Further improvement of infrared single photon sources is a major challenge for future implementations of quantum information and quantum communication applications. In this paper, we give further insight into a recently presented, conceptually novel method for the generation of single photons.<sup>1</sup> The method is of particular interest for spectral domains where stable room temperature single photon sources are not available. For example, this is the presently the case for the near-infrared. This wavelength regime is important for data transfer over long distances where optical losses in fibers are minimal. The presented method is based on the following idea. The fundamental key requirement for single photon generation is the generation of a single excitation in an optically active system. It is not the presence of a single quantum system. The presented method is applied to realize a stable, non-blinking, room temperature infrared single photon source by converting visible single photons from a defect center in diamond to the near infrared. For the presented implementation, the theoretical conversion efficiency was estimated to be 26 %. In a first prove of principle experiment, a conversion efficiency of 0.1 % was achieved.
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 (<i>Q</i> ≈ 900) opens new routes for the control of light-matter
interaction at the nanoscale.
We introduce a novel approach to assemble fundamental nanophotonic model systems. The approach is based
on the controlled manipulation of single quantum emitters (defect centers in diamond) via scanning probes.
We demonstrate coupling of a single diamond nanocrystal to a planar photonic crystal double-heterostructure
cavity as well as to a silica toroidal resonator. Our studies represent an important step towards well-controlled
cavity-QED experiments with single defect centers in diamond.
We report on the fabrication and optical characterization of photonic crystal cavities for visible wavelengths
made from silicon nitride (SiN). We note significant improvements in fabrication process with respect to our
previous studies. The intrinsic luminescence of the SiN membranes was used as an internal light source to study
the quality factor of the cavity modes. We experimentally found values as high as 3400, which are up to the
present unsurpassed for photonic crystal resonators in the visible spectra range. Finite difference time domain
(FDTD) simulations suggest another boost by a factor of two is possible by further optimizing the fabrication
process. We describe a method by which arbitrary emitters or other nanoscopic objects can be coupled in a
deterministic way by using the manipulation capabilities of an atomic force microscope.
We demonstrate a hybrid approach for the realization of novel nanophotonic devices by combining lithographic
fabrication techniques with a nano-manipulation method. In particular, we report on the fabrication of photonic
crystal cavities as a platform to which arbitrary emitters or other nanoscopic objects can be coupled in a
deterministic way by exploiting the manipulation capabilities of an atomic force microscope. In addition, the
optical properties of such particle-cavity systems are analyzed with regard to changes of the quality factor and
resonance wavelength of the cavity mode. Our approach is well suited to create improved single photon sources
and also complex photonic devices with several emitters coupled coherently via shared cavity modes.
The paper presents our experimental results achieved on the field of investigation of LPCVD silicon nitride based two
dimensional photonic crystals for visible wavelengths. Our research concentrates on the photonic band gap and defect
engineering with respect to the use of silicon nitride based photonic crystals as optical resonators in the visible range of
electromagnetic spectra. In order to optically characterize the fabricated photonic crystals, transmission setup utilizing
broad band white light source is being used. Using this setup, photonic band gaps in the range between 500 and 900 nm,
and thus covering the entire transmission range of LPCVD silicon nitride in the visible range, could be identified for
various values of the slab thickness. By incorporating line defects, we fabricated and investigated several photonic
crystal filter demonstrators. By optimizing the defect geometry, we achieved transmission values of over 85%.
SiN is a promising candidate for the fabrication of photonic crystals (PCs)
with band gaps in the wavelength range between 550 nm and 850 nm. Here, we investigate the optical properties of
cavities in SiN PC membranes by fluorescence spectroscopy of embedded emitters. For this purpose a dye solution is spin-cast on top of the PC membranes and the fluorescence is studied using a confocal microscopy setup. We observe strong emission resonances of molecules spatially and spectrally coupled to the cavity modes. These resonances are compared to finite-difference time-domain simulations of the PC structures, allowing an optimization of the cavity geometry to achieve high quality factors (several hundreds to nearly one thousand). Furthermore, we study routes to selectively incorporate single emitting particles into the cavities applying scanning probes. In this way we introduce SiN PC cavities as universal tools for the manipulation of the emission properties of a huge variety of different emitters in the visible.
We investigate the potential of photonic crystals (PCs) for use as novel sensing devices. For this purpose we study the interaction of nanoscopic dielectric particles with the near field of planar PCs by means of 3D FEM calculations. In particular, we have simulated PC waveguide structures incorporating a single cavity-like defect that interacts with a single dielectric nanosphere in a liquid environment. The resonance of the PC cavity shifts in the presence of the particle, as can be monitored by corresponding transmission measurements. As a second aspect, we investigate the mechanical forces acting on the particle due to the high field gradient in the cavity when in resonance. These forces give rise to a stable trapping of the particle in the cavity in analogy to the trapping in optical tweezers. In combination with microfluidic devices this gives prospect to novel techniques for ultra-sensitive detection and spectroscopy with only minimal amounts of analyte. We also present a scheme for experimental investigations of the particle-PC interaction, which makes use of an optical tweezer to actively move dielectric nanospheres in the near field of the PC, and which allows both for fluorescence as well as very sensitive force measurements.