Ultrathin fiber-taper coupling with nitrogen vacancy centers in   nanodiamonds at cryogenic temperatures
  We demonstrate cooling of ultrathin fiber tapers coupled with nitrogen vacancy (NV) centers in nanodiamonds to cryogenic temperatures. Nanodiamonds containing multiple NV centers are deposited on the subwavelength 480-nm-diameter nanofiber region of fiber tapers. The fiber tapers are successfully cooled to 9 K using our home-built mounting holder and an optimized cooling speed. The fluorescence from the nanodiamond NV centers is efficiently channeled into a single guided mode and shows characteristic sharp zero-phonon lines of both neutral and negatively charged NV centers. The present nanofiber/nanodiamond hybrid systems at cryogenic temperatures can be used as NV-based quantum information devices and for highly sensitive nanoscale magnetometry in a cryogenic environment. 
Masazumi Fujiwara, Hong-Quan Zhao, Tetsuya Noda, Kazuhiro Ikeda,   Hitoshi Sumiya, and Shigeki Takeuchi
quant-ph cond-mat.mes-hall