We just moved one step closer to a true 'quantum internet'

Dutch researchers have brought us all one step closer to ultra-secure, superfast internet connections using quantum technologies.

A team at QuTech, a collaboration between Delft University of Technology in the Netherlands and the Netherlands Organisation for Applied Scientific Research, achieved a first-of-its-kind transmission of information over a very small quantum network of three nodes.

The nodes of the network were built using small quantum processors and sending quantum information between these processors has been a major hurdle, but is also essential to harnassing the quirks of quantum mechanics to transmit information.

What the researchers did was create a quantum "teleporter" using two entangled quantum "processors", which they designated Alice and Charlie. Transferring quantum information between two entangled processors isn't entirely new but earlier efforts were limited to adjacent quantum processors. This was an important step, but if quantum information transfer between two points is going to be functionally useful, then we'll have to have points that are at some distance from one another.

Is quantum teleportation possible?

Ultimately, why do all of this and what does it actually mean? The QuTech team believes it has created one of the fundamental building block of a quantum internet, and while a huge key will be the replicability of this work, these are still very encouraging results.

"We are now building small quantum networks in the lab,” Ronald Hanson, a Delft physicist who oversees the QuTech team, said in the New York Times. “But the idea is to eventually build a quantum internet."

What makes the idea of that quantum internet so appealing is that it would allow for the seemingly instantaneous transfer of data from one place to another using a phenomenon called quantum teleportation.

"The idea of quantum teleportation is that one can teleport the information carried by a qubit, but not the physical qubit itself," Dr. Sophie Hermans, the lead author of the study published on May 25 in the journal Nature, told Interesting Engineering. "To do so, one would need an entangled state between two qubits held by the sender and receiver. An entangled state is a property only known in quantum mechanics, and it represents a very strong connection, even between very distant qubits."

The researchers at QuTech appear to have done exactly that by utilizing a third processor, designated Bob, which was capable of taking quantum information from Charlie and passing it to Alice, which effectively entangled Charlie and Alice, allowing them to transfer information between them.

"Once the entangled state—the connection—is established, one can use it to teleport the information stored on a third qubit that is held by the sender. By doing a special type of measurement (a Bell measurement), the information disappears from the qubit at the sender, and appears on the qubit of the receiver."

There's a lot more involved, especially around how the data is received in the end, so "for the information to be of any use," Hermans told us, "one has to perform an operation—like a bit inversion, for instance—depending on the outcomes of the Bell measurement."

Quantum teleportation isn't the same thing as the physical teleportation seen in science fiction, though it looks a lot like it. The difference with quantum teleportation is that no physical matter is relayed, only information, thanks to a quirk in quantum mechanics that allows two quantum particles to "share" a quantum state.

The best way to describe this quantum state is that it's like describing a pair of gloves. When you see which hand one of those gloves goes on, you know which one the other goes on as well, even if you never see it. Keep in mind, this is a very basic description of the phenomenon since even a century after the founding of quantum mechanics, there is still a lot we don't actually know about the quantum world—but we appear to know enough that we're able to start extending our knowledge into practical applications like a quantum internet.

Is quantum teleportation faster than light?

No, unfortunately, and it's likely that it can never be. This is due to something known as the no-communication theorem which posits that when a quantum measurement is taken by one observer, the information cannot be transmitted to another more distant observer faster than the speed of light.

"The fact that the receiver needs to know the outcomes of the Bell measurement [for the information to be interpreted], creates the need to communicate these results," Hermans told us. "This can be done using classical or normal communication, but this prevents any faster than light communication."

Still, the transmission of information is significantly faster than what is currently being, namely fiber optics and digital bits encoded in light. And while it might sound like light would be the faster of the two, light also has a major issue, namely the eventual signal loss that currently hampers classical digital communication. 

Quantum teleportation preserves this information intact through the "teleportation" process, and has the added benefit of being more secure. Because it is quantum information, any attempt to intercept the data will cause it to decohere, and without the proper information to interpret the resulting information, the intercepted data would look like random bits. What's more, the intended receiver would be able to detect this decoherence as well, which would signal that the connection was being intercepted.

But, it still requires work to get us to that point, and we're still about a decade or more away from truly functional quantum internet, but we're one step closer to making it a reality, and that is something.