Storage and retrieval of optical skyrmions with topological characteristics

TL;DR

The paper demonstrates a first experimental demonstration that optical skyrmions can be coherently stored and retrieved in a dual-path EIT memory using cold rubidium atoms, while preserving the skyrmion number as a topological invariant. The authors generate skyrmion states from Laguerre-Gaussian modes and map them into two spatial storage paths, showing invariant topological texture for storage times up to microseconds despite imbalanced path losses and control-power perturbations. This provides direct evidence of topological protection in a quantum memory and suggests a robust subspace for photonic information processing. The work opens avenues for encoding quantum information in skyrmion-based topological subspaces and informs the development of resilient photonic technologies.

Abstract

Optical skyrmions are topological structures of light whose defining property, the skyrmion number, is robust against perturbations. This makes them attractive for applications in quantum information storage, where resilience to decoherence is paramount. However, their preservation during coherent storage remains unexplored. We report the first experimental demonstration of storing and retrieving optical skyrmions in a cold $^{87}$Rb vapor using a dual-path electromagnetically induced transparency memory. Crucially, we show that the skyrmion number remains invariant for storage times up to several microseconds, even when subjected to imbalanced loss between the two paths and substantial perturbations in control beam power. Our work demonstrates the survival of a non-trivial topological invariant in a quantum memory, marking a significant step towards topologically protected photonic technologies.

Figures (4)

• Figure 1: (a) Simulated polarization and intensity distributions of paraxial optical skyrmions for ${N}_\mathrm{skyr}=1$, 2, 3 in Eq. (\ref{['eq1']}). (b) 3D perspective of simulated Stokes vectors for optical skyrmions with the corresponding ${N}_{\rm{skyr}}$ values. (c) The schematic diagram of optical storage. The probe beam drives the level $|1\rangle$ to $|3\rangle$ in each path, and the control beam simultaneously drives the level $|2\rangle$ to $|3\rangle$ in both paths. We input the signals that need to be stored in the atomic storage medium, and obtain the output (retrieved) signals after storage. More details are in the main text. The left bottom inset shows the Stokes vector $\pmb{s}$ on the unit Poincaré sphere. And the mapping relationship between arrows and polarizations are indicated by the same color.
• Figure 2: (a) Experimental setup for the optical skyrmion storage. The control beam, with a waist size of 4 mm and a power of 33 mW, and is incident on the atomic medium at a $1^\circ$ angular separation relative to probe beams. By controlling the timing sequence of the MOT and optical switching (top left inset), as well as locking the frequency and phase of two beams (top right inset), the storage and retrieving processes are achieved. Full spatially resolved Stokes tomography (optional) is performed to characterize the polarization structure. Optical elements: H, half-wave plate; L, lens; M, mirror. (b) Temporal waveforms of the input LG beams, which both have Gaussian temporal profiles with 0.5 $\mu$s width, and their corresponding retrieved signals. The storage efficiencies for all paths are presented. The non-stored (smaller) remnants of the pulses are the leakage.
• Figure 3: Left: The measured topological textures of input and output optical skyrmions with ${N}_\mathrm{skyr}$=1, 2 and 3 (from top to bottom). The experimentally calculated ${N}_\mathrm{skyr}$ are presented with respect to each sub-figure, with error bars representing the standard deviation of five runs. The insets on the side are the normalized local Stokes parameters. Right: Comparison between experimental data and theoretical simulation. The blue (red) solid lines represent the relationship of storage efficiency of the $\rm{LG}^{0}_{0}$ ($\rm{LG}^{\it{l}}_{0}$) mode against storage time, while the blue (red) circles represent the experimental data of the respective modes. The yellow solid line represents the measured input ${N}_\mathrm{skyr}$, and the data points represent the experimental data after storage.
• Figure 4: Experimental results of storage under different control beam power, for an optical skyrmion with ${N}_\mathrm{skyr}$=2 and a storage time of $0.5\,\mu$s. Top: The measured topological textures of input optical skyrmions with ${N}_\mathrm{skyr}$=2. The normalized local Stokes parameters and calculated ${N}_\mathrm{skyr}$ are on the left and below respectively. The error bars represent the standard deviation of five runs. Bottom: The input and retrieved temporal waveforms of the input $\rm{LG}^{0}_{0}$ and $\rm{LG}^{2}_{0}$ modes. Additionally, the storage efficiencies are calculated and presented. The non-stored remnants of the pulses are the leakage.