Quantum Is Still Surprising Us

Most of us don’t think about quantum mechanics very much, if at all, even though our everyday life depends on it (such as in semiconductors or GPS). It is said to be the most accurate theory in terms of testable predictions, even though the fundamentals of the theory don’t make sense in our everyday life. Light is both a particle and a wave? Particles can be “entangled” even when they are vast distances apart? Cats that can be alive and dead at the same time?  

Ready for quantum batteries? Credit: Quantum Insider

It’s so counterintuitive that a recent Nature survey found that even leading quantum physicists don’t agree on what it really means. “I find it remarkable that people who are very knowledgeable about quantum theory can be convinced of completely opposite views,” says Gemma De les Coves, a theoretical physicist at the Pompeu Fabra University.

Quantum computing has become a big thing lately, thought to be the future of computing. The Wall Street Journal says: “The emerging technology promises better medicine, faster internet and more sustainable food production,” not to mention upending all existing cryptography. We’re quickly rushing into the AI world, but quantum may be the next gold rush.

I knew all that, but what I did not know was that included in the quantum revolution are quantum batteries.

We all know about batteries, whether they’re for our phones, our cars, our flashlights, our computers, and a host of other applications. Batteries have existed for several hundred years, and basically all have relied on some form of chemical reaction. Quantum batteries, on the other hand, use what is called quantum superposition, moving electrons into higher energy states to store energy.

The field is still in early days, and one of the major problems has been how long researchers could get the quantum batteries to store energy. They charged rapidly, but also lost their charge rapidly, in a matter of nanoseconds. Now researchers from RMIT University and CSIRO (Australia’s national science agency) have announced a new method that lasts a 1,000 times longer – we’re talking microseconds now, folks. The results were published in PRX Energy.

That's what a quantum battery looks like? Credit: RMIT

I won’t try to get into the weeds to explain the approach, other than to regurgitate what was in the title, that they used molecular triplets in Dicke Quantum Batteries. The researchers’ “popular summary” explains:

Quantum batteries may offer scalable charging power density. Those based on the Dicke model enable a cavity-enhanced energy transfer process called superabsorption, but the lifetime is limited by fast radiative emission losses and super radiance. Here, the authors show a promising approach to extend the energy storage lifetime using molecular triplet states, which they test on five devices across a triplet-polariton resonance. One device shows a 1000-fold increase in storage time compared to previous demonstrations.

Study co-author and RMIT PhD candidate Daniel Tibben said: “While we’ve addressed a tiny ingredient of the overall piece, our device is already much better at storing energy than its predecessor.”

“While a working quantum battery could still be some time away, this experimental study has allowed us to design the next iteration of devices,” study co-author and RMIT chemical physicist Professor Daniel Gómez said. “It’s hoped one day quantum batteries could be used to improve the efficiency of solar cells and power small electronic devices.”

Coauthor Francesco Campaioli notes that, while the storage is still only microseconds: “It’s the equivalent of having a phone that charges in 30 minutes and runs out of battery after about 20 days if left idle. Not too shabby.” He adds: “There is still a lot of work to do to develop these ideas into a technology that could impact everyday life. What matters to me is that we have a clear understanding of the challenges that we need to overcome to make it happen.”

And that’s not all the recent news in quantum batteries.

A new paper from researchers at PSL Research University in Paris and the University of Pisa proposes “a deceptively simple quantum battery model that displays a genuine quantum advantage, saturating the quantum speed limit.”  

"Our model consists of two coupled harmonic oscillators: one acts as the 'charger,' and the other serves as the 'battery,'" explained Vittoria Stanzione and Gian Marcello Andolina, co-authors of the paper, to Phys.org. "The key ingredient enabling the quantum advantage is an anharmonic interaction between the two oscillators during the charging process. This anharmonic coupling allows the system to access non-classical, entangled states that effectively create a 'shortcut' in Hilbert space, enabling faster energy transfer than in classical dynamics.”

Got it?

They added: "To the best of our knowledge, this work provides the first rigorous certification of a genuine quantum advantage in a solvable model. Furthermore, the proposed setup can be realized with current experimental technologies."

It seems like a big deal that it outperforms “classical” approaches and is achievable with existing technology.

Finally, researchers from Hubei University, the Chinese Academy of Sciences, and Lanzhou University have proposed a “diamond-based” approach to quantum batteries, using the nitrogen-vacancy (NV) center in diamond. Who knew diamonds had a nitrogen vacancy?

Schematic illustration of the QB scheme. Credit: Jun-Hong An

The paper was published in Physical Review Letters, and deals with the issue of quantum batteries “self-discharging” (due to what is called decoherence). "The main advantage of our QB scheme in the NV center is that the unique hyperfine interaction between the electron and the ¹⁴N nucleus, which is absent in other platforms, permits us to coherently optimize this ratio," Jun-Hong An, co-senior author of the paper, told Phys.org. "This is the irreplaceable feature of our QB scheme in the NV center. This irreplaceability endows us with the ability to mitigate the self-discharging on one hand, and to maximize the extractable work on the other."

Again, both of those are big deals.

As a result, the researchers conclude: “our results pave the way for the practical realization of the QB.” Professor An believes: "A quantum-technology revolution is underway, which uses quantum resources to overcome various performance limitations of devices set by classical physics."

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Quantum computing seems like it is where AI was five years ago, still around the corner but turning that corner faster than we realized. And I feel like quantum batteries are where quantum computing was five or so years ago, starting to overcome the practical issues that had once seemed insurmountable.

They’re going to happen, sooner than we think.

I don’t think they’re going to replace the existing power grid, and maybe not even your cell phone battery, but in a world of the Internet of Things, nanobots, and other things that edge closer to the quantum level, they’re going to be important.