Interstellar Quantum Communication: Feasibility, Engineering Challenges, and SETI Implications
To the point
Arjun Berera argues quantum coherence could persist across galactic distances in space, and Latham Boyle extends this to an interstellar quantum link for SETI where qubits enable advanced protocols such as quantum cryptography, teleportation, dense coding, remote state preparation, and entanglement distillation; however the channel would suffer losses from the interstellar medium, Earth's atmosphere, and beam spreading, so a usable quantum link would require ultraviolet wavelengths (below about 320 nm) to avoid depolarization and extremely large or coherently combined telescope arrays spanning tens of kilometers, making a practical implementation dependent on future infrastructure, with benefits including high information density, quantum error correction, cryptography, and ultra-high angular resolution via long-baseline interferometry with quantum repeaters, plus the provocative idea that a civilization capable of such communication could also check whether we have built similar gear, all while respecting the speed of light and the fact that entanglement alone cannot carry messages.
