Quantum Hardware

Researchers Link Topology to Exponential Growth in Quantum Correlations

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October 2, 2026 by Ivy Delaney

Directional amplification in driven-dissipative systems is closely connected to non-Hermitian topology, a property that has attracted interest for quantum information processing and signal-control technologies. While previous studies primarily examined this connection through classical responses and mean fields, researchers have now investigated how non-Hermitian topology affects quantum fluctuations, correlations, and entanglement in coupled bosonic systems.

The study by Niladri Chakraborty and Clara C. Wanjura develops an analytical description of quantum correlations in chains of dissipative bosonic modes. The results show that nontrivial topological phases can produce correlations that increase exponentially with the distance between modes, while the corresponding correlation length diverges at topological phase transitions. However, despite these long-range correlations, quantum entanglement remains spatially localized.

Quantum Langevin Dynamics in Dissipative Bosonic Chains

The researchers considered chains containing N coupled bosonic modes, described by operators (c_j). The modes can interact through hopping terms between neighbouring sites and through squeezing interactions. Coupling the system to input-output waveguides introduces dissipation, making the dynamics inherently driven and lossy.

The evolution of the bosonic fields is governed by a dynamic matrix that can be non-Hermitian. Unlike Hermitian systems, non-Hermitian systems can have complex eigenvalues and nonorthogonal eigenvectors, with their topology characterized by properties such as point gaps and winding numbers.

Directional amplification has previously been shown to correspond directly to nontrivial point-gap topology in the dynamic matrix. This relationship can survive disorder and extend to systems with multiple bands and higher dimensions. Experimental demonstrations have also been reported in platforms including optomechanical and superconducting circuits.

The new work asks whether the same topology also determines the behaviour of quantum fluctuations rather than only the average response.

Topology Produces Long-Range Correlations

For phase-preserving amplifiers, the researchers derived analytical expressions for both normal and anomalous correlations between bosonic modes. In nontrivial topological phases, these correlations can grow exponentially with the separation between modes, approaching limits imposed by quantum uncertainty relations.

This behaviour contrasts with trivial phases, where correlations generally decay rapidly as the distance between modes increases. The associated correlation length was found to diverge at topological phase transitions, providing a connection between the geometry of the non-Hermitian phase and the spatial structure of quantum correlations.

The results indicate that non-Hermitian topology can therefore influence how quantum fluctuations are distributed across a dissipative system, extending the connection between topology and directional amplification into the quantum regime.

Bosonic Kitaev Chain Separates Correlated Regions

The researchers also investigated a bosonic Kitaev chain, which acts as a phase-sensitive amplifier because of its squeezing interactions. In the topological regime, the chain separates into two internally correlated sections.

Modes within each section can become strongly correlated, with normalized anomalous correlations approaching the maximum values permitted by quantum uncertainty relations. However, the two sections remain mutually uncorrelated.

This distinction is important because strong correlations between distant modes do not necessarily imply long-range quantum entanglement. The analysis shows that the spatial structure of correlations and entanglement can behave differently in non-Hermitian systems.

Entanglement Remains Localized

Despite the exponentially increasing correlations associated with nontrivial topology, the researchers found that entanglement remains localized. In other words, non-Hermitian topology can generate strong connections between distant modes without causing genuine quantum entanglement to spread throughout the entire chain.

The result highlights a distinction between correlation and entanglement in driven-dissipative quantum systems. Amplification and long-range correlations can arise from the non-Hermitian structure, while the distribution of entanglement is determined by additional factors, including mode occupations and the balance between normal and anomalous correlations.

Implications for Quantum Technologies

The findings establish a connection between non-Hermitian topology and the structure of quantum correlations in driven-dissipative bosonic systems. They extend the previously established relationship between topology and directional amplification from classical responses to quantum fluctuations.

The analytical results could help guide future investigations of non-Hermitian quantum systems and their potential applications in quantum information processing and sensing. Platforms such as cavity optomechanics and superconducting circuits provide possible experimental settings for studying these effects.

The work also shows that strong long-range correlations do not automatically produce long-range entanglement, providing a more detailed picture of how topological properties influence quantum information in systems with gain and loss.

👉 More information
🗞 Non-Hermitian topology in driven-dissipative systems: correspondence with quantum correlations and a resource for entanglement
✍️ Niladri Chakraborty and Clara C. Wanjura
🧠 ArXiv: https://arxiv.org/abs/2609.09312

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Entanglement non-Hermitian topology Quantum Fluctuations
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Ivy Delaney

Ivy Delaney has been working with neural networks and machine learning since the mid-nineties, back when a couple of hidden layers and a long afternoon of training counted as ambitious. She has watched the field go from academic curiosity to the thing quietly running underneath everything, and she brings that long view to quantum computing. For Quantum Zeitgeist she covers the ground where the two fields meet. That means quantum machine learning and the variational algorithms it leans on, and it also means the less glamorous but more interesting story of classical machine learning already doing real work inside quantum machines, decoding error-correcting codes, calibrating noisy hardware and learning the error models that simulators depend on. She writes about the hardware those algorithms have to run on too, and about the post-quantum cryptography scramble that the same hardware has set off. Her stories typically start with the paper, whether that is peer-reviewed work, conference proceedings or an arXiv preprint, with the source linked so you can hold a claim up against the research it came from. She is unimpressed by benchmarks that will not say what they beat, and by demonstrations that only work in the press release.

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