Josephson Diode Effect in Parallel-Coupled Double-Quantum Dots Connected to Unalike Majorana Nanowires.

We study theoretically the Josephson diode effect (JDE) when realized in a system composed of parallel-coupled double-quantum dots (DQDs) sandwiched between two semiconductor nanowires deposited on an s-wave superconductor surface. Due to the combined effects of proximity-induced superconductivity, strong Rashba spin-orbit interaction, and the Zeeman splitting inside the nanowires, a pair of Majorana bound states (MBSs) may possibly emerge at opposite ends of each nanowire. Different phase factors arising from the superconductor substrate can be generated in the coupling amplitudes between the DQDs and MBSs prepared at the left and right nanowires, and this will result in the Josephson current. We find that the critical Josephson currents in positive and negative directions are different from each other in amplitude within an oscillation period with respect to the magnetic flux penetrating through the system, a phenomenon known as the JDE. It arises from the quantum interference effect in this double-path device, and it can hardly occur in the system of one QD coupled to MBSs. Our results also show that the diode efficiency can reach up to 50%, but this depends on the overlap amplitude between the MBSs, as well as the energy levels of the DQDs adjustable by gate voltages. The present model is realizable within current nanofabrication technologies and may find practical use in the interdisciplinary field of Majorana and Josephson physics.

AND Gate Response in a Double Mesoscopic Ring.

BACKGROUND: Normal metal mesoscopic rings are being used in designing quantum logical gates due to the quantum interference effect and quantum confinement. This study focused on examining electronic transport through normal metal mesoscopic rings that have one dimension, and suggested how such rings can be employed to design nanoscale AND gate. A double mesoscopic ring was utilized for AND gate operation, every ring was threaded by magnetic flux, and the magnetic flux was considered as the key tuning parameter in the AND gate action. For a particular value of magnetic flux equal to the half of elementary flux-quantum, a logical AND gate operation was used depending on the applied gate voltages. Two gate voltages were externally applied to the lower arm of every ring, which acted as the two inputs of the AND gate. Few relevant patents to the designing and fabrication of quantum logical gates have been reviewed and cited. METHODS: All the calculations are based on the time-dependent Hamiltonian model, the steady state is used to obtain the transmission probability. RESULTS: The transmission probability, the current and the noise power of current fluctuations were calculated in the weak-coupling and strong-coupling regimes. CONCLUSION: This study paved the way for the production of an electronic logic gate.