Superconducting memory bit based on Josephson varphi junction

What is it about?

We demonstrate an operation of a single bit of a superconducting memory based on a varphi Josephson junction. Such a junction has two generate ground states, which are used to store information. Writing and readout are performed by applying a small magnetic field or the bias current. A varphi Josephson junction is fabricated as superconductor-insulator-ferromagnet-superconductor multilayer with tailored thickness of the ferromagnet. Integration with RSFQ logic is straightforward.

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Why is it important?

Although, in the current implementation we use Josephson junction with ferromagnetic interlayer, the information is stored NOT in the ferromagnet, but in one of the two internal states (-varphi and +varphi) of varphi Josephson junction. Thus, no remagnetisation is required! Ferromagnet is only needed to create varphi junction. In turn, varphi JJ can also be implemented using other technologies, e.g. based on d-wave superconductors.