Dutch scientists have taken a big step towards quantum computer networks by teleporting quantum information between two nodes that had no direct link to each other. This breakthrough announces a faster and more secure communication system.
As their name suggests, quantum computers exploit several principles of quantum mechanics to perform calculations that are beyond the reach of traditional computers. And just like our current Internet, these quantum computers will need to be interconnected to reach their full potential. However, sending information between them is tricky, as the quantum nature of this data makes it susceptible to being lost or disrupted by the environment.
Instead, this information can essentially be “teleported” between nodes, thanks to a phenomenon known as quantum entanglement. Two particles can become so tightly bound to each other that it becomes impossible to describe one without the other, and any changes to one will instantly affect the other, regardless of their distance. It’s a concept that unsettled Einstein himself, but it was repeatedly confirmed in experimentation.
In the context of a quantum computing network, quantum bits (or qubits) of information can be teleported to a node by making changes to its entangled partner, typically by performing what is called a state measurement. Bell (BSM). This has already been demonstrated between two adjacent nodes, but for the new study, researchers from the QuTech collaboration were able to teleport information between two non-neighboring nodes.
This requires the use of a third node acting as a kind of mediator – for simplicity the team named the three nodes Alice, Bob and Charlie, each containing a diamond-based qubit. To create the network, the team first creates entangled states between Alice and Bob, and between Bob and Charlie. Then, performing a BSM in Bob’s node, Alice’s and Charlie’s states also become entangled, even though they are not adjacent in the network.
To teleport information to Alice, Charlie first creates a “message” by writing data to a qubit in his node’s memory. It could be a 1, or a 0, or quantum-frighteningly, a strange intermediate state. Then it performs a BSM on that memory qubit and the qubit that is entangled with Alice’s. And just like that, Alice’s qubit instantly changes to reflect Charlie’s message.
However, if Alice wants to read the message, she must decrypt it first, and Charlie has the key. The result of the BSM he performed on his qubit explains what operation Alice must perform on hers to decipher the teleported information.
QuTech researchers have achieved this feat consistently across numerous experiments, with a fidelity of approximately 71%. This was achieved through several breakthroughs made by the team to protect quantum information in the network. For one thing, the entanglement between Alice and Bob had to be stored in a qubit of quantum memory while Bob formed a bond with Charlie. Other optimization techniques have reduced noise in the system.
By performing this type of non-direct quantum teleportation, the researchers claim to have created a fundamental building block of a practical quantum network. But of course, there is still a long way to go. A key next step is to increase the number of memory qubits in the system to increase the types of operations it can perform.
The team also plans to investigate how to teleport information already stored in quantum memory, rather than having to create that message once the link is established. This will allow quantum teleportation to be performed on demand, which is crucial for this technology to become a useful reality.
The research was published in the journal Nature. The experiments are explained in more detail in the video below.
From Alice to Charlie – the next step for the quantum internet
Sources: QuTech, Nature