08/04/2021 at 3:12 AM #33479Anonymous UserParticipant
Heat engine on an atomic scale
Atomic gasoline engine: Physicists have turned individual atoms into tiny heat engines – engines in atomic format. Instead of a piston, the absorbed heat energy moves the spin of these atoms and flips it over. The special thing about it: This Otto cycle on a quantum scale is efficient, controllable and surprisingly stable in terms of fluctuations, as the researchers report in the specialist journal “Nature Communications”.
Whether internal combustion engine or steam engine: Classic heat engines convert thermal energy into mechanical work. Ideally, they are efficient, run smoothly and deliver high performance with the lowest possible heat input. At the same time, the laws of thermodynamics ensure that part of the energy is always lost – a perpetual motion machine is therefore impossible.
An atom as a heat engine
But can the principle of the heat engine also be transferred to the nanoscale? Around ten years ago, researchers constructed a steam engine only a few micrometers in size. But the first disruptive effects occurred even at this magnitude: The self-movement of the water molecules triggered by the heat caused the micromotor to stutter.
Now a research team led by Quentin Bouton from the Technical University of Kaiserslautern has taken the miniaturization of the heat engine to extremes: its engine consists of only one atom. The aim of the physicists was to design this quantum machine in such a way that, despite the fluctuations and disruptive effects typical of the quantum scale, it runs smoothly and controllably.
Heat exchange through atomic collisions
To do this, the researchers first cooled a cloud of several thousand rubidium atoms down to almost absolute zero. They serve as heat exchangers and buffers for the actual engine. This consists of ten individual cesium atoms that are inserted into this ultra-cold atomic cloud. Heat exchange between the atomic quantum machine and the surrounding atoms always occurs when the atoms collide.
“When the so-called spin exchange collisions take place, the rotary movements of the colliding cesium and rubidium atoms tilt in the other direction,” explains Bouton’s colleague Jens Nettersheim. Depending on the initial ratio of the two spins, these collisions gradually increase or decrease the energy state of the cesium atoms – the maximum or minimum is reached after six spin exchange collisions.
Not stuttering Otto cycle
In principle, this creates an Otto cycle in the quantum world: As in a macroscopic heat engine, the cesium atom converts the supply or release of thermal energy in the form of collisions into mechanical movement – here in the change of its spin direction. In order to make the work done usable, one could, for example, couple a microparticle with this spin via the magnetic field, explain the physicists.
The decisive factor, however, is that your heat engine on a quantum scale runs without stuttering and delivers consistently high performance with high efficiency, as Bouton and his colleagues report. This is achieved by driving the cesium atoms into a kind of saturation state through multiple collisions. “After a certain period of time, they remain in one state, so fluctuations can be controlled,” explains senior author Artur Widera.
Adjustable down to the last quantum
At the same time, the behavior of the cesium atoms and their rubidium environment can be easily controlled. “The unique features of this system not only allow us to regulate and monitor the heat exchange between the two at the individual quantum level. We can also operate the quantum machine in a targeted manner in a regime with high efficiency, high performance and low performance fluctuations, ”the researchers state.
According to the scientists, this system offers a versatile experimental platform for researching fundamental new effects in quantum machines and interactions. (Nature Communications, 2021; doi: 10.1038 / s41467-021-22222-z)
Source: Technical University of Kaiserslautern
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