What is a quantum battery and how do you build one?
The quantum battery (QB) has been proposed as an alternative to the electrochemical energy storage devices we know so well.
Rather than using the transfer of ions of lithium, sodium or lead to generate power, the quantum battery stores the energy from photons. These can charge almost instantaneously thanks to quantum effects such as entanglement and superabsorption. They will not power electric vehicles any time soon, but could be used for quantum communications and might improve the efficiency of solar cells. They could even be used in parallel for small electronic devices, and researchers in Italy in February compiled a detailed table of the materials that could be used to build them (see below).
The quantum battery was first proposed in 2013 by Robert Alicki of the University of Gdańsk in Poland and Mark Fannes of KU Leuven in Belgium but so far, there are only proof-of-concept demonstrations. The idea is that entangled photons can store small amounts of energy for a short period of time. This can be done in organic materials in a microcavity, or in supercooled materials, and can potentially be scaled up to work as practical batteries.
Planckian
Back in 2023, Planckian in Italy raised €2.7m with the intention of developing the QB technology.
“Interest in the new frontiers of quantum physics, particularly in the field of so-called quantum thermodynamics, and the study of unconventional properties of quantum materials, has never been so strong. We believe the time has come to develop new technologies for energy management that can exploit the unique properties of quantum mechanics,” said Marco Polini, the chief scientific officer (CSO) and co-founder along with CEO Vittorio Giovannetti.
It has since moved to developing quantum processors, last week teaming with University of Naples to test is next generation quantum processors in the University’s QTLab.
“We began our journey with the vision that scaling quantum technologies requires combining traditional quantum information science with innovative approaches from emerging fields, particularly materials science and quantum thermodynamics,” said the company.
“Initially, our research concentrated on the concept scientifically known as a “quantum battery,” which explores quantum thermodynamics to create novel techniques for precise, efficient, and robust qubit manipulation.”
The company has since used that research for a qubit control scheme for quantum computers.
“Over the past year, we recognized that emerging ideas to qubit control could be significantly enhanced and expanded by integrating them with our existing approach. This led us to focus our efforts on developing a new quantum processor architecture that can build upon this synergy to overcome fundamental challenges that limit quantum computer scalability.”
In the meantime, researchers from the Riken Centre for Quantum Computing in Japan and Huazhong University of Science and Technology in China have conducted a theoretical analysis demonstrating how a “topological quantum battery” could be efficiently designed.
The work holds promise for applications in nanoscale energy storage, optical quantum communication and distributed quantum computing.
Topological quantum battery
This topological approach uses a photonic waveguide for long distance charging of a quantum battery. Photonic systems that use bent, non-topological waveguides to channel the photons show dispersion and degradation in the energy storage efficiency. Other obstacles include environmental dissipation, noise, and disorder, all of which induce decoherence of the photons and degrade the performance of the batteries.
However the dissipation can also be used to enhance the charging power of quantum batteries, just one of several advantages could make topological quantum batteries feasible for practical applications.
One crucial finding by the researchers at Riken was that it is possible to achieve near-perfect energy transfer by using the topological properties of the waveguides. The team also found that as dissipation exceeds a critical threshold, the charging power undergoes a transient enhancement, breaking the conventional expectation that dissipation always hinders performance.
“Our research provides new insights from a topological perspective and gives us hints toward the realization of high-performance micro-energy storage devices. By overcoming the practical performance limitations of quantum batteries caused by long-distance energy transmission and dissipation, we hope to accelerate the transition from theory to practical application of quantum batteries,” said Zhi-Guang Lu, the first author of the study.
“Looking ahead we will continue working to bridge the gap between theoretical study and the practical deployment of quantum devices,” said researcher Cheng Shang at Riken.
Other physical systems have been designed and theoretically studied for the implementation of a QB, including ensembles of interacting spins. Other possible materials include cold atoms, topological superconductors and graphene quantum dots (QDs) with irregular boundaries in strong applied magnetic fields.
QB with spin states
Researchers at the University of Genoa in Italy have also developed an idea for a quantum battery that uses the spin states at very low temperatures to store energy. By using the paramagnetism and ferromagnetism in supercooled materials, they can enhance the stability of the energy trapped into the quantum systems.
James Quach, now Chief Scientist at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia and colleagues at the University of Adelaide have been developing microcavities that store the entangled photons at room temperature.
These are built from thermal deposition to create cavity quantum battery systems with active layers that are just a few nanometres thick. In collaboration with the University of Melbourne, ultra-fast laser pulses are used to study the complicated charging dynamics of each system.
Quantum microcavities
One of the platforms for the implementation of QBs relies on microcavities enclosing an ensemble of organic molecules. Here, the Fabry-Pérot resonator is typically used as the microcavity architecture. It is formed by a layer of organic material sandwiched between two high-reflectivity plane parallel mirrors. Mirrors can be thin metallic films, distributed Bragg reflectors (DBRs) 1D crystals, or combinations of the two.
Recently hybrid metal-DBR mirrors made of a thick silver layer coated with a few layers of silicon dioxide and niobium oxide (SiO2/Nb2O5). These hybrid mirrors allow for achieving broadband reflectivity and enhanced confinement, as well as simplifying the fabrication method.
DBRs can also be manufactured by alternating polymer and nanocomposite layers with different refractive indexes with spin-coating, dip coating or doctor blading.
While demonstrating charging, the study by Quach did not show controlled storage and discharge of the accumulated energy, as the light energy absorbed by the cavity was re-emitted on an ultrafast timescale. The key challenge for practical applications of organic microcavities as solid-state QBs is the design and realization of devices in which energy can be efficiently stored and extracted on demand.
To address such a challenge, the active material of the cavity can be designed as a pair, with one cavity acting as a donor and the other as an acceptor. This stores energy for tens of microseconds and is seen as a promising approach. .
Other researchers at the University of Bremen in Germany built a pillar microcavity with about 200 QDs coupled to the cavity mode. The cavity was made by two AlAs/GaAs DBRs with a top mirror with 20 pairs and a bottom mirror with 23 pairs operating at 10 K.
A team at the University of Twente is aiming to use the information encoded in nuclear or magnetic impurity spins for energy harvesting. The current research mostly focuses on the interfacial states of topological insulators, in which the electron spin is locked to its momentum direction: upon driving a current through the material, spin can be transferred for electrons to nuclei via spin-flip interactions, generating a finite nuclear spin polarization. When this polarization thermally relaxes to a disordered state, these spin-flip interactions will drive a finite charge current, which can be used to extract electronic work.
Yet others are looking at the same lead halide perovskites that are used in low cost solar panels to build quantum batteries. The spacing of the energy levels of these materials allows for room temperature operation rather than supercooled. The properties of the perovskite materials can also be tuned by external fields, such as electrical fields and optical pulses to create materials with long-lived states. The photoelectric conversion effects seen in perovskite materials can also be used in the discharging phase.
Materials for quantum batteries
An other important factor is that the recent advances in large-scale synthesis and processing of perovskite materials, driven by the development of solar cells, are highly relevant for future upscaling of potential QB production, says Andrea Camposeo, research director at the Nanoscience Institute of the CNR in Pisa, Italy, who along with Planckian co-founder Marco Polini recently assessed the range of materials and approaches for quantum batteries in the table below.
Table: Properties of the materials considered for potential QBs realization and the related processing methods Courtesy Camposeo et al, Pisa
|
Material |
Stability |
Costs of raw materials |
Manufacturing of devices |
Scalable processing [Y/N] |
Operating temp [K] |
|
Metals for mirrors |
High |
1–10 €/g |
Thermal evaporation, electron beam evaporation, sputter deposition |
Y |
RTc) |
|
Dielectrics for DBR |
High |
10−1–1 €/g |
Electron beam evaporation, sputter deposition, molecular beam epitaxy |
Y |
RT |
|
Organic molecules |
Good. Could be enhanced by suitable device encapsulation |
10–104 €/g |
Spin coating, drop casting, thermal evaporation, blade coating, ink-jet printing |
Y |
RT |
|
QDs |
High |
103–104 €/g |
Spin coating, drop casting, metal-organic chemical vapor deposition, lithography, ink-jet printing |
Y |
From few K to RT |
|
Perovskites |
Good. Could be enhanced by passivation and encapsulation methods |
10–103 €/g |
Spin coating, thermal annealing, exfoliation, antisolvent vapor-assisted crystallization. |
Y |
RT |
|
Normal Superconductors |
High |
1–10 €/g |
Optical lithography, electron beam lithography etching processes, metal evaporation |
Y |
10-50 mK |
|
High-temperature superconductors |
High |
102–103 €/g |
Electron-beam lithography, ion beam etching |
Y |
– |
Quantum technologies will likely be primary users of QBs, particularly for operating quantum devices that require coherence and entanglement. But while these are still in the experimental stages, there are many groups around the world working on the technology to scale up the energy storage over the coming years.
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