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The competition between superconducting and ferromagnetic orderings in Josephson devices has promoted fundamental and applicative studies of high impact for superconducting digital technology, cryogenic memories, and spintronics, where the possibility of switching between different magnetic states is a crucial advantage. Here, we report on fabrication and characterization of very high quality tunnel ferromagnetic Josephson junctions (JJs) with aluminum electrodes, demonstrating hysteretic behavior of the magnetic field pattern preserving typical transport properties of Al junctions, underdamped behavior, and very low quasiparticle dissipation. The proposed technology paves the way for the possible implementation of Al tunnel-ferromagnetic JJs in superconducting quantum circuits, toward alternative approaches based on digital control of the Josephson device.

We have fabricated and studied a stacked superconducting double tunnel junction device with transistor-like properties. The intermediate electrode is a bilayer consisting of a Nb film together with an Al film that acts as a quasiparticle trap. Large current gains of more than 50 are observed at 4.2 K when the Al layer is normal. The operation is highly directional. Results are explained on the basis of trapping of quasiparticles from a superconductor into a normal metal, together with a conversion of relaxation energy into electronic excitations. Similar devices should have wide applications in low-temperature measurement and detection systems.

The attainment of high-quality Josephson junctions on electro-optical substrates constitutes a key step toward the fabrication of functional superconducting opto-electronics. We report on the fabrication of high-quality all-refractory niobium superconducting tunnel junctions deposited on X-cut LiNbO3 single crystals. A high quality factor Vm = 0.7 ?IgR2 mV (where ?Ig is the current jump at the sum gap voltage and R2 mV the static resistance at V = 2 mV) up to 61 mV has been measured at T = 4.2 K. The very low contribution of subgap leakage currents is demonstrated by the BCS-like quasiparticle current measured at V = 0.1 mV down to T = 1.9 K.