Establishing communication with an alien intelligence is one of the news items I, and I’m sure many others, long to see. Since we have started the search for advanced civilisations we have tried numerous ways to detect their transmissions but to date, unsuccessfully. A new paper suggests quantum communication may be the ideal method for interstellar communication. It has many benefits but the challenge is that it would require a receiver over 100km across to pick up a signal. Alas they know we don’t have that tech yet!
The search for alien signals has been undertaken under the banner of the search for extraterrestrial intelligence or SETI for short. It began in 1960 when Frank Drake commenced the first search. It was of course not fruitful but since then, large radio telescopes have been used to undertake searches. There have been many projects but of particular interest has been Project Breakthrough. It has used advanced technology and international collaborations but still there has been no success.
Frank Drake writing his famous equation on a white board. Credit: SETI.orgTo be able to effectively search for alien signals its imperative to fully understand the nature of communication. A quest that started back in 1948 with the development of the modern theory of classical communication. In 1959 it was proposed that human technology was available to send or receive interstellar classical communication which simply requires a message, someone to send it and someone to receive it.
Over the years that followed communication theories developed and quantum information theory emerged. It explores how quantum mechanics has an affect on the storage of and transmission of information. At the centre of the theory is the quantum bit or qubit which can exist in a number of states all at once due to the phenomenon of superposition. In classical information theory, bits of information are either 0 or 1 but in quantum theory they can be any infinite number of combinations with certain probabilities until measured. At that point, the wave function collapses to one of the definite states.
Another key element of quantum theory is entanglement where two or more particles are interconnected so that the state of one is related to the state of the other no matter how far apart they are. With qubits linked in this way data processing can be far faster than in classical model and more secure too. The paper authored by Latham Boyle from the University of Edinburgh suggests that it may be possible to send or receive information between the stars using quantum communications. A previous study by Arjun Berera proposed photon qubits could be used to transmit information over interstellar and even possibly intergalactic distances without loss of coherence.
The concept of quantum coherence describes the ability to maintain the specific quantum state but this alone is not enough for communication. The communication channel must also have sufficient capacity. In addition, specific wavelengths must be used (or avoided for example wavelengths less than 26.5 cm to avoid issues with the cosmic microwave background.) To facilitate this, radio telescopes with a diameter of 100 km must be used. Currently we don’t have the capability to build such instruments and this may explain why, in such a large and old universe, we still haven’t detected any aliens yet! We may simply have to wait until we can build such instruments before aliens can communicate with us.
Source : On Interstellar Quantum Communication and the Fermi Paradox
