We present a high throughput and systematic method for screening of colour centres in diamond. We aim at the search and reproducible creation of new optical centres, down to the single level, potentially of interest for the wide range of diamond-based quantum applications. The screening method presented here should moreover help identifying some already indexed defects among hundreds in diamond [1] but also some promising defects of still unknown nature, such as the recently discovered ST1 centre [2,3]. We use ion implantation in a systematic manner to implant several chemical elements. Ion implantation has the advantage to address single atoms inside the bulk with defined depth and high lateral resolution, but the disadvantage of defect production such as vacancies. The sample is annealed in vacuum at different temperatures (between 600°C and 1600°C with 200°C steps) and fully characterised at each step in order to follow the evolution of the defects: formation, dissociation, diffusion, reformation and charge state, at the ensemble level and, if possible, at the single centre level. We review the unavoidable ion implantation defects (with the example of the GR1 and 3H centres), discuss ion channeling and thermal annealing and estimate the diffusion of vacancies, nitrogen and hydrogen. We use different characterisation methods best suited for our study (from widefield fluorescence down to sub-diffraction optical imaging of single centres) and discuss reproducibility issues due to diamond and defect inhomogeneities. Nitrogen is also implanted as a reference, taking advantage of the large 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.

Erbium doped low symmetry Y2SiO5 crystals attract a lot of attention in perspective of quantum information applications. However, only doping of the samples during growth is available up to now, which yields a quite homogeneous doping density. In the present work, we deposit Er 3+ -ions by the focused ion beam technique at Yttrium sites with several fluences in one sample. With a photoluminescence study of these locally doped Er 3+ :Y2SiO5 crystals, we are able to evaluate the efficiency of the implantation process and develop it for the highest efficiency possible. We observe the dependence of the ion activation after the post-implantation annealing on the fluence value.Keywords: rare earth, concentration dependance, annealing, activation Rare-earth (RE) doped materials are in the focus of interest for modern physics due to their specific properties, such as the presence of high coherence transitions inside the 4f shell and long optical and microwave coherence times. The rapid progress with the REs has been expressed in number of dramatic achievements: the demonstration of long living optical holes in europium-doped yttrium silicate Among other REs, the erbium doped crystals are outstanding due to the presence of optical transitions inside the telecom C-band at the wavelength of around 1530-1565 nm. Moreover, the Er 3+ :Y 2 SiO 5 (Er:YSO) crystal possesses the longest measured optical coherence time of about 6 ms among all other solid state systems [5,6]. On the hand of the magnetic properties, erbium ions possess a very large magnetic moment of 7µ B . Electron Spin Resonance (ESR) studies revealed that the T 2 coherence time can reach the huge value of 100 ms [7]. The development of high fidelity and long-life quantum memory will boost the implementation of long distance quantum communication protocols in already existing fiber optical networks [8,9].So far, all of these research deals with the doped-asgrown Er 3+ :Y 2 SiO 5 crystals. However, implementation of Focused Ion Beam (FIB) technique for doping of the YSO crystals looks as a rather handy possibility to perform different types of quantum elements and quantum gates on one chip without mask-and alignment processes. It is especially advantageous in circuit Quantum Electrodynamics (QED) implementations, where one wants to separate the memory elements from the computation elements on the chip. FIB possesses a wide range of flexible parameters, which allow to perform implantation with controlled fluences at different depths at selected positions. Proper adjustment of these implantation parameters, as well as annealing procedure, makes it possible to implant the Erbium ions in the Yttrium sites and recover the distorted site-symmetry. In this letter, we discuss the results of FIB implantation of the Y 2 SiO 5 crystals with the Erbium ions.The implantation was performed into a nominally undoped YSO crystal, supplied by the Scientific Materials Inc. Doped as-grown Er:YSO 0.005 % crystal was taken as reference. All the crystals have the same orientation of opt...

The field of quantum information processing offers secure communication protected by the laws of quantum mechanics and is on the verge of finding wider application for the information transfer of sensitive data. To improve cost-efficiency, extensive research is being carried out on the various components required for high data throughput using quantum key distribution (QKD). Aiming for an application-oriented solution, we report the realization of a multichannel QKD system for plug-and-play high-bandwidth secure communication at telecom wavelengths. We designed a rack-sized multichannel superconducting nanowire single photon detector (SNSPD) system, as well as a highly parallelized time-correlated single photon counting (TCSPC) unit. Our system is linked to an FPGA-controlled QKD evaluation setup for continuous operation, allowing us to achieve high secret key rates using a coherent-one-way protocol.

The discrete-variables (DV) time-frequency (TF) quantum key distribution (QKD) protocol is a BB84-like protocol, which utilizes time and frequency as complementary bases. As orthogonal modulations, pulse position modulation (PPM) and frequency shift keying (FSK) are capable of transmitting several bits per symbol, i.e., per photon. However, unlike traditional binary polarization shift keying, PPM and FSK do not allow perfectly complementary bases. So information is not completely deleted when the wrong-basis filters are applied. Since a general security proof does not yet exist, we numerically assess DV-TF-QKD. We show that the secret key rate increases with a higher number of symbols per basis. Further we identify the optimal pulse relations in the two bases in terms of key rate and resistance against eavesdropping attacks

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