Kwant is a Python package for numerical quantum transport calculations. It aims to be a user-friendly, universal, and high-performance toolbox for the simulation of physical systems of any dimensionality and geometry that can be described by a tight-binding model. Kwant has been designed such that the natural concepts of the theory of quantum transport (lattices, symmetries, electrodes, orbital/spin/ electron-hole degrees of freedom) are exposed in a simple and transparent way. Defining a new simulation setup is very similar to describing the corresponding mathematical model. Kwant offers direct support for calculations of transport properties (conductance, noise, scattering matrix), dispersion relations, modes, wave functions, various Greenʼs functions, and out-of-equilibrium local quantities. Other computations involving tight-binding Hamiltonians can be implemented easily thanks to its extensible and modular nature. Kwant is free software available at http://kwant-project.org/.

We present a calculation of current-induced torques in metallic magnetic multilayers derived from the spin-dependent transmission and reflection properties of the magnetic layers. A scattering formalism is employed to calculate the torques in a magnetic-nonmagnetic-magnetic trilayer, for currents perpendicular to the layers, in both the ballistic and diffusive regimes.

We report on first-principles calculations of spin-dependent properties in graphene induced by its interaction with a nearby magnetic insulator (europium oxide, EuO). The magnetic proximity effect results in spin polarization of graphene π orbitals by up to 24%, together with a large exchange-splitting band gap of about 36 meV. The position of the Dirac cone is further shown to depend strongly on the graphene-EuO interlayer. These findings point toward the possible engineering of spin gating by the proximity effect at a relatively high temperature, which stands as a hallmark for future all-spin information processing technologies.

In this report we review the present state of the art of the control of propagating quantum states at the single-electron level and its potential application to quantum information processing. We give an overview of the different approaches that have been developed over the last few years in order to gain full control over a propagating single-electron in a solid-state system. After a brief introduction of the basic concepts, we present experiments on flying qubit circuits for ensemble of electrons measured in the low frequency (DC) limit. We then present the basic ingredients necessary to realise such experiments at the single-electron level. This includes a review of the various single-electron sources that have been developed over the last years and which are compatible with integrated single-electron circuits. This is followed by a review of recent key experiments on electron quantum optics with single electrons. Finally we will present recent developments in the new physics that has emerged using ultrashort voltage pulses. We conclude our review with an outlook and future challenges in the field.

We review current challenges and perspectives in graphene spintronics, which is one of the most promising directions of innovation, given its room-temperature long-spin lifetimes and the ability of graphene to be easily interfaced with other classes of materials (ferromagnets, magnetic insulators, semiconductors, oxides, etc), allowing proximity effects to be harvested. The general context of spintronics is first discussed together with open issues and recent advances achieved by the Graphene Spintronics Work Package consortium within the Graphene Flagship project. Based on such progress, which establishes the state of the art, several novel opportunities for spin manipulation such as the generation of pure spin current (through spin Hall effect) and the control of magnetization through the spin torque phenomena appear on the horizon. Practical applications are within reach, but will require the demonstration of wafer-scale graphene device integration, and the realization of functional prototypes employed for determined applications such as magnetic sensors or nano-oscillators. This is a specially commissioned editorial from the Graphene Flagship Work Package on Spintronics. This editorial is part of the 2D Materials focus collection on 'Progress on the science and applications of twodimensional materials,' published in association with the Graphene Flagship. It provides an overview of key recent advances of the spintronics work package as well as the mid-term objectives of the consortium.

We consider the spin torque induced by a current flowing ballistically through a magnetic domain wall. In addition to a global pressure in the direction of the electronic flow, the torque has an internal structure of comparable magnitude due to the precession of the electrons' spins at the "Larmor" frequency. As a result, the profile of the domain wall is expected to get distorted by the current and acquires a periodic sur-structure. PACS numbers:With the advent of "spintronics", which aims at using the spin of charge carriers in devices, electronic transport in ferromagnets is being revisited from a different viewpoint. The focus has been for a long time on the effect of magnetism on transport properties (e.g. Magneto Resistance, MR) [1], but it is now realized that the electronic current can be a tool to change the magnetization direction. The relevant effect, known as spin torque has attracted considerable interest recently in the context of ferromagnetic-normal metal-ferromagnetic trilayers [2]. There, the first magnetic layer acts as a spin filter, and the incident polarized electrons exert a torque on the second layer. At the heart of this physical effect is the fact that spin currents are not preserved when electrons cross a magnetic layer, and as a result some angular momentum is transferred to the magnetization. It was shown experimentally that for strong enough current densities this mechanism can lead to magnetic reversal [3]. This demonstrates the feasability of current controlled magnetic memory cells, but the current needed for complete reversal might be too high for industrial implementation. An alternative would be to use the current to move a domain wall (DW) in between two stable positions. The idea that a current can apply a force on a DW is due to Berger [4] in the seventies. It is the aim of this letter to study in detail the spin torque exerted on a DW in the presence of an electric current. Our main finding is that in addition to a global pressure, the torque has a spatially dependant component that will lead to a deformation of the DW in a periodic sub-structure.

Numerical simulation has become a major tool in quantum electronics both for fundamental and applied purposes. While for a long time those simulations focused on stationary properties (e.g. DC currents), the recent experimental trend toward GHz frequencies and beyond has triggered a new interest for handling time-dependent perturbations. As the experimental frequencies get higher, it becomes possible to conceive experiments which are both time-resolved and fast enough to probe the internal quantum dynamics of the system. This paper discusses the technical aspectsmathematical and numerical -associated with the numerical simulations of such a setup in the time domain (i.e. beyond the single-frequency AC limit). After a short review of the state of the art, we develop a theoretical framework for the calculation of time-resolved observables in a general multiterminal system subject to an arbitrary time-dependent perturbation (oscillating electrostatic gates, voltage pulses, time-varying magnetic fields, etc.) The approach is mathematically equivalent to (i) the time-dependent scattering formalism, (ii) the time-resolved non-equilibrium Green's function (NEGF) formalism and (iii) the partition-free approach. The central object of our theory is a wave function that obeys a simple Schrödinger equation with an additional source term that accounts for the electrons injected from the electrodes. The time-resolved observables (current, density, etc.) and the (inelastic) scattering matrix are simply expressed in term of this wave function. We use our approach to develop a numerical technique for simulating timeresolved quantum transport. We find that the use of this wave function is advantageous for numerical simulations resulting in a speed up of many orders of magnitude with respect to the direct integration of NEGF equations. Our technique allows one to simulate realistic situations beyond simple models, a subject that was until now beyond the simulation capabilities of available approaches.

In the presence of direct trajectories connecting source and drain contacts, the conductance of a quantum dot may exhibit resonances of the Fano type. Since Fano resonances result from the interference of two transmission pathways, their lineshape (as described by the Fano parameter q) is sensitive to dephasing in the quantum dot. We show that under certain circumstances the dephasing time can be extracted from a measurement of q for a single resonance. We also show that q fluctuates from level to level, and calculate its probability distribution for a chaotic quantum dot. Our results are relevant to recent experiments by Göres et al. PACS numbers: 73.20.Dx., 73.23.Hk, 73.40.Gk Perhaps one of the most fundamental issues in the field of mesoscopic physics is that of phase coherence: under what conditions are electrons able to retain a well-defined phase? This issue is of particular interest for quantum dots in the Coulomb blockade regime, where the electrical conductance is suppressed except for points of charge degeneracy [1]. Despite the fact that interactions are strong in these dots, the shape of the conductance peaks can be well understood in terms of single-particle wavefunctions. Unfortunately, a simple conductance measurement cannot discriminate between coherent and incoherent (sequential) tunneling, as both mechanisms give rise to lineshapes of Breit-Wigner form [2]. Instead, to establish phase coherence, the quantum dot has to be embedded in an interferometer. This was first done by Yacoby et al. [3], who included a quantum dot in one arm of an Aharonov-Bohm ring (see also Ref. [4]).Given this result, it is natural to question the extent to which transport is phase coherent. This question could not be fully addressed in Ref. [3], because dephasing in the quantum dot and in the arms of the interferometer cannot easily be separated. An extremely promising development in this respect is found in a recent work by Göres et al. [5], who observed resonances with a Fano lineshape in the conductance of Coulomb-blockaded dots [6], instead of the usual Breit-Wigner form. Fano resonances are caused by the interference of two transport pathways, a resonant and a nonresonant one, and are thus sensitive to phase coherence. In the dots of Ref.[5], the direct pathway is probably direct transmission through the dot, as schematically depicted in Fig. 1. In this sense, the dot serves as its own interferometer! Fano resonances have a lineshape of the formwhere G is the conductance, measured in units of 2e 2 /h, ε the energy, set by a gate voltage, Γ the resonance width, G d the nonresonant conductance, and q the (complex) "Fano parameter". The resonance form (1) Through the complex Fano parameter q, Fano resonances contain more information than Breit-Wigner resonances. Moreover, as the direct and resonant paths are not spatially separated, no source of decoherence other than dephasing inside the quantum dot can affect the lineshape. In fact, as we will show below, in the presence of time-reversal symmetry (TRS) or fo...