Fedja Orucevic

Observation of Cold Collisions between Trapped Ions and Trapped Atoms

We study cold collisions between trapped ions and trapped atoms in the semiclassical (Langevin) regime. Using Yb+ ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes over three decades of collision energies down to 3 mueV (k_{B}x35 mK). The minimum measured rate coefficient of 6x10;{-10} cm;{3} s;{-1} is in good agreement with that derived from a Langevin model for an atomic polarizability of 143 a.u.

Transmittance and near-field characterization of sub-wavelength tapered optical fibers.

We have produced high transmission sub-wavelength tapered optical fibers for the purpose of whispering gallery mode coupling in fused silica microcavities at 780 nm. A detailed analysis of the fiber transmittance evolution during tapering is demonstrated to reflect precisely the mode coupling and cutoff in the fiber. This allows to control the final size, the number of guided modes and their effective index. These results are checked by evanescent wave mapping measurements on the resulting taper.

Excitation mapping of whispering gallery modes in silica microcavities

We report the direct observation of the electromagnetic-field distribution of whispering gallery modes in silica microcavities (spheres and toroids). It is revealed by their excitation efficiency with a tapered fiber coupler swept along the meridian. The originality of this method lies in the use of the coupler itself for the near-field mapping, eliminating the need of additional tools used in previous work. This method is successfully applied to microspheres and microtoroids.

Nano-cluster engineering: A combined ion implantation/co-deposition and ionizing radiation

We have used the energy deposited due to the electronic excitation by post-implantation irradiation to induce the nucleation of nano-clusters of Au in silica. We have produced the Au/silica by two methods. (A) MeV Au implantation into silica, (B) producing thin films of a combined Au and silica on a silica substrate, using co-deposition of gold and silica. The process of ion beam assisted nucleation of nano-clusters was used to reduce the threshold implantation dose, or the Au concentration in the silica host, required to produce Au nano-crystals by at least two orders of magnitude. In this presentation, we applied a similar technique, post-irradiation electronic excitation, to films produced by both ion implantation of Au into silica as well as to films produced using co-deposition of gold and silica. By a co-deposition technique, gold and silica (co-deposited at various concentrations) are grown, then post-irradiated. The resultant Au nano-cluster formation was observed and studied using optical spectroscopy, X-ray diffraction, RBS and TEM.

An integrated fiber trap for single-ion photonics

We report on a novel single-photon source using a single calcium ion trapped between the end facets of two optical fibers. The optical fibers act as photonic channels, and in addition their metallic jackets provide a trapping electric field for the ion. Our system successfully combines a stable single-atom emitter with fiber optics, demonstrating remarkable compactness and scalability. In consequence, it is very well suited for use in quantum networks, where single ions interface with single photons traveling through optical fibers. We have demonstrated the non-classical character of the photons generated by this efficient source in continuous as well as pulsed mode.We have realized a compact system to efficiently couple the fluorescent light emitted by a single trapped ion to two opposing optical fibers. The fibers are tightly integrated in the center electrodes of a miniature endcap trap. They capture light from the ion with a numerical aperture of 0.34 each, corresponding to 6% of the solid angle in total. The high collection efficiency and high signal-to-background ratio make the setup an ideal quantum light source. We have observed strong antibunching of the photons emitted from the two fibers. The system has a range of applications from single-ion state detection in quantum information processing to strong coupling cavity-QED with ions.

Novel laser machining of optical fibers for long cavities with low birefringence

We present a novel method of machining optical fiber surfaces with a CO₂ laser for use in Fiber-based Fabry-Perot Cavities (FFPCs). Previously FFPCs were prone to large birefringence and limited to relatively short cavity lengths (≤ 200 μm). These characteristics hinder their use in some applications such as cavity quantum electrodynamics with trapped ions. We optimized the laser machining process to produce large, uniform surface structures. This enables the cavities to achieve high finesse even for long cavity lengths. By rotating the fibers around their axis during the laser machining process the asymmetry resulting from the lasers transverse mode profile is eliminated. Consequently we are able to fabricate fiber mirrors with a high degree of rotational symmetry, leading to remarkably low birefringence. Through measurements of the cavity finesse over a range of cavity lengths and the polarization dependence of the cavity linewidth, we confirmed the quality of the produced fiber mirrors for use in low-birefringence FFPCs.

Neodymium Photoluminescence in Whispering Gallery Modes of Toroidal Microcavities

We report on light emission from high-Q neodymium-implanted silica microtoroids. Following the description of the fabrication process of microtoroids, neodymium light emission is analysed. This emission is coupled to various cavity modes. Using evanescent wave coupling we achieve selective detection of Whispering Gallery Modes of a microtoroid.

The UK National Quantum Technologies Hub in sensors and metrology (Keynote Paper)

The UK National Quantum Technology Hub in Sensors and Metrology is one of four flagship initiatives in the UK National of Quantum Technology Program. As part of a 20-year vision it translates laboratory demonstrations to deployable practical devices, with game-changing miniaturized components and prototypes that transform the state-of-the-art for quantum sensors and metrology. It brings together experts from the Universities of Birmingham, Glasgow, Nottingham, Southampton, Strathclyde and Sussex, NPL and currently links to over 15 leading international academic institutions and over 70 companies to build the supply chains and routes to market needed to bring 10–1000x improvements in sensing applications. It seeks, and is open to, additional partners for new application development and creates a point of easy open access to the facilities and supply chains that it stimulates or nurtures.

The UK National Quantum Technology Hub in Sensors and Metrology

The UK National Quantum Technology Hub in Sensors and Metrology is one of four flagship initiatives in the UK National of Quantum Technology Program. As part of a 20-year vision it translates laboratory demonstrations to deployable practical devices, with game-changing miniaturized components and prototypes that transform the state-of-the-art for quantum sensors and metrology. It brings together experts from the Universities of Birmingham, Glasgow, Nottingham, Southampton, Strathclyde and Sussex, NPL and currently links to over 15 leading international academic institutions and over 70 companies to build the supply chains and routes to market needed to bring 10–1000x improvements in sensing applications. It seeks, and is open to, additional partners for new application development and creates a point of easy open access to the facilities and supply chains that it stimulates or nurtures.

Silica microspheres as high-Q microcavities for semiconductor quantum-dot lasers

We report an experiment where InAs/GaAs self-organized Quantum Dots (QD) are coupled to the evanescent field of very-high-Q Whispering Gallery Modes (WGM) in a silica microsphere. The high performance of these microcavity and nanoemitters allowed to achieve very low threshold (200 μm) laser operation at room temperature, involving a few thousands of QD. We show that such a low threshold relies heavily on WGM deconfinement and reconstruction in the micromesa etched in GaAs sample. Next, we present some prospects on further experiments involving various semiconductor nanostructures coupled to microspheres or to silica microtoroids integrated on a Si chip (as recently introduced by K.J.~Vahala and coworkers at Caltech).