle measurement from gravitational-wave observations. Comparing to the known dominant systematic uncertainty for standard sirens, the ≤2% gravitational-wave calibration uncertainty, the effects from the viewing angle appear to be more significant. Therefore, the systematic uncertainty from the viewing angle might be a major challenge before the standard sirens can resolve the tension in the Hubble constant, which is currently ∼9%.We realize moiré fringe induced gauge field in a double-layer photonic honeycomb metacrystal with mismatched lattice constants. Benefitting from the generated strong effective gauge field, we report direct measurement of the band diagrams of both Landau level flat bands and intermagnetic-domain edge states. Importantly, we observe the correlation between the momentum and orbital position of the Landau modes, serving as an evidence of the noncommuteness between orthogonal components of the momentum. Without complicated time driving mechanics and careful site-by-site engineering, moiré superlattices could emerge as a powerful means to generate effective gauge fields for photonics benefiting from its simplicity and reconfigurability, which can be applied to nonlinearity enhancement and lasing applications at optical frequencies.