Energy Efficiency in Computing Logical Operations: Fundamental Limits with and Without Feedback

The exponential increase in the ability to compute and store massive amount of data is fueling transformative changes in the human condition. It has led to a highly connected world with information being accessible at remote parts of the world. The current focus on interconnection of infrastructural systems such as the, power grid, financial markets, health care systems, and the Internet of Things (IoT), all bear a direct relationship to the advances in the integrated chips, where the complexity and the number of components has doubled almost every two years, following the Moore's law. Less known is the fact that the energy dissipation per computation has outpaced Moore's law which is at the heart of the mobile computation revolution, enabling, small form-factor devices packed with high computational capabilities that include, light laptops, tablets, and cell-phones. With such exponential increases, it is inevitable that limits of current approaches and practices for computation and memory related technologies are reached. This proposal addresses the basic operations of computation and memory with respect to the fundamental limits on the energy dissipation needed to perform the operations. It also studies the energy cost associated with measurement and feedback actions for performing computing and memory management operations. It provides proof of concept experiments and methods to demonstrate realizability of the computational and memory related operations with energetics tens of order smaller than the current practices. The associated analysis of fundamental primitives of computational operations and the proof of concept experiments will guide realizations of future energy efficient computational platforms and will continue the remarkable increase in speed and efficiencies with which computations are performed.

The focus of the project is on the fundamental limits on the energetics of computations and memory. The project investigates primitives of computational operations both analytically and experimentally. It uses the abstraction of the state of a memory bit via the position of a particle in a double well potential in a thermal bath. Transfer of particle across the wells in a potential landscape is used to realize AND, NOT and erasure operations. Under the project goals, bounds on the minimum energetics of transferring the state of the particle in the double well potential will be analytically derived. Here, key aspect of the approach is to estimate the change in entropy from the initial to the final state, and, relating the change in entropy to the energy associated with the transfer of state. The transfer of state can be accomplished with or without measuring the state of the particle in the double well potential; here, the effect of feedback where the measurement guides the protocol for transferring the state will be understood and analyzed. The theoretical foundations that link computations, statistical mechanics, and feedback will be accompanied by a versatile experimental platform. Double-well potentials will be realized by controlling optical fields which have the scale of energetics suited for the study. The experimental protocols will accommodate the need for different speeds of transferring the state; important to emulate quasi-static processes. Accurate and precise measurements of the position of the particle will be used for the estimation of the energy required in moving the particle across wells. The measurement protocols will be precisely characterized that will enable the study of closed-loop strategies that alter the transfer protocol based on measurements. The project will provide both analytics and proof-of-concept experimental realizations of basic primitives of computations with orders in magnitude smaller energy footprint.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.