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Quantum information processing offers new protocols and functionalities in the field of communications by providing an absolute security guaranteed by the quantum physics laws as well as in the field of quantum computing, with the perspective to drastically speed up massively parallel computations. The second quantum revolution is now about to take place with theoretical concepts being brought into concrete applications thanks to integrated technological solutions. Photons are an excellent physical implementation of quantum bits for these two applications. Photonic quantum information processing requires three key functionalities: a source of single photons, a reconfigurable circuits for their manipulation and a single photon detector. The objective of this PhD work is to design, fabricate and characterize superconducting single photon detectors integrated on silicon photonic circuits, with very high efficiency above 95%, a large spectral operating range at telecom wavelength and the ability to resolve the number of received photons. This PhD will take place at CEA, in collaboration between INAC and LETI institutes to benefit from their complementary expertise. This PhD work will be conducted in parallel with developments of single photon sources and will bring an essential building block for the integration of complex circuits able to generate, manipulate and detect tens of photonic qubits for secured communications and quantum computing.; Le traitement quantique de l'information apporte de nouveaux protocoles et de nouvelles fonctionnalités dans le domaine des communications en garantissant une sécurité absolue du transfert de l'information et dans le domaine du calcul, avec la perspective d'effectuer très rapidement des calculs massivement parallèles. La deuxième révolution quantique est amorcée car ces concepts sortent des laboratoires théoriques pour devenir des applications industrielles concrètes grâce aux technologies intégrées. Les photons constituent un excellent support de l'information quantique pour ces deux applications. Trois composants-clés sont nécessaires : une source de photons uniques, un circuit passif reconfigurable permettant de les manipuler et un détecteur de photons uniques. L'objectif de cette thèse est de concevoir, fabriquer et caractériser des détecteurs de photons uniques supraconducteurs intégrés sur silicium, présentant une grande largeur spectrale autour de la longueur d'onde telecom de 1.55 µm, avec une absorption supérieure à 95% et la possibilité de résoudre le nombre de photons reçus. Cette thèse sera effectuée en collaboration entre l'INAC et le département d'optique et photonique du Leti, permettant d'allier les expertises et savoir-faire complémentaires des deux laboratoires. Cette thèse sera effectuée en parallèle de développements de sources de photons uniques intégrées sur silicium et apportera une brique essentielle pour l'intégration sur la même puce d'un circuit complet permettant de générer, manipuler et détecter des photons uniques pour les communications sécurisées et le calcul quantique.

Recently it has been demonstrated that the pair-exchange coupling of quasi-one-dimensional (Q1D) bands with conventional higher-dimensional bands in one multiband superconducting material can result in the formation of robust aggregate pair condensate. In particular, it has been found that the Q1D thermal pair fluctuations are suppressed in the presence of deep conventional band(s), where the Fermi level is much larger than the characteristic cut-off energy. Here we report that impact of the Q1D fluctuations is significantly weakened even in the presence of nearly shallow higher-dimensional band(s), which shed new light on robust superconducting state observed in emerging chain-like-structured superconducting materials A_2Cr_3As_3 (A = K, Rb, Cs)., Comment: 12 pages, 3 figures

Bi-2212 is one of the most hopeful superconducting material by virtue of its excellent irreversible field and isotropic electromagnetic characteristic. We developed Bi-2212 insert coil for the sake of testing the uniform performance of the round wire (RW). Some important explorations were made including the preliminary test of coil insulation, sealing and heat treatment. In the end, the insert coil achieved a critical performance of 130 A at 12 T and 4.2 K. The experiment results indicated that Bi-2212 RW had met the future application.

A new type of graphene-based quantum Hall standards is tested for electrical quantum metrology applications at alternating current (ac) and direct current (dc). The devices are functionalized with Cr(CO)(3) to control the charge carrier density and have branched Hall contacts based on NbTiN superconducting material. The work is an in-depth study about the characteristic capacitances and related losses in the ac regime of the devices and about their performance during precision resistance measurements at dc and ac.

Cluster formation is a focus of interdisciplinary research in both chemistry and physics. Here we discuss the exotic example of this phenomenon in the vortex matter of a thin superconductor. In superconducting films, the clustering takes place because of particular properties of the vortex interactions in the crossover or intertype regime between superconductivity types I and II. These interactions are controlled by the two parameters that are responsible for the crossover, Ginzburg-Landau parameter κ, which specifies the superconducting material of the film, and film thickness d, which controls effects due to stray magnetic fields outside the sample. We demonstrate that their competition gives rise to a complex spatial dependence of the interaction potential between vortices, favoring the formation of chainlike vortex clusters.

The high temperature phase of SrPd2Sb2 polymorphs exhibits bulk superconductivity below 0.6 K. The electron phonon coupling constant and density of states are two major factors that control the superconductivity in this intermetallic compound. Here we report the detailed physical properties including structural, elastic, electronic, and optical properties of this superconducting phase by using DFT-based computational method. The calculated lattice parameters and density of states show good agreement with the experimental data. This intermetallic is ductile and comparatively soft with respect to other members of this family. This compound exhibits metallic conductivity mostly emerging from Pd and Sb atoms that is different from other similar type of superconducting materials. The strong covalent interactions in Sb-Sb and Sb-Pd bonds define the electronic characteristics of this superconducting material. The optical properties of this superconductor are fairly comparable with other similar compounds in this family.

Railway transportation is of safety, convenience, economy, and environmental friendliness. However, with energy issues becoming increasingly important in this century, it is important to assess the situation in the transportation sector. When the superconducting cable is used as a feeder of the railway electrification system, the voltage drop can be significantly reduced. Therefore, the superconducting feeder has many effects, for example, the reduction transmission losses, the improvement of the regeneration factor, and the reduction of substations. We designed superconducting feeder and introduced to the Izuhakone Railway Sunzu line in Japan. After the system was checked from the aspect of cooling and current properties, the train running test was conducted. From the result of switching notch tests, it was found that the current flows continuously via the superconducting cable according to the notch operation. Furthermore, to inspect the influence of superconducting material, a large pulse current test was performed using the transmission equipment of a railway. It can be confirmed that superconductor can be used as railway feeder because the materials can cope with the current change peculiar to railway required for practical use.

The superconducting material BPSCCO-2212 with doping Pb = 0,2 has been synthesized by the wet mixing method. Calculation is caried out at 800 °C for 10 hours. While sintering is done at 825 °C, 830 °C, 835 °C and 840 °C for 20 hours. The synthesis result were characterized by XRD X-Ray Diffraction) and SEM (Scanning Electron Microscopy). The XRD spectrum analysis results that have been processed using celref, show that in general the samples produced have formed the BPSCCO-2212 phase (indicated the presence of Bi-2212 peaks) and have been oriented (indicated the existence of peaks with h = k = 0, l even number). For the calculation result obtanced the highest volume fraction value at 830 °C sintering temperature with a value FV = 66,97 % and the highest degree of orientation at 825 °C with a value of P = 76,54 %. The results of the SEM photo recorder generally show that the crystals formed are oriented.

Here, we report the successful synthesis of electron- (Ni) and hole- (K) doped bulk B a F e 2 A s 2 compounds by means of mechanical alloying (MA) process. The MA technique allows one to obtain amorphous phase B a F e 2 A s 2 with a homogeneous distribution of doping atoms at room temperature without continuous heating. We found the optimum time for high-energy milling is in the range between 1 and 1.5 h. Using pre-synthesised F e A s and N i A s precursors, we successfully obtained B a F e 2 − x N i x A s 2 and B a 1 − x K x F e 2 A s 2 superconducting bulk samples after short-range heat treatment. This method can be easily scaled according to industrial needs to provide high-quality bulk superconducting material for wires, trapped-field magnets and other applications.

We apply the Roeser–Huber formula to the (RE)Ba2Cu3O7−δ (REBCO with RE= rare earths) high-Tc superconducting material class to calculate the superconducting transition temperature, Tc, using the electronic configuration and the crystallographic data. In a former publication (H. P. Roeser et al., Acta Astronautica 2008, 62, 733–736), the basic idea was described and Tc was successfully calculated for the YBa2Cu3O7−δ compound with two oxygen doping levels δ= 0.04 and 0.45, but several open questions remained. One of the problems remaining was the determination of Tc for the δ= 0.45 sample, which can be explained regarding the various oxygen arrangements being possible within the copper-oxide plane. Having established this proper relation and using the various crystallographic data on the REBCO system available in the literature, we show that the Roeser–Huber equation is capable to calculate the Tc of the various REBCO compounds and the effects of strain and pressure on Tc, when preparing thin film samples. Furthermore, the characteristic length, x, determined for the REBCO systems sheds light on the size of the δTc-pinning sites being responsible for additional flux pinning and the peak effect.

The design of a high-quality mechanical oscillator made of a superconducting material, whose frequency is changed by an external magnetic field, has been proposed and tested.

Superconductivity up to 76 K has been achieved in Se substituted Tl-1212 phase, (Tl1−xSex)Sr2CaCu2O7. X-ray diffraction patterns showed the presence of Tl-1212 as the major phase in most samples. The highest volume fraction of Tl-1212 phase (88%) was observed in the x = 0.1 sample. The electrical resistance measurement showed the highest onset temperature, Tc−onset (76 K) for x = 0.2 and 0.4. AC susceptibility (χ = χ + iχ″) measurements showed the highest superconducting transition temperature Tcχ′ = 71 K for x = 0.4. The peak temperature, Tp of the imaginary part of the susceptibility, χ″ was also the highest for x = 0.4 sample (Tp = 69 K). The inter-grain critical current density at the peak temperature, Jc(Tp) for all samples was between 17 and 19 A cm−2. This work showed that in addition to Bi, Pb, Cr, V, Re and rare-earth elements, Se substitution for Tl also resulted in the formation of a superconducting material in the TlSr2CaCu2O7−δ phase.

Design and test of superconducting magnet (SM) for a superconducting synchronous generator (SSG) are studied in this paper. First, a suitable superconducting material is selected to make SM by analyzing the characteristics and application background of the five practical superconducting materials, and the applicability and feasibility of the selected superconducting materials are demonstrated. Second, the initial structural parameters of the SM are obtained by finite element method (FEM). In addition, the influence of structural parameters of SM on the performance of SSG is analyzed by simulation. Then, an optimal algorithm combining response surface methodology (RSM) and particle swarm optimization (PSO) is proposed to optimize the structure of SM in order to give full play to the advantages of SM. The simulated results verify that the proposed optimal algorithm is feasible and effective. Finally, the prototype of SM is made by the optimized size, and the SM is tested at a low temperature to obtain the critical temperature and critical current of the SM; the experimental results verify that the designed SM can meet the requirements of SSG.

With the progress of a high-temperature superconducting material production technology, the full superconducting magnets with a high magnetic field above 25 T have been realized for recent years. However, they cannot operate with persistent mode (PCM) since there is difficulty in jointing without resistance or low enough jointing resistance in HTS tapes. The bitter-like HTS magnet is a full superconducting magnet composed of ReBCO annular plates, and the power supply technology is an effective method for achieving PCM. In this paper, we choose inner and outer excitations to energize a bitter-like HTS magnet in 77 K. It was found that the HTS magnet reaches saturation faster by using the inner excitation than the outer excitation for the same bitter-like HTS magnet. The magnetic field was measured with a Hall probe at 77 K. The results illustrated that the inner excitation is much faster than the outer excitation, but the saturation field in former is lower than the latter one.

We present a microscopic study of the behavior of the order parameters near boundaries of a two-band superconducting material, described by the standard tight-binding Bardeen-Cooper-Schrieffer model. We find superconducting surface states. The relative difference between bulk and surface critical temperatures is a nontrivial function of the interband coupling strength. For superconductors with weak interband coupling, boundaries induce variations of the gaps with the presence of multiple length scales, despite non-zero interband Josephson coupling., 7 pages, 7 figures

In this paper, we study the crystalline properties and superconducting critical temperature of ultra-thin (5–9 nm) NbN films deposited on 8-inch silicon wafers by reactive sputtering. We show that the deposition of NbN on a thin (10–20 nm) AlN buffer layer, also synthesized by reactive sputtering, improves the critical temperature by several Kelvin, up to 10 K for 9 nm NbN on 20 nm AlN. We correlate this improvement to the higher-crystalline quality of NbN on AlN. While NbN deposited directly on silicon is polycrystalline with randomly oriented grains, NbN on AlN(0001) is textured along (111), due to the close lattice match. The superconducting properties of the NbN/AlN stack are validated by the demonstration of fibre-coupled normal-incidence superconducting nanowire single photon detectors. The whole fabrication process is CMOS compatible, with a thermal budget compatible with the integration of other passive and active components on silicon. These results pave the way for the integration of a large number of surface or waveguide-integrated detectors on large-scale silicon wafers. Furthermore, as AlN is transparent over a broad wavelength range from the visible to the near-infrared, the optimized superconducting NbN/AlN stack can be used for a wide variety of applications, from imaging to quantum communications and quantum computing.

Recent ferromagnetic resonance experiments and theory of Pt/Nb/Ni_{8}Fe_{2} proximity-coupled structures strongly suggest that spin-orbit coupling (SOC) in Pt in conjunction with a magnetic exchange field in Ni_{8}Fe_{2} are the essential ingredients to generate a pure spin supercurrent channel in Nb. Here, by substituting Pt for a perpendicularly magnetized Pt/Co/Pt spin sink, we are able to demonstrate the role of SOC and show that pure spin supercurrent pumping efficiency across Nb is tunable by controlling the magnetization direction of Co. By inserting a Cu spacer with weak SOC between Nb and Pt/(Co/Pt) spin sink, we also prove that Rashba-type SOC is key for forming and transmitting pure spin supercurrents across Nb. Finally, by engineering these properties within a single multilayer structure, we demonstrate a prototype superconductor spin-wave device in which lateral spin-wave propagation is gateable via the opening or closing of a vertical pure spin supercurrent channel in Nb.

Linear electric generators (LEGs) are attractive devices for new efficient and sustainable ways of developing power generating technologies. This research work contributes in determining the increase of energy potential of LEGs while using superconductor coils instead of stator and actuator made of heavy and high permeability materials, necessary when conventional conductive material such copper is used to generate electrical energy. The proposed work highlights the technoeconomic aspects of using superconductive materials in the LEG coil. Moreover, the design features of the LEG using superconductors, the electromagnetic analysis performance with finite-element simulations, and the experimentation results are presented. The comparison of the power extracted using copper coil and superconducting material is established, and three times more power is obtained with the superconductor coil.

In this paper, we prove the uniform-in- σ regularity for 3D time-dependent Ginzburg–Landau model in superconductivity in the case of Coulomb gauge. Here σ is the normal conductivity of the superconducting material.

Our research show that the higher packing density of the unreacted material (Mg +2B) by 8%, especially for Mg in the solid state, allows to eliminate the large number of large voids (20 mu m), improves the homogeneity and density of the MgB2 superconducting material, allows to obtain a greater number and longer lengths of connections between MgB2 grains, eliminates the formation of the intermetallic phase (iron borides), allows to obtain MgB2 grains of a uniform size and shape, increase irreversible magnetic field (Birr), critical temperature (T-c) and upper magnetic field (B-c2). Research show that spherical grains significantly reduce the number of inter-grain connections in the material with low and high density of unreacted material and allows to obtain the more superconducting phase. Research shows that MgB2 grains with a plate-like and rectangular shape allow to obtain more connections between the grains. Studies show that thermal treatment under high iso-static pressure does not allow to obtain the large amount of superconducting phase for the unreacted material of low density. Moreover, studies show that the high packing density of unreacted material and thermal treatment under high isostatic pressures (0.8 GPa and 1.1 GPa) allow to obtain a large amount of superconducting phase even for Mg in the solid state. Additionally, studies points that heat treatment under medium isostatic pressure (0.3 GPa) significantly reduce B-irr and B-c2. Our results are important for long superconducting wires made by using the powder-in-tube (PIT) technique. Because they indicate that the higher packing density of the unreacted material (Mg +2B) will allow to obtain a the superconducting material with greater homogeneity and density, and improve the critical parameters e.g. coils. (C) 2021 Elsevier B.V. All rights reserved.

We report the influences of the high hot isostatic pressure (HHIP) on Ba(Fe 0.92 ,Co 0.08 ) 2 As 2 superconducting bulks materials. Magnetic measurements showed that this material has a critical temperature ( T c ) of 26 K. The HHIP process increases the density of flux pinning centers without altering the dominant flux pinning mechanisms and without decreasing of T c . Structural studies have shown that the HHIP process increases the density of the material, reduces the size of voids, and thus allows to obtain homogeneous distribution of the components. Additionally, the HHIP process removes cracks in polycrystalline Ba(Fe 0.92 ,Co 0.08 ) 2 As 2 , creates more superconducting phase and forms less amount of Ba precipitates.

ZrSe2 is a band semiconductor studied long time ago. It has interesting electronic properties, and because its layers structure can be intercalated with different atoms to change some of the physical properties. In this investigation we found that Zr deficiencies alter the semiconducting behavior and the compound can be turned into a superconductor. In this paper we report our studies related to this discovery. The decreasing of the number of Zr atoms in small proportion according to the formula ZrxSe2, where x is varied from about 8.1 to 8.6 K, changing the semiconducting behavior to a superconductor with transition temperatures ranging between 7.8 to 8.5 K, it depending of the deficiencies. Outside of those ranges the compound behaves as semiconducting with the properties already known. In our experiments we found that this new superconductor has only a very small fraction of superconducting material determined by magnetic measurements with applied magnetic field of 10 Oe. Our conclusions is that superconductivity is filamentary. However, in one studied sample the fraction was about 10.2 %, whereas in others is only about 1 % or less. We determined the superconducting characteristics; the critical fields that indicate a type two superonductor with Ginzburg-Landau ? parameter of the order about 2.7. The synthesis procedure is quite normal fol- lowing the conventional solid state reaction. In this paper are included, the electronic characteristics, transition temperature, and evolution with temperature of the critical fields., Comment: Accepted in J of superconductivity and novel magnetism