Researchers at Chalmers University of Technology and the University of Gdańsk have designed a quantum battery charger that achieves a work-like signal-to-noise ratio near unity, even with thermal noise and moderate disorder. The charger uses a driven bosonic Kitaev chain, where chiral squeezing transforms incoming fluctuations into ordered battery states. Unlike typical amplifiers, this scheme effectively stores energy, demonstrating a charging process resilient to disturbances. The work proposes a method for injecting energy while minimizing fluctuations, a key challenge in developing practical quantum batteries.
Driven Bosonic Kitaev Chain for Quantum Battery Charging
The driven bosonic Kitaev chain (BKC) actively transforms initially passive input fluctuations into ordered, non-passive battery energies, a process central to a newly proposed charging scheme. This conversion occurs through chiral squeezing, where bidirectional propagation amplifies and squeezes fluctuations into orthogonal quadratures at opposing ends of the chain, effectively directing energy flow. Unlike conventional amplification methods, this system prioritizes energy storage, demonstrating a charging process resilient to environmental factors.
The BKC’s unique structure, using parametric-pump terms to create and annihilate excitations in pairs, breaks excitation-number conservation and facilitates this chiral transport. This pairing is equivalent to two decoupled Hatano-Nelson chains for the x and p quadratures with opposite chiralities, a configuration that enhances energy transport. The charging dynamics are dominated by these fluctuations, rather than a coherent input pulse, which contributes negligibly to stored battery energy due to its finite duration and accumulated dissipation.
The team modeled the BKC as a uniform one-dimensional bosonic chain of length 2N + 1, with nearest-neighbor hopping h and parametric-pump induced two-particle pairing Δ. This configuration allows for phase-sensitive chiral transport of a coherent input pulse, while simultaneously amplifying and squeezing fluctuations. “The BKC is a paradigmatic one-dimensional (1D) bosonic lattice,” the authors write, “in which nearest-neighbor hopping is supplemented by parametric-pump terms that create and annihilate excitations in pairs.” The potential for realizing this BKC in physical systems is growing, with accessible platforms including superconducting circuits and optomechanical systems.
These technologies offer the control and robustness needed to engineer energy transport in driven bosonic networks. The researchers set the Planck constant to ℏ = 1 in their calculations, simplifying the model without sacrificing its core principles. The work proposes a charging scheme that actively processes both coherent input and input fluctuations, leading to high extractable work.
The ability to maintain a near-unity SNR despite the presence of disorder and thermal noise positions this BKC-based charger as a promising candidate for future quantum energy storage technologies. The team’s findings suggest that harnessing and controlling fluctuations, rather than simply minimizing them, can be a powerful strategy for optimizing quantum battery performance.
Chiral Squeezing Converts Fluctuations to Battery Energy
The ability to harness normally detrimental fluctuations for energy storage represents a departure from conventional quantum battery design, as demonstrated by a new charging scheme using a driven bosonic Kitaev chain. Rather than suppressing these fluctuations, the system actively converts them into ordered energy states within the battery, a process enabled by chiral squeezing. This mechanism transforms passive input fluctuations into non-passive energies, circumventing limitations seen in systems reliant on coherent inputs alone.
This robustness is a critical advancement, as maintaining signal integrity is paramount in quantum systems. Chirality within the BKC arises from parametric pairing, creating a quadrature dependence where the x and p sectors behave as Hatano-Nelson chains with opposite directional amplification. This active pairing process not only amplifies but also squeezes fluctuations, directly converting them into usable energy.
Analysis of the charging dynamics reveals that the stored energy is not simply a result of coherent input, but is significantly influenced by the quadrature-resolved fluctuation contributions. The team modeled the energy contributions to both left and right batteries, demonstrating how fluctuations can be actively harnessed to increase stored energy.
BKC Dynamics: Phase-Sensitive Transport and Amplification
The charging process within this new quantum battery relies on bidirectionally propagating fluctuations amplified and squeezed into orthogonal quadratures at opposite ends of the chain, a departure from conventional amplification methods. This approach allows for the conversion of unavoidable input fluctuations into useful, extractable work, addressing a key challenge in quantum battery development. This robustness stems from the unique properties of the driven bosonic Kitaev chain, where parametric pairing breaks excitation-number conservation and establishes chiral transport.
This chirality enables topologically protected directional amplification and enhanced quantum sensing, features absent in traditional passive lattices. The researchers found that the parametric pump terms, proportional to Δ, actively drive this amplification, requiring an energetic cost accounted for in their calculations.
The amplification process doesn’t simply boost the signal; it actively reshapes and orders the fluctuations into non-passive energy, resulting in a contribution to battery storage that significantly exceeds that of the initial coherent pulse. “We emphasize that is an effective rotating-frame Hamiltonian that contains parametric pump terms,” the paper states, highlighting the active role of external resources in enabling this dynamic.
The design’s stability relies on maintaining a balance between hopping strength (h) and parametric pairing (Δ), with a dynamically stable system requiring |h| > |Δ|. When |h| < |Δ|, the dynamics become unstable, preventing well-defined wave transport.
Analysis of the stored energies originating from an injected Gaussian pulse with an initial phase of θ = π/2 reveals that the coherent wavepacket is predominantly transported toward the left battery, while its contribution to the right remains negligible. This phase-sensitive chirality is a direct consequence of the system’s unique structure and the underlying chiral transport mechanisms. The researchers demonstrated that the fluctuations are amplified in both directions, a key factor in achieving efficient energy storage.
This amplification, coupled with the squeezing of fluctuations, allows the system to overcome the limitations of passive noise and maintain a high signal-to-noise ratio. The ability to extract largely extractable energy, even when subjected to disorder, positions this approach as a promising pathway toward practical quantum battery technologies.
Extractable Work Achieved Near Unity Signal-to-Noise Ratio
Achieving a work-like signal-to-noise ratio approaching unity, the design demonstrates a surprising result given the typical degradation of performance caused by thermal noise and disorder in quantum systems. This near-unity ratio indicates the charger efficiently converts input fluctuations into usable energy, even with imperfections present. Unlike conventional amplifiers that simply magnify existing signals, and their accompanying noise, this system actively reshapes fluctuations into a more ordered, extractable form.
Results show the ratio rapidly approaches unity as the chain length increases, indicating a scalable charging process unaffected by moderate thermal noise. Even with varying levels of thermal occupancy, the performance remains remarkably consistent for larger chain sizes, demonstrating a robustness not typically seen in quantum energy storage.
The analysis reveals a correlated growth between extractable work and energy fluctuations as the chain length increases, suggesting that enhancing the system’s size simultaneously improves both energy storage and the ability to harness it. The authors evaluated this ratio as a function of the chain’s half-length and thermal occupancy.
Bosonic Kitaev Chain as Decoupled Hatano-Nelson Chains
The driven bosonic Kitaev chain (BKC) functions as two decoupled Hatano-Nelson chains, each handling a quadrature, position (x) and momentum (p), with opposing chiralities, a characteristic revealed by the rotating-frame Hamiltonian detailed in the work. This decomposition isn’t merely a mathematical curiosity. It directly enables phase-sensitive chiral transport, where the direction of wavepacket propagation depends on its initial phase, a phenomenon absent in traditional passive lattices.
The x component preferentially couples to the right, while the p component favors the left, creating a fundamental asymmetry in how excitations move through the chain. The authors demonstrate that this process actively reshapes input fluctuations, converting them from passive noise into ordered, non-passive states suitable for battery charging. This contrasts sharply with conventional amplifiers, which struggle to maintain signal integrity while boosting power, often amplifying noise alongside the desired signal.
The analysis shows that the BKC’s unique structure bypasses this limitation by fundamentally altering the nature of the fluctuations themselves. The decoupling into Hatano-Nelson chains isn’t simply a theoretical observation; it’s a functional aspect of the BKC’s design, enabling a specific type of chiral squeezing. This squeezing, the conversion of passive input fluctuations into ordered battery states, is achieved through the parametric pump terms that create and annihilate excitation pairs.
The system’s performance is further bolstered by the fact that the BKC’s Hamiltonian, , is an effective rotating-frame Hamiltonian containing these parametric pump terms. The authors emphasize that the BKC’s design allows for a work-like signal-to-noise ratio (SNR) approaching unity, even in the presence of thermal noise and moderate symmetry-preserving disorder.
Parametric Pumping and Energetic Cost in the BKC
The energetic demands of maintaining the chiral squeezing essential to this quantum battery charger are directly accounted for in the design, a feature distinguishing it from many theoretical proposals. Researchers define pump work as having two primary contributions: the energy supplied by an initial coherent Gaussian pulse and the ongoing cost of the parametric pump itself, a factor quantified by the squeezing parameter r. Indeed, the contribution from the parametric pump vanishes entirely when r equals zero, demonstrating its direct link to the amplification process.
The total stored energy within the batteries is a key metric, but equally important is the overall charging efficiency, defined as the ratio of stored energy to the total active energy cost. This efficiency, denoted as η(t), initially increases as amplified, ordered fluctuations are directed to the chain ends and loaded into the batteries, reaching a maximum at a time t*.
However, the efficiency then decreases due to continued energy exchange between the chain and batteries, coupled with the accumulation of the pump’s energetic cost. This dynamic suggests an optimal charging duration beyond which efficiency declines. A detailed analysis of on-site detuning disorder is provided in a supplemental note, indicating the system’s robustness is not merely theoretical.
The researchers found that for open boundaries, a lossless bosonic Kitaev chain remains dynamically stable when the absolute value of h exceeds the absolute value of Δ, but becomes unstable when the opposite is true, resulting in undefined wave transport. The work also introduces individual charging efficiencies, ηL(t) and ηR(t), for the left and right batteries, respectively, allowing for a granular assessment of performance across the system. When the setup is maintained continuously, η(t) initially rises as ordered fluctuations are transported and loaded, then falls after t* due to energy exchange and cost accumulation.
This detailed accounting of energy flow and cost is important for evaluating the practicality of the BKC as a viable quantum battery charger. The team’s analysis provides a framework for optimizing the balance between charging speed, energy storage and the energetic overhead of maintaining the chiral squeezing necessary for efficient operation.
👉 More information
🗞 Charging Quantum Batteries with Chiral Squeezing
✍️ Borhan Ahmadi, André H. A. Malavazi, Janine Splettstoesser, Paweł Horodecki and Lei Du
🧠 DOI: http://link.aps.org/doi/10.1103/zg87-t4y5
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