A team of German physicists has just created the world's smallest working engine. Powered by a single electrically-charged calcium atom, the new device is claimed to have the equivalent thermodynamic efficiency (if scaled to size) of an average automobile engine. Basically a heat-exchange engine, its single-atom acts as both fuel and powerplant and is heated by electrical noise and cooled by laser beam.
Heat-exchange engines convert thermal energy into mechanical work (a car engine is one such type) in line with the first and second laws of thermodynamics, in that the energy applied to the system is conserved in the process of converting heat to mechanical motion, and that efficiency limits and energy flows are observed.
In the same way, this new minuscule nano-powerhouse also undergoes a thermodynamic cycle just like the processes that occur in the cylinders of a standard car engine, only that the power generated is converted into a vibration of the atom so that it plays the role of both the motor and the energy store alike.
Scientists working at Johannes Gutenberg University Mainz (JGU) in collaboration with theoretical physicists from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), created the engine by capturing and confining a single calcium atom in a tapered ion trap (known as a Paul Trap and named for the physicist Wolfgang Paul, who shared the Nobel Prize in Physics in 1989 for his work), and then driving it thermally by coupling it alternately to hot and cold reservoirs.
In this case the "hot" reservoir being opposing voltage noise waveforms applied to the outer electrodes of the Paul trap, while the "cold" reservoir was created by shooting a 397 nm laser beam at the atom. By switching between heating and cooling at precise intervals, the engine maintained a harmonic oscillation in the axial direction. In other words, the atom moved back and forth driven by heat and cooling cycles just like a normal heat-exchange engine.
Given that it also delivered an output of 10-22 watts, and had a claimed efficiency of around 0.3 percent, it actually produced a significant amount of work for the input energy converted.
To verify that the picayune powerplant was actually behaving like an engine, the amplitude of the steady-state oscillation of the atom (that is, the amount that the atom moved back and forth) was measured by recording fluorescence images with an ultra-fast Intensified Charged Couple Device (ICCD) camera using an exposure time of just 700 ns (700 billionths of a second).
Once a mere speculation by the great physicist Richard Feynman, who envisioned tiny motors working at the single-atom level, this breakthrough research is the realization of that dream. But more than this, the new device may see a range of innovative practical uses, such as in single-ion refrigerators and pumps (particularly as the process may be reversed to remove heat).
From a quantum physics perspective, the system could – with a few appropriate modifications – allow the study of small quantum machines and research into quantum effects within thermodynamics, such as quantum coherence (such as that described in quantum energy transport systems), as well as providing the means to test quantum resource theory predictions.
The results of this research were recently published in the journal Science.
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