Loophole-free Bell inequality violation with superconducting circuits.

Superposition, entanglement and non-locality constitute fundamental features of quantum physics. The fact that quantum physics does not follow the principle of local causality1-3 can be experimentally demonstrated in Bell tests4 performed on pairs of spatially separated, entangled quantum systems. Although Bell tests, which are widely regarded as a litmus test of quantum physics, have been explored using a broad range of quantum systems over the past 50 years, only relatively recently have experiments free of so-called loopholes5 succeeded. Such experiments have been performed with spins in nitrogen-vacancy centres6, optical photons7-9 and neutral atoms10. Here we demonstrate a loophole-free violation of Bell's inequality with superconducting circuits, which are a prime contender for realizing quantum computing technology11. To evaluate a Clauser-Horne-Shimony-Holt-type Bell inequality4, we deterministically entangle a pair of qubits12 and perform fast and high-fidelity measurements13 along randomly chosen bases on the qubits connected through a cryogenic link14 spanning a distance of 30 metres. Evaluating more than 1 million experimental trials, we find an average S value of 2.0747 ± 0.0033, violating Bell's inequality with a P value smaller than 10-108. Our work demonstrates that non-locality is a viable new resource in quantum information technology realized with superconducting circuits with potential applications in quantum communication, quantum computing and fundamental physics15.

Determination of the surface diffusion coefficient and the residence time of adsorbates via local focused electron beam induced chemical vapour deposition.

In this paper we present a model for local gas assisted focused electron beam induced deposition which allows estimating the surface diffusion coefficient and the residence time of volatile precursor adsorbates. Elaborating the existing continuum model for one adsorbate species and using a novel set of parameters we simplified the differential equation describing the dynamics of this process. We will show that stationary exposure experiments do not allow for a unique determination of the parameters residence time, surface diffusion coefficient, and net cross-section. Rather an estimation of parameter windows is possible by assuming meaningful values for the electron dissociation cross section. The model was applied to the experimental results for Cu(hfac)2 as a gas precursor.

Granular Co-C nano-Hall sensors by focused-beam-induced deposition.

We investigated the performance of Hall sensors with different Co-C ratios, deposited directly in nanostructured form, using Co(2)(CO)(8) gas molecules, by focused-electron or ion-beam-induced deposition. Due to the enhanced intergrain scattering in these granular wires, the extraordinary Hall effect can be increased by two orders of magnitude with respect to pure Co, up to a magnetic field sensitivity of 1 Omega T(-1). We show that the best magnetic field resolution at room temperature is obtained for Co ratios between 60% and 70% and is better than 1 microT Hz(-1/2). For an active area of the sensor of 200 x 200 nm(2), the room temperature magnetic flux resolution is phi(min) = 2 x 10(-5)phi(0) in the thermal noise frequency range, i.e. above 100 kHz.

Realizing a deterministic source of multipartite-entangled photonic qubits.

Sources of entangled electromagnetic radiation are a cornerstone in quantum information processing and offer unique opportunities for the study of quantum many-body physics in a controlled experimental setting. Generation of multi-mode entangled states of radiation with a large entanglement length, that is neither probabilistic nor restricted to generate specific types of states, remains challenging. Here, we demonstrate the fully deterministic generation of purely photonic entangled states such as the cluster, GHZ, and W state by sequentially emitting microwave photons from a controlled auxiliary system into a waveguide. We tomographically reconstruct the entire quantum many-body state for up to N = 4 photonic modes and infer the quantum state for even larger N from process tomography. We estimate that localizable entanglement persists over a distance of approximately ten photonic qubits.

Spatially and time-resolved magnetization dynamics driven by spin-orbit torques.

Current-induced spin-orbit torques are one of the most effective ways to manipulate the magnetization in spintronic devices, and hold promise for fast switching applications in non-volatile memory and logic units. Here, we report the direct observation of spin-orbit-torque-driven magnetization dynamics in Pt/Co/AlOx dots during current pulse injection. Time-resolved X-ray images with 25 nm spatial and 100 ps temporal resolution reveal that switching is achieved within the duration of a subnanosecond current pulse by the fast nucleation of an inverted domain at the edge of the dot and propagation of a tilted domain wall across the dot. The nucleation point is deterministic and alternates between the four dot quadrants depending on the sign of the magnetization, current and external field. Our measurements reveal how the magnetic symmetry is broken by the concerted action of the damping-like and field-like spin-orbit torques and the Dzyaloshinskii-Moriya interaction, and show that reproducible switching events can be obtained for over 1012 reversal cycles.