Reliable logic circuit elements that exploit nonlinearity in the presence of a noise floor.

The response of a noisy nonlinear system to deterministic input signals can be enhanced by cooperative phenomena. We show that when one presents two square waves as input to a two-state system, the response of the system can produce a logical output (NOR/OR) with a probability controlled by the noise intensity. As one increases the noise (for fixed threshold or nonlinearity), the probability of the output reflecting a NOR/OR operation increases to unity and then decreases. Changing the nonlinearity (or the thresholds) of the system changes the output into another logic operation (NAND/AND) whose probability displays analogous behavior. The interplay of nonlinearity and noise can yield logic behavior, and the emergent outcome of such systems is a logic gate. This "logical stochastic resonance" is demonstrated via an experimental realization of a two-state system with two (adjustable) thresholds.