Chains of quantum dots coupled to superconductors are promising for the realization of the Kitaev model of a topological superconductor. While individual superconducting quantum dots have been explored, control of longer chains requires understanding of interdot coupling. Here, double quantum dots are defined by gate voltages in indium antimonide nanowires. High transparency superconducting niobium titanium nitride contacts are made to each of the dots in order to induce superconductivity, as well as probe electron transport. Andreev bound states induced on each of dots hybridize to define Andreev molecular states. The evolution of these states is studied as a function of charge parity on the dots, and in magnetic field. The experiments are found in agreement with a numerical model.

We perform transport measurements on double quantum dots defined in Ge/Si core/shell nanowires and focus on Pauli spin blockade in the regime where tens of holes occupy each dot. We identify spin blockade through the magnetic field dependence of leakage current. We find both a dip and a peak in the leakage current at zero field. We analyze this behavior in terms of the quantum dot parameters such as coupling to the leads, interdot tunnel coupling as well as spin-orbit interaction. We find a lower bound for spin-orbit interaction with lso = 500 nm. We also extract large and anisotropic effective Landé g-factors, with larger g-factors in the direction perpendicular to the nanowire axis in agreement with previous studies and experiments but with larger values reported here.Studies of spin blockade in quantum dots are largely motivated by the proposals to build a spin-based quantum computer 1 , as spin blockade can be used for qubit initialization and readout 2,3 . At the same time, spin blockade and its lifting mechanisms offer a direct insight into spin relaxation and dephasing processes in semiconductors and provide deeper understanding of interactions between spin localized in a quantum dot and its environment, be it the lattice and its vibrations or nuclear spins, spin-orbit interaction, or coupling to spins in nearby dots or in the lead reservoirs 4-8 .Holes in Ge/Si nanowires offer a relatively unexplored platform for such studies 9 . On the one hand, hyperfine interaction is expected to be greatly reduced owing to the low abundance of nonzero nuclear spin isotopes in the group IV materials 10 . Moreover, holes weakly couple to nuclear spins due to their p-wave Bloch wave symmetry, thus they are expected to come with longer spin relaxation times 11 . Heavy/light hole degeneracy may also influence the spin blockade regime 12 . On the other hand, spin-orbit interaction is predicted 13 and suggested by experiments 14-17 to be strong in Ge/Si core/shell nanowires. This offers a path to electrical spin manipulation 18,19 , as well as to realizing Majorana fermions [20][21][22][23] .In this work we perform transport measurements on electrostatically defined double quantum dots 2 made in Ge/Si core/shell nanowires, and detect Pauli spin blockade at several charge degeneracy points. We expand and adapt a previously developed rate equation model to analyze the magnetic-field evolution of the leakage current 24 . We also observe large and anisotropic g-factors in these dots, which supports recent theoretical predictions 25 and experimental observations 26,27 .The devices are fabricated on n-doped Si substrates covered with 500 nm of thermal SiO 2 and patterned with local gate arrays of Ti/Au stripes with center to center distance of 60 nm. The gates are covered by a 10 nm layer of HfO 2 dielectric. Using a micromanipulator 28 the nanowires with a typical length of 4 µm and diameter of 30 nm are placed on top of these gates as shown in the inset of Fig. 1. After wet etching with buffered hydrofluoric acid, we sputter 15...

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One of the critical pieces of the self-driving puzzle is understanding the surroundings of the self-driving vehicle (SDV) and predicting how these surroundings will change in the near future. To address this task we propose MultiXNet, an end-to-end approach for detection and motion prediction based directly on lidar sensor data. This approach builds on prior work by handling multiple classes of traffic actors, adding a jointly trained second-stage trajectory refinement step, and producing a multimodal probability distribution over future actor motion that includes both multiple discrete traffic behaviors and calibrated continuous uncertainties. The method was evaluated on a large-scale, real-world data set collected by a fleet of SDVs in several cities, with the results indicating that it outperforms existing state-of-the-art approaches.

We study transport mediated by Andreev bound states formed in InSb nanowire quantum dots. Two kinds of superconducting source and drain contacts are used: epitaxial Al/InSb devices exhibit a doubling of tunneling resonances, while in NbTiN/InSb devices Andreev spectra of the dot appear to be replicated multiple times at increasing source-drain bias voltages. In both devices, a mirage of a crowded spectrum is created. To describe the observations a model is developed that combines the effects of a soft induced gap and of additional Andreev bound states both in the quantum dot and in the finite regions of the nanowire adjacent to the quantum dot. Understanding of Andreev spectroscopy is important for the correct interpretation of Majorana experiments done on the same structures.The superconductor-semiconductor hybrid structures are of recent interest due to the possibility of inducing topological superconductivity accompanied by Majorana bound states (MBS) [1][2][3][4]. More generally, when a semiconductor is of finite size, proximity to a superconductor gives rise to subgap quasiparticle excitations, the so-called Andreev bound states (ABS), that appear due to successive Andreev reflections at the interfaces. Single ABS have been demonstrated in a variety of structures including self-assembled quantum dots, semiconductor nanowires, atomic break junctions, carbon nanotubes and graphene [5][6][7][8][9][10][11]. ABS exhibit many similarities to MBS, and therefore ABS can be served as a prototypical system for Majorana studies [12,13]. A powerful experimental method for investigating both MBS and ABS is via tunneling, either from a nanofabricated probe or by scanning tunneling spectroscopy. The latter is typically performed on Yu-Shiba-Rusinov states which are closely analogous to ABS but originate from magnetic impurities in superconductors [14,15].In this paper, we focus on the mesoscopic effects within the tunneling probes. We show that the non-trivial densities of states (DOS) in the probes can drastically affect tunneling characteristics by generating multiple replicas of ABS. To experimentally investigate these effects, we use semiconductor nanowires coupled to superconductors. ABS are induced in a quantum dot by strongly coupling the dot to one superconducting contact. A second superconducting contact and a nanowire segment ad-jacent to it act as a tunneling probe. To explain our observations, we consider the effects of soft induced superconducting gap in the nanowire, and of additional ABS induced in nanowire segments adjacent to the dot. The surprising observation of sub-gap negative differential conductance (NDC) is found to be consistent with a peak in the density of states of the probe at zero chemical potential, which is present even at zero magnetic field. The exact origin of this anomalous density of states remains an open question. Our findings emphasize the importance of understanding the spectral structure of the measuring contacts to interpret tunneling experiments in mesoscopic systems. We expect t...