Optimal design of nanomagnets for on-chip field gradients

The generation of localized magnetic field gradients by on-chip nanomagnets is important for a variety of technological applications, in particular for spin qubits. To advance beyond the empirical design of these nanomagnets, we propose a systematic and general approach based on the micromagnetic formulation of an optimal field gradient source. We study the different field configurations that can be realized and find out quantitatively the most suitable ferromagnetic layer geometries. Using micromagnetic simulations, we then investigate the minimum requirements for reaching magnetic saturation in these nanomagnets. In terms of either longitudinal or transverse field gradient, the results provide an optimal solution for uniform, saturated nanomagnets, where the magnetic material can be selected according to the strength of the external fields that can be used.Comment: 10 pages, 4 figures, supplemental material. All comments most welcom

Towards hybrid circuit quantum electrodynamics with quantum dots

Cavity quantum electrodynamics allows one to study the interaction between light and matter at the most elementary level. The methods developed in this field have taught us how to probe and manipulate individual quantum systems like atoms and superconducting quantum bits with an exquisite accuracy. There is now a strong effort to extend further these methods to other quantum systems, and in particular hybrid quantum dot circuits. This could turn out to be instrumental for a noninvasive study of quantum dot circuits and a realization of scalable spin quantum bit architectures. It could also provide an interesting platform for quantum simulation of simple fermion-boson condensed matter systems. In this short review, we discuss the experimental state of the art for hybrid circuit quantum electrodynamics with quantum dots, and we present a simple theoretical modeling of experiments.Comment: Minor differences with published versio

Existence of global strong solutions to a beam-fluid interaction system

We study an unsteady non linear fluid-structure interaction problem which is a simplified model to describe blood flow through viscoleastic arteries. We consider a Newtonian incompressible two-dimensional flow described by the Navier-Stokes equations set in an unknown domain depending on the displacement of a structure, which itself satisfies a linear viscoelastic beam equation. The fluid and the structure are fully coupled via interface conditions prescribing the continuity of the velocities at the fluid-structure interface and the action-reaction principle. We prove that strong solutions to this problem are global-in-time. We obtain in particular that contact between the viscoleastic wall and the bottom of the fluid cavity does not occur in finite time. To our knowledge, this is the first occurrence of a no-contact result, but also of existence of strong solutions globally in time, in the frame of interactions between a viscous fluid and a deformable structure

Regularity issues in the problem of fluid structure interaction

We investigate the evolution of rigid bodies in a viscous incompressible fluid. The flow is governed by the 2D Navier-Stokes equations, set in a bounded domain with Dirichlet boundary conditions. The boundaries of the solids and the domain have H\"older regularity $C^{1, \alpha}$, $0 < \alpha \le 1$. First, we show the existence and uniqueness of strong solutions up to collision. A key ingredient is a BMO bound on the velocity gradient, which substitutes to the standard $H^2$ estimate for smoother domains. Then, we study the asymptotic behaviour of one $C^{1, \alpha}$ body falling over a flat surface. We show that collision is possible in finite time if and only if $\alpha < 1/2$

Direct oriented growth of armchair graphene nanoribbons on germanium

Graphene can be transformed from a semimetal into a semiconductor if it is confined into nanoribbons narrower than 10nm with controlled crystallographic orientation and well-defined armchair edges. However, the scalable synthesis of nanoribbons with this precision directly on insulating or semiconducting substrates has not been possible. Here we demonstrate the synthesis of graphene nanoribbons on Ge(001) via chemical vapour deposition. The nanoribbons are self-aligning 3 degrees from the Ge &lt; 110 &gt; directions, are self-defining with predominantly smooth armchair edges, and have tunable width to &lt;10 nm and aspect ratio to &gt;70. In order to realize highly anisotropic ribbons, it is critical to operate in a regime in which the growth rate in the width direction is especially slow, &lt;5 nm h(-1). This directional and anisotropic growth enables nanoribbon fabrication directly on conventional semiconductor wafer platforms and, therefore, promises to allow the integration of nanoribbons into future hybrid integrated circuits

The Glyceraldehyde-3-Phosphate Dehydrogenase and the Small GTPase Rab 2 Are Crucial for Brucella Replication

The intracellular pathogen Brucella abortus survives and replicates inside host cells within an endoplasmic reticulum (ER)-derived replicative organelle named the “Brucella-containing vacuole” (BCV). Here, we developed a subcellular fractionation method to isolate BCVs and characterize for the first time the protein composition of its replicative niche. After identification of BCV membrane proteins by 2 dimensional (2D) gel electrophoresis and mass spectrometry, we focused on two eukaryotic proteins: the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the small GTPase Rab 2 recruited to the vacuolar membrane of Brucella. These proteins were previously described to localize on vesicular and tubular clusters (VTC) and to regulate the VTC membrane traffic between the endoplasmic reticulum (ER) and the Golgi. Inhibition of either GAPDH or Rab 2 expression by small interfering RNA strongly inhibited B. abortus replication. Consistent with this result, inhibition of other partners of GAPDH and Rab 2, such as COPI and PKC ι, reduced B. abortus replication. Furthermore, blockage of Rab 2 GTPase in a GDP-locked form also inhibited B. abortus replication. Bacteria did not fuse with the ER and instead remained in lysosomal-associated membrane vacuoles. These results reveal an essential role for GAPDH and the small GTPase Rab 2 in B. abortus virulence within host cells

Synthetic spin–orbit interaction for Majorana devices

International audienc

Vacuum-field-induced THz transport gap in a carbon nanotube quantum dot

International audienceAbstract The control of light-matter interaction at the most elementary level has become an important resource for quantum technologies. Implementing such interfaces in the THz range remains an outstanding problem. Here, we couple a single electron trapped in a carbon nanotube quantum dot to a THz resonator. The resulting light-matter interaction reaches the deep strong coupling regime that induces a THz energy gap in the carbon nanotube solely by the vacuum fluctuations of the THz resonator. This is directly confirmed by transport measurements. Such a phenomenon which is the exact counterpart of inhibition of spontaneous emission in atomic physics opens the path to the readout of non-classical states of light using electrical current. This would be a particularly useful resource and perspective for THz quantum optics

K-Rich Rubbly Bedrock at Glen Torridon, Gale Crater, Mars: Investigating the Possible Presence of Illite

International audienceIntroduction: The Curiosity rover reached the Glen Torridon (GT) area around sol 2300 (January 2019). GT is known to display relatively strong and extensive smectite signatures from orbit [1]. During the last two years of exploring this area, Curiosity has revealed variations in chemical compositions correlated with bedrock facies [2-4]. The spatially dominant type of rock in the lowermost part of GT (which is a lateral continuation of the Jura member) is described as the "rubbly" bedrock because it outcrops as small pieces of bedrock embedded in soil. The rubbly bedrock is composed of finely-laminated mudstones and is characterized by enrichments in K2O and SiO2 [3], whereas the slabs of coherent bedrock adjacent to it are lower in K2O but enriched in MgO [3]. Another mudstone layer with a low MgO/high K2O type of composition is also observed in the overlying Knockfarril Hill member, between Glen Etive and Central Butte. X-ray diffraction (XRD) analyses performed by the CheMin instrument showed that the Jura coherent bedrock contains ~30 wt% of Fe-smectites [5]. However, no XRD analysis was performed on the rubbly bedrock, and the discussion below is thus based solely on elemental compositions measured by ChemCam [6,7]. The objective of this work is to discuss clues regarding the mineralogy of the GT rubbly bedrock: in particular whether the enrichment in K2O is related to partial illitization of the clay minerals, or to a mixing with K-feldspars? Elevated K2O abundances were previously observed in the Kimberley area [8-9], on the floor of Aeolis Palus [10], where CheMin results showed an associated enrichment in K-feldspar (sanidine) [9]. K-feldspars were also observed in igneous rocks such as trachytes [11,12]. In this study, data from the rubbly bedrock of GT are therefore compared to data from Kimberley and from the trachytic igneous rocks observed at Bradbury. Some plagioclase-rich igneous rocks are also used for comparison [12]. Methodology: ChemCam uses the LIBS technique to perform remote chemical analyzes [6,7,12]. The laser beam (300-500 µm, [13]) is large enough that it mostly samples mixtures of mineral phases (as opposed to pure phases), especially in mudstones. Therefore, we used trends in elemental ratios to interpret the mineralogy of the rocks. Compositions with a sum of oxides <90 % were discarded in order to minimize the contribution of the ubiquitous Ca-sulfate veins. Concerning minor elements, peak areas have been used, as described in [11]. Data used to be compared with the GT rubbly bedrock have been filtered in order to have relatively pure phases. For that, data points were plotted in mineralogical plot t