Energetic cost of feedback control

Successful feedback control of small systems allows for the rectification thermal fluctuations, converting them into useful energy; however, itself requires work. This paper emphasizes fact that controller is a physical entity interacting with feedback-controlled system. For specifically designed class controllers, reciprocal interactions become nonreciprocal due to large timescale separation, which considerably simplifies situation. We introduce minimally dissipative model, illustrating findings using simple example. find work required run must at least compensate decrease in entropy operation.