Insider Brief

• The Fermi Paradox assumes that there should be many civilizations in the vastness of the universe that can communicate with each other, but that there is little evidence for the existence of these signals.
• Current efforts in the search for extraterrestrial intelligence (SETI) focus on detecting radio waves or laser signals sent across interstellar distances.
• One researcher suggests the next advance in SETI could be studying quantum communication in search of evidence of conversations between aliens.

It has been a topic of debate and ridicule ever since Enrico Fermi raised the issue during a lunchtime discussion at Los Alamos National Laboratory in 1950: If the sky is so full, why is it so quiet?

In other words, this Fermi Paradox suggests that there should be many, many civilizations in the far reaches of the universe that can communicate with each other, but that there is little evidence of these signals. This debate has at least partly inspired the Search for Extraterrestrial Intelligence (SETI), which has traditionally focused on detecting radio waves or laser signals sent across interstellar distances – and is therefore guided by the principles of classical communication.

However, a recent study by a Canadian researcher suggests that the next leap in SETI could be in the area of ​​quantum communication. This new take on this long-standing puzzle could not only explain the puzzling Fermi Paradox and give new impetus to quantum communication research, but—who knows?—even put us on the same wavelength as our alien neighbors.

Background to quantum communication

Quantum communication is a field that studies the transmission of information using quantum bits, or qubits. Unlike classical bits, which can be either 0 or 1, qubits can exist in superpositions of both states simultaneously. This unique property allows quantum communication to perform certain tasks that classical communication cannot, such as quantum cryptography, teleportation, and super-dense coding.

In a study published on ArXiv, Latham Boyle of the Higgs Centre for Theoretical Physics at the University of Edinburgh, UK, and the Perimeter Institute for Theoretical Physics investigates the feasibility of interstellar quantum communication and its implications for SETI.

Boyle argues that “photon qubits can maintain their quantum coherence across interstellar (and even intergalactic) distances, opening the prospect of interstellar quantum communication.”

This concept assumes that civilizations could communicate using quantum signals – rather than classical signals – that would be undetectable with current SETI methods.

The challenge of quantum capacity

One of the reasons science is so much fun is that it offers the opportunity to dissuade people from the idea that things can be easy or simple. Boyle does this in his assessment of the possibility of quantum communication across vast interstellar spaces.

To assess the potential of quantum communication over interstellar distances, the study analyzes the quantum capacity of an interstellar channel. Quantum capacity is the maximum rate at which qubits can be reliably transmitted over a communication channel. For quantum communication to be possible, this capacity must be greater than zero, according to the researcher.

Boyle describes specific criteria that must be met for interstellar quantum communication to take place:

Wavelength limitations: The wavelength of the photons must be below 26.5 cm to avoid interference from cosmic microwave radiation.

Boyle explains: “Using constraints on quantum depolarization channels and the properties of the diffuse astrophysical background radiation, we show that the exchanged photons must have certain properties for quantum information to be successfully transmitted.”

Telescope size: The telescopes involved in the communication will need to have a much larger effective diameter than those we currently have. Boyle points out that for effective communication between Earth and Proxima Centauri, the closest star to our solar system, the telescopes would need to be over 100 kilometers in diameter. For comparison, the diameter of Greater London is about 50 kilometers, so a circle of 100 kilometers would be about twice the size of London. The largest telescopes today are only about 40 meters in diameter.

These limitations underscore the technological challenges of implementing interstellar quantum communications. Anyone who spends day-to-day sitting in traffic during simple roadworks probably knows that building a 100-kilometer-long telescope is a little beyond our capabilities, but the study suggests that such advances may one day be possible.

A new perspective on the Fermi Paradox

Despite the obstacles to interstellar communication, Boyle believes that if advanced civilizations could overcome these hurdles and use quantum communication, their signals would be undetectable with current technology that scans the skies for aliens.

Boyle explains: “The signal must be so strongly directed that only the intended receiving telescope has a chance of detecting any signs of communication.”

This is in contrast to classical communication, where signals are often sent randomly. Therefore, civilizations communicating through quantum channels could send signals that are virtually invisible to us.

Furthermore, the study suggests that civilizations capable of quantum communication would likely have the means to determine whether we have the technology necessary to receive their signals.

“If the transmitter has a large enough telescope to communicate with us quantumly, it must necessarily also have sufficient angular resolution to detect that we do not yet have a large enough receiving telescope,” writes Boyle.

Future directions and opportunities

Although this concept of interstellar quantum communication is still theoretical, the study opens up new possibilities for the future of SETI. The potential benefits of quantum communication, such as increased security and speed, make it an attractive area of ​​research for physicists and astronomers.

One of the intriguing applications mentioned in the study is Astronomically Long Baseline Interferometry (ALBI). This technique would use quantum communications to link telescopes across astronomical distances, creating “effective angular resolution” that could greatly improve our ability to observe distant objects in the universe.

The study also suggests that quantum repeaters, devices that extend the range of quantum communication, could play a crucial role in establishing interstellar channels. Placing these repeaters at strategic points along a communication path could reduce the need for massive telescopes and make quantum communication more practical.

Although it’s easy to joke about “ET Quantum Phone Home,” the study’s investigation of interstellar quantum communication actually presents a thought-provoking challenge. By expanding our understanding of communication beyond classical paradigms, the ideas in the study could help researchers find new ways to discover extraterrestrial intelligence and resolve the Fermi Paradox.

While the technological hurdles are significant, the potential benefits are equally significant. Boyle concludes: “While our galaxy and universe allow interstellar quantum communication, the limitations mentioned above represent a severe technological hurdle that we have not yet reached.”

While we’re unlikely to be sharing memes about interstellar quantum IM with our alien friends any time soon, the work could serve as inspiration for Earth-based improvements to the quantum communications research agenda.

For example, the proposed constraints to enable quantum communication over vast interstellar distances may pose a daunting challenge. However, overcoming this challenge could encourage researchers to push the boundaries of telescope technology and develop new methods for secure communication, data transmission and data processing by exploiting the properties of quantum mechanics.