What is a quantum battery
In April, researchers at the Korea Institute for Basic Science (IBS) proposed a new theory for a quantum battery that could charge electric vehicles 200 times faster , which means charging time at home will be reduced from 10 hours to about 3 hours minute. At high-speed charging stations, charging time will be reduced from 30 minutes to just a few seconds. A related paper was published in the journal Physical Review Letters [1].
So, what exactly is a quantum battery?
Recently, AZoQuantum conducted an interview with three authors, Dominik Šafránek, Ju-Yeon Gyhm and Dario Rosa [2].
How did you start working on battery charging and quantum batteries?
Dario: In my case, it started because a friend invited me to start working on this topic: he told me about the concept of quantum batteries. I realized that some of my background in quantum mechanics might be useful. Because essentially, charging a battery is studying how to make the time evolution of quantum states efficient. So, given my background, they said: well, why not? This is my start.
Dominik: Actually I already knew about quantum batteries, but Dario got me involved in this project. Another kind of physics I'm working on also has expertise in the latest areas: that includes constraints on the rate of evolution.
Ju-Yeon: For me, Dario also suggested that I look into quantum batteries. The first topic he gave me was actually his research, and while I couldn't understand what he was doing, I thought I could do other things to improve the results of quantum batteries.
What does quantum battery mean?
Dario: Simply put, it goes something like this: a quantum battery is in a quantum state, and we can think of a quantum state as the quantum version of the "bits" in a computer. You can relate energy to quantum states by starting from a very low energy state and performing the charging process. Bring a low energy state to another state - this state has high energy where energy is stored and can be used at a later stage by restoring the state to its original configuration.
Dominik: Discharging in a classical battery changes the basic chemistry of the battery, which is the same, but now using a quantum state. In quantum computers, they use superconducting qubits. These are also in quantum states because they can have different energy levels. Ultimately, quantum batteries are to classical batteries what quantum computers are to classical computers.
Dario: A new idea that came up in 2012 was to ask: Can we use the energy level of a state to store our energy for a period of time and then use it? This gave rise to the idea of quantum batteries. This means that the state needs to be raised to a highly excited point, hold this energy, and then release it when needed.
How important are electric vehicles in tackling the emissions that contribute to the climate crisis, and how can quantum technology be applied?
Dominik: None of us are experts on the climate crisis, but I can speak as a physicist. In my impression, there are still some unresolved issues with electric vehicles. This is mainly because the current technology for recycling lithium-ion batteries is limited: it actually takes a lot of carbon dioxide to make them, and if they're not recycled, it's lost; I know of companies that are working on this. There is also a potential problem with the global supply of the necessary ingredients for lithium-ion batteries, so if these things end up fighting the climate crisis, it could be of a slightly different design.
As of now, electric vehicles could be a huge step toward things of the future that could actually handle this crisis. Ultimately, given the resolution of the above issues, it is still important to consider where the power is coming from. For example, if it were made by burning wood or coal, an electric car would actually be far worse than current combustion engine cars; natural gas is cleaner, but still far from zero-emissions goals.
So I think it will be necessary, sooner or later, to shift our economy to renewable energy in any way possible. In renewable energy I mainly want to emphasize nuclear fusion, we can use the energy of hydrogen, hydrogen can be collected from sea water, there will not be any carbon dioxide emissions, and there will be no nuclear waste; so it will also be a more stable energy source , does not depend on clouds or wind.
A large-scale project of this type, a demonstration of a future power plant, is currently under construction in France.
Dario: Our paper is not directly related to cars. We are theorists, so applications such as electric vehicles are a good way to envision how this possibility of charging using quantum technology could be useful in the future.
Anytime you have a battery (made up of many smaller cells), you have room to gain potential advantages by using quantum resources. Also, there is still a long way to go to use this technology in applications such as electric vehicles, and sometimes I like to joke that maybe I won't live long enough to see a car with quantum technology! But to be more specific, we know that electric cars are made of large cells with about two hundred small cells. Here's a potential point: quantum effects can be huge and lead to huge advantages.
How can quantum batteries achieve faster charging?
Dominik: If you're charging through an electrical outlet, you have 230 volts inside -- we call it "potential". A larger potential means faster charging. In fact, if you use the quantum method, the advantage comes from the fact that you can have one source of potential and charge all the batteries at the same time. Say you have 10 classic batteries, you need 10 times the voltage to charge them because they all have to have their own potential.
Using quantum resources can require 10 times less potential to charge: due to the global operation, different cells all use this one potential resource and can go through some highly entangled states.
Dario: This global operation makes charging faster, not because its state can get to the final state faster, but because they can find a shorter path : all batteries share the same charging source, not run faster , they get smarter in finding the right way to get to a certain point.
Your research provides a theorem for the design of quantum batteries. Could you please describe how to achieve this?
Dario: We don't do experiments. But we can try to prove the theorem. We can say that our result is rock solid because it is based on quantum mechanics; however the disadvantage is that we only have theorems for batteries.
Ju-Yeon: As Dario said, we want to charge all the batteries at the same time. In quantum mechanics, states evolve from some other operating field, and we find the necessary conditions for this field. This is the result of our theorem. We can say that the conditions in our paper must be met if we want to charge a quantum battery very quickly.
Dominik: Basically, our paper says "If you want to achieve this, you need to include this or meet this requirement in the experimental design or engineering design". Therefore, it is impossible to make a quantum battery without this. This proves that it is possible in principle, and is required to implement it, rather than a specific design.
Dario: What we are proving is a conjecture that was proposed by another team in 2017.
Do you wish someone or yourself would make a plan in the future to build a physical battery based on your model?
Dario: At the experimental level, there have been two large experiments that have demonstrated the existence of a "quantum advantage," basically demonstrating that using these components and global operations, really super-linear scaling of charging power can be achieved.
How much faster do quantum batteries charge compared to conventional batteries?
Dario: It can be up to N times faster, where N is the number of cells to make the battery. Of course, to achieve this, as we've described, requires a fully global operation. This is extremely complicated technically, even experimentally. So, at best, there may be a compromise between what you can do and what you can do in principle.
Dominik: Some Korean EV developers have batteries with only six cells, while Tesla's battery consists of 7,000 cells; in principle, it can be 6 times or 7,000 times faster. But the problem is, the technology is not yet at the level where we can control these very large entangled states that are shared between so many different parts. This is experimentally very challenging.
What timetable should the development of quantum technology have?
Dominik: Perhaps three quantum technologies worth mentioning have been used, the first being quantum cryptography : Now, Chinese banks are using quantum cryptography to communicate securely with each other. Then, the 2017 Nobel Prize was awarded to the study of gravitational wave detection using quantum sensors , a technique based on large interferometers from quantum physics that has been implemented and is very useful. Sure, we have quantum computers, and they're built, but they're not very useful. They may become very useful in the next 10-20 years.
I think we may need about five years of experiments on quantum batteries. Then, maybe in 5-10 years, some really useful applications for the industry can be considered.
Dario: Of course, the first applications will be super customized for very high technology.
How far-reaching do you think this research will be?
Dominik: Our results are a step toward the future design of quantum batteries. Probably experimental demonstrations first, followed by engineering and industry applications. Our three-person team was doing basic research and couldn't do experiments and engineering at the same time. Therefore, this research requires a global effort involving thousands of people to achieve a global transformation.
Dario: From my background, I come from a very different field and am doing something completely different. I did my PhD in string theory, and when I entered the field of quantum thermodynamics, I found it remarkable that there is a joint effort and communication between experimentalists and theorists and so on.
I would say that quantum thermodynamics is probably less well known in the enterprise at the moment. Many companies are investing in quantum computing, but not many are investing in quantum thermodynamics. One possibility is that the field is much younger, so maybe it's just part of the game.
Dominik: I think our research may lead to more institutional and public support to fund these technological shifts. If you can tell them "well, what is the end goal, what can be achieved in principle", then you can ask for more money so we can hand it over to experimentalists and engineers.
Before companies can provide funding, they need to see the potential, but they can't just see the benefits from theoretical papers. Therefore, some funding for the experiment is required.
Which questions remain to be answered?
Dario: At the model level, with this theorem we can say that the search for the best power that can be achieved is done. Once you reach this highly excited state with a lot of energy, of course you want to harness that energy. Therefore, even at a theoretical level, a theorem needs to be developed on how to extract energy from such highly entangled states.
This is still incomplete or not very practical, so is one of the main questions we hope to answer soon.
Dominik: If you have a battery and you want to charge the phone with that battery, you need to discharge the battery, right?
Dario: We're working on that. What we found is the maximum achievable bound, but Ju-Yeon is doing more research on how to better characterize, which states are suitable for reaching such bounds.
Ju-Yeon: Right now I'm interested in how to quantify measurements to give off energy. So it's more about setting better boundaries for quantum batteries.
Dominik Šafránek
Šafránek was born in the Czech Republic. He pursued PhD studies in Nottingham, UK and Vienna, Austria, before continuing as a postdoc in Santa Cruz, California. Now, he lives in Daejeon, South Korea, as an independent researcher. He is a physicist working on concepts of quantum information, quantum metrology, thermalization of quantum systems and entropy.
Dario Rosa
Rosa is a theoretical physicist currently working on quantum chaos, quantum many-body physics, and quantum thermodynamics. In 2014 he received his PhD in String Theory and Quantum Gravity from the University of Milan-Bicocca. After that, he came to Korea and worked as a postdoctoral fellow at Seoul National University (2014-2016), Korea Advanced Institute (KIAS, 2016-2020), and Korea Institute of Science and Technology (KAIST, 2020), and joined IBS in 2021, leading "Chaos Quantum of Many-Body Systems" research group. From March 2022, he will be an associate professor at the Korea Institute of Science and Technology University (UST).
Ju-Yeon Gyhm
Ju-Yeon Gyhm was born in Seoul, South Korea. He received a bachelor's degree in physics from Seoul National University, worked as a research assistant at the Institute of Basic Science, and is now pursuing a master's program at Seoul National University. He works on quantum batteries (batteries that store and convert energy in a quantum state), in particular the constraints on the quantum advantage of power in quantum batteries. Now, he studies how to quantify entanglement to estimate the quantum advantage of quantum batteries and quantum meteorology.
Reference link:
[1] https://arxiv.org/pdf/2108.02491.pdf
[2] https://www.azoquantum.com/Article.aspx?ArticleID=332
