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...
The strong radial confinement and the pronounced evanescent field of the guided light in optical nanofibers yield favorable conditions for ultra-sensitive surface spectroscopy of molecules deposited on the fiber. Using the guided mode of the nanofiber for both excitation and fluorescence collection, we present spectroscopic measurements on 3,4,9,10-perylenetetracarboxylic dianhydride molecules (PTCDA) at ambient conditions. Surface coverages as small as 1 per thousand of a compact monolayer still give rise to fluorescence spectra with a good signal to noise ratio. Moreover, we analyze and quantify the self-absorption effects due to reabsorption of the emitted fluorescence light by circumjacent surface-adsorbed molecules distributed along the fiber waist.
We review our recent progress in the production and characterization of tapered optical fibers with a sub-wavelength diameter waist. Such fibers exhibit a pronounced evanescent field and are therefore a useful tool for highly sensitive evanescent wave spectroscopy of adsorbates on the fiber waist or of the medium surrounding. We use a carefully designed flame pulling process that allows us to realize preset fiber diameter profiles. In order to determine the waist diameter and to verify the fiber profile, we employ scanning electron microscope measurements and a novel accurate in situ optical method based on harmonic generation. We use our fibers for linear and non-linear absorption and fluorescence spectroscopy of surface-adsorbed organic molecules and investigate their agglomeration dynamics. Furthermore, we apply our spectroscopic method to quantum dots on the surface of the fiber waist and to caesium vapor surrounding the fiber. Finally, towards dispersive measurements, we present our first results on building and testing a single-fiber bi-modal interferometer.Comment: 13 pages, 18 figures. Accepted for publication in Applied Physics B. Changes according to referee suggestions: changed title, clarification of some points in the text, added references, replacement of Figure 13
The control over the transmission properties of tapered optical fibers (TOFs) is an important requirement for a whole range of applications. Using a carefully designed flame pulling process that allows us to realize preset fiber radius profiles, we fabricate TOFs with a nanofiber waist. We study the spectral transmission properties of these TOFs as a function of the taper profile and the waist length and show how the transmission band of the TOF can be tuned via different fiber profile parameters. Based on these results, we have designed a nanofiber-waist TOF with broadband transmission for surface spectroscopy of organic molecules. Moreover, our method allows us to analyze the loss mechanisms of optical nanofibers.
Entangled quantum states have applications as a model system for strongly correlated many body states, as resource for quantum information processing and as a tool for enhanced precision measurements. Deterministic entanglement schemes create the desired state by transferring the system under the action of a carefully chosen Hamiltonian into an entangled state. The system must follow a unitary evolution, and uncontrolled parasitic interactions with the environment leading to spontaneous decay or partial measurements of the state have to be avoided.Entangled states can also be created in a probabilistic manner: By performing a suitable partial measurement of the system's state, the probe measurement outcome indicates whether the system has been laser projected into the desired state or not by the measurement's backaction. Such probabilistic schemes can relax the stringent requirements on the suppression of dissipation in our cavity-QED system [1,2]. cavity In our experiment, we load a chosen number of doppler-cooled mirror caesium atoms from a magneto-optical trap into a standing wave optical dipole trap. The positions of the individual atoms are then determined with sub-micrometer precision, enabling us to prepare, to manipulate and to read out the quantum state of each atom. Using the dip dipole trap as an optical conveyor belt, the atoms are transported into dipole trap the mode of a high-finesse optical cavity. The cavity consists of two dielectric mirrors with a distance of 160 rtm, a finesse of F 106 and mode volume of V=6 66104 ltm3. These parameters lead to a conveyo maximum theoretical single-atom cooperativity parameter of about belt 120. The resonance frequency of the cavity is stabilized to the caesium transition at 852 nm using a lock laser which is 16 nm cavity detuned. mirror By observing the transmission of a weak resonant probe laser we can detect the presence of a single atom coupled to the cavity mode and observe the dynamics of one or more strongly coupled atoms. Sudden changes of the transmitted intensity indicate jumps in the detector r position of the trapped atom. Cooling by the probe laser extends the observation time to more than one second. We analyze the magnitude Conceptual drawing of trapped atoms and the stability of the atom-cavity coupling obtained in the being transported from a magneto-optical experiment for one and more atoms. Our goal is to perfectly control trap (MOT) into an optical cavity. the interaction of two or more atoms with the cavity field. Finally we discuss the possibility of implementing probabilistic entanglement schemes.[1] A. S. S0rensen and K. M0lmer, Measurement Induced Entanglement and Quantum Computation with Atoms in Optical Cavities, Phys. Rev. Lett. 91, 097905 (2003) [2] J. Metz, M. Trupke, and A. Beige, Robust Entanglement through Macroscopic Quantum Jumps, Phys. Rev. Lett. 97, 040503 (2006)
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