Searching for interstellar quantum communications (2104.06446v2)

Abstract: The modern search for extraterrestrial intelligence (SETI) began with the seminal publications of Cocconi & Morrison (1959) and Schwartz & Townes (1961), who proposed to search for narrow-band signals in the radio spectrum, and for optical laser pulses. Over the last six decades, more than one hundred dedicated search programs have targeted these wavelengths; all with null results. All of these campaigns searched for classical communications, that is, for a significant number of photons above a noise threshold; with the assumption of a pattern encoded in time and/or frequency space. I argue that future searches should also target quantum communications. They are preferred over classical communications with regards to security and information efficiency, and they would have escaped detection in all previous searches. The measurement of Fock state photons or squeezed light would indicate the artificiality of a signal. I show that quantum coherence is feasible over interstellar distances, and explain for the first time how astronomers can search for quantum transmissions sent by ETI to Earth, using commercially available telescopes and receiver equipment.

• The paper introduces quantum communications as a novel channel for SETI, arguing that ETI might use these secure, efficient signals over classical methods.
• It evaluates theoretical feasibility, demonstrating that quantum states can maintain coherence over interstellar distances with current observational tools.
• It outlines actionable detection strategies, including photon bunching and spectral anomaly methods, to supplement traditional radio searches.

An Examination of Interstellar Quantum Communications as a Target for SETI

The paper "Searching for interstellar quantum communications" by Michael Hippke explores an innovative direction for the Search for Extraterrestrial Intelligence (SETI). Historically, SETI has focused on detecting classical communication signals via radio waves and optical laser pulses. However, these efforts have yielded no positive results. Hippke proposes that future endeavors should include searches for interstellar quantum communication signals, suggesting that extraterrestrial intelligence (ETI) might use advanced quantum channels, which have so far been overlooked.

Re-evaluating SETI Strategies

SETI has traditionally concentrated on beacon-like signals; powerful, narrow-band, isotropic emissions intended to be found. However, Hippke suggests that a paradigm shift towards targeted quantum communications is necessary. Quantum communication offers significant advantages over classical methods, such as enhanced security and more efficient information transmission. Importantly, these quantum signals might appear as nothing more than ambient starlight if current detection methodologies are applied, evading traditional search methodologies.

Theoretical Underpinnings for Quantum Preference

Hippke provides four key arguments in favor of why ETI might choose quantum over classical communications:

1. Gate-keeping: Advanced civilizations might opt for communication techniques that less sophisticated societies cannot access, thus maintaining a form of exclusivity.
2. Quantum Supremacy: Quantum computers and networks promise dramatic computational efficiencies and secure communication, potentially forming the backbone of interstellar communication infrastructure.
3. Information Security: Utilizing quantum key distribution ensures secure communication channels, which would be advantageous for civilizations with varied factions or diplomatic constraints.
4. Information Efficiency: Quantum channels can potentially deliver more information per photon, thereby maximizing the energetic efficiency of interstellar communications.

Technical Feasibility and Implementation

An essential aspect of Hippke’s proposal is demonstrating the feasibility of quantum coherence over interstellar distances. The paper discusses the potential for quantum states to maintain coherence and viable communication pathways despite the vast interstellar medium. This finding is crucial as it indicates that astronomical distances do not inherently disrupt quantum communications.

Hippke outlines practical methodologies for detecting such signals, advocating the use of available technology, including certain detections of photon bunching, spectral anomalies, and squeezed light detection. These methods hinge on the unique quantum characteristics that would not naturally arise in astrophysical environments.

Implications and Future Directions

Hippke’s work presents substantial implications for both theoretical SETI and practical astronomical observation. Incorporating quantum communication searches into SETI efforts could unravel previously inaccessible communication methods, potentially revealing advanced extraterrestrial civilizations employing technology beyond current human capabilities. Moreover, these findings contribute to our understanding of potential future human technologies and interstellar communication paradigms.

The theoretical discussion is backed by proposals for experimental methods using existing observational tools, which suggests an actionable path forward for quantum SETI. This initiative could act as a supplementary line of inquiry alongside classical searches, broadening SETI’s scope.

Conclusion

In conclusion, Hippke’s paper invites a rethinking of SETI strategies, emphasizing the exploration of quantum communications as a potentially untapped domain. If advanced extraterrestrial networks do indeed rely on quantum channels, adjusting our observational strategies may be paramount. These developments foreshadow a technological trajectory that could involve humans in future interstellar networks, leveraging both classical and quantum methodologies. The integration of classical strength with quantum finesse provides an extended toolkit in our search for cosmic counterparts.