On Interstellar Quantum Communication And The Fermi Paradox

Since it began Cocconi Morrison, the search for extraterrestrial intelligence (SETI) has focused on interstellar classical communication. Recently, Berera:2020rpl pointed out that, at certain frequencies, photon qubits can retain their quantum coherence over interstellar (and even intergalactic) distances, raising the prospect of interstellar quantum communication.

This is an intriguing possibility, since quantum communication permits certain tasks that would be impossible with classical communication, and allow exponential speed-ups for others. (We suggest some motivations in the interstellar context.)

But quantum coherence alone is not sufficient for quantum communication: here, for the first time, we analyze the quantum capacity Q of an interstellar channel. We point out that, to have non-zero quantum capacity Q>0, interstellar communication over a distance L must use wavelengths λ<26.5cm (to avoid depolarization by the cosmic microwave background), and enormous telescopes of effective diameter D>0.78λL‾‾‾√ (to satisfy quantum erasure constraints).

For example, for two telescopes of diameter D on Earth and Proxima Centauri, this implies D>100km! This is a technological threshold that remains to be crossed in order for reliable one-way quantum communication to become possible, and suggests a fundamental new resolution of the Fermi paradox.

Latham Boyle

Comments: 4+3 pages, 2 figures
Subjects: Quantum Physics (quant-ph); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2408.02445 [quant-ph] (or arXiv:2408.02445v1 [quant-ph] for this version)
https://doi.org/10.48550/arXiv.2408.02445
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Submission history
From: Latham Boyle
[v1] Mon, 5 Aug 2024 13:11:39 UTC (249 KB)
https://arxiv.org/abs/2408.02445
Astrobiology, SETI,