Reversible Fluxon Logic with shift registers

Reversible digital logic can improve energy efficiency over irreversible logic. Reversible logic gates in superconducting circuits are currently made in the adiabatic type, where drive fields evolve the bit state, but we are developing Reversible Fluxon Logic (RFL) in the ballistic type – key gates are solely powered by bit state inertia. RFL represents the bit states by the two topological charges (flux polarities) of fluxons in a Long Josephson Junction (LJJ). Ballistic gates consist of at least two LJJ connected by a circuit interface and use a resonant conversion of an input fluxon to and from a localized field at the interface. At the end of this process a new fluxon is created in another LJJ and its polarity may deterministically differ from the input bit, thus enabling bit switching. In simulations 1- and 2-bit RFL gates can restore 97% of the input fluxon energy in the output fluxons. While previous RFL 2-bit gates require synchronous input bits, newly developed gates store an internal flux state by which the timing restriction is lifted (asynchronous). This is demonstrated with the shift register – the input state is stored as internal flux while the previously stored flux state transfers to a ballistic output fluxon. We apply a model developed to describe RFL dynamics.