We present a nanomechanical device, operating as a reprogrammable logic gate, and performing fundamental logic functions such as AND/OR and NAND/NOR. The logic function can be programmed (e.g., from AND to OR) dynamically, by adjusting the resonator's operating parameters. The device can access one of two stable steady states, according to a specific logic function; this operation is mediated by the noise floor which can be directly adjusted, or dynamically "tuned" via an adjustment of the underlying nonlinearity of the resonator, i.e., it is not necessary to have direct control over the noise floor. The demonstration of this reprogrammable nanomechanical logic gate affords a path to the practical realization of a new generation of mechanical computers.A practical realization of a nanomechanical logic device, capable of performing fundamental logic operations, is yet to be demonstrated despite a longstanding effort toward scalable mechanical computation. [1][2][3][4] This effort can be traced back to 1822 (at least), when Charles Babbage presented a mechanical computing device that he called the "Difference Engine", to the Royal Astronomical Society. 1 Before this event, though, the search for mechanical computing devices had already been inherent in attempts to build machines capable of computation. This search has, today, taken on added urgency as we seek to exploit emerging techniques for the manipulation of matter at nanometer length scales. With Boole's ideas on logic operations with two states an added dimension to computing, logic elements or gates have come to dominate modern computation. However mechanical logic, especially at the very small length scales and in the presence of a noise floor, has proven difficult to realize despite some recent experimental efforts. [5][6][7] The control and manipulation of mechanical response at nanometer scales can be realized by exploiting a (seemingly) counterintuitive physical phenomenon, stochastic resonance (SR): 8 in a noisy nonlinear mechanical system, the controlled addition of noise can enhance the system response to an external stimulus. Signal amplification in such a setup has been experimentally realized in nonlinear nanomechanical resonators configured as two-state devices. [9][10][11] Recently, it has been demonstrated 12 that when two square waves are applied as input stimuli to a two-state system, the response can result in a specific logical output with a probability (for obtaining this output) controlled by the noise intensity. Furthermore, changing the threshold (either via adjusting the nonlinearity strength or applying a controlled asymmetrizing dc signal) can change or "morph" the system output into a different logic operation. 12 Our experimental logic device consists of a nanomechanical resonator, operating in the nonlinear regime, wherein two different vibrational states coexist; for an underdamped system underpinned by an a priori monostable (but nonparabolic) potential energy function, these vibrational steady states are induced by biasing the...
