An ideal emitter of entangled photon pairs combines the perfect symmetry of an atom with the convenient electrical trigger of light sources based on semiconductor quantum dots. Our source consists of strain-free GaAs dots self-assembled on a triangular symmetric (111)A surface. The emitted photons reveal a fidelity to the Bell state as high as 86(±2)% without postselection. We show a violation of Bell's inequality by more than five times the standard deviation, a prerequisite to test a quantum cryptography channel for eavesdropping. Due to the strict nonlocal nature the source can be used for real quantum processing without any postprocessing. The remaining decoherence channel of the photon source is ascribed to random charge and nuclear spin fluctuations in and near the dot.

Photoredox-catalyzed vicinal chlorotrifluoromethylation of alkene is described. In the presence of Ru(Phen)3Cl2, CF3SO2Cl was used as a source for the CF3 radical and chloride ion under visible light irradiation. Various terminal and internal alkenes were transformed to their vicinal chlorotrifluoromethylated derivatives. Biologically active compounds were applied under the condition to obtain desired products, suggesting that the method could be feasible for late-stage modification in drug discovery.

The emission cascade of a single quantum dot is a promising source of entangled photons. A prerequisite for this source is the use of a symmetric dot analogous to an atom in a vacuum, but the simultaneous achievement of structural symmetry and emission in a telecom band poses a challenge. Here we report the growth and characterization of highly symmetric InAs/InAlAs quantum dots self-assembled on C3v symmetric InP(111)A. The broad emission spectra cover the O (λ ∼ 1.3 µm), C (λ ∼ 1.55 µmm), and L (λ ∼ 1.6 µm) telecom bands. The distribution of the fine-structure splittings is considerably smaller than those reported in previous works on dots at similar wavelengths. The presence of dots with degenerate exciton lines is further confirmed by the optical orientation technique. Thus, our dot systems are expected to serve as efficient entangled photon emitters for long-distance fiber-based quantum key distribution.Semiconductor quantum dots (QD) are expected to play a central role in quantum information networks. A noteworthy device based on dots is the solid-state single photon source, which ensures absolute security in quantum key distribution (QKD)1 . Since QDs can confine charged carriers in nanometer-sized regions, recombination enables single photons to appear on demand, i.e., synchronously with a master clock shared in networks 2 . QKD over a 50 km commercial fiber has already been demonstrated with QD photon sources, which emitted at a wavelength of 1.5 µm 3 . The transmission distance in that work was limited purely by the absorption loss of silicate fibers. Exceeding this fundamental limit requires the development of quantum link protocols, which exploit the nonlocality inherent in quantum theory. An efficient source of entangled photon pairs is a key element in the realization of such protocols, examples of which include quantum teleportation 4 and entanglement swapping 5 . The generation of entangled photons with semiconductor QDs is directly linked to the singlet configuration of two excitons (X), which form a biexciton (XX). Eventually, two photons associated with the XX-X cascade show polarization correlations independent of the choice of measurement basis, yielding quantum entanglement in the polarization state. However, a common class of QDs exhibits considerable fine-structure splittings (FSS) 6-10 , which exclude entanglement in emitted photons 11 . Numerous attempts have been made to suppress FSS and recover the symmetry of QDs grown on conventional (001) oriented substrates [12][13][14][15][16][17][18][19] . However, from a practical point of view, the reproducible growth of symmetric dots with (at least) near-zero FSS is highly desirable.A noteworthy strategy for achieving such high QD symmetry is the application of C 3v symmetric (111) makes it possible to grow QDs on (111) substrates. Hence, a great reduction in FSS was observed in these QDs 23,24 , which led to the demonstration of entangled photon emission in pyramidal QDs on patterned (111)B substrates 25 , and the filtering-free violation ...