Solid-state quantum emitters are in high demand for emerging technologies such as advanced sensing and quantum information processing. Generally, these emitters are not sufficiently bright for practical applications, and a promising solution consists in coupling them to plasmonic nanostructures. Plasmonic nanostructures support broadband modes, making it possible to speed up the fluorescence emission in room-temperature emitters by several orders of magnitude. However, one has not yet achieved such a fluorescence lifetime shortening without a substantial loss in emission efficiency, largely because of strong absorption in metals and emitter bleaching. Here, we demonstrate ultrabright single-photon emission from photostable nitrogen-vacancy (NV) centers in nanodiamonds coupled to plasmonic nanocavities made of low-loss single-crystalline silver. We observe a 70-fold difference between the average fluorescence lifetimes and a 90-fold increase in the average detected saturated intensity. The nanocavity-coupled NVs produce up to 35 million photon counts per second, several times more than the previously reported rates from room-temperature quantum emitters.

On-chip integration of quantum optical systems could be a major factor enabling photonic quantum technologies. Unlike the case of electronics, where the essential device is a transistor and the dominant material is silicon, the toolbox of elementary devices required for both classical and quantum photonic integrated circuits is vast. Therefore, many material platforms are being examined to host the future quantum photonic computers and network nodes. We discuss the pros and cons of several platforms for realizing various elementary devices, compare the current degrees of integration achieved in each platform and review several composite platform approaches. References and links 1.C. H. Bennett and G. Brassard, "Quantum cryptography: Public key distribution and coin tossing," Proc. IEEE Int. Conf. Comput. Syst. Signal Process. 175, 8 (1984). 2.N. Gisin and R. Thew, "Quantum communication," Nat. Photonics 1, 165-171 (2007). 3.H.-K. Lo, M. Curty, and K. Tamaki, "Secure quantum key distribution," Nat. Photonics 8, 595-604 (2014 553-558 (1992). 6. L. K. Grover, "A fast quantum mechanical algorithm for database search," in Proceedings of the XXVIII Annual ACM Symposium on Theory of Computing -STOC '96 (ACM Press, 1996), pp. 212-219. 7.S. J. Devitt, W. J. Munro, and K. Nemoto, "Quantum error correction for beginners," Reports Prog. Phys. 76, 76001 (2013). 8.T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe, and J. L. O'Brien, "Quantum computers.," Nature 464, 45-53 (2010). 9.H. J. Kimble, "The quantum internet," Nature 453, 1023-1030 (2008). 10.U. L. Andersen, G. Leuchs, and C. Silberhorn, "Continuous-variable quantum information processing," Laser Photon. Rev. 4, 337 (2010). 11.C. Weedbrook, S. Pirandola, R. García-Patrón, N. J. Cerf, T. C. Ralph, J. H. Shapiro, and S. Lloyd, "Gaussian quantum information," Rev. Mod. Phys. 84, 621-669 (2012). 12.U. L. Andersen, J. S. Neergaard-Nielsen, P. Van Loock, and A. Furusawa, "Hybrid discrete-and continuous-variable quantum information," Nat. Phys. 11, 713-719 (2015). 13.E. Knill, R. Laflamme, and G. J. Milburn, "A scheme for efficient quantum computation with linear optics," Nature 409, 46-52 (2001 Zeilinger, "Experimental one-way quantum computing," Nature 434, 169-176 (2005). 17.R. Raussendorf, J. Harrington, and K. Goyal, "Topological fault-tolerance in cluster state quantum computation," New J. Phys. 9, 199-199 (2007 A 192-196 (2015 O. Benson, "Assembly of hybrid photonic architectures from nanophotonic constituents.," Nature 480,

The use of nanoscale plasmonic metamaterials can optimize photon-matter interactions

We propose highly efficient hybrid plasmonic bullseye antennas for collecting photon emission from nm-sized quantum emitters. In our approach, the emitter radiation is coupled to surface plasmon polaritons that are consequently converted into highly directional out-of-plane emission. The proposed configuration consists of a high-index titania bullseye grating separated from a planar silver film by a thin low-index silica spacer layer. Such hybrid systems are theoretically capable of directing 85% of the dipole emission into a 0.9 NA objective, while featuring a spectrally narrow-band tunable decay rate enhancement of close to 20 at the design wavelength. Hybrid antenna structures were fabricated by standard electron-beam lithography without the use of lossy adhesion layers that might be detrimental to antenna performance. The fabricated antennas remained undamaged at saturation laser powers exhibiting stable operation.For experimental characterization of the antenna properties, a fluorescent nanodiamond containing multiple nitrogen vacancy centers (NV-center) was deterministically 1 arXiv:1804.04433v1 [physics.optics] 12 Apr 2018 placed in the bullseye center, using an atomic force microscope. Probing the NV-center fluorescence we demonstrate resonantly enhanced, highly directional emission at the design wavelength of 670 nm, whose characteristics are in excellent agreement with our numerical simulations.Efficient collection of photons from single quantum emitters (QE) is a key requirement for many quantum technological applications, 1 utilizing on-demand photon generation, optical spin read-out 2,3 or coalescence of indistinguishable photons. 4,5 The efficiency by which photons can be collected is, however, often compromised by the non-unity quantum yield and relatively omnidirectional emission pattern of typical QEs, whether it is a molecule, quantum dot or solid state defect. 6 Fortunately, both aspects can be improved upon by engineering the photonic enviroment. Quantum yield may be increased by accelerating the radiative spontaneous decay rate, relative to intrinsic nonradiative decay, via the Purcell effect. 7 Directional emission is typically achieved by two approaches; 8 either a geometricalor a mode-coupling approach. The geometrical approach relies on redirecting far-field emission by reflection or refraction on appropriately shaped surfaces, such as a parabolic mirror 9 or solid immersion lens. 10 Alternatively, the mode-coupling approach is based on near-field coupling QE emission to an antenna or waveguide mode. The emission pattern then conforms to that of the antenna, 11 while for detection with an objective, plane film waveguide modes may be redirected to free space by leakage into high index substrates 12 or scattering on periodic gratings. 13,14 For highly directional emission, the circular symmetric bullseye grating is particularly attractive as tight beaming of photons is achievable by appropriate

Quantum emitters coupled to plasmonic nanostructures can act as exceptionally bright sources of single photons, operating at room temperature. Plasmonic mode volumes supported by these nanostructures can be several orders of magnitude smaller than the cubic wavelength, which leads to dramatically enhanced light-matter interactions and drastically increased photon production rates. However, when increasing the light localization further, these deeply subwavelength modes may in turn hinder the fast outcoupling of photons into free space. Plasmonic hybrid nanostructures combining a highly confined cavity mode and a larger antenna mode circumvent this issue. We establish the fundamental limits for quantum emission enhancement in such systems and find that the best performance is achieved when the cavity and antenna modes differ significantly in size. We experimentally support this idea by photomodifying a nanopatch antenna deterministically assembled around a nanodiamond known to contain a single nitrogen-vacancy (NV) center. As a result, the cavity mode shrinks, further shortening the NV fluorescence lifetime and increasing the single-photon brightness. Our analytical and numerical simulation results provide intuitive insight into the operation of these emitter-cavity-antenna systems and show that this approach could lead to single-photon sources with emission rates up to hundreds of THz and efficiencies close to unity.