The Strange World of Entanglement, Encryption, and Einstein’s Biggest Doubt
Reading Time: 4 minutesEinstein’s Doubt
One of the notable science stories of the century concerns a strange implication of the discoveries of quantum physics in the 1920’s. This was the phenomenon of entanglement. Entangled particles are formed together—for example, when a single high-energy photon splits into two lower-energy photons in a particle collider. From that moment on, measuring the property of one of the particles here, causes an instantaneous change in the twinned particle existing over there – with the rub being that ‘over there’ might be a million miles away! That’s right: when the two particles are entangled, they form a kind of twin relationship—what happens to one instantly affects the other, no matter how far apart. This bizarre correlation defies classical physics, in which no signal can be transmitted at greater than the speed of light, and on those grounds was derisively described by Einstein as ‘spooky action at a distance’ – something he refused to accept.
Of course, at the time this prediction was made, there was no way of validating it experimentally, as there were as yet no particle colliders. It was one of several implications of quantum physics that Einstein just couldn’t accept, and indeed he devoted considerably ingenuity in his later years to arguing against it. During the 1930’s, he co-authored a paper about it with two colleagues, Boris Podolsky and Nathan Rosen, published as the EPR Paradox, claiming to show how entanglement couldn’t be true. But at the time of his death, it was still an open question.
However, it has since been confirmed by experimental observation that the ‘spooky action’ does indeed take happen, exactly as quantum physics predicted. This was the result of the work of some brilliant physicists, first by John Stewart Bell, who worked out what it would take to confirm such a prediction, and then by several experimental physicists actually carrying out the experiment.
(The 2022 Nobel Prize in Physics was awarded to Alain Aspect, John Clauser, and Anton Zeilinger for proving that entangled particles truly behave as quantum mechanics predicts, instantaneously affecting each other across vast distances. These experiments definitively confirmed what Einstein had once dismissed. Quite how it happens is still an unsolved mystery, but there was no longer any doubt that it does.)
Enter the Hippies
Beyond the intrinsic fascination of quantum entanglement, there’s another intriguing backstory—the origins of the idea of using ‘spooky action at a distance’ for communication and a way to put this astounding principle to practical use. And that idea didn’t emerge from mainstream physics at all, but from a group of brilliant, if offbeat, thinkers who gathered at the Lawrence Livermore Research Laboratory and in the countercultural scene of 1970s San Francisco. Calling themselves The Fundamental Fysiks Group, they were as comfortable debating the mysteries of quantum mechanics as they were holding forth in the Esalen hot tubs. Their exploits—and their influence on modern physics—are chronicled in David Kaiser’s 2012 book, How the Hippies Saved Physics.
One of their members, Nick Herbert, was the first to suggest using quantum entanglement for instantaneous, long-distance communications. As it turned out, Herbert’s math didn’t quite hold up, and mainstream physicists dismissed the idea—but in the process of disproving him, they inadvertently discovered the foundation of something that came to be known as ‘quantum encryption‘. It’s an example of how even a flawed idea can serendipitously set the stage for a revolutionary breakthrough. And while Herbert’s math didn’t pan out, his basic intuition — that entanglement could be harnessed for something more than paradoxes—was ultimately validated.
Refutation Becomes Refinement
While Herbert’s idea of using entanglement for instant communication didn’t hold up to mathematical scrutiny, his speculation led mainstream physicists to examine the problem more closely. In the process, researchers like William Wootters, Wojciech Zurek, and Charles Bennett uncovered a crucial limitation in quantum mechanics: the No-Cloning Theorem, which showed that entangled particles couldn’t be used to transmit information faster than light.
But far from ruling out practical applications, their findings led to something even more revolutionary—Quantum Key Distribution (QKD). This encryption method allows cryptographic keys to be securely shared using entangled particles, forming the foundation of quantum-secure communication. Since entangled particles remain instantaneously linked, any attempt to intercept or manipulate one will immediately disrupt the other—making eavesdropping instantly detectable.
Entangled in Space
Fast forward several decades, and what began as a countercultural thought experiment had by now become a real-world technology. In 2017, physicists in China launched an ambitious experiment to take quantum encryption beyond the laboratory and into space. This was the Micius satellite.
The satellite was the foundation of the $100 million Quantum Experiments at Space Scale program. Launched in August 2016, it enabled Jian-Wei Pan, a physicist at the University of Science and Technology of China in Shanghai, to design and run an experiment to test the principle of entanglement on a grand scale. ‘In their first experiment, the team sent a laser beam into a light-altering crystal on the satellite. The crystal emitted pairs of photons entangled so that their polarization states would be opposite when one was measured. The pairs were split, with photons sent to separate receiving stations in Delingha and Lijiang, 1200 kilometers apart, in the mountains of Tibet, reducing the amount of air the fragile photons had to traverse.’ (Science, see references.)
Apart from being an amazing piece of technological innovation, what was impressive about this result is the distance involved; until now, such experiments had been limited to much smaller scales, but this achievement opens up the possibility of commercial applications in satellite communications. It provides the means to make absolutely secure encryption, which no amount of hacking will ever penetrate, because as soon as anyone reads one of the paired keys, the other ‘knows’ it. And this, by triangulating and sending encrypted information between the satellite and receiving stations in the high mountains of Tibet, among other places — a mind-boggling technological feat!
Postscript
Since the Micius satellite’s groundbreaking experiments in 2017, quantum encryption has moved from the laboratory into real-world deployment. China has now integrated quantum-secure networks over thousands of kilometers, collaborated with European scientists to achieve intercontinental QKD, and even developed portable ground stations to bring quantum encryption closer to practical application.
What was once fringe physics is rapidly becoming the backbone of a future global quantum-secure communication network—a vision that started with ‘spooky action at a distance’ but is now transforming cybersecurity on a planetary scale.
References
How the Hippies Saved Physics, David Kaiser, Norton, 2012
China’s quantum satellite achieves ‘spooky action’ at record distance, Science, 15th June 2017