Harnessing 'Spooky Action at a Distance' To Make a Better Battery
Quantum entanglement exploiting 'quantacells' are still a ways off, but here's proof that it works.
While there are some pretty serious hurdles in between quantacell theory and quantacell realization, an international group of physicists has at least offered a tantalizing hint of the potential of quantum mechanics in battery technology.
Their work, which is published in the current New Journal of Physics, describes an example or model of a battery engineered around the concept of qubits—a qubit being the generalized form of a quantum information carrier—and quantum entanglement, which is the strange ability of pairs or groups of particles to share quantum states over large distances, what Einstein famously (or infamously, perhaps) dubbed "spooky action at a distance."
The idea is fairly intuitive. Quantum entanglement allows multiple particles to share identical states, in a sense, and this corresponds to energy levels too. If we boost one particle, we can spread that around to all of the particles in that system. This entanglement idea is usually thought of more in terms of information than energy, but energy and information are intimately connected via thermodynamics.
"What we find is that if you allow for protocols which generate entanglement, then greater charging powers can be achieved than if you had only standard 'classical' correlations," John Goold, a study co-author and physicist at the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy, told me.
In any realistic device there is a trade off between efficiency—in this case the maximal energy deposited in a charge—and power, e.g. the amount of charge per unit of time. Usually, when you require higher power, you'll lose efficiency. The authors show that the power of charging a quantum battery can be enhanced via entanglement.
Imagine a long line of wind-up toys. Your task is to wind them all up, which is a way of storing energy in a mechanical system. You can go on down the line winding each toy up one by one, which is one way of charging the system. Or, you can imagine that all of those toys share a single "winder." To wind up all of the toys, you just need to wind one. You'll need to spend the same amount of energy winding, but without having to go all of the distance to wind the toys one at a time. This is obviously a pretty helpful property.
"When charging more than one battery you could still charge them all individually, using each battery's individual 'winder,'" Felix Binder, a fellow co-author and Oxford physicist, explained. "This would take the same time as for a single battery. If quantum correlations are allowed during charging, a larger set of possible charging operations becomes available. In the wind-up toy picture, single winders that charge all toys at once would correspond to such entangling operations."
"Amongst those 'global' winders we could pick a particularly good one to reduce the charging time for N batteries by a factor of 1/N," Binder continued. "The advantage in the example lies solely in the speedup: The same work is done, but faster. An explanation of this speedup is that a shorter distance can be chosen for the charging path through state space."
The catch here is that the energy scales involved in quantum systems are very, very small. The most efficient battery in the universe is pretty much worthless if it can't hold enough energy to do any real work.
"'Size' is here a question of energy scales," Goold said. "Our study is a theoretical proof-of-principle that quantum physics can provide a speedup in depositing energy into a system. These speedup effects would be relevant in two cases: 1) Mechanical devices become small enough that energy scales are comparable to current implementations of quantum systems. 2) Quantum systems are scaled up and robustly controllable at energy scales that are of practical importance."
Binder noted that his group is currently thinking through the next stage of quantacell research, which is relating all of the above to experiments that can actually be conducted in a laboratory in a specific real-life system. In the meantime, it will have to remain just a pretty cool idea.