Progress Towards Reversible Computing With nSQUID Arrays

Circuits of nSQUIDs are expected to be able to operate reversibly in both classical and quantum modes. Here we present the first circuit that is fully operational classically at up to 5 GHz clock frequencies. The circuit contains two shift registers (i.e., cells that transfer the input data to the outputs) with a common clock ring. We estimate that the dissipated power is close to the thermodynamic threshold of k _B T ln 2 per switching. We also show that after a proper scaling of parameters, the nSQUID circuits should work similarly in the quantum mode. In this case, the unique advantage of nSQUID circuits is their ability to transfer the quantum data along the chip and therefore form complex multi-qubit circuits bypassing the problem of controllable keys. In the fully quantum regime, the nSQUID arrays should implement directly the scheme of universal adiabatic quantum computation.