PhD student Johannes Roßnagel in collaberation with other physicists and engineers recently created the world’s smallest engine that runs off of just one atom which may have the potential to become the most efficient engine ever created.
Traditional thermodynamics were developed in an era when typical engines weighed over a ton. However as quantum effects become better understood, the well-known limitations governing typical engines can be exceeded by incredibly small engines where the limits no longer apply. A paper published in Physical Review Letters discussed in 2014 a nano engine that could have an efficiency greater by at least a factor of four higher than the classical Carnot limit governing conventional heat engines. The scientists claimed “the efficiency at maximum power of up to a factor of 4 is reached, largely exceeding the Carnot bound”. However, just recently the engine has become a reality, establishing it as the world’s smallest engine ever created by creating an engine that runs off of just one atom.
[Image Source : Gutenberg University Mainz]
The Carnot limit determines the limit of the maximum efficiency (work output divided by heat output) for an internal combustion engine driven by two temperature differences between two thermal reservoirs designed to sustain thermal equilibrium. A heat engine uses thermal energy (combustion) which is converted into mechanical work (motion) and is generally created by the combustion of a large number of particles (like kerosene, diesel, gas, or other combustibles).
Example of a heat engine: A Turbofan Jet [Image Source: K. Aainsqatsi]
The experimental single-atom heat engine uses a linear Paul trap (see diagram below) that traps a single negatively charged atom of calcium. The atom, when low in energy, is attracted to the closed end of the electrodes where it is introduced to a large electrostatic force and a laser acting as the hot reservoir by accelerating the atom. The two negative fields repel each other, giving the atom thermal energy and propelling it to the large side of the engine. The atom is then cooled through Doppler cooling by another laser which acts as the cold reservoir on the large side of the cone, therefore sending it shooting back towards the hot end. The atom repeats this cycle causing it to vibrate incredibly fast, making it the engine and the part of the fuel (with some laser input).
Paul Trap holding atom with blue lasers in between charged electrodes [Image Source: Science Mag]
Although the energy is stored within the engine, Roßnagel says, “if you imagine that you put a second ion by the cooler side, it could absorb the mechanical energy of our engine, much like a flywheel [in a car engine],” thus harnessing the power of the engine. The nano engine also possesses a feature which has a profound effect, one that Roßnagel argues could increase the efficiency so much, it could overcome the current limitations defined by Carnot’s law- the law that is supposed to give an engine its maximum efficiency range. As the atom is heated and cooled, its size varies ever so slightly which alters the probability of where the atom exists. Since the atom is tightly confined within the electrodes, the temperature change forces the atom to vibrate back and forth with the expansions and contractions in its size. The frequency of the laser which heats and cools the atom is matched to the frequency that the atom naturally vibrates at in order to achieve maximum efficiency. The atoms varying size gives the engine a boost, much like a supercharger giving it the capability to surpass the Carnot Limit by a large margin.
As the atom is heated and cooled, its size varies ever so slightly which alters the probability of where the atom exists. Since the atom is tightly confined within the electrodes, the temperature change forces the atom to vibrate back and forth with the expansions and contractions in its size. The frequency of the laser which heats and cools the atom is matched to the frequency that the atom naturally vibrates at in order to achieve maximum efficiency. The atoms varying size gives the engine a boost, much like a supercharger giving it the capability to surpass the Carnot Limit by a large margin.The engine was able to sustain a power output of 3.4 × 10 ^-22 joules per second, which is rather impressive given the mass of one calcium atom is 6.3 x 10^-23 grams, an incredibly efficient ratio.
Although the engine is impressive, the claims that the engine can “break” any laws of physics should receive heavy scrutiny and skepticism. Although the use of the squeezing method increases the efficiency of the engine, one must take into consideration the force required to create the effect, a force that requires a work input that uses up some of the energy. The technology is impressive, but the sheer size of the engines alone which require a large amount of laboratory space will hinder the engine from being seen outside the lab anytime soon. Perhaps one day these engines could help cool down quantum computers, power nanobots, or maybe give us an incredibly reliable source of energy. However, the technology still has still yet a ways to develop before it becomes usable as an energy source.