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Ensembles of nitrogen-vacancy color centers in diamond hold promise for ultra-precise magnetometery, competing with superconducting quantum interference device detectors. Sensor and metrology applications for situations involving high sensitivity require efficient manipulation of the nitrogen-vacancy color centers electronic spins within large volume. Thus, the design of microwave antennas providing a uniform and strong microwave magnetic field over a relatively large volume is on a high demand. In this paper we report different antenna designs based on low loss high permittivity dielectric materials for coherent manipulation of a large ensemble of nitrogen-vacancy color centers in diamond. The operational principle of the proposed antennas is based on excitation of transverse electric (TE) or hybrid electromagnetic (HEM) modes of dielectric resonators. The first antenna design is based on TE01 mode excited inside the resonator made on a ceramic with permittivity of 80. The uniformity of the microwave magnetic field generated by the antenna was verified by measurement of the optically detected magnetic resonance and Rabi frequency in a high-density ensemble of nitrogen-vacancy color centers placed in the center bore of the antenna. Rabi frequency of 10 MHz in a volume of 7 cubic millimeters with a standard deviation of less than 1% at 5 W pump power has been measured at the room temperature. This is enough to coherently excite all color centers in commercially available diamond plates at room temperature. The second antenna design is based on HEM11δ mode excited in the ceramic resonator characterized by the permittivity of 235. The numerical simulations predict the Rabi frequency value of 34.85 MHz in a volume of 6 cubic millimeters with a standard deviation of less than 5% at 5 W pump power. The obtained result paves the way to improve the sensitivity of cutting-edge nitrogen-vacancy color centers based magnetometers by several orders of magnitude, practically reaching superconducting quantum interference device detectors level of sensitivity.

Integration of solid-state quantum emitters such as NV center in diamond with tapered optical fiber is demanded by number of applications ranging from sensing and imaging to quantum communications and computations. Nevertheless, utilization of a single NV center coupled with an optical fiber meets significant challenge of fiber fluorescence that can considerably mask emission of the quantum object. In this paper, we analyze main sources of such fluorescence for the case of NV center coupled to tapered single mode optical fiber and discuss possible ways of improving signal to noise ratio in this case.

NV center in diamond is attracting a lot of attention in quantum information processing community [1]. Been spin system in clean and well-controlled environment of diamond it shows outstanding performance as quantum memory even at room temperature, spin control with single shot optical readout and possibility to build up quantum registers even on single NV center. Moreover, NV centers could be used as high-resolution sensitive elements of detectors of magnetic or electric field, temperature, tension, force or rotation. For all of these applications collection of the light emitted by NV center is crucial point. There were number of approaches suggested to address this issue, proposing use of surface plasmoms [2], manufacturing structures in diamond [3] etc. One of the key feature of any practically important interface is compatibility with the fiber technology. Several groups attacking this problem using various approaches. One of them is placing of nanodiamonds in the holes of photonic crystal fiber [4], another is utilization of AFM to pick and place nanodiamond on the tapered fiber[5]. We have developed a novel technique of placing a nanodiamond with single NV center on the tapered fiber by controlled transfer of a nanodiamond from one “donor” tapered fiber to the “target” clean tapered fiber. We verify our ability to transfer only single color centers by means of measurement of second order correlation function. With this technique, we were able to double collection efficiency of confocal microscope. The majority of the factors limiting the collection of photons via optical fiber are technical and may be removed allowing order of magnitude improved in collection. We also discuss number of extensions of this technique to all fiber excitation and integration with nanostructures. References: [1] Marcus W. Doherty, Neil B. Manson, Paul Delaney, Fedor Jelezko, Jorg Wrachtrup, Lloyd C.L. Hollenberg , " The nitrogen-vacancy colour centre in diamond," Physics Reports, vol. 528, no. 1, p. 1–45, 2013. [2] A.V. Akimov, A. Mukherjee, C.L. Yu, D.E. Chang, A.S. Zibrov, P.R. Hemmer, H. Park and M.D. Lukin, "Generation of single optical plasmons in metallic nanowires coupled to quantum dots," Nature, vol. 450, p. 402–406, 2007. [3] Michael J. Burek , Yiwen Chu, Madelaine S.Z. Liddy, Parth Patel, Jake Rochman , Srujan Meesala, Wooyoung Hong, Qimin Quan, Mikhail D. Lukin and Marko Loncar High quality-factor optical nanocavities in bulk single-crystal diamond, Nature communications 6718 (2014) [4] Tim Schroder, Andreas W. Schell, Gunter Kewes, Thomas Aichele, and Oliver Benson Fiber-Integrated Diamond-Based Single Photon Source, Nano Lett. 2011, 11, 198-202 [5]Lars Liebermeister, et. al. “Tapered fiber coupling of single photons emitted by a deterministically positioned single nitrogen vacancy center”, Appl. Phys. Lett. 104, 031101 (2014)

The results of frequency-modulation (FM) spectroscopy of coherent dark resonances from the Zeeman sublevelsof the transition F =2 $ F =1 of D 1 line in absorption of 87 Rb atoms are presented and discussed in detail.By contrast with the conventional spectroscopy of coherent dark resonances employing two laser beams, relativefrequency of which can be varied, these data has been obtained with the help of a single frequency-modulatedlaser ¯eld. Variation of the modulation frequency plays then similar role with variation the relative frequencyin conventional spectroscopy. Experimental data are ¯t to the theoretical calculations, which are based onthe theory of FM spectroscopy of coherent dark resonances recently developed by us. Feasibility of using suchexperimental technique for accurate measurements of magnetic ¯elds is also discussed.Keywords: Coherent population trapping, absorption, dark resonance, magnetometry, metrology 1. INTRODUCTION The coherent population trapping (CPT) is one of the most intriguing quantum interference phenomena thatcan be most vividly seen in a three-level system in ¤-con¯guration. In this system, if two monochromaticpumping ¯elds are tuned into the resonance with the respective transitions, all the population is captured in thecoherent superposition of two low-lying levels, which gives the name of the phenomenon|coherent populationtrapping [1]. This means that the media of such three-level atoms under CPT will not emit °uorescence and donot absorb photons. In absorption spectra it is revealed as a narrow sharp dip in the absorption pro¯le whilescanning frequency of one of the pumping laser ¯elds. These resonances are called the coherent dark resonances.Due to the rather small spectral width of the dark resonances they found applications in precision spectroscopicapplications, such as metrology

A theoretical model of the coherent population trapping (CPT) in multilevel samarium atom and its comparison with experimental spectroscopic data are presented. Theoretical model describes a degenerated (Lambda) -system in Sm atom formed of the transitions 4f66s2(7F0) mutually implies 4f6(7F)6s6p(3Po)9Fo1 mutually implies 4f66s2(7F1) and includes also a fourth level 4f66s2(7F2), which complements the model making it an open system. An open character of the system reduces the contrast of the resonance curves in the CPT- spectra, but does not change the width of the CPT resonance. Numerical modeling of the CPT resonances in Sm atom was carried out for the case of applied longitudinal and transverse magnetic fields in 7- and 12-level models, as well.

A current status and perspectives of the work on a high density polarized 3He target are reported. The problems of high-power laser design for optical pumping are discussed. A general formulation for the analysis of an arbitrary linear resonator with internal lens of variable focal length, which represents the rod of a solid-state laser is presented. It is shown that mode spot size is stable with respect to lens optical power fluctuations in one part of resonator when it reaches a minimum on a laser rod. The rules for the design of stable resonators with two or more variable lenses are proposed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.