Synopsis: “Squeezed” Engine Could Break Thermodynamic Limits

A theoretical analysis shows that nanoengines based on quantum squeezed states can perform several times more efficiently than classical engines.
Synopsis figure
Courtesy Johannes Roßnagel/University of Mainz

Classical thermodynamics developed in an era when the typical engine weighed over a ton. Now, researchers study engines small enough that quantum effects can be considered and well-known limits may no longer apply. In a paper in Physical Review Letters, physicists envision a nanoengine that takes advantage of “squeezed” states whose noise is concentrated in one parameter and reduced in another. The authors find that the efficiency of this device could be at least a factor of 2 higher than the classical Carnot limit.

The Carnot limit gives the maximum efficiency (work output divided by heat input) for a heat engine driven by the temperature difference between two thermal reservoirs. However, this limit does not apply to reservoirs that are engineered to be out of thermal equilibrium. Recent theoretical work has shown that engines coupled to reservoirs exhibiting quantum correlations or coherence can surpass the Carnot bound.

Johannes Roßnagel from the University at Mainz, Germany, and his colleagues have imagined a new nanoengine design where squeezing puts the system out of equilibrium. A squeezed state has a nonuniform distribution of noise. For example, an oscillator might have less noise in its amplitude but more noise in its phase. The researchers investigated an engine consisting of a single trapped ion, whose state is characterized by its oscillation around the trap axis. The reservoirs in this case are two laser fields tuned to add or remove oscillation energy from the ion. When the higher-temperature reservoir is squeezed, more energy is added to the ion, allowing it to produce more work. In their calculations, the researchers adjusted the engine’s parameters for maximum power and found that squeezing can raise the efficiency to 20% for a realistic trapped ion system. – Michael Schirber


More Features »


More Announcements »

Subject Areas

Atomic and Molecular PhysicsStatistical Physics

Previous Synopsis


Tossing and Turning

Read More »

Related Articles

Viewpoint: Sensing Magnetic Fields with a Giant Quantum Wave
Strongly Correlated Materials

Viewpoint: Sensing Magnetic Fields with a Giant Quantum Wave

A refined version of a Bose-Einstein-condensate microscope detects static magnetic fields near the surface of a chip with unprecedented sensitivity and over a wide temperature range. Read More »

Synopsis: Straying from the Norm in Pedestrian Movements
Complex Systems

Synopsis: Straying from the Norm in Pedestrian Movements

Experiments tracking people as they walk down a corridor reveal universal behaviors that, if incorporated into models, could ensure safe flow in large crowds. Read More »

Focus: Atomic Impersonator

Focus: Atomic Impersonator

Calculations show that a carefully engineered laser pulse can induce an atom to emit light as if it were a different atom. Read More »

More Articles