Abstract:
Long-lived quantum memories (QMs) are required in numerous tasks in future space-based quantum information experiments. As such, Bose-Einstein condensates (BECs) are ideal candidates for implementing such QMs: not only have they been successfully produced in space, but their ultralow temperature also enables high-performance operation in terms of noise and efficiency. However, due to density-dependent interatomic collisions, the same high density required for efficient operation causes decoherence, which in turn limits the achievable
storage time in a trapped BEC to ~100 ms timescales.
Here, we propose a novel protocol [1] that utilizes matter-wave optics techniques to suppress such density-dependent effects. Optical atom lenses are employed to first collimate and then refocus an initially expanding BEC, enabling high-density write-in and read-out operations, while reducing the collision rate and consequent decoherence in the expanded quantum gas during the storage period. Implementing this protocol in a microgravity environment, as found in space applications, prevents the fall of the BEC’s center of mass during storage.
Using this method, we demonstrate a potential improvement in the expected memory lifetime by many orders of magnitude compared to ground-based experiments that haven't implemented it, and we find that the memory lifetime would be ultimately limited by the background vacuum quality.

[1] E. Da Ros et. al., Phys. Rev. Research 5, 033003 (2023)