Where Are We At With Teleportation – Will It Ever Be A Reality?

Teleportation – but not how you think 

Quantum computers are the computational machines of the future as they can perform calculations well beyond what even the most powerful supercomputer is capable of. Their power comes from harnessing the properties of quantum mechanics so that their unit of information, the qubit (quantum bit), can be used to do more than a regular bit can. 

Quantum teleportation is a crucial tool for transmitting quantum information, not matter, between locations. This allows for the transmission of a quantum state from one place to another without having to move the actual qubit. 

There's one thing which is very commonly misunderstood: that entanglement allows instantaneous communication. That is a myth, that is wrong.

Prof Prem Kumar

“You can physically move the particle with its quantum state. That's what we call normal transmission, for example, with photons [the particles of light]. The photons are in a quantum state and you transmit the photon down an optical fiber. That's the physical transport of the quantum state along with the particle,” Professor Prem Kumar of Northwestern University, who works on quantum communications, explained to IFLScience. 

“However, there is also the disembodied transfer of quantum state. That is teleportation – and that is not Star Trek’s transportation. We do not know how to do that!”

Quantum teleportation works in the following way. Imagine you have two people with a qubit each. Let’s call them Alice and Bob – a standard naming convention, but you can think of them as Bert and Ernie or whoever your favorite duo is, if you want. For quantum teleportation to work, you need a quantum channel and a classical channel.

Alice has a qubit in a certain state and wants to transfer that to Bob without sending it physically. Alice and Bob share a number of entangled photons. Entanglement is an intriguing quantum phenomenon: It is possible to entangle particles so that even though there are many components, they are in a single quantum state. Affecting one particle, such as taking a measurement, will affect the rest of the system instantaneously, even if the particles are across the universe from each other. 

“There's one thing which is very commonly misunderstood: that entanglement allows instantaneous communication. That is a myth, that is wrong,” Professor Kumar said. 

“It is true if you have an entangled state, two particles that are entangled, they can physically move to very long distances away from each other, and if nothing happens to them and you make a measurement on one, the state collapse on the other side is instantaneous but that state collapse is unactionable.”

This point is crucial to how the teleportation takes place. Alice combines her entangled photon with her qubit, performing a joint measurement on a 2-qubit state known as a Bell measurement. This will create a change in the entangled state that instantaneously affects the entangled photon that Bob has. This is the quantum channel, but this is not quantum teleportation just yet. Bob needs to know the details of Alice’s Bell measurements.

That’s why you need the classical channel too. Alice needs to communicate to Bob what she’s done. Once he has that information, he can combine his photon and his qubit; this will turn his qubit into the one that Alice had. 

The entangled photons are no longer entangled and the qubit at Alice’s location is no more. But the qubit at Bob’s location is exactly the same as the original one at Alice’s location. The qubit has been “teleported”. 

A “quantum internet”

That is the theory of quantum teleportation; the practice is a bit more complex. There is no quantum memory storage for Alice and Bob (or Bert and Ernie). Quantum teleportation requires those entangled photons to be produced by Alice or Bob, or even by Clara, and sent to the parties that need to teleport the state.

Quantum entanglement is a fragile state. Interaction between the photon and other particles might break it, so a lot of current work is focusing on transmission with high fidelity – the accurate reproduction of signals with minimal distortion or loss. The record for the longest distance used a satellite, allowing quantum teleportation to happen over 1,400 kilometers (870 miles). This has demonstrated that long-distance quantum communication is indeed possible. 

There is, however, the question of what infrastructure this quantum communication network of the future, a possible “quantum internet”, might need. Professor Kumar and his team have just recently shown that we might not need to rip up the fiber optics infrastructure that already exists by demonstrating that it is possible to transmit entangled particles even on noisy internet cables. 

This might almost seem counterintuitive – two paragraphs ago, I stated that entanglement is fragile, and now these special photons can zip past the regular light that makes up internet traffic? Somehow, yes. Kumar and colleagues chose a quantum wavelength of 1,290 nanometers to entangle photons and transmit them through a 30.2-kilometer (18.8-mile) optical fiber, which simultaneously carried 400 Gbps internet traffic in the widely used C-band transmission light (1,547 nanometers). To test the integrity of the entanglement, they disturbed the photons at one end and observed whether corresponding changes occurred at the other.

“We found we could perform quantum communication without interference from the classical channels that are simultaneously present,” Kumar said in a statement at the time. 

This work, like much in this field, is a proof of principle. Quantum computers and quantum communication have great potential, but they are not yet ready to tackle those unsolved problems. 

If qubits, then why not humans?

Often enough, once the question of “what is quantum teleportation?” is answered, the following question is to wonder if, in a hypothetical future, we can teleport not just a qubit but a whole human being. Unfortunately, as far as we know, quantum mechanics doesn’t allow that.

In our experience of reality, if you know the properties of an object, you can rebuild it, like following Lego instructions to make what is shown on the box. But quantum mechanics doesn’t agree at all. 

“A person is made up of molecules, atoms, or whatever atomic sub-constituents. The idea is if I can measure all of them, how they are arranged, given that the elementary particles are available universally, then I can reconstitute the object, the person, or table, or whatever. It's akin to a fax machine. You have information on a piece of paper, you can digitize, send the information; paper is universally available, you reprint it,” Professor Kumar told IFLScience, before throwing a bucket of ice-cold water on this idea. 

“But quantum mechanically that's not possible.”

Let’s ignore for the moment that for this teleportation, the original quantum state needs to be destroyed, and the ethical implications of putting a human through the transporter system (but hey, faster travel) – there are two things that stop you from having a Star Trek teleportation experience. Quantum mechanics has a no-cloning theorem. This means that you cannot create an independent, identical copy of an unknown quantum state, so no The Prestige-type tricks either. Another technology in Star Trek, the replicator, cannot possibly assemble things from fundamental particles. It is simply not allowed. You try and a big red klaxon starts going off. 

Maybe there is science that we don't know yet, but that's a different story.

Prof Prem Kumar

But do not start thinking that if we were to know the properties of the quantum states of the particles in our bodies, we could reconstruct them. First of all, let’s consider the task itself from an information point of view. The average human body has about 7 billion billion billion atoms. That is a 7 followed by 27 zeros. Atoms are not fundamental particles, but let’s make our lives easier and consider just those, and state that we can somehow encode the properties of each atom on a single computer byte. 

The total data stored in the world in 2024 was around 150 zettabytes, or 15 followed by 22 zeros. The data storage that you’d need for one single human being in our simplistic explanation is about 50,000 times the whole data stored in the world today. 

However, we are in the realm of thought experiments. If we could get that data storage, could we use it to reconstruct a person? The big red klaxon is going off again. In quantum mechanics, you will never know enough to be able to reconstruct this person just as they were. This is due to Heisenberg’s uncertainty principle. 

This cornerstone of quantum mechanics states that you cannot know the position and velocity of a particle with arbitrary precision. If you were capable of exactly pinpointing an electron’s position, you wouldn’t know its speed and in which direction it was going. And you need to know both. Even lying still, we are a dynamic system; from the blood flowing through our veins to electrons orbiting around the atoms in our bodies, everything is moving. 

“You cannot really measure the quantum state of the object that you want to send à la Star Trek and recreate it on the other side. The uncertainty just does not allow that. So this Star Trek transporter is not possible with the science we know currently,” Professor Kumar explained, before adding with a smile: “Maybe there is science that we don't know yet, but that's a different story.”

Quantum teleportation is very real and it will be extremely useful for the communications of the future. Regular teleportation, on the other hand, will require a complete overhaul of everything we know about fundamental physics. But hey, you never know, in a nice twist of fate, maybe quantum computers will be the ones that bring forth that revolution. 

This feature first appeared in Issue 33 of our digital magazine CURIOUS. Older issues of CURIOUS are free for all users. To access new issues, become an All Access Member.