Miniaturization of quantum optical devices down to μm-dimensions and integration into fibre optical networks
is a major prerequisite for future implementations of quantum information communication and processing applications.
Also scalability, long-term stability and room-temperature operation are important properties of such
devices. Lately there have been major improvements in down-sizing logical structures and functionalizing optical
fibers. Here we present an alignment free, μm-scale single photon source consisting of a single quantum emitter
on an optical fiber operating at room temperature. It easily integrates into fiber optic networks for quantum
cryptography or quantum metrology applications. Near-field coupling of a single nitrogen-vacancy center is
achieved in a bottom-up approach by placing a pre-selected nanodiamond directly on the fiber facet. Its high
photon collection efficiency is equivalent to a far-field collection via an objective with a numerical aperture of 0.82.
Furthermore, simultaneous excitation and recollection through the fiber is possible introducing a fiber-connected
single emitter sensor that allows near-field probing with quantum mechanical properties.
Single photon sources are key devices for optical quantum information processing, miniaturized optical elements,
as well as light standards. Several systems have been exploited so far such as semiconductor quantum dots, defect
centers in diamond, alkali atoms, and parametric down-conversion sources. In this contribution we will review
some of these sources and highlight their unique properties with respect to applications in quantum information
processing. A focus lies on two different room temperature sources based on cavity-enhanced parametric downconversion
and on nitrogen-vacancy centers in diamond.
We propose and demonstrate a hybrid cavity system in which metal nanoparticles are evanescently coupled to a
dielectric photonic crystal cavity using a nanoassembly method. While the metal constituents lead to strongly
localized fields, optical feedback is provided by the surrounding photonic crystal structure. The combined effect
of plasmonic field enhancement and high quality factor (Q ≈ 900) opens new routes for the control of light-matter
interaction at the nanoscale.
We present a high-temperature single-photon source based on a CdSe quantum dot in a ZnSe nanowire. The
nanowires have been grown by Molecular Beam Epitaxy in the Vapour-Liquid-Solid growth mode. We utilized a
two-step growth process, where a thin, defect free ZnSe nanowire on a top of a nanoneedle is grown. Quantum
dots are formed by incorporating a narrow zone of CdSe into the nanowire. We observe an intense and highly
polarized photoluminescence. Efficient photon anti-bunching was observed up to 220 K, while conserving a
normalized anti-bunching dip of at most 36%.
High-efficient single-photon sources are important for fundamental experiments as well as for modern applications in the field of quantum information processing. Therefore, both the overall collection efficiency as well as the photon generation rate are important parameters. In this article, we use cascaded two-photon emission from a single quantum dot in order to double the efficient transmission rate in a quantum key distribution protocol by multiplexing on a single photon level. The energetically non-degenerate photons are separated with a single photon add/drop filter based on a Michelson interferometer. For optimizing the collection efficiency, coupling of quantum emitters to microcavities is advantageous. We also describe preliminary results towards coupling of a single quantum dot grown on a micrometer-sized tip to the whispering gallery modes of a microsphere cavity.