Car magnetic key holder11/18/2023 ![]() ![]() (b) ECT-induced current as a function of the magnetic field orientation. (a) CAR-induced current as a function of the magnetic field direction, extracted with the same method detailed in Fig. S1 and used in the rest of the paper. See Fig. S7 for data corresponding to other spin configurations. The QD spin configuration is ↓ ↑ for all panels. Each panel is taken at fixed V PG and | B → | = 80 mT. (a)–(d) Spherical plots: The center of every colored tile corresponds to a specific magnetic field orientation. Tuning CAR and ECT with magnetic field orientation. The background noise level is approximately 30 pA (see Supplemental Material ). (f) A high-resolution measurement of CAR and ECT amplitudes while tuning V PG. (e) A toy-model calculation of the transmission probability as a function of μ. (d) G LL as a function of V L and V PG showing a single ABS. Comparing data to theory, we estimate α ∼ 0.01. ![]() μ and V PG are related via μ = − e α ( V PG − V 0 ), where α is the gate lever arm and V 0 = 35 mV is an offset. (c) E ABS, and u, v as a function of μ calculated in the atomic limit, where E ABS = Γ 2 + μ 2 with Γ = 160 μ eV. (b) Two possible paths for CAR: An electron from the left QD enters the ABS followed by another electron arriving from the right QD (solid gray arrow) and the same processes in reversed order (dashed green arrow). (a) Two possible paths for ECT: An electron hops from the left QD to the center ABS, followed by an escape from the ABS to the right QD (solid gray arrow), and the processes in the opposite order (dashed green arrow). Reuse & Permissionsĭetailed study of CAR and ECT through an ABS. The values of V LI and V RI are kept constant during measurements in (b), (c), and (e). (k) CAR- and ECT-induced currents as a function of V PG measured using the N ↔ N + 1 transition in both QDs. G LL and G RL are calculated by taking the numerical derivative after applying a Savitzky-Golay filter of window length 11 and polynomial order 1 to the measured I L and I R currents, respectively. (j) G RL as a function of V L and V PG in the same settings as (b). (i) G LL as a function of V L and V PG when setting the gates in the tunneling spectroscopy configuration. (g),(h) Measurement of the ECT-induced current (g) and the CAR-induced current (h), as in Ref. , around a charge degeneracy point. (f) Configuration with QDs: Applying low voltages on V LO, V LI and V RI, V RO forms a QD on the left and right side of the superconducting segment. Blue curves sketch the desired voltage profile defined with the gates voltage barriers are not to scale. (e) Spectroscopy configuration: Yellow bars depict voltage bias in normal ( N) contacts, while blue rectangles represent the superconductor ( S). Two Cr / Au leads (yellow) are attached to both sides of the wire. An InSb nanowire (green) is coated by a thin Al shell (blue, Al + Pt for device A), on top of seven finger gates (red). (d) Schematic illustration of our devices and experimental setup. (c) Scanning electron micrograph of device A. (a),(b) Illustration of the ECT (a) and CAR (b) processes. We back these findings with theoretical calculations and put them to use to realize Majorana states in such systems.įuture work will focus on a deterministic approach to the creation of Majorana bound states using the understanding of the microscopic process governing the interactions between the quantum dots.Ĭorrelation between ABS and CAR or ECT processes. In this work, we show that both processes happen via discrete states appearing in a semiconducting-superconducting hybrid and that they can be controlled by either an electrostatic gate or an external magnetic field. The two processes that must be balanced are elastic cotunneling, in which an electron hops between two sites via an intermediate state, and crossed Andreev reflection, wherein two electrons enter or exit a superconductor simultaneously and split into two separate leads. Here, we show that a system that consists of two quantum dots coupled by a semiconducting-superconducting hybrid material can achieve this fine-tuning of the interactions. An alternative bottom-up approach proposes to form Majorana states by coupling quantum dots via two processes that must be perfectly balanced. ![]() The top-down approach for finding such states is very demanding from the material-science perspective, and it is unclear if it is achievable. One potential type of building block of such qubits is a “Majorana bound state,” a special case of a type of fermionlike quasiparticle that is its own antiparticle. Robust, practical quantum computing requires quantum bits, or qubits, that can tolerate environmental noise.
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