[INVITED] Superconducting electronics : from the Josephson junction to computers

Pascal Febvre

Pascal Febvre

A test setup bench is being implemented in the laboratory to test digital superconducting circuits under various conditions of operation. I will present in a first step the computer-controlled test environment developed to extract the main parameters of Josephson devices used in digital circuits and to test the circuits at low frequencies. Some results obtained on some Josephson junction arrays and circuits will be shown to illustrate this part. In a second step, I will review the microwave and optical signal feeds and readout that are under development in order to trigger and diagnose digital circuits at higher frequencies. Finally, a study of the expected performance of an on-chip diagnostic system aimed at discriminating different signal waveforms generated by superconducting digital circuits will be presented.

Tycho J. Blom, Thomas Mechielsen, Remko Fermin +3 more

Josephson junctions are the building blocks of superconducting electronics, with well-established applications in precision metrology and quantum computing. Fabricating a Josephson junction has been a resource-intensive and multistep procedure, involving lithography and wet-processing, which are not compatible with many applications. Here, we introduce a fully additive direct-write approach, where a scanning electron microscope can print substrate-conformal Josephson devices in a matter of minutes, requiring no additional processing. The junctions are made entirely by electron-beam-induced deposition (EBID) of tungsten carbide. We utilize EBID-tunable material properties to write, in one go, full proximity junctions with superconducting electrodes and metallic weak links and tailor their Josephson coupling. The Josephson behavior of these junctions is established and characterized by their microwave-induced Shapiro response and field-dependent transport. Our efforts provide a versatile and nondestructive alternative to conventional nanofabrication and can be expanded to print three-dimensional superconducting sensor arrays and quantum networks.

Pascal Febvre

Lei Jiang, Yong Xu, Chuanwei Zhang

Atomtronics has the potential for engineering new types of functional devices, such as Josephson junctions (JJs). Previous studies have mainly focused on JJs whose ground states have zero or $\ensuremath{\pi}$ superconducting phase difference across the junctions, while arbitrary phase-tunable JJs may have important applications in superconducting electronics and quantum computation. Here we show that a phase-tunable JJ can be implemented in a spin-orbit-coupled cold atomic gas with the magnetic tunneling barrier generated by a spin-dependent focused laser beam. We consider the JJ confined in either a linear harmonic trap or a circular ring trap. In the ring trap, the magnetic barrier induces a spontaneous mass current for the ground state of the JJ, demonstrating the magnetoelectric effects of cold atoms.