16,788 research outputs found
Characterization of four-qubit states via Bell inequalities
A set of Bell inequalities classifying the quantum entanglement of four-qubit
states is presented. These inequalities involve only two measurement settings
per observer and can characterize fully separable, bi-separable and
tri-separable quantum states. In addition, a quadratic inequality of the Bell
operators for four-qubit systems is derived
Tightly bound excitons in monolayer WSe2
Exciton binding energy and excited states in monolayers of tungsten
diselenide (WSe2) are investigated using the combined linear absorption and
two-photon photoluminescence excitation spectroscopy. The exciton binding
energy is determined to be 0.37eV, which is about an order of magnitude larger
than that in III-V semiconductor quantum wells and renders the exciton excited
states observable even at room temperature. The exciton excitation spectrum
with both experimentally determined one- and two-photon active states is
distinct from the simple two-dimensional (2D) hydrogenic model. This result
reveals significantly reduced and nonlocal dielectric screening of Coulomb
interactions in 2D semiconductors. The observed large exciton binding energy
will also have a significant impact on next-generation photonics and
optoelectronics applications based on 2D atomic crystals.Comment: 19 pages, 4 figures, to appear in PR
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