Tim Schröder

Evaluation of nitrogen- and silicon-vacancy defect centres as single photon sources in quantum key distribution

We demonstrate a quantum key distribution (QKD) testbed for room temperature single photon sources based on defect centres in diamond. A BB84 protocol over a short free-space transmission line is implemented. The performance of nitrogen-vacancy (NV) as well as silicon-vacancy defect (SiV) centres is evaluated. An extrapolation for the future applicability of such sources in quantum information processing is discussed.

Integrated and compact fiber-coupled single-photon system based on nitrogen-vacancy centers and gradient-index lenses.

A fiber-coupled single-photon system is presented. Gradient-index lenses are utilized for single-photon collection and fiber coupling of a nitrogen-vacancy defect center in a nanodiamond. Integrated filter technology separates excitation and laser light. Therefore, the system is ultracompact with 120 mm(3) in dimension as no bulky free beam optics are used. The commercial availability of all components and their simple assembly allows the implementation of a low-cost single-photon system, possibly approaching single-photon count rates of 500 kcts/s.

Assembly of fundamental photonic elements from single nanodiamonds

We demonstrate the ability to modify the emission properties and enhance the interaction strength of single emitters coupled to nanophotonic structures based on metals and dielectrics. Assembly of individual diamond nanocrystals, metal nanoparticles and photonic crystal cavities to meta-structures is introduced. Experiments concerning controlled coupling of single defect centers in nanodiamonds to silver nanowires with the goal to investigate quantum plasmonic effects are reported. Furthermore, we demonstrate the formation of a hybrid cavity system in which metal nanostructures are evanescently coupled to a dielectric photonic crystal cavity. This structure allows combined exploitation of both resonant dielectric as well as plasmonic enhancement.

Using defect centres in diamonds to build photonic and quantum optical devices

Abstract: In this chapter, we introduce defect centres in diamond nanocrystals as building blocks of fundamental photonic and quantum optical devices. We first present the motivation for these devices and introduce the optical properties of nanodiamond. We then describe some approaches to establishing enhanced light–matter interaction on the nanoscale and introduce a method for controlled assembly. Integrated nanophotonic and nanoplasmonic elements are the topic of the next section, and we then present two applications of a fundamental light source based on nanodiamonds. We conclude the chapter with the future prospects for nanodiamond research.

Assembly of quantum optical hybrid devices via a scanning probe pick-and-place technique

Combination of pre-selected nanoparticles with micro- and nanostructures is a crucial task in building hybrid quantum optical devices. Here a scanning probe based pick-and-place technique is introduced, capable of transferring nanoparticles to nearly arbitrarily shaped structures. This is demonstrated by building a variety of hybrid quantum optical and plasmonic systems using nitrogen vacancy centers in nanodiamonds as emitters.

Ultra-bright and efficient single photon generation based on integrated nanodiamonds containing single defect centers

We present integrated and highly efficient single photon sources based on defect-centers in nanodiamonds as fundamental components for future implementations of quantum information technologies. We achieve count rates of 2.4 Mcts/s and source efficiencies of 20%.

One-by-one coupling of single photon emitters to high-Q modes of optical microresonators

We present the on-demand coupling of single NV- defect centers in nanodiamonds to a polystyrene microspherical resonator. From an ensemble on a coverslip we select out single nanodiamonds containing a single defect proven by a pronounced antibunching dip. With the help of a scanning near-field probe we can attach these nanodiamonds to a microsphere resonator one-by-one. A clearly modulated fluorescence spectrum demonstrates coupling of the single defect centers to high- whispering-allery modes. Our experiments establish a toolbox to assemble complex systems consisting of single quantum emitters and (coupled) microresonators.