Researchers at Texas A&M University, in collaboration with Argonne National Laboratory, present a novel approach to storing and retrieving hard X-ray photons using nuclear frequency comb memory. Existing X-ray storage methods offer benefits like increased bandwidth and reduced noise compared to optical systems, but on-demand retrieval has proven difficult due to the need for precise mechanical control. This team proposes a hybrid magnetic-Doppler nuclear frequency comb, utilising resonant absorbers with manipulated nuclear spin, to broaden the comb structure and simplify the process. By reversing magnetic fields and absorber velocities in synchronisation, the system enables efficient, on-demand photon retrieval with significantly less mechanical complexity, representing a substantial advancement in X-ray photon storage technology.

The system sharply reduces mechanical complexity previously required for on-demand photon retrieval, utilising 57 absorbers to combine Doppler-shifted resonant absorbers with lifted nuclear spin degeneracy and create an expanded comb structure. This enables efficient on-demand photon retrieval and represents a step for advancing X-ray quantum technologies.

Yanli Shi and colleagues have unveiled a streamlined method for storing and retrieving hard X-ray photons, simplifying existing storage processes by lessening the need for precise mechanical movements. The team’s innovation centres on this ‘hybrid magnetic-Doppler nuclear frequency comb’, a technique that expands upon existing methods for managing these high-energy photons.

This comb structure utilises 57 absorbers to efficiently store information, overcoming limitations of previous systems that demanded precise, synchronised movement of numerous components. By reversing the direction of both magnetic fields and absorber velocities, Yanli Shi and colleagues achieve time-reversed phase evolution dynamics, effectively rewinding the storage process to retrieve the photon, creating a strong and manageable system through the use of lifted nuclear spin degeneracy.

Hybrid comb surpasses efficiency limits for X-ray quantum memory storage

A hybrid magnetic-Doppler nuclear frequency comb, utilising 57 absorbers, achieves a peak storage efficiency of 54 percent, exceeding the 36 percent maximum attained by previous Doppler-only methods. Efficiencies below 50 percent severely limit the scalability of quantum information processing, representing a key threshold for practical quantum memories. Previously, achieving such high efficiency without complex mechanical control was impossible. The expanded comb structure, created by combining Doppler-shifted resonant absorbers with lifted nuclear spin degeneracy, allows for efficient on-demand photon retrieval by synchronously reversing magnetic fields and absorber velocities.

Incorporating internal degenerate transitions within the comb structure effectively doubles the bandwidth for a given storage time, driving this enhanced performance. A six-tooth comb configuration yielded efficiencies up to 50 percent, a significant improvement over a three-tooth Doppler-only comb.

Simulations revealed a fidelity of 94.83 percent alongside the 54 percent efficiency, indicating high-quality photon retrieval0.57FeBO3, a material with a strong internal hyperfine field of 15.6 Tesla, lifts nuclear spin degeneracy while maintaining the same mechanical complexity as previous designs using three absorbers. Existing approaches, such as Doppler frequency combs, rely on precisely organised mechanical movements, introducing significant engineering hurdles. The team’s proposal for a hybrid magnetic-Doppler comb elegantly sidesteps this issue, but depends on achieving stable and predictable manipulation of nuclear spin, a phenomenon where atomic nuclei behave like tiny magnets.

Successful demonstration of this concept would represent an advancement towards building strong quantum memories capable of handling high-bandwidth, low-noise X-ray photons for future quantum technologies. This system combines the principles of Doppler-shifted resonant absorbers, utilising the change in frequency of light due to movement, with manipulation of nuclear spin, a fundamental property of atomic nuclei behaving like tiny magnets. Careful control of both magnetic fields and absorber velocities achieves time-reversed phase evolution dynamics, effectively reversing the storage process to release the photon.

The researchers demonstrated a hybrid magnetic-Doppler nuclear frequency comb capable of efficiently retrieving stored X-ray photons. This new approach reduces the mechanical complexity required for on-demand retrieval, a significant challenge in previous designs. Using a six-tooth comb configuration with 0.57FeBO3, they achieved retrieval efficiencies up to 50 percent with a fidelity of 94.83 percent. The team intends to address current limitations by accounting for photon-electron scattering and exploring methods for longer storage times and more complex quantum states.

👉 More information
🗞 On Demand magnetic-Doppler nuclear frequency comb memory for hard X-ray photons
✍️ Yanli Shi, Xiwen Zhang, Yuri Shvyd’ko and Olga Kocharovskaya
🧠 ArXiv: https://arxiv.org/abs/2608.08271

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