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New research indicates that single atoms could be transformed into engines or refrigeration, with an application in fuel cells that could be the backbone of a green energy revolution.
As the quest to miniaturize machines continues in labs across the world, researchers from Singapore may have made a breakthrough that is tough to surpass. In a new paper published in the journal npj Quantum Information, the team from the Singapore University of Technology and Design (SUTD) has revealed a method of turning a single atom into a machine — an atomic engine, or even an atomic refrigerator.
Nanotechnological devices will undoubtedly form the future of most devices, although it is hard to imagine a device smaller than a single atom. The breakthrough has significant implications for green energy and devices that require cooling, such as future computers and fuel cells in particular.
Fuel cells generate electricity via a chemical reaction and are generally considered to be a much cleaner way of generating energy than the burning of fossil fuels as emissions are much lower. Fuel cell technology is certainly emerging as a viable commercial concern with large companies taking a major interest in their use.
Car manufacturer BMW has just pledged $32 billion to research and development — a portion of which chairman of the board, Oliver Zipse, has dedicated to hydrogen fuel cell development.
The problem with fuel cells is that some energy is lost as heat during the process. The difficulty with such devices is making them efficient and cheap enough to replace more traditional ways of generating power. Increasing their efficiency means reducing the amount of energy lost as heat. The single-atom devices could do just this, taking the heat and storing it for later use.
Engines, Fridges, and Electrons
Understanding how this is the case requires a look at thermodynamics — the realm of physics that deals with how heat relates to other forms of energy. Both engines and fridges are thermodynamical machines that can effectively be considered polar opposites of each other. Whereas an engine turns energy into ‘work,’ a fridge uses work to transfer heat and reduce the local temperature.
While tiny heat engines have been manufactured in the past by using the defects in diamonds, the physics of such devices is poorly understood. The team from Singapore aimed to improve this situation by researching the thermodynamics of a single atom of barium.
The team achieved this by developing a scheme in which a laser cycles one of the barium atom’s electrons between energy states. Electrons in atomic nuclei exist in well-defined energy states which we can imagine as rungs on a ladder. Like a foot on a rung, an electron can sit in a particular state, but it cannot exist between states.
By absorbing a photon of the necessary energy an electron can ‘step up’ an energy rung. Likewise, by randomly emitting a photon of the same energy, the electron takes a step down the energy ladder. Particles tend to exist at the lowest possible energy level, described by physicists as the ground state — meaning that any excited state above this is temporary.
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The laser shifting the electron between energy states results in some of its energy being transferred into the vibrations of the barium atom. The net result of this is that the barium atom is using energy from the laser to increase its heat energy.
The atom’s vibration becomes analogous to a battery storing this energy - this stored energy can be discharged and used at a later point. The researchers also demonstrated that they could reverse the cycle to turn this atomic engine into an atomic fridge — removing energy from the vibrations of the atom.
The researchers point out that at this stage things become “fuzzy.” The problem is that it becomes less possible to simply do work on the system without transferring heat. This “fuzziness” clearly impacts the efficiency of the process the team developed, but fortunately, with the aid of scientists from NUS Physics, they were able to develop a workaround.
To examine this workaround, we return to the electron energy ladder. Deliver enough energy to the electron and it can be completely liberated from the atom. Therefore, the atom becomes ionized and its charge changes. As the number of negatively charged electrons in a neutral atom balances the number of positively charged protons in its nucleus, losing an electron results in the atom becoming positively charged.
The team used an ionized barium atom which, due to its positive charge, could be held still by electrical fields in a metal chamber. A vacuum is then created in the chamber and the team uses the laser to move the barium atom repeatedly through a cycle consisting of four stages. Through observation of the atom between cycles, the team could see that the atom’s vibrational energy increased during engine cycles and decreased during fridge cycles.
The team says that this setup can be considered a quantum engine as well as a quantum refrigerator that can store waste energy such as heat and discharge it at a later point, making it more efficient. The breakthrough could not only make the fan system of your computer obsolete but it also, by its application in fuel cells, could make fossil fuel burning a thing of the past.
References and Further Reading
Van Horne, N., Yum, D., Dutta, T. et al. (2020) Single-atom energy-conversion device with a quantum load. npj Quantum Inf 6, 37. https://doi.org/10.1038/s41534-020-0264-6
Edelstein. S. (2020) BMW re-ups electric-vehicle commitment—and hydrogen fuel-cell investment. [Online] Green Car Reports. Available at: https://www.greencarreports.com/news/1128075_bmw-re-ups-electric-vehicle-commitment-and-hydrogen-fuel-cell-investment (Accessed on 19 May 2020).