Hello my lovely readers, you may be few, but I love you all the same.

Having had a read through my previous articles since I started this whole bringing physics to the masses journey, I noticed there’s a nice progression developing: Gravity > Relativity > Entanglement > Bell’s Proof, a quick side step into the footy  (let’s not talk about that), which leads naturally onto this week’s article:

Quantum teleportation.

Now then, there’s a misconception about teleportation, and I’ve touched on it with my Star Trek allegories in previous articles.

When most of us hear the word teleportation, we probably all think of Captain James T. Kirk demanding that Scotty gets the malfunctioning transporter fixed pronto and beams him up (or Benjamin Sisko making the same demand of Chief O’Brien, or Captain Janeway…. Sorry, got a bit carried away, on with the article). Quantum teleportation is both less dramatic and far more profound (every time I type the word profound, I can hear Prof Brian Cox saying it in my head).

Unfortunately, scientists have not discovered a way to transport humans, objects, genesis devices, or even particles from one place to another. What they have discovered is a way to transport the quantum state of a particle, that is a complete description of its quantum properties, from one particle to another, potentially over vast distances.

In other words, quantum teleportation does not move matter, it moves information.

And that distinction may reveal something fundamental about the nature of reality.

So, if it’s not Star Trek personnel being teleported, what is?

To understand quantum teleportation, we first need to understand a quantum state.

Again, as I mentioned previously, unlike a classical bit, which can be either 0 or 1, a quantum bit, or qubit to give it its correct term, can exist in a superposition of all states simultaneously: it can be zero, one, or both, at the same time. The state of a qubit contains all the information that can be known about it.

The remarkable achievement of quantum teleportation is that the exact state of one qubit can be recreated in another distant qubit without ever measuring and copying the original state. The original state disappears, and the new state appears elsewhere. There is nothing physical travelling between the two except for a teeny tiny amount of ordinary information.

Quantum teleportation relies on three extraordinary ingredients.

The first ingredient is quantum entanglement.

When two particles become entangled, they cease behaving as independent objects. Instead, they become part of a larger quantum system whose properties are linked regardless of the distance separating them. You know what’s coming, don’t you? Yep, you’ve got it, this is what our old mate Albert Einstein famously referred to as “Spooky action at a distance.”

You’ve read my previous article on Bell’s Inequalities, so you know this already, but I’m going to repeat myself again anyway.

Today, entanglement is one of the most experimentally verified phenomena in physics.

On to ingredient number two. The sender (traditionally called Alice, but who I have renamed Betty in honour of my dear old late Mum), performs what’s known as a Bell-state measurement on the particle she wants to teleport and her half of an entangled pair. This measurement destroys the original quantum state, this destruction is not a bug though, it’s a requirement.

Ingredient three is the classical communication.

Betty then sends Bob, the receiver, two ordinary classical bits describing the measurement result.

It is only after Bob receives those bits that he can perform the operation needed to reconstruct the original state on his entangled particle.

At that moment, the teleportation is complete.

Sound familiar? If you read my “Spooky Action at a Distance” series, it should. I’m about to reuse that same trick about entanglement and the speed limit on information. If you haven’t read it yet… well, what are you waiting for?

Now we have one of the biggest misconceptions concerning quantum teleportation. Why doesn’t it break the speed of light?

Because entanglement creates correlations that appear instantaneous, but usable information still cannot travel faster than light. Bob cannot reconstruct the teleported state until Betty’s classical message arrives. This keeps Einstein’s theory of relativity perfectly safe and intact. No matter how strange quantum teleportation appears, and I know I’m repeating myself here, it does not allow faster-than-light communication.

Let’s look at the rule that makes this all possible, which is a fundamental principle of quantum mechanics called the No-Cloning Theorem. This rule states that an unknown quantum state cannot be copied perfectly, essentially meaning teleportation doesn’t produce two versions of the same particle state, the original state is destroyed, and the distant state is created. Quantum teleportation is a transfer, not a duplication.

The theory of quantum teleportation was first proposed in 1993 by Charles Bennett, Gilles Brassard, Claude Crépeau, Richard Jozsa, Asher Peres, and William Wootters. Their groundbreaking paper showed how an unknown quantum state could be transferred using a combination of entanglement and classical communication. If you really want to have a deep dive into it, let me know and I’ll send you the paper. It took only four years for researchers to successfully demonstrate the effect experimentally using photons in 1997. I remember being really, REALLY, excited at the time, I still get goosebumps looking back to when I first heard the news.

What had once sounded like science fiction had become a laboratory reality.

To me, and I’m sure to many others, this has become one of the greatest ironies of modern physics. Poor Einstein, the phenomenon he disliked most of all, quantum entanglement, became the foundation of quantum teleportation. However, the universe turned out to be even stranger than Einstein imagined.

That’s where Bell came in with his theorem I tried to explain (and hopefully succeeded) in my previous article before the footy one.

For decades, some scientists hoped that hidden variables might explain away Einstein’s quantum weirdness. John Bell showed that certain predictions of quantum mechanics could be experimentally tested and the results repeatedly favoured quantum mechanics and ruled out large classes of local hidden-variable theories.

If it wasn’t for Bell, quantum teleportation might still be considered an interesting mathematical idea rather than a physical reality.

Ah, another question from you? How far have we been able to teleport?

Well, it’s actually a great deal further than you probably think. Quantum states have been teleported using photons, atoms, electrons, superconducting circuits, and solid-state quantum systems.

Researchers have demonstrated space-based teleportation using China’s Micius satellite over distances exceeding 1,000 kilometres. And more recent experiments have teleported quantum information between different physical systems and over telecom-compatible networks designed to support future quantum communications. Just this year, researchers reported teleporting a photon’s state between physically separate quantum dots connected across a 270-metre free-space link, another step toward practical quantum networking.

Looking to the future of this amazing technology, scientists believe quantum teleportation will one day become one of the foundational technologies of a future quantum internet.

Instead of simply sending data, future quantum networks may distribute entanglement between thousands or millions of devices. Quantum teleportation could be used to transfer qubits between quantum computers. It could also be used to construct ultra-secure communication links, enable distributed quantum computing, and build true global-scale quantum networks.

Can you imagine quantum processors in London, New York, and Tokyo acting like pieces of a single giant computer? Well folks, that’s the long-term vision.

Ok, ok, I know you’re desperate to ask the question everyone asks. Could we teleport a person?

Well, in principle, quantum mechanics doesn’t obviously forbid it, but in practice, it is almost unimaginably difficult.

A human body contains roughly 10²⁸ atoms, each participating in an immensely complex web of quantum interactions. Capturing every detail required to reconstruct a person would involve a truly humongously astronomical quantity of information. Oh, there’s also another problem.

Don’t forget the no-cloning theorem in the rules above. The original transported person would have to be destroyed during the process, which raises a somewhat disturbing philosophical question. If a perfect copy appears elsewhere while the original is destroyed, did the person actually travel? Or were they killed while an identical replacement appeared at the other end.

That is a question that science currently has no answer for.

And here we can link back to black holes and wormholes. Deep developments in modern theoretical physics suggest that quantum teleportation may connect to mysteries far beyond communication technology.

Researchers studying black holes discovered unexpected relationships between entanglement, information, spacetime, and wormholes.

There’s the famous proposal, known as ER = EPR, yep, that one from another of my previous articles, which suggests that entanglement and wormholes may be two descriptions of the same underlying phenomenon. Although this is still speculative, these ideas hint that teleportation may reveal something truly profound (there goes Prof B. Cox again. I didn’t know it was possible to have one person saying a single word as an earworm) about the structure of the universe itself.

And then we get to the biggest mystery of them all. Perhaps the most extraordinary aspect of quantum teleportation is that nobody fully understands why reality allows it.

The mathematics works flawlessly and the experiments work repeatedly. And the technology is rapidly advancing.

Yet the deeper philosophical question remains.

Why should information be able to move through the universe in this way?

Quantum teleportation sits at the crossroads of quantum mechanics, information theory, computing, cosmology, and philosophy. Beginning as a clever theoretical idea in 1993, today it is helping scientists build the foundations of the quantum internet.

Who knows, tomorrow, it may help explain nothing less than the nature of space, time, and reality itself! Wouldn’t that truly be profound!

Just a quick note before we start: I got a bit carried away with this one. What was meant to be one article on quantum entanglement turned into something closer to a small dissertation, so I’ve split it into two parts rather than dumping the whole lot on you in one sitting which will also give me an extra week do the research and get Part Two much more readable.

This week, Part One: entanglement itself, what Einstein got wrong (and sort of right), and why it doesn’t break the universe. Next Friday, Part Two: what entanglement actually builds, and how deep the rabbit hole goes. Right, on with the show…

Hello, my lovely readers, how about today we take a friendly deep dive into the universe’s strangest connection: Quantum Entanglement.

At some point in your life, you were probably told the universe works like a well-behaved machine. Things move, collide, push, and pull. Causes lead neatly to effects. Objects exist whether or not you’re looking at them.

Then quantum physics came along and politely, but firmly, said:

“Er… Excuse me? I like your thinking, but that’s not quite right.”

And at the heart of that disruption is something both beautiful and unsettling, something the physics boffins call quantum entanglement. The term was first coined by Erwin Schrödinger, you know, the guy with the cat in the box you’re always hearing about?

Einstein famously mocked it as “spooky action at a distance.” He thought it was a flaw, but it actually turned out to be a feature.

Let me try and unpack what that really means, without getting lost in too much maths, (as, I’ve mentioned before, maths isn’t one of my strong points), but still going deeper than the usual surface explanations.

So, what is entanglement?

Imagine two particles created together, say, two photons born from the same event. From that moment on, their properties become linked. They are not just similar, and not just predictable. They are shared, which means if you measure something about one such as its orientation or “spin”, you instantly know the corresponding property of the other.

Even, and this is the truly mind blowing bit, if it’s on the other side of the galaxy.

Well, that doesn’t sound so weird, right? At first glance, it feels normal, I’ll go with the classic analogy, say you have two gloves, one left and one right and you put them in separate boxes. You send one to Norwich and the other one to Waitangi (I chose these two places as I live in Norwich and I googled what is the antipodal point of Norwich City UK; here’s a link for no reason: https://tinyurl.com/4ap8w4d3). When you open one you immediately know what the other one is. No mystery, right? Except this analogy quietly assumes something critical and that is the gloves already had definite identities before you looked.

Unfortunately, quantum particles don’t behave that way.

The twist is that reality isn’t really set until you look. In quantum mechanics, particles can exist in a superposition which is a blend of possibilities. Before measurement, an electron doesn’t have a definite “spin” like up or down, it simply exists in a cloud of probabilities. Are you still with me? I’m going to carry on regardless even if you’re not as you’ll get it at the end, I promise. If I can understand it, absolutely anyone can.

So, when two particles are entangled, it’s not that they secretly agreed in advance that is what they were going to do, it’s more like they didn’t fully decide until one of them was observed and then they both snapped into agreement instantly!

Einstein didn’t like this at all and that’s the part he just couldn’t accept, and was quite vocal about it for many years. He believed in two key ideas: locality, where nothing can influence something else faster than light, and realism: where physical properties exist whether we observe them or not.

Einstein’s big problem with entanglement was that it seems to violate both. So, in 1935, Einstein and colleagues proposed the EPR paradox (I’ll attempt to actually explain this a bit later).

“Quantum mechanics must be incomplete. Something deeper must be going on.”

He suspected hidden variables, unknown factors quietly determining outcomes behind the scenes.

This debate simmered on and on for decades, it sounded philosophical and almost untestable until in 1964, physicist John Bell made a breakthrough.

He showed that if Einstein was right, that is, if hidden variables governed everything, then there should be strict limits on how correlated entangled particles can be. Right?

These limits are called Bell inequalities.

Basically, (without attempting any heavy maths), Bell’s logic boiled down to this:

If particles carry pre-existing answers, and no influence travels faster than light, then their measurement correlations must stay within certain bounds.

Right? Get it? No? Me neither at first and it’ll take yet another blog post to explain it fully, so just go with it for now and I’ll have to tell you all about Bell Inequalities in a different post.

Anyway, back to where we were: quantum mechanics predicts something different. It predicts stronger correlations than classical physics allows.

Physicists tested Bell’s predictions with real experiments, over and over, by taking entangled particles, separating them, and measuring them in different ways.

The result showed that quantum mechanics wins. Every time. Without fail. The observed correlations broke Bell’s Inequality, they couldn’t be explained with hidden variables, and they couldn’t be explained by local interactions either. Furthermore, recent experiments have ruled out all the usual loopholes.

This means we are forced to accept something different and more radical; the universe isn’t both local and real in the classical sense, which means something about our everyday intuition is wrong.

Hang on just a minute, didn’t you say in your last article that you couldn’t have faster than light messaging? If one particle instantly affects another, why can’t we use this to send messages faster than light?

And the answer to that question is quite a simple one, you can’t control the outcome of your measurement. When you measure a particle, you can’t choose “spin up” versus “spin down”; you can only observe whatever happens. Which means you get a random result. While the correlation is instant, there’s no way to encode and transmit information. Nature gives you Einstein’s spooky connection but keeps communications firmly limited by relativity.

And there we have it, the end of Part One, a short one this week as all the extra fun stuff will be packed in to Part Two, which judging by my draft, will be a tad longer. Thanks again for reading, and stay tuned folks, if I pull my finger out and crack on I’ll have Part Two ready for this time next week.