Tapered fiber coupling of single photons emitted by a deterministically positioned single nitrogen vacancy center

Abstract

A diamond nano-crystal hosting a single nitrogen vacancy (NV) center is optically selected with a confocal scanning microscope and positioned deterministically onto the subwavelength-diameter waist of a tapered optical fiber (TOF) with the help of an atomic force microscope. Based on this nano-manipulation technique we experimentally demonstrate the evanescent coupling of single fluorescence photons emitted by a single NV-center to the guided mode of the TOF. By comparing photon count rates of the fiber-guided and the free-space modes and with the help of numerical FDTD simulations we determine a lower and upper bound for the coupling efficiency of (9.5 ± 0.6)% and (10.4 ± 0.7)%, respectively. Our results are a promising starting point for future integration of single photon sources into photonic quantum networks and applications in quantum information science.PACS numbers: 03.67. 42.50.Ex, 78.67.Bf Efficient collection of single photons radiated by a single solid state quantum emitter -like the nitrogen vacancy (NV) center in diamond 1 -is an important prerequisite for future applications in applied physical and quantum information science, like ultra-sensitive fluorescence spectroscopy and linear optical quantum computation 2-4 . A standard technique for fluorescence collection is confocal microscopy. However, when applied to defect centers in bulk diamond, total internal reflection limits the collection efficiency to few percent. Recently, the collection efficiency of NV-fluorescence has been increased by one order of magnitude by combining confocal microscopy with solid immersion lenses (SILs) 5-7 , respectively photonic nanowires 8 . In the latter system the improvement is based on efficient coupling of NV-fluorescence photons to the strongly confined mode (HE 11 ) 9-11 of diamond nanowires. For defect centers in diamond nano-crystals, tapered optical fibers (TOFs) 12 with a subwavelength diameter waist are a particularly attractive alternative platform. Due to the strong evanescent field at the surface, such TOFs promise coupling efficiencies up to 36%13,14 and approaching unity when combined with Bragg-grating cavities 15,16 . Until now, evanescent coupling of fluorescence photons to a single guided mode of a TOF has been achieved for a) email: lars.liebermeister@physik.uni-muenchen.de b) email: markusweber@lmu.de various solid state quantum emitters 17-20 , molecules 21 , and laser-cooled atomic vapors 22 . To bring these emitters into the strong evanescent optical field at the surface of the nano-fiber several non-deterministic deposition techniques like dip-coating 17,18 , picoliter-dispensers 19,20 , and optical surface traps 23 have been applied. However, for real applications in quantum information science, e. g., the photonic quantum-bus mediated coupling of NVcenters in a lattice 24 , deterministic positioning of single solid state quantum emitters onto the submicron waist of a TOF with nm position control is desirable. In this letter we demonstrate significant steps towards deterministic coup...

Determining the internal quantum efficiency of shallow-implanted nitrogen-vacancy defects in bulk diamond

“…Mohtashami and Koenderink [15] considered diamond nanocrystals containing native single NV defects, and found that for NV defects in 25-nm nanodiamonds the IQE is distributed between 0 and 20%, while for 100-nm nanodiamonds the IQE has an even larger distribution in the range 10-90%. The result for the smallest nanodiamonds is partially supported by fitting the measured secondorder correlation function of a NV defect with that of a three-level system [16]. Interestingly, it was shown in [15] that the wide IQE distribution is due to a variation in both the radiative as well as the non-radiative decay rates among the different nanocrystals.…”

Diamond Nanophotonics

“…Via the taper, the evanescent mode and thus the single photons are converted into the mode of a standard single mode fiber. Reproduced with permission from Ref [95] .Copyright 2014 AIP Publishing LLC (b)…”

“…For many applications in QIP, especially for quantum cryptography, it is highly desirable to efficiently couple single photons from diamond color centers into optical fibers to enable integration with existing telecommunication technologies. Several approaches using incorporation of nanodiamonds into the optical fiber [92] , as well as placing nanodiamonds on photonic crystal fiber end facets [93] and tapered fibers have been pursued [94,95] . Using the latter approach, 10% of the single photons from an NV center were collected using a tapered single mode fiber (diameter in taper: 260 nm).…”

Optical nanofiber-based cavity induced by periodic air-nanohole arrays

“…To reduce complexity and to compensate for the general unsatisfactory scalability of light-matter systems in free space, optical nanofibers (ONFs) are proving to be a very useful tool for hybrid quantum devices wherein quantum emitters are coupled to the fiber-guided modes via the evanescent field extending from the nanofiber surface. In recent years, significant research effort has been invested in order to interface various quantum emitters, including neutral atoms, 1-7 semiconductor quantum dots, 8,9 and nitrogenvacancy centers in diamond, 10 to the light fields of ONFs. With tight, transverse-mode confinement and the relatively high intensity of the evanescent field, efficient light-matter coupling 11 and low optical power nonlinearities [12][13][14] have been experimentally demonstrated.…”