On Interstellar Quantum Communication and the Fermi Paradox
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866911977433989120 |
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| author | Boyle, Latham |
| author_facet | Boyle, Latham |
| contents | Since it began \cite{CocconiMorrison}, the search for extraterrestrial intelligence (SETI) has focused on interstellar \emph{classical} communication. Recently, Berera \cite{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 \emph{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 \emph{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 $λ< 26.5\,cm$ (to avoid depolarization by the cosmic microwave background), and \emph{enormous} telescopes of effective diameter $D>0.78\sqrt{λL}$ (to satisfy quantum erasure constraints). For example, for two telescopes of diameter $D$ on Earth and Proxima Centauri, this implies $D>100\,km$! 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2408_02445 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | On Interstellar Quantum Communication and the Fermi Paradox Boyle, Latham Quantum Physics Instrumentation and Methods for Astrophysics Since it began \cite{CocconiMorrison}, the search for extraterrestrial intelligence (SETI) has focused on interstellar \emph{classical} communication. Recently, Berera \cite{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 \emph{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 \emph{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 $λ< 26.5\,cm$ (to avoid depolarization by the cosmic microwave background), and \emph{enormous} telescopes of effective diameter $D>0.78\sqrt{λL}$ (to satisfy quantum erasure constraints). For example, for two telescopes of diameter $D$ on Earth and Proxima Centauri, this implies $D>100\,km$! 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. |
| title | On Interstellar Quantum Communication and the Fermi Paradox |
| topic | Quantum Physics Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2408.02445 |