Quantum batteries could charge more efficiently by skirting conventional rules of causality.
at the University of Tokyo and his colleagues analysed whether a particularly counterintuitive quantum phenomenon could play a role in powering quantum batteries 鈥� energy storage devices that could harness quantum effects.
In the classical world, causality goes in just one direction: if event A causes event B, then it is clear that B did not also cause A. But at the quantum scale, Chen says that it can be impossible to tell which way such causality goes 鈥� this is called indefinite causal order. Both directions of causality can be put in a special quantum superposition where both and neither are simultaneously true.
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He and his colleagues applied this idea to two chargers powering a quantum battery. They calculated how much energy the battery would gain and how efficiently it would charge for three protocols: one where the chargers were connected sequentially, one where the chargers simultaneously powered the battery and one where it was impossible to tell which charger was at work because these two causalities were in a superposition.
This last approach gave the battery the most energy in the most efficient way even when the connection between the chargers and the batteries was relatively weak. This means the charging process could work well even for suboptimal chargers.
Chen and his colleagues performed a proof-of-principle experiment with quantum light that showed that this indefinite causality protocol could be implemented with a device called a quantum switch. However, they didn鈥檛 directly test charging a full-fledged quantum battery yet.
at the University of Hong Kong in China, whose team introduced the quantum switch as a demonstration of indefinite causality in 2009, says it is thrilling to see that it could be part of something as useful as charging quantum batteries. 鈥淚t is definitely one exciting new idea and a striking illustration that foundational ideas on quantum theory can lead to practical applications,鈥� he says.
Though the new work is intriguing, just how much indefinite causal order can do for quantum batteries will be revealed in future experiments, says at the Institute of Photonic Sciences in Castelldefels in Spain. Most studies of quantum batteries are currently theoretical so devising experimentally testable charging procedures is important, he says.
Reference: Physical Review Letters,
