[BRIEF NOTE] On the latest breakthrough in neutrino communication systems

It’s a minor surprise that the Economist has become my go-to site for breakthroughs in neutrino-based communications.

The neutrino is a unique particle, an exceptionally light and electrically neutral that’s most notable for traveling almost exactly at the speed of light (likely just short of the speed of light, notwithstanding debunked claims of faster-than-light travel) and for hardly interacting with normal matter at all. To be sure of intercepting the average neutrino produced by the sun in the course of its nuclear fusion, you’d need a solid barrier of lead one light-year thick. The difficulty of intercepting neutrinos makes them of interest to scientists who are interested in examining environments impervious to the electromagnetic spectrum, places like the interior of the sun (or other stars).

More recently, the durability of the neutrino has made people interested in extraterrestrial intelligences wonder if advanced civilizations might make use of neutrinos to create unstoppable signals across interstellar distances. I first came across the idea in this 2009 Centauri Dreams post speculating about Antarctic neutrino observatory, but a 2011 article from the Economist went into greater detail, suggesting that neutrino beams could be used not only as signals but as awesome tools that could manipulate the fluctuations of Cepheid variable stars into intelligible signals. An article printed this month announced that, for the first time, neutrinos have been used to communicate data. This news was expanded upon by a post at the Economist‘s technology blog, Babbage. The facilities of Fermilab in Chicago, including the MINERvA neutrino detector, were key.

MINERvA uses a beam of neutrinos sent from Fermilab’s accelerator, the Main Injector, to a detector roughly 1km (0.6 miles) away. The beam is created by smashing pulsed bunches of trillions of protons into a graphite target. For a week before the start of a maintenance break, however, it runs at half its typical intensity, not ideal for MINERvA’s day job, but just dandy for the communications test. (The data collected are nonetheless used for MINERvA’s everyday research.)

The detector is hidden underground to ensure that the rare events observed in it are due to neutrinos and not cosmic rays, which do not penetrate rock. As a result, the experiment’s neutrinos must travel 240 metres through the Earth’s crust, precisely the sort of thing the theorists envisaged.

The message, which read “neutrino”, was transcribed into a string of “0s” and “1s” using the standard code employed in digital communications. The beam was then tweaked so that a pulse created using a full bunch of protons corresponded to a “1”, while one with no protons signalled a “0”. The pulses were separated by 2.2 seconds and the message was repeated in cycle for about two hours.

At the receiving end, each “1” translated into an average of 0.8 neutrino events registered in the detector; a “0”, naturally, translated into none. This was enough to reconstruct the message accurately.

Practical neutrino-phones are, of course, a long way off. For a start, the data-transmission rate, at a piddling 0.1 bits per second with a bit error rate of 1%, leaves a lot to be desired, though it could be improved with a more intense beam, which would anyway be required to send messages over long distances. A bigger problem is that MINERvA’s detector, at 5 metres long, 3.5 metres high and weighing 170 tonnes, is not exactly portable. And the Main Injector is many times heftier still. All the same, who said fundamental physics has no real-world applications?

The paper in question is “Demonstration of Communication using Neutrinos”, available at arXiv.

That site’s blog suggested one practical use for neutrino communications systems, in communicating with underwater craft like submarines. When submerged, submarines can communicate with surface facilities only through extremely low frequency (ELF) radio waves that firstly can only penetrate a hundred or so metres and secondly can only transmit around 50 bits per second. A neutrino-based communications system that transmitted at comparable speeds and could be picked up at unlimited depths anywhere on the world’s oceans would be an obvious replacement for ELF radio. As the blog notes the data transmission rate for neutrino communications systems would need to be improved by several orders of magnitude, while the bulkiness of the detector systems–MINERvA masses five tons–is another issue. Still, I’m not inclined to bet against further progress in this domain.