Defects in diamond have evolved as unique object for their potential application for Optical imaging and Nano-photonics. High pressure high temperature (HPHT) grown type-Ib diamond particles were milled down to the size of ~ 80 nm and purified to remove iron & graphitic carbon impurities and irradiated with 35 KeV He+ ions to create vacancies in the diamond lattice. Vacancies diffuse close to substitutional nitrogen impurities of nano-diamond particles upon thermal treatment. Characteristic sharp emission of NV centers were observed at 575.5 nm and 637.9 nm corresponding to NV° and NV− charged states in addition to a broad emission in the range 550-750 nm. Structural and photo-physical behavior of these fluorescent diamonds was found to depend on the method of purification adopted. Samples purified through acid reflux were found suitable for bio-imaging applications while, sample purified through air oxidation shows properties desirable for Nano-photonic applications. Photon-correlation measurements of emission from individual diamond nanoparticles using Hanbury Brown and Twiss interferometer (HBT) shows anti-bunching curve with g2(t)= 0 confirming their suitability as single photon source. Such sources of indistinguishable photons are highly desirable for quantum computation and quantum optics applications.
Defects in diamond have evolved as unique object for their potential application for Optical imaging and Nano-photonics. High pressure high temperature (HPHT) grown type-Ib diamond particles were milled down to the size of ~ 80 nm and purified to remove iron & graphitic carbon impurities and irradiated with 35 KeV He+ ions to create vacancies in the diamond lattice. Vacancies diffuse close to substitutional nitrogen impurities of nano-diamond particles upon thermal treatment. Characteristic sharp emission of NV centers were observed at 575.5 nm and 637.9 nm corresponding to NV° and NV− charged states in addition to a broad emission in the range 550-750 nm. Structural and photo-physical behavior of these fluorescent diamonds was found to depend on the method of purification adopted. Samples purified through acid reflux were found suitable for bio-imaging applications while, sample purified through air oxidation shows properties desirable for Nano-photonic applications. Photon-correlation measurements of emission from individual diamond nanoparticles using Hanbury Brown and Twiss interferometer (HBT) shows anti-bunching curve with g2(t)= 0 confirming their suitability as single photon source. Such sources of indistinguishable photons are highly desirable for quantum computation and quantum optics applications.
For applications in Quantum Information and Quantum Key Distribution an on-demand source of single photons is desirable because absolute security is of utmost importance. Photons are quantum systems; hence encoding information onto them offers a secure alternative to classical cryptography as a measurement cannot be performed on photons without altering their properties. The Nitrogen Vacancy (NV) centre in diamond is a good source of such photons. It is photo-stable and its location in diamond offers robustness. It has zero phonon line at 637 nm and its relative short luminescence life-time of about 12 ns makes it suitable for generating single photons. This thesis covers two aspects: Firstly the characterization of defects in diamonds and subsequent selection of diamonds suitable for use in the single photon setup and secondly, the development of the experimental setup for single photon generation. This thesis sets out to describe the development of a laboratory based single photon source using the NV centre in diamond. For this purpose a suite of diamond samples were selected and subjected to various spectroscopic tests in order to characterize and classify the samples, especially the presence of the NV centres and their concentrations. The characterization of the defects was done through the use of the following spectroscopic techniques: UltravioletVisible-Near infrared spectroscopy, Infrared spectroscopy, Electron Spin Resonance and Photoluminescence. These techniques enabled us to understand the types and origins of crystal defects that were present in the diamond samples used in this study and to use this to select diamonds that are most suitable for use in generation of single photons. The experimental setup for single photon generation using the NV centre is based on a confocal microscope arrangement. Single NV centres were identified by measuring the second order autocorrelation function of the fluorescence light emitted by the sample when illuminated with a laser. This measurement was done using a Hanbury-Brown Twiss (HBT) interferometer.
Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.
The development of reliable devices to generate single photons is crucial for applications in quantum cryptography, as well as for fundamental quantum optics experiments. Due to their extremely high photostability at room temperature, optically active defects in solids, the so called color centers, are among the most promising candidates. Single NV (nitrogen-vacancy) centers in diamond have been demonstrated to be able to generate single photons and have already shown advantages compared to attenuated laser pulses in a quantum cryptography experiment. The nitrogen-vacancy center (NV center) in diamond consists of a substitutional nitrogen atom and an adjacent vacancy. This complex exhibits an optical transition with a fluorescence lifetime of 11.6 ns. The room temperature spectrum of the NV center consists of the zero-phonon line at 637 nm and broad phononic sidebands with a FWHM of more than 100 nm. Due to the existence of a shelving level the efficiency of the NV center as a single photon source is limited. Additionally, the high diffraction index of bulk diamond restricts the efficiency to collect the fluorescence light.
Quantum communication and quantum metrology established a demand for an accessible solid state systems which can generate a stream of single photons on demand [1]. Although single photon emission has been demonstrated from quantum dots (QD)[1,2], single molecules [3] and nanowires [4], their practical operation is limited by the temperature or photostability. Diamond crystals, however, are the most promising platform for generation of robust, photo-stable, single photons at room temperature [5,6]. Nevertheless, out of more than 500 existing optical centers in diamond only three known centers demonstrated a clear single photon emission: the nitrogen-vacancy complex [6,7], the silicon-vacancy complex [8] and the nickel-nitrogen complex [9,10]. Recent progress in materials science and fabrication techniques of diamond color centers unveiled novel quantum emitters with photo-physical properties surpassing the current mainstream [11,12,13]. Consequently, the versatility of the diamond lattice to host various impurities which give luminescence signals lead to a dramatic discovery of ultra bright single photon emitters operating in the MHz regime [14]. These new centers, comparable with QD in terms of brightness [1], but have the tremendous advantage of their room temperature operation and photo-stability. Furthermore, it opened a new avenue to investigate essentially an unknown group of single photon emitters. A brief description of the fabrication methods and a detailed quantum optical characterization of this class of diamond emitters is the subject of this presentation. In particular we will present the photo-physical properties of a novel family of single photon emitters, most likely originated from Cr impurities within the chemical vapor deposition grown nano-diamond crystals. We concentrate on the typical emission lines in the range of 740 - 790 nm, which exhibit single photon emission with count rate in the range of 0.8-3.2 106 counts/s at the limit of infinite optical excitation power, and life time as short as 1 ns. Even more, some of the emitters exhibit a photon statistics without any photon bunching, indicating a two-level system with unitary quantum efficiency. We will also show preliminary results of a resonant excitation at 4 K. We will highlight future directions to optimize these sources and avenues to investigate the fundamental properties of these centers.
The nanodiamond technology has developed the first packaged, single-photon source that operates at room temperature and in well-lit environments, where an ideal single-photon source produces one photon per pulse. These sources are key components for building quantum information systems that can implement quantum-key distribution (QKD) for ultrasecure communications. The optically active color centers in diamond have been found to exhibit attractive optical properties through the nitrogen-vacancy (N-V) center emission ranging 600 to 750 nm, and that have realized the practical sources of single-photon emission. Photo statistics has to be determined to measure the performance of a single-photon source, which can be measured by the autocorrelation function g2 (0) using Hanbury-Brown and Twiss interferometer. The results showed that the SPS 1.01 demonstrates stable single-photon performance without requirement of recalibration.
This work investigates the emission properties of single color centers in natural diamond nanoparticles for potential use as single photon sources and photostable biomarkers. Two emitters, H3 and H4, were identified by their sharp zero-phonon lines at 503 nm and 496 nm, respectively, in the photoluminescence spectra. Using a modified Hanbury Brown and Twiss setup, we observed complete photon antibunching for the H3 center. No fluorescence blinking was detected for a single H3 emitter on the ms timescale, indicating weak coupling between the electronic transition A11↔B11 and adjacent metastable states of this nitrogen-vacancy-nitrogen point defect.