Reversible Fluxon Logic: Topological particles enable gates beyond the standard adiabatic limit

Reversible digital logic aims at improved energy efficiency compared with irreversible logic gates. Conventionally it uses adiabatic drive fields, which set a speed constraint for energy-efficient gates. We study fluxons as bits in newly designed reversible gates. Fluxons arise as topological solitons in a Long Josephson Junction (LJJ). To form gates, LJJs are connected by a circuit interface, such that an incoming fluxon exchanges energy with the interface before another particle is emitted in an output LJJ. The output particle type (fluxon polarity) may deterministically differ from the input type, thus enabling switching of bit states. This process conserves potential energy through particle number conservation, unlike irreversible logic. Unlike adiabatic reversible logic, the scattering-based gates operate within a short gate time on the order of the Josephson period. We have designed and simulated an initial set of 1- and 2-bit reversible gates which can dissipate as little as 3% of the input fluxon energy. We present a CNOT gate which is made from 2-bit gate structures, operating with input of either two or one fluxon at a circuit interface, along with register cells for flux storage and polarity-dependent routing.