Abstract
The efficient conversion of thermal energy to mechanical work by a heat engine is an ongoing technological challenge. Since the pioneering work of Carnot, it has been known that the efficiency of heat engines is bounded by a fundamental upper limit—the Carnot limit. Theoretical studies suggest that heat engines may be operated beyond the Carnot limit by exploiting stationary, nonequilibrium reservoirs that are characterized by a temperature as well as further parameters. In a proof-of-principle experiment, we demonstrate that the efficiency of a nanobeam heat engine coupled to squeezed thermal noise is not bounded by the standard Carnot limit. Remarkably, we also show that it is possible to design a cyclic process that allows for extraction of mechanical work from a single squeezed thermal reservoir. Our results demonstrate a qualitatively new regime of nonequilibrium thermodynamics at small scales and provide a new perspective on the design of efficient, highly miniaturized engines.
- Received 25 April 2017
DOI:https://doi.org/10.1103/PhysRevX.7.031044
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
Squeezed Environment Boosts Engine Performance
Published 13 September 2017
A tiny engine can surpass the Carnot limit of efficiency when researchers engineer the thermal properties of the environment.
See more in Physics
Popular Summary
Designing efficient and powerful engines at the microscale and nanoscale—engines whose dimensions can be measured in millionths, or even billionths, of a meter—is currently one of the most far-reaching challenges of physics and engineering. Such engines could have novel applications in nanotechnology and in the life sciences, such as robot-aided manipulation of biological cells. Similar to their macroscopic counterparts, the underlying principle of microengines and nanoengines is the conversion of fuel, which provides thermal or chemical energy, into mechanical work. The efficiency of this conversion is generally restricted to the Carnot limit, which says that the maximum efficiency of an engine is set by the ratio of the hottest to coldest temperatures. In a proof-of-principle experiment, we demonstrate a minimalist nanomechanical engine operating with an efficiency beyond the Carnot limit by using what is known as a squeezed thermal heat bath.
Squeezed thermal states, in which fluctuations of one property (for example, momentum) are reduced at the expense of greater fluctuations in another parameter (such as position), are the mechanical analog of more well-known squeezed states of light. Our engine consists of a simple nanobeam structure that oscillates when exposed to a changing electric field. We show that it is possible to design a cyclic process that allows for extraction of mechanical work from a single squeezed thermal reservoir.
Our results quantitatively test our understanding of nonequilibrium thermodynamics at small scales and provide a new perspective on the design of efficient, highly miniaturized engines.