Optimizing single-photon-source heralding efficiency at 1550 nm using periodically poled lithium niobate

We explore the feasibility of using high conversion-efficiency periodically-poled crystals to produce photon pairs for photon-counting detector calibrations at 1550 nm. The goal is the development of an appropriate parametric down-conversion (PDC) source at telecom wavelengths meeting the requirements of high-efficiency pair production and collection in single spectral and spatial modes (single-mode fibers). We propose a protocol to optimize the photon collection, noise levels and the uncertainty evaluation. This study ties together the results of our efforts to model the single-mode heralding efficiency of a two-photon PDC source and to estimate the heralding uncertainty of such a source.Comment: 14 pages, 2 tables and 3 figures, final version accepted by Metrologi

Single Photon Source with Individualized Single Photon Certifications

As currently implemented, single-photon sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand. The scheme uses a heralded photon source based on parametric downconversion, but by effectively breaking the trigger detector area into multiple regions, we are able to extract more information about a heralded photon than is possible with a conventional arrangement. This scheme allows photons to be produced along with a quantitative ``certification'' that they are single photons. Some of the single-photon certifications can be significantly better than what is possible with conventional downconversion sources (using a unified trigger detector region), as well as being better than faint laser sources. With such a source of more tightly certified single photons, it should be possible to improve the maximum secure bit rate possible over a quantum cryptographic link. We present an analysis of the relative merits of this method over the conventional arrangement.Comment: 11 pages, 5 figures, SPIE Free-Space Laser Communication and Laser Imaging II. To appear in the proceeding of SPIE Free-Space Laser Communication and Laser Imaging II, vol 482

Radiative and nonradiative decay rates in chromium-related centers in nanodiamonds

We address for the first time the measurement of nonradiative decay rates in Cr-related centers in nanodiamonds. Compared to our previous quantum efficiency measurement of Cr centers created in bulk diamond, separate measurements of radiative and nonradiative decay rates in grown nanodiamonds prove more challenging due to size dependence effects. We demonstrate in this Letter that, using defocused dipole imaging and collection efficiency calculation via finite-difference time-domain (FDTD), a quantum efficiency up to 0.9 can be inferred to Cr-related centers showing a 2-level system photon statistic

Hyperbolic Metamaterial Resonator-Antenna Scheme for Large, Broadband Emission Enhancement and Single Photon Collection

We model the broadband enhancement of single-photon emission from color centres in silicon carbide nanocrystals coupled to a planar hyperbolic metamaterial, HMM resonator. The design is based on positioning the single photon emitters within the HMM resonator, made of a dielectric index-matched with silicon-carbide material. The broadband response results from the successive resonance peaks of the lossy Fabry Perot structure modes arising within the high-index HMM cavity. To capture this broadband enhancement in the single photon emitters spontaneous emission, we placed a simple gold based cylindrical antenna on top of the HMM resonator. We analyzed the performance of this HMM coupled antenna structure in terms of the Purcell enhancement, quantum efficiency, collection efficiency and overall collected photon rate. For perpendicular dipole orientation relative to the interface, the HMM coupled antenna resonator leads to a significantly large spontaneous emission enhancement with Purcell factor of the order of 250 along with a very high average total collected photon rate, CPR of about 30 over a broad emission spectrum, 700 nm to 1000 nm. The peak CPR increases to about 80 at 900 nm, corresponding to the emission of silicon-carbide quantum emitters. This is a state of the art improvement considering the previous computational designs have reported a maximum average CPR of 25 across the nitrogen-vacancy centre emission spectrum, 600 nm to 800 nm with the highest value being about 40 at 650 nm

Photophysics of chromium-related diamond single-photon emitters

A detailed study of the photophysical properties of several chromium-related color centers produced within chemical vapor deposition diamond is presented. These emitters show narrow luminescence lines in the range of 740-770nm. Single-photon emission was verified with continuous and pulsed excitation with detected emission rates at saturation in the range of (2-3)×106 counts/s, while direct lifetime measurements reveal excited state lifetimes for the distinct centers ranging 1-14 ns. In addition, a number of quantum emitters demonstrate two-level behavior with no bunching present in the second-order correlation function. The three-level systems revealed typically photoluminescence lines with width half-maximum of ~4nm while the two-level emitters have full width half-maximum of ~10nm at room temperature. In addition, the quantum efficiency of the two-level system was measured to be four times higher than that of the three-level syste

Phonon-induced dephasing of chromium colour centres in diamond

We report on the coherence properties of single photons from chromium-based colour centres in diamond. We use field-correlation and spectral lineshape measurements to reveal the interplay between slow spectral wandering and fast dephasing mechanisms as a function of temperature. We show that the zero-phonon transition frequency and its linewidth follow a power-law dependence on temperature indicating that the dominant fast dephasing mechanisms for these centres are direct electron-phonon coupling and phonon-modulated Coulomb coupling to nearby impurities. Further, the observed reduction in the quantum yield for photon emission as a function of temperature is consistent with the opening of additional nonradiative channels through thermal activation to higher energy states predominantly and indicates a near-unity quantum efficiency at 4 K

Fluorescent emission in different silicon carbide polytypes

Silicon carbide (SiC) is a widely used material in several industrial applications such as high power electronics, light emitting diodes, and in research application such as photo-voltaic and quantum technologies. As nanoparticles it can be synthetised in many sizes and different polytypes from 200 nm down to 1 nm. In the form of quantum dots they are used as optical biomarkers, and their emission, occurring from the blue to the orange spectral region, is based on quantum confinement effect. In this work we report on emission in the red and near infrared in different SiC polytypes, specifically in 4H, 6H and 3C. In 4H SiC the red visible emission yielded non classical light attributed to an intrinsic defect, identified as a carbon-antisite vacancy pair. Similar spectral emission was observed in 3C SiC bulk and nanoparticles, also yielding very bright single photon emission. Emission in the far red has been observed in homogeneous hetero-structure in SiC tetrapods. © 2013 Copyright SPIE

Fractal Graphene Patch Antennas and the THz Communications Revolution

Fractal antennas have and are continuing to receive attention in regard to the futureof wireless communications. This is because of their wide- and multi-band capabilities, theopportunity of fractal geometries to drive multiple resonances, and, the ability to make smallerand lighter antennas with fewer components and radiative elements with higher gains. Smallscale (i.e. on the micro- and nano-scale) and ultra high frequency (in the Terahertz or THz range)fractal antennas composed of Graphene have the potential to enhance wireless communicationsat a data rate that is unprecedented, i.e.∼1012bits per second. A Fractal Graphene antennais a high-frequency tuneable antenna for radio communications in the THz spectrum, enablingunique applications such as wireless nano-networks. This is because (mono-layer) Grapheneis a one-atom-thick two-dimensional allotrope of Carbon with the highest known electricalconductivity that is currently unavailable in any other material, including metals such as Goldand Silver. Thus, combining the properties of Graphene with the self-affine characteristics ofa fractal at the micro- and nano-scale, provides the potential to revolutionise communications,at least in the near field (the order of a few metres) for low power systems. In this paper, weconsider the basic physics and some of the principle mathematical models associated with thedevelopment of this new disruptive technology in order to provide a guide to those engagedin current and future research, a fractal Graphene antenna being an example of an advancedmaterial for demanding applications. This includes some example simulations on the THz fieldpatterns generated by a fractal patch antenna composed of Graphene whose conductivity istaken to scale with the inverse of the frequency according to a ‘Drude’ model. The approachto generating THz sources using Graphene is also explored based on Infrared laser pumping toinduce a THz photo-current

Tracking emission rate dynamics of nitrogen vacancy centers in nanodiamonds

Spontaneous emission from crystal centers is in uenced by both the photonic local density of states and non- radiative processes. Here we monitor the spontaneous emission of single nitrogen vacancy (NV) centers as their host diamond is reduced in size from a large monolithic crystal to a nanocrystal by successive cycles of oxidation. The size reduction induces a quenching of the NV radiative emission. New non-radiative channels lead to a decrease of the uorescence intensity and the excited state lifetime. In one case we observe the onset of blinking which may provide a route to understand these additional non-radiative decay channels

Fractal Graphene Patch Antennas and the THz Communications Revolution

Fractal antennas have and are continuing to receive attention in regard to the futureof wireless communications. This is because of their wide- and multi-band capabilities, theopportunity of fractal geometries to drive multiple resonances, and, the ability to make smallerand lighter antennas with fewer components and radiative elements with higher gains. Smallscale (i.e. on the micro- and nano-scale) and ultra high frequency (in the Terahertz or THz range)fractal antennas composed of Graphene have the potential to enhance wireless communicationsat a data rate that is unprecedented, i.e.∼1012bits per second. A Fractal Graphene antennais a high-frequency tuneable antenna for radio communications in the THz spectrum, enablingunique applications such as wireless nano-networks. This is because (mono-layer) Grapheneis a one-atom-thick two-dimensional allotrope of Carbon with the highest known electricalconductivity that is currently unavailable in any other material, including metals such as Goldand Silver. Thus, combining the properties of Graphene with the self-affine characteristics ofa fractal at the micro- and nano-scale, provides the potential to revolutionise communications,at least in the near field (the order of a few metres) for low power systems. In this paper, weconsider the basic physics and some of the principle mathematical models associated with thedevelopment of this new disruptive technology in order to provide a guide to those engagedin current and future research, a fractal Graphene antenna being an example of an advancedmaterial for demanding applications. This includes some example simulations on the THz fieldpatterns generated by a fractal patch antenna composed of Graphene whose conductivity istaken to scale with the inverse of the frequency according to a ‘Drude’ model. The approachto generating THz sources using Graphene is also explored based on Infrared laser pumping toinduce a THz photo-current