Turbulence Modelling Reveals Interference in Quantum Free-Space Optical Links

Key Takeaways

• First‑principles wave‑optical model captures turbulence‑induced crosstalk.
• Model maps turbulence to correlated n‑qubit erasure channel.
• Indistinguishable photons cause complex interference, affecting error rates.
• Erasure‑extended encoding enables tailored quantum error‑correction codes.
• Simulations show reliable multi‑qubit entanglement over 10 km free‑space link.

Pulse Analysis

The ability to transmit quantum information through the atmosphere has long been hampered by the unpredictable nature of turbulence. Traditional statistical models such as Gamma‑Gamma or Log‑Normal treat the channel as a simple fading process, ignoring the wavefront distortions that cause inter‑modal crosstalk and aperture loss. Peng et al. bypass these approximations by solving the wave equation directly, producing a first‑principles model that tracks the full optical field as it propagates through random refractive‑index fluctuations. This level of fidelity reveals error‑rate reductions that make ten‑kilometre free‑space entanglement feasible, a milestone for long‑distance quantum links.

The authors translate the complex physics into a tractable communication model by representing the quantum MIMO link as a correlated n‑qubit erasure channel. In this formulation, turbulence and photon loss appear as known erasures rather than random bit flips, allowing designers to apply erasure‑specific quantum error‑correcting codes. The introduced erasure‑extended encoding maps each turbulence‑induced loss to a distinct erasure state, simplifying capacity analysis and enabling near‑optimal coding strategies. By treating loss as erasure, the model sidesteps the destructive measurement problem that plagues conventional quantum error correction.

While the simulation results are promising, real‑world deployment still faces hurdles. Precise polarization alignment, beam pointing stability, and weather events such as rain or snow can reintroduce unpredictable losses that the current model does not yet capture. Nonetheless, the framework provides a clear roadmap for integrating spatial multiplexing and adaptive optics into future quantum networks. As commercial interest in satellite‑based quantum key distribution and distributed quantum computing grows, having a reliable turbulence model will be essential for designing robust protocols and meeting the security expectations of enterprise users.