Screening and engineering of colour centres in diamond

We present a high throughput and systematic method for the screening of colour centres in diamond with the aim of searching for and reproducibly creating new optical centres down to the single defect level, potentially of interest for a wide range of diamond-based quantum applications. The screening method presented here should, moreover, help to identify some already indexed defects among hundreds in diamond (Zaitsev 2001 Optical Properties of Diamond (Berlin: Springer)) but also some promising defects of a still unknown nature, such as the recently discovered ST1 centre (Lee et al 2013 Nat. Nanotechnol. 8 487; John et al 2017 New J. Phys. 19 053008). We use ion implantation in a systematic manner to implant several chemical elements. Ion implantation has the advantage of addressing single atoms inside the bulk with defined depth and high lateral resolution, but the disadvantage of producing intrinsic defects. The implanted samples are annealed in vacuum at different temperatures (between 600 degrees C and 1600 degrees C with 200 degrees C steps) and fully characterised at each step in order to follow the evolution of the defects: formation, dissociation, diffusion, re-formation and charge state, at the ensemble level and, if possible, at the single centre level. We review the unavoidable ion implantation defects (such as the GR1 and 3H centres), discuss ion channeling and thermal annealing and estimate the diffusion of the vacancies, nitrogen and hydrogen. We use different characterisation methods best suited for our study (from widefield fluorescence down to subdiffraction optical imaging of single centres) and discuss reproducibility issues due to diamond and defect inhomogeneities. Nitrogen is also implanted for reference, taking advantage of the considerable knowledge on NV centres as a versatile sensor in order to retrieve or deduce the conditions and local environment in which the different implanted chemical elements are embedded. We show here the preliminary promising results of a long-term study and focus on the elements O, Mg, Ca, F and P from which fluorescent centres were found.Peer reviewe

Coherent control of solid state nuclear spin nano-ensembles

Detecting and controlling nuclear spin nano-ensembles is crucial for the further development of nuclear magnetic resonance (NMR) spectroscopy and for the emerging solid state quantum technology. Here we present the fabrication of a $\approx$ 1 nanometre thick diamond layer consisting of $^{13}$C nuclear spins doped with Nitrogen-Vacancy centres (NV) embedded in a spin-free $^{12}$C crystal matrix. A single NV in the vicinity of the layer is used for polarization of the $^{13}$C spins and the readout of their magnetization. We demonstrate a method for coherent control of few tens of nuclear spins by using radio frequency pulses and show the basic coherent control experiments - Rabi oscillations, Ramsey spectroscopy and Hahn echo, though any NMR pulse sequence can be implemented. The results shown present a first steps towards the realization of a nuclear spin based quantum simulator

Strukturierte NV-Qubits durch hochaufgelöste räumlich-selektive Einzelionenimplantation

Hochaufgelöste räumlich-selektive Einzelionenimplantation ist eine Schlüsseltechnologie um Festkörper-Qubits herzustellen. Der in dieser Arbeit verwendete Nanoimplanter benutzt zur Kollimation eines niederenergetischen Ionenstrahls auf Nanometerebene eine Rasterkraftmikroskop-(AFM-)Spitze, welche mit einer Nanoapertur ausgestattet ist. Diese Technik wurde bereits für verschiedene Quantenanwendungen genutzt. In dieser Arbeit wird sie auf die Erzeugung strukturierter Stickstoff-Fehlstellen-(NV-)Zentren weiterentwickelt und optimiert. Dies umfasst unter anderem die Installation eines neuen AFM-Systems, welches den Aufbau mit zwei nützlichen Funktionen aufrüstet: die In-situ-Aperturvermessung und die Untersuchung von Ionen-sensitiven Fotolacken. Weiter werden die zwei wichtigsten limitierenden Faktoren der räumlichen Auflösung durch Simulationen und Experimente detailliert untersucht. Die Ergebnisse geben Aufschluss über optimale Nanoaperturen und Implantationsbedingungen. Streueffekte an der AFM-Spitze und Gitterführungen in Diamant können dadurch maßgeblich reduziert werden. Weiter werden NV-limitierende Effekte durch mehrere Ausheizschritte sowie Ionen- und Elektronenbestrahlungen untersucht. Zuletzt werden erstmals diamantbasierte Ionendetektoren hergestellt, welche mit Kapazität- und Strom-Spannungs-Messungen, durch Röntgenbestrahlung und Ionenstrahl-induzierter Ladung (IBIC) charakterisiert werden. Die Ergebnisse zeigen, dass die angefertigten Detektoren die Bedingungen für eine deterministische Implantation erfüllen, so dass dieses Prinzip zukünftig in den Nanoimplanter integriert werden kann.High-resolution spatial-selective single ion implantation is a key technology to produce solid state qubits. The nanoimplanter used in this work collimates a low-energy ion beam at the nanometer level using an atomic force microscope (AFM) tip, which is provided with a nanoaperture. This technique has already been used for various quantum applications. In this thesis it is further developed and optimized for the generation of structured nitrogen vacancy (NV) centers. This includes the installation of a new AFM system, which upgrades the setup with two useful functions: in-situ aperture measurement and the investigation of ion sensitive photoresists. Furthermore, the two most significant limiting factors of spatial resolution are studied in detail by simulations and experiments. The results indicate optimized nanoapertures and implantation conditions. Scattering effects at the AFM tip and ion channeling in diamond can be significantly reduced. Moreover, NV-limiting effects are investigated by several heating steps as well as ion and electron irradiations. Finally, novel diamond based ion detectors are manufactured, that are characterized by capacitance and current-voltage measurements, by X-ray irradiation and ion beam induced charge (IBIC). The results show these detectors fulfill the conditions for a deterministic implantation, so that this concept can be integrated into the nanoimplanter in the future

Strukturierte NV-Qubits durch hochaufgelöste räumlich-selektive Einzelionenimplantation

Hochaufgelöste räumlich-selektive Einzelionenimplantation ist eine Schlüsseltechnologie um Festkörper-Qubits herzustellen. Der in dieser Arbeit verwendete Nanoimplanter benutzt zur Kollimation eines niederenergetischen Ionenstrahls auf Nanometerebene eine Rasterkraftmikroskop-(AFM-)Spitze, welche mit einer Nanoapertur ausgestattet ist. Diese Technik wurde bereits für verschiedene Quantenanwendungen genutzt. In dieser Arbeit wird sie auf die Erzeugung strukturierter Stickstoff-Fehlstellen-(NV-)Zentren weiterentwickelt und optimiert. Dies umfasst unter anderem die Installation eines neuen AFM-Systems, welches den Aufbau mit zwei nützlichen Funktionen aufrüstet: die In-situ-Aperturvermessung und die Untersuchung von Ionen-sensitiven Fotolacken. Weiter werden die zwei wichtigsten limitierenden Faktoren der räumlichen Auflösung durch Simulationen und Experimente detailliert untersucht. Die Ergebnisse geben Aufschluss über optimale Nanoaperturen und Implantationsbedingungen. Streueffekte an der AFM-Spitze und Gitterführungen in Diamant können dadurch maßgeblich reduziert werden. Weiter werden NV-limitierende Effekte durch mehrere Ausheizschritte sowie Ionen- und Elektronenbestrahlungen untersucht. Zuletzt werden erstmals diamantbasierte Ionendetektoren hergestellt, welche mit Kapazität- und Strom-Spannungs-Messungen, durch Röntgenbestrahlung und Ionenstrahl-induzierter Ladung (IBIC) charakterisiert werden. Die Ergebnisse zeigen, dass die angefertigten Detektoren die Bedingungen für eine deterministische Implantation erfüllen, so dass dieses Prinzip zukünftig in den Nanoimplanter integriert werden kann.High-resolution spatial-selective single ion implantation is a key technology to produce solid state qubits. The nanoimplanter used in this work collimates a low-energy ion beam at the nanometer level using an atomic force microscope (AFM) tip, which is provided with a nanoaperture. This technique has already been used for various quantum applications. In this thesis it is further developed and optimized for the generation of structured nitrogen vacancy (NV) centers. This includes the installation of a new AFM system, which upgrades the setup with two useful functions: in-situ aperture measurement and the investigation of ion sensitive photoresists. Furthermore, the two most significant limiting factors of spatial resolution are studied in detail by simulations and experiments. The results indicate optimized nanoapertures and implantation conditions. Scattering effects at the AFM tip and ion channeling in diamond can be significantly reduced. Moreover, NV-limiting effects are investigated by several heating steps as well as ion and electron irradiations. Finally, novel diamond based ion detectors are manufactured, that are characterized by capacitance and current-voltage measurements, by X-ray irradiation and ion beam induced charge (IBIC). The results show these detectors fulfill the conditions for a deterministic implantation, so that this concept can be integrated into the nanoimplanter in the future

Production of bulk NV centre arrays by shallow implantation and diamond CVD overgrowth

The nanometer-scale engineering of single nitrogen-vacancy (NV) centres in diamond can be obtained by low-energy (keV) nitrogen implantation with limited straggling. However, shallow NV centres (a few nanometres deep) generally have inferior overall properties than deeply implanted or deep native NV centres, due to the surface proximity. It has already been shown that the spin coherence time of shallow NVs is improved by overgrowth of a thin diamond layer. However the influence of the overgrowth on the survival, the optical properties and the charge state of the centres has not been studied in detail. In this article, we have overgrown three diamond samples (containing NV centres implanted at different depths) using different procedures. We show the successful overgrowth of a pattern of very shallow (2 nm) implanted NV centres using an optimised overgrowth process. Furthermore, the charge state of ensembles and single NV centres was found to be shifted from NV0 to NV− and stabilised in the negative charge state after overgrowth. The combination of low-energy high-resolution ion implantation and high-purity chemical vapour deposition (CVD) overgrowth procedures opens the way towards the fabrication of scalable and efficient quantum devices based on single defects in diamond

Passive charge state control of nitrogen-vacancy centres in diamond using phosphorous and boron doping

International audienceThe control and stabilisation of the charge state of nitrogen‐vacancy centres in diamond is an important issue for the achievement of reliable processing of spin‐based quantum information. The effect of phosphorous and boron doping of diamond on the charge state of nitrogen‐vacancy (NV) centres is shown here. Ensembles of NV centres are produced at a depth of 60 nm in ultrapure diamond by implantation of nitrogen ions. Overlapping with the NV ensembles, donor and acceptor doped regions of different doping levels are prepared by ion implantation of phosphorus and boron followed by annealing in vacuum at 1500 °C. We show how the charge state of NV centres is controlled by the presence of phosphorous or boron atoms in their neighbourhood. For the lowest doping level, spectral measurements on the ensemble of NV centres reveal a higher amount of NV0 in the case of boron and a higher amount of NV− in the case of phosphorus, as compared with undoped regions. This behaviour is strengthened when the doping level is increased. Interestingly, the charge state control of native silicon‐vacancy centres is also evidenced. Finally, we discuss the role of the surface termination of diamond on the average charge state of the NV ensemble (still dominant even at a depth of 60 nm) and confirm that the surface 2D‐hole‐gas (H‐termination) can be compensated by nitrogen itself