New Approach to Quantum Battery Utilizing Waveguides Proposed by Researchers

March 7, 2024

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Article by Tejasri Gururaj, Phys.org

Researchers at Boston University have suggested a novel quantum battery (QB) charging scheme in a new study. This scheme, which involves a rectangular hollow metal waveguide, is designed to circumvent problems like environmental interference and charging distance limitations. These findings can be found in the publication, Physical Review Letters.

Currently, there is an increasing demand for batteries with improved storage, longevity, and charging capabilities. To meet these needs, scientists are creating quantum batteries, capable of storing and supplying energy through the principles of quantum mechanics.

Fundamental quantum mechanics principles, such as entanglement and coherence, are used in the aim to surpass the limitations of classical physics. The ultimate goal being enhanced charging power, increased charging capacity, and greater work extraction in relation to classical counterparts.

The new study examines the QB by locating the battery and charger within a rectangular hollow waveguide. This methodology is intended to mitigate the effects of decoherence to achieve sustainable and effective QB performance.

Explaining the team's inspiration to investigate quantum batteries, Prof. Jun-Hong An of Lanzhou University, China stated that the aging of QB, commonly known as the spontaneous energy loss of QB, arises due to "decoherence challenges". Another challenge to the practical performance of QB is its weak charging efficiency due to the delicate coherent interactions between the QB and its charger. They hope to overcome these issues.

The QB model is dependent on two two-level systems (TLSs), systems with two different energy levels. Traditionally, these energy levels are characterized as a ground state and an excited state.

One system is the QB, and the other is the charger. The charging and energy exchange procedures between these TLSs have a crucial role in the QB system's operation. The TLSs are charged via the establishment of a coherent coupling with other TLSs or external fields.

Within the framework of QBs, a coherent coupling is a coordinated interaction between these quantum systems, permitting the transfer or exchange of energy. These delicate interactions introduce decoherence into these systems.

Prof. Jun-Hong explained that any quantum system can't be fully isolated from its outside environment, resulting in undesired decoherence.

However, this charging model introduces rectangle hollow waveguides to tackle both the distance-based charging efficiency decline and the decoherence problem.

A rectangular hollow metal waveguide functions by gathering and directing the electromagnetic field to mediate energy transfer between the QB and the charger explained Prof. Jun-Hong. This model allows energy transfer without direct contact, introducing a new approach to QB charging.

The use of a waveguide in their model revolves around the quantized interaction between the electromagnetic field and matter within it.

Inside the waveguide, the electromagnetic field contains specific dispersion relations and bandgap structures, which influence its propagation and interactions within the quantum system. Initially, when the electromagnetic field is in a vacuum state with the QB in the ground state and the charger in an excited state, a photon is emitted in the electromagnetic field as the charger transitions from the excited state to the ground state. This introduces an excitation in the electromagnetic field, which leads to infinite modes.

Afterward, the QB absorbs the photon causing it to transition to its excited state. Despite typically inducing decoherence, the researchers surprisingly found that the infinite-mode field acts as an environment that actually aids in the coherent energy exchange between the QB and charger.

'Our work reveals a mechanism for making a coherent QB-charger energy exchange happen by the mediation role of the infinite-mode electromagnetic field,' explained Prof. Jun-Hong.

The unexpected finding that decoherence in the system doesn't lead to the aging of the QB contradicts popular belief. Instead, the researchers note that the energy exchange is an optimal charging process—typically expected in scenarios where the charger and QB directly interact.

Further, their QB scheme showed a long range for wireless charging, with the formation of two bound states in the energy spectrum of the total systems (QB-charger-environment) playing a crucial role.

'A take-home message of our work is that the quantum interconnects favored by the waveguide supply us with a useful way to overcome the challenges in the practical realization of QB,' added Prof. Jun-Hong.

This improves the effectiveness of QB and opens the door to the possibility of lighter and thinner devices with greater facilitation, which also stands out for its durability.

Prof. Jun-Hong also highlighted that their device was completely safe and harmless as the electromagnetic field is always confined within the waveguide and the QB's energy storage, free from electrochemical reactions, promotes infinite reusability without environmental pollution.

The next step for the researchers is to scale their QB scheme.

'More specifically, we plan to develop a many-body QB model working in the way of remote wireless charging. This could permit us to efficiently incorporate the superiority of quantum entanglement in enhancing the charging power, charging capacity, and the extractable work of a remote-charging and anti-aging QB,' concluded Prof. Jun-Hong.

Journal information: Physical Review Letters , arXiv

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