WHY THIS MATTERS IN BRIEF
Being able to communicate without sending any data, and without using any particles as intermediaries, sounds impossible but scientists have just demonstrated it working and it could change everything about technology and communications as we know it.
Firstly I’m going to get this one out of the way, the process of transmitting information without transmitting any information is an insanely complicated topic that makes quantum computing and quantum mechanics look like Computers 101 and Maths 101 and it’s taken me all day to get my head around the concept. That said though I’ve tried to simplify it for you, a lot, and if you can stick with the article then everything you know about the future of communications and technology will have just changed forever. And that’s big.
Grab a coffee and an Aspirin, you might need the latter later, sit down, and listen to my story of Counterfactual Communication. And yes, I agree it’s a catchy name.
All of us connect and communicate with each other via particles – telephone calls and texts ride flecks of light, and web sites and photographs load on electrons. All communication is, essentially, physical and information is recorded and broadcast on actual objects – even those we can’t see.
Physicists also connect with the world when they communicate with it, and they send glimmers of light towards particles or atoms and wait for the light to be reflected so they can measure whatever it is they’re measuring. The light itself interacts with bits of matter, and how this “interaction” changes the light reveals the properties of the matter. For example this is one of the techniques we use to assess the chemical composition of distant stars, and the term of art for such a candid affair is a “measurement.”
Particles even connect and interact with each other using other particles. The force of electromagnetism between two electrons, for example, is conveyed by particles of light, and quarks huddle inside a proton because they exchange gluons.
It’s all fun stuff.
Physics therefore is, basically, the study of interactions, and information is always conveyed through interactions – whatever their form.
Quantum mechanics is, arguably, the ultimate theory of particles so it naturally describes both measurements and interactions, and during the past few decades, as companies race to develop new quantum computing platforms, the ultimate theory has been reframed to encompass information too.
What quantum mechanics implies for measurements and interactions is notoriously bizarre, and its implications for information is stranger still. One of the strangest of these implications refutes the material basis of communication and now an increasing number of physicists believe that we may be able to communicate without transmitting any particles at all.
In 2013, for example, an amateur physicist named Hatim Salih even devised a “protocol,” or thesis to you and I, where he posited that information can be read from a place where particles never travel, and it turns out that information can be disembodied, and that communication may not be so physical after all.
Still with me? Don’t worry, we’ll get to the how soon.
In April a short article about Salih’s protocol entitled “Direct counterfactual communication via quantum Zeno effect” appeared online in the Proceedings of the National Academy of Sciences (PNAS), and as it turned out most of the article’s authors were members of the University of Science and Technology of China, but the final author was Jian-Wei Pan, the world renowned physicist responsible for building and overseeing the teams who created China’s, and the world’s, first quantum communications satellite system which the other week beamed entangled quantum particles over a distance of 1,200km – a world record by a long, long, long way, by over 1,075km in fact.
Pan and his collaborators are prolific publishers but the paper they published in April, which was co-written by Yuan Cao and Yu-Huai Li, was exceptional.
In it they described an experiment where they sent a black and white image of a Chinese knot to a computer, without transmitting any particles, and extraordinary claims require extraordinary evidence. Even the person whose work dug the original foundation for the team’s evidence, Lev Vaidman, doubts their claim, but so far their experiment, and more importantly, their results, have stood up to scrutiny.
At stake now though is nothing less than the very foundation of all of tomorrows information technology products because if we can process information without particles, we could build a computer that doesn’t need to turn on, weird eh? It’s a quantum mechanics thing apparently. And we may be able to communicate with absolute secrecy – after all, there wouldn’t be anything to intercept and therefore there’d be nothing to hack and while quantum computing itself is deemed ultra-secure this new technology could prove to be the ultimate in secret communications.
The possibility that you can communicate without sending any information, or using any particles comes from the fact that it’s possible to store information, bits, not just on particles, but also “in” quantum wave functions.
In layman’s terms, light is made up of two components – photons, that, for example, scientists were recently able to store 10 bits of information on, and waves, which aren’t particle based, and it’s these waves that are the key here. The crests and troughs of the light can be made to undulate up and down or side to side, and this binary property, called polarisation, which is the same thing that your $10.99 sunglasses filter out, can be used to encode bits, and that’s how, apparently, we can transmit the information without having to use particles.
If you want to call this by its proper name then the phenomenon is called “Counterfactual Communication,” and if you want more information on the phenomenon then frankly my head still hurts so go and find a physicist.
Credit: Jen Christiansen
In the paper published in April Pan and his colleagues wrote:
“Although several publications are presently available regarding the theoretical aspects of [counterfactual communication], a faithful experimental demonstration, however, is missing.”
In other words, it was time for an experiment on the theory of Counterfactual Communication to speak for itself, so the group started planning their experiment to end the heated debate.
In order to achieve perfect communication using this technique the team would have needed an infinite number of interferometers, devices that are used in physics to measure small displacements, refractive index changes and surface irregularities, which, funnily enough, Pan and his team acknowledged was impractical, so they simplified the protocol for Michelson interferometers and built four, with two smaller ones nested inside. They then set their source of single photons, their beam splitters and their mirrors on a small table that was temperature controlled and isolated against vibrations.
The hope was that the Counterfactual Communication would occur across 50 centimeters, inside a lab in Shanghai. Pan’s collaborators, Cao and Li, designed a number of images to send, and the group voted for a Chinese knot. As Cheng-Zhi Peng explained, “it is symmetric and beautiful.”
The group then wrote software to run their experiment automatically, without any human interference and on May 31, 2013, they sat at a computer and waited through the night to see if the image loaded on a screen. While they trusted their instruments they also quietly hoped that nothing would appear, because a negative result would imply that quantum mechanics is wrong, and no one had ever observed that.
Over a period of five hours, 10 kilobytes of information passed the 50 empty centimeters between the sender and receiver and many of the bits had to be transmitted several times before they registered. As it turned out the computer was better at recognising 1s than 0s, but eventually a monochrome bitmap appeared even though they hadn’t transmitted any particles that they could discern.
Credit: Jen Christiansen; Source: PNAS
Once they saw the image, after sunrise, they disbanded to sleep before they celebrated. They posted a short article one year later but did not submit their paper for publication for more than three years – they were too busy building communication satellites, and they wanted some time to think about the result.
Pan and his colleagues are now working to transmit a picture in shades of grey, and they hope to send pure quantum information based on another protocol pointed out by Salih. To ensure that no photons pass through the transmission channel, they also plan to do a weak measurement to determine where the photon goes.
Although Pan is in the business of communication satellites, it’s no surprise that counterfactual communication piques banks and militaries interest but today’s data rate, unsurprisingly, is still very slow – they’ve got to start somewhere after all.
Pan and colleagues attribute the mystery of counterfactual communication to the wave-particle duality, and meanwhile Salih has another interpretation.
“I believe this experiment has something to say in support of the reality of the quantum wave function – if physical particles did not transfer information then what did?”
Salih is now working on a proof of counterfactuals, using weak measurements, to outflank his critics, and when Vaidman was asked what would convince him that no particles were ever transmitted, he replied:
“If an object was found in a counterfactual way, there should be zero trace [of particles] near it.”
Meanwhile Pan’s collaborators said jokingly: “Although our demonstration hasn’t solved the issue entirely, we do believe that our work shed some light on the discussion.”
Quantum mechanics has survived nearly 100 years and as physicists continue to discover new ways to adapt its mysteries to information technology one day we might see a time when we communicate without communicating and the impact could be enormous.
Not only will the rules of communications and technology have to be completely re-written but perhaps we could communicate with human colonies on Mars at the speed of light – something not possible today, or, if we can really unravel the secrets of quantum entanglement and quantum communications, which admittedly is a slightly different topic, Maths 201 perhaps, who knows we might also be able to communicate across the vast void of space in real time.
Now take your Aspirin I’m done, and I hope you enjoyed consuming the particles I used to transmit my article into your brain.