This thesis is focused on the production and characterization of diamond films and diamond nanoparticles containing custom colour centres. These defects intentionally created into the diamond lattice are promising candidates for single photon sources, and are becoming more important for quantum information technologies as photons can carry quantum information over long distances. With outstanding properties such as up to 80% of the photons emitted into the zero phonon line (ZPL), single photon count rates up to several Mcps under continuous excitation and a narrow ZPL at room temperature, the SiV centre has recently attracted more attention. Although different approaches for the creation of colour centres have been reported, this thesis details the creation of SiV centres by chemical vapour deposition. Colour centres are created through the incorporation of impurities during diamond growth. While Si doping can easily be achieved due to plasma etching of Si substrates or the incorporation of a Si solid source inside the reactor vacuum chamber, controlling the exact amount of Si present in the gas phase or effectively incorporated is still a handicap. Chapters five and six show comprehensive studies performed towards the creation of diamond nanoparticles with single emitters. Control over the Si content within the gas phase is achieved using silane as gas source. The subsequent milling of the diamond films hosting the SiV centres and their inclusion into a stable solution, will facilitate SiV coupling and incorporation into cavities or emission-enhancer devices.
This thesis is focused on the production and characterization of diamond films and diamond nanoparticles containing custom colour centres. These defects intentionally created into the diamond lattice are promising candidates for single photon sources, and are becoming more important for quantum information technologies as photons can carry quantum information over long distances. With outstanding properties such as up to 80% of the photons emitted into the zero phonon line (ZPL), single photon count rates up to several Mcps under continuous excitation and a narrow ZPL at room temperature, the SiV centre has recently attracted more attention. Although different approaches for the creation of colour centres have been reported, this thesis details the creation of SiV centres by chemical vapour deposition. Colour centres are created through the incorporation of impurities during diamond growth. While Si doping can easily be achieved due to plasma etching of Si substrates or the incorporation of a Si solid source inside the reactor vacuum chamber, controlling the exact amount of Si present in the gas phase or effectively incorporated is still a handicap. Chapters five and six show comprehensive studies performed towards the creation of diamond nanoparticles with single emitters. Control over the Si content within the gas phase is achieved using silane as gas source. The subsequent milling of the diamond films hosting the SiV centres and their inclusion into a stable solution, will facilitate SiV coupling and incorporation into cavities or emission-enhancer devices.
We introduce a process for the fabrication of high-quality, spatially isolated nano-diamonds on iridium via microwave-plasma-assisted chemical vapour deposition (CVD) growth. We perform spectroscopy of single silicon-vacancy (SiV) centres produced during the growth of the nano-diamonds. The colour centres exhibit extraordinary narrow zero-phonon-lines down to 0.7 nm at room temperature. Single photon count rates up to 4.8 Mcps at saturation make these SiV centres the brightest diamond-based single photon sources to date. We measure for the first time the fine structure of a single SiV centre, thus confirming the atomic composition of the investigated colour centres.
Progress in controlling diamond synthesis has made it possible to produce very pure crystals and to incorporate and control atomic impurities and carbon vacancies in the crystal lattice. The appropriate impurity-vacancy combinations can give rise to special defects known as color centers, such as the nitrogen-vacancy (NV) or the silicon-vacancy (SiV), which exhibit exceptional quantum properties with spins that are optically addressable. The use of diamond containing color centers has paved the way for the development of innovative quantum technologies, such as very high-resolution magnetometry and quantum information processing. Nevertheless, the development of quantum sensors at the nanometric scale remains one of the most interesting challenges. In this context, the development of a reliable nanoparticle synthesis technique that allows the desired defects to be incorporated and their quantum optical properties to be modulated is crucial. In this seminar, an efficient and recent method to produce diamond nanoparticles containing NV, SiV and germanium-vacancy (GeV) centers is proposed through direct plasma assisted chemical vapour deposition (CVD) growth. This technique allows good control of both nanoparticle growth processes and color centers formation. The optimization of the CVD nanodiamond growth process is presented, showing the impact of different plasma parameters and gas phasecomposition on nanoparticle crystallinity, size and shape. Morphological characterizations reveal the production of small (around 100 nm) and well faceted nanodiamond particles. In addition, the SiV and GeV color centers incorporation can be tuned within this material by varying the gas phase composition which emphasizes the high flexibility of the CVD growth technique. Finally, the quantum properties of the incorporated color centers have been successfully investigated under extreme pressure conditions (up to ~ 180 GPa) showing a monotonic blue shift of their optical zero-phonon line. Since their luminescence remains stable, SiV and GeV centers emerge as high-pressure nanosensors.
Fluorescent emitters in diamond are considered to be a valuable resource for fields such as quantum communication, quantum photonics, and biological imaging. In this paper, we report a wide range of narrow bandwidth ( ~ 1.5 nm) spectral emission lines arising from different color centers at room temperature. The defects were created by chemical vapor deposition of thin diamond films grown on silica substrates seeded with nanoparticles of diamond and nickel. These fluorescent lines also possess single or few centers photon statistics. We correlate the zero-phonon lines, observed using confocal microscopy, with previously identified nickel-related centers which have been observed in high-pressure high-temperature diamond, with a Si/Ni complex and silicon vacancy defects. We compare our findings with recent results demonstrating single-photon emission in diamond associated with nickel-related centers to clarify and summarize previous studies concerning this specific dopant. The great variety of emission lines observed in the synthesized material, mainly associated with nickel-related centers, could be an important resource for applications relying on the presence of several emitters of single photons in the same sample. Moreover, the possibility of mass production of these centers in nanodiamonds in colloidal suspension may provide an important resource for biomarking and microscopy.
A huge variety of optical colour centres can be found in diamond, emitting in its whole wide transparency range. Although several of these centres have been demonstrated as single-photon emitters, none of them meets all of the requirements of an ideal single-photon source. In this view, we discuss the properties of prominent optical centres, such as the nitrogen vacancy, the silicon vacancy or the so-called NE8 centre, as well as recently found centres ascribed to defects containing Ni, Si, Cr and Xe. Besides suitable intrinsic properties, it is necessary for practical applications that optical centres can be created artificially on demand. Of all known methods, only ion implantation allows for the most controlled creation of such defect centres. In this paper, we discuss how nanoscalability, that is, the nanometre placement and the deterministic creation of optical centres, can, could or cannot be achieved by the available ion implantation techniques. A fine analysis of individual optical centres is now possible, thanks to the recently developed subdiffraction optical microscopy methods.
The work in this thesis is embedded in the framework of quantum metrology and explores quantum effects in solid state emitters and optical sensing. Specifically, the thesis comprises studies on silicon vacancy centres in nanodiamonds, phase measurements and cavity optomechanics utilising optical squeezed states, and a theoretical study on quantum amplifiers. Due to its similarity to single atoms, colour centres in diamond are ideal objects for exploring and exploiting quantum effects, because they are comparably easy to produce, probe and maintain. While nitrogen vacancy centres are the most renowned colour centres, we studied the silicon vacancy (SiV−) centre. In bulk diamond it features strong zero-phonon-line emission and, at cryogenic temperatures, a linewidth of hundreds of MHz, but it displays a weak spin coherence in the order of ns. To suppress the relaxation process which limits the coherence time, we utilised SiV− centres in nanodiamond. By means of confocal microscopy and resonant excitation at cryogenic temperatures, we measured linewidths in recently developed nanodiamond which were an order of magnitude smaller compared to previous studies on SiV− nanodiamonds. Furthermore, we identified spectral diffusion as the main hindrance in extending spin coherence times. Overcoming this issue will provide a promising candidate as an emitter for quantum information. Next, the question of how squeezed states of light can improve optical sensing was addressed. For this purpose, a squeezed light source was designed and built from scratch, which achieved a noise suppression of −8 dB at an optical pump power of 40mW. The generated squeezed light was first used to demonstrate how Gaussian states and detection can beat the shot noise limit and Rayleigh criterion in phase measurements simultaneously. Compared to quantum phase measurements based on single photon states, this approach is inherently deterministic. In addition, the applied homodyne detection enables close-to-unity detection efficiencies and thereby outperforms single photon state strategies which rely on comparably inefficient or demanding detection techniques. A second experiment combined squeezed light and feedback control to cool an optomechanical system. This proof-of-principle study is the first reported squeezing enhanced optomechanical cooling experiment. Despite losses of more than 50% (a resulting noise suppression of −2 dB), the mechanical resonator was cooled from room temperature to 130K. This represents a 12% improvement compared to the use of a coherent state protocol. Finally, we theoretically investigated the fundamental properties of quantum amplifiers. Such devices can be used in information and sensing technology to amplify signals to overcome e.g. technical detection limitations. Amplified communication channels were characterised by applying the measure of mutual information I, as it offers strict bounds on the maximum achievable performance, which enabled a fair comparison between different applications scenarios. As a result, we identified two peculiar configurations: A configuration where amplification does not affect I, and a configuration where quantum correlations do not always lead to an enhanced I.
Quantum photonics platforms hold considerable potential for the rapid development and deployment of quantum information and computing technologies. Color centers in diamond, such as silicon-vacancy (SiV) centers, have numerous attractive properties for such applications, including high brightness, narrow zero-phonon line (ZPL) linewidths at 737nm, and stable single-photon emission insusceptible to electric field fluctuations [1]. Color centers in photonic diamond nanostructures have been demonstrated recently [2], but their fabrication is challenging and requires sophisticated techniques and equipment.