Quantum Data Storage Gains Stability with Fibre Optic Error Correction

A new all-optical quantum memory for building scalable quantum networks and fault-tolerant photonic quantum computers has been quantitatively analysed. Kaustav Chatterjee and colleagues at the Centre for Macroscopic Quantum States, Technical University of Denmark, analysed an architecture storing a qubit in a fibre loop and stabilising it with teleportation-based error correction. Modelling reveals that optimising the syndrome decoder sharply improves performance, identifying a practical design rule for segment length largely independent of storage time. Storage times exceeding 400ms with logical infidelity below 1% are achievable at 17 dB squeezing, establishing clear benchmarks and trade-offs between photon loss, squeezing, and correction frequency in continuous-variable systems. These findings offer actionable design principles for near-term photonic quantum memory and advance the pursuit of scalable, all-optical quantum storage. Syndrome decoder optimisation enables sustained high-fidelity quantum storage Logical infidelity in all-optical quantum memory, utilising Gottesman-Kitaev-Preskill (GKP) encoding, has fallen below 1% after achieving storage times exceeding 400 milliseconds. Previously, such durations with acceptable fidelity were unattainable, hindering the development of practical quantum repeaters and distributed quantum computing. GKP encoding represents a continuous-variable approach to quantum information processing, encoding a qubit into an infinite-dimensional Hilbert space using the displacement operator, offering inherent resilience against certain types of noise. This contrasts with traditional discrete-variable qubits, such as those based on photons’ polarisation, which are more susceptible to decoherence. The core innovation lies in the optimisation of the syndrome decoder, a crucial component responsible for identifying and correcting errors that accumulate during storage. Moving beyond standard grid-based approaches, which can introduce significant overhead and limit performance, the researchers implemented a more efficient decoding strategy that maximises memory lifetime and establishes clear performance benchmarks. The system operates effectively above a 6.7 decibel squeezing threshold, where repeated error correction becomes beneficial, and demonstrates remarkably consistent optimal spacing between correction nodes largely independent of desired storage duration. Modelling fibre optic cable transmission as a process of signal loss, and representing each error correction cycle as a logical operation on the quantum bit, enabled a streamlined analysis of the entire memory channel at 17 decibels of squeezing. Photon loss, a fundamental limitation in optical fibre communication, arises from absorption and scattering within the fibre material. The researchers treated this loss as a pure-loss channel, simplifying the analysis while still capturing the dominant error mechanism. Representing each correction round as an effective logical map acting on the Bloch vector, a geometrical representation of a qubit’s state, allowed for a concise and computationally efficient simulation of the error correction process. This consistent ideal spacing between correction points remains unaffected by storage duration, offering a practical guideline for building these fibre-loop quantum memories. Specifically, the optimal spacing allows for efficient error detection and correction without introducing excessive overhead. Sustained storage exceeding 400 milliseconds with a logical infidelity below 1% represents a key step towards reliable long-distance quantum communication. The level of noise reduction, termed ‘squeezing’, directly impacts achievable storage times, and provides a benchmark for future development, allowing for a streamlined analysis of the entire memory channel. Squeezing reduces the quantum noise in one quadrature of the electromagnetic field at the expense of increased noise in the other, effectively enhancing the signal-to-noise ratio and improving the fidelity of quantum operations. Optimal node spacing enhances long-distance quantum data storage Building strong memories capable of storing fragile quantum states for extended periods is fundamental to the promise of quantum communication and the realisation of a quantum internet. Quantum repeaters, which rely on quantum memories to extend the range of quantum communication, are particularly sensitive to memory performance. This work concentrates on mitigating photon loss, the gradual decay of light signals, while assuming ideal conditions for state preparation and measurement. The choice of fibre optic cable is also critical; low-loss fibres with minimal dispersion are essential for maintaining signal integrity over long distances. It is important to acknowledge that these experiments rely on carefully controlled laboratory settings, as real-world fibre networks present additional noise and signal degradation not fully accounted for here. Factors such as temperature fluctuations, mechanical vibrations, and imperfections in fibre manufacturing can all contribute to increased noise and reduced coherence times. Nevertheless, this detailed analysis establishes important benchmarks for building practical quantum memories. Specifically, it identifies an optimal spacing between correction nodes, offering a straightforward design rule that simplifies the construction of longer-duration storage systems and accelerates progress towards scalable quantum networks. This spacing is determined by balancing the need for frequent error correction to combat photon loss with the overhead associated with each correction operation.

This research delivers a practical advance in building all-optical quantum memories, demonstrating stable qubit storage within a fibre optic loop. Optimising the process of error correction increased gate fidelity five-fold, paving the way for more robust and efficient quantum networks. A higher gate fidelity translates to a lower error rate in quantum computations, enabling more complex and reliable algorithms. The findings highlight the importance of carefully controlling experimental conditions and acknowledging the challenges of translating laboratory results to real-world fibre networks. Future work will focus on addressing the effects of realistic noise sources and developing techniques for characterising and mitigating these impairments in deployed quantum networks. Furthermore, exploring alternative error correction codes and optimising the squeezing parameters could further enhance the performance and scalability of all-optical quantum memories. The research demonstrated stable storage of a quantum bit, or qubit, within a fibre optic loop using a technique called teleportation-based error correction. This matters because reliable qubit storage is vital for building practical quantum networks capable of transmitting information securely and performing complex calculations. By optimising the error correction process, researchers achieved a five-fold increase in gate fidelity, a measure of accuracy. This work identifies an optimal spacing between correction nodes within the fibre loop, offering a practical design rule for extending storage times and potentially enabling networks utilising low-loss fibres exceeding 400 milliseconds of storage. 👉 More information🗞 All-optical quantum memory using bosonic quantum error correction codes🧠 ArXiv: https://arxiv.org/abs/2603.21721 Tags: