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Tapered optical fibers are promising one-dimensional nanophotonic waveguides that can provide efficient coupling between their fundamental mode and quantum nanoemitters placed inside them. Here, we present numerical studies on the coupling of single nitrogen-vacancy (NV) centers (single point dipoles) in nanodiamonds with tapered fibers. Our results lead to two important conclusions: (1) A maximum coupling efficiency of 53.4% can be realized for the two fiber ends when the NV bare dipole is located at the center of the tapered fiber. (2) NV centers even in 100-nm-sized nanodiamonds where bulk-like optical properties were reported show a coupling efficiency of 22% at the taper surface, with the coupling efficiency monotonically decreasing as the nanodiamond size increases. These results will be helpful in guiding the development of hybrid quantum devices for applications in quantum information science.

The magnetic properties of thin Cr layers in epitaxial V/Cr multilayered structures were investigated at room temperature and 15 K via 119Sn Mössbauer spectroscopy. The magnetic moment and the Néel temperature of Cr, as inferred from the magnetic hyperfine fields transferred to the 119Sn monatomic layers inserted in Cr layers, were found to reduce on decreasing the Cr layer thickness below 40 Å. The local magnetic structure along the growth direction of 80 Å thick Cr layers was investigated by changing the Sn probe positions. The effect of the V/Cr interface on the Cr magnetism is discussed.

Fe/Cr multilayers with monatomic Sn layers embedded in the Cr layers were grown epitaxially on MgO(001) substrates, and the magnetic hyperfine field at the 119Sn nuclear sites was examined using Mössbauer spectroscopy. It was found that nonzero hyperfine field is induced at the Sn sites at room temperature and that the value reduces drastically from 10 to 2 T when the Cr layer thickness decreases from 80 to 10 A. The result indicates that the Cr layers are magnetically ordered even when the thickness is very small and that the magnetic moments of Cr become smaller as the Cr layer thickness decreases.

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