Imagine a battery that charges almost instantly and holds far more energy than today’s best options. This is the promise of a quantum battery, a cutting-edge energy storage device that taps into quantum phenomena like entanglement and superposition. A recent study has outlined a design for such a battery, and if future experiments confirm its potential, it could revolutionize the way we think about energy storage.

“Traditional batteries that are still in use, such as lithium-ion, alkaline, and lead-acid batteries, operate based on electrochemical reactions that involve the motion of ions between two electrodes through an electrolyte,” said a team of researchers in a recent paper published in Advanced Quantum Technologies describing the idea. “Quantum batteries, on the other hand, are a novel concept that probe the potential of quantum mechanics to enhance energy storage.”

Despite their theoretical promise, developing a working quantum battery is fraught with challenges. The most serious of which is the difficulty of maintaining quantum coherence, where the battery exists in multiple quantum states simultaneously. This is crucial for the battery’s functionality but can be easily disrupted, making it difficult to maintain.

Moreover, for quantum batteries to work, their various components must remain in a delicate state of entanglement not only with each other but also with the element responsible for charging the battery. The problem lies in the fragility of these quantum states, which are easily disrupted by interactions with the external environment, and eliminating these interactions entirely is practically impossible.

Designing a quantum battery

In their study, the researchers proposed a simple yet innovative design for a quantum battery that might solve these problems. It consists of a single atom, whose quantum states are used to store energy, coupled with an intermediate cavity containing an electromagnetic field. This cavity mediates the interactions between the atom and its environment, potentially protecting the quantum battery’s delicate state from destructive external disturbances.

“The presence of a mediated cavity can have several effects,” the authors wrote. “It may serve as a means to protect [the quantum battery] from external disturbance, helping to preserve the [battery’s] delicate quantum state. [It] can assist in maintaining coherence and reducing decoherence, which are crucial factors in quantum systems. So, this mediation can lead to more controlled and efficient energy transfer processes.”

This innovative approach highlights the importance of the environment in quantum battery performance. There are two primary types of environments to consider when evaluating quantum systems: memory-less and memory-affected environments.

In the first, known as a “memory-less” environment, the battery’s external surroundings, such as a charger or the air,  do not retain any information about past interactions with it. In a memory-less environment, these interactions don’t leave any lasting impact on the surroundings. It’s as if each time the battery interacts with its environment, it’s happening for the very first time.

This type of environment is easier to study and work with both in theory and practice. Since the surroundings don’t retain any information or get affected by past events, it’s simpler to understand and predict how the battery will behave. However, it may not always accurately reflect the complexities of real-world environments or quantum systems, potentially limiting its applicability and predictive power.

The second approach involves environments with memory effects, such as crystals or systems with multiple entangled atoms. In these environments, the surroundings remember their past interactions with the quantum battery.

This memory helps maintain the battery’s quantum coherence — essentially keeping its delicate quantum states stable — because the environment can better manage and control energy exchanges over time. This allows for more precise charging and discharging of the battery. However, working with such environments is more complex due to the numerous factors and interactions that need to be considered, making both the study and practical use more challenging.

Which model worked best?

The team determined that the memory environment, though more complex, boosts the battery’s capacity and energy extraction rates by 10-20% by measuring how the strength of interactions between the battery, its cavity, and the surrounding environment affects the battery’s performance.

“It is observed that, during the charging process, the energy obtained by the quantum battery increases with the enhancement in the [battery]-cavity coupling strength, while it decreases with the strengthening of the cavity-environment coupling. It is also observed that maximum ergotropy increases by amplifying the [battery]-cavity coupling and decreases with increasing the effective cavity environment coupling.”

Next steps will be to translate these findings into a working prototype that can be validated experimentally. Additionally, because their battery design involves only a single atom, the resulting capacity is expected to be very low, even under ideal conditions. For a quantum battery to be truly functional and offer advantages over traditional designs, it will be necessary to maintain a large number of atoms in a state of quantum entanglement — a task that presents further challenges, even if this model were to get off the ground.

But this could represent a crucial first step toward the development of real quantum batteries–however long that might take. The wait might be worth it as these batteries have the potential to revolutionize electric vehicles, renewable energy storage, and consumer electronics like smartphones, computers, and smartwatches.

The journey from theoretical concept to practical application may be long, but the rewards could be nothing short of transformative.

Reference: Maryam Hadipour et al, Proposed Scheme for a Cavity-Based Quantum Battery, Advanced Quantum Technologies (2024). DOI: 10.1002/qute.202400115

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