Delft researchers have been successful in teleporting quantum information through a crude network. This groundbreaking experiment is a crucial first step toward a future quantum internet. This innovation was made possible by a much-improved quantum memory and improved quantum connectivity between the network’s three nodes.
The scientists are publishing their findings in the scholarly magazine Nature today. The researchers are part of QuTech, a partnership between Delft University of Technology and the Netherlands Organisation for Applied Scientific Research (TNO).
The capacity to transmit quantum information (also known as quantum bits) across network nodes is the foundation of a future quantum internet’s power. This will make it possible to use a wide range of applications, including linked quantum sensors that are extremely accurate and can securely exchange sensitive data between several quantum computers.
Sending quantum information
Small quantum processors make up the nodes of such a quantum network. It’s difficult to send quantum information across these processors. One option is to communicate quantum bits using light particles, however this will very certainly fail because to the unavoidable losses in glass fiber cables, especially over long distances.
The loss of a light particle signifies the irretrievable loss of the quantum information because it is fundamentally impossible to simply reproduce quantum bits.
Quantum information can be sent more effectively by teleportation. The name of the quantum teleportation protocol comes from the way that the quantum bit appears on the side of the receiver and vanishes on the side of the sender in science fiction movies.
There is no possibility of a quantum bit being lost because it does not need to go across the intervening space. As a result, quantum teleportation is a key method for a potential quantum internet.
Good control over the system
A quantum entangled link between the transmitter and recipient, a trustworthy way of reading out quantum processors, and the ability to temporarily store quantum bits are all necessary for the ability to teleport quantum bits. Previous work at QuTech has shown that quantum bits can be transported between two nearby nodes.
The QuTech researchers have now successfully shown teleportation between non-adjacent nodes, or over a network, proving for the first time that they can meet the set of requirements. With the aid of a connecting node named “Bob,” they were able to transport quantum bits from node “Charlie” to node “Alice.”
Teleporting in three steps
There are three steps in the teleportation process. The “teleporter” must first be set up, which entails creating an entangled state between Alice and Charlie. Although Alice and Charlie are not physically related, Bob is their common link.
Alice and Bob entangle their CPUs together to do this. Bob stores his piece of the entangled state after that. Bob then induces Charlie into an entangled condition.
The next step is a quantum mechanical “sleight of hand” in which Bob, via a particular measurement in his processor, effectively “sends on” the entanglement. Results: The teleporter is ready to be activated, and Alice and Charlie are now intertwined!
Making the “message” for the quantum bit to be transported is the second stage. This might be ‘1’ or ‘0’ or a number of other intermediate quantum values, for instance. This quantum data is prepared by Charlie. The researchers repeated the entire experiment for several quantum bit values to demonstrate that the teleportation functioned generally.
The actual teleportation from Charlie to Alice takes place in step three. Charlie does a joint measurement using the message on his quantum processor and on his side of the entangled state for that reason (Alice has the other half).
The information then vanishes on Charlie’s side as a result of this measurement and instantly reappears on Alice’s side, which is something that can only happen in the quantum realm.
Even while you might believe that everything is over at that point, this couldn’t be further from the reality. In actuality, the quantum bit has already been encrypted at the point of transfer; Charlie’s measurement result provides the key.
Charlie therefore transmits Alice the measurement result, and Alice then performs the necessary quantum operation to decrypt the quantum bit. As an illustration, a “bit flip” turns 0 into 1 and 1 into 0. The quantum information is suitable for further use once Alice has performed the right operation. The teleportation has succeeded!
Teleporting several times
The first two steps of the teleportation procedure will be reversed as the subject of further study. Creating (or receiving) the quantum bit that will be transported must come first, and only then can the teleporter be set up to do the teleportation.
Because the quantum information that needs to be transported must be stored while the entanglement is being formed, reversing the order is particularly difficult. The teleportation can therefore be totally performed “on request,” which is a big benefit.
This is important, for instance, if the outcome of a challenging calculation is contained in the quantum information or if teleportation requires several attempts. Therefore, in the long term, this kind of teleportation will act as the quantum Internet’s foundation.
Funding details
Financial support comes from the EU Flagship on Quantum Technologies through the project Quantum Internet Alliance (EU Horizon 2020, grant agreement no. 820445); from the European Research Council (ERC) through an ERC Consolidator Grant (grant agreement no. 772627 to R. Hanson); from the Netherlands Organisation for Scientific Research (NWO) through a VICI grant (project no. 680-47-624) and the Zwaartekracht program Quantum Software Consortium (project no. 024.003.037/3368) and from an Erwin-Schrödinger fellowship (QuantNet, no. J 4229- N27) of the Austrian National Science Foundation (FWF).
