ZARM Talk: Quantum Memories in Space

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 ultra-low 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.

In her publication in Physical Review Research [1], Elisa proposes a novel protocol that leverages 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 the storage. This then eliminates the need for any inhomogeneous field to suspend the atoms, which would otherwise introduce further decoherence mechanisms.

Using this method, we demonstrate a potential improvement in 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. We will also present the experimental efforts in our lab to implement a ground-based version of this protocol.

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