Delft researchers have succeeded in teleporting quantum information over a rudimentary network in the laboratory. This scoop is an important step towards a future quantum internet. The breakthrough was made possible by a much improved quantum memory and increased quality of the quantum connections between the three nodes of the network. The researchers working at QuTech – a collaboration between TU Delft and TNO – publish their results today in the scientific journal Nature.
The power of the future quantum internet is based on being able to share or send quantum information (quantum bit) between the nodes of the network. This makes all kinds of applications possible, such as the secure sharing of confidential information, connecting multiple quantum computers to increase their computing power, and using interconnected, highly sensitive quantum applications.
Send quantum information
The nodes in such a quantum network consist of small quantum processors. It is not so easy to send quantum information between these processors. One possibility is to send quantum bits with light particles, but due to unavoidable losses in fiber optic cables, there is a high chance that the light particles will not reach, certainly over long distances. Because simply copying quantum bits is fundamentally impossible, the loss of a light particle means that the quantum information is irretrievably lost.
A better way to send quantum information is teleportation. The quantum teleportation protocol gets its name from similarities to teleportation in science fiction movies: the quantum bit disappears on the sender side and appears on the receiver side. Since the quantum bit does not have to travel through the intervening space, there is no longer any chance of it being lost. This makes quantum teleportation an interesting technique for a future quantum internet.
Good control over the system
Teleporting quantum bits requires a number of ingredients: a quantum entangled connection between sender and receiver, a reliable readout method for quantum processors, and the capacity to temporarily store quantum bits. Previous research from QuTech showed that it is possible to teleport quantum bits between two neighbor sheet music. The QuTech researchers are now showing for the first time that they can meet the requirements and demonstrate teleportation between them non-neighbor nodes or over a network. They teleport quantum bits from node “Charlie” to “Alice”, using an intermediate node “Bob”.
Teleport in three stages
The teleportation consists of three steps. First of all, the “teleporter” must be prepared, that is, a tangled state must be created between Alice and Charlie. Alice and Charlie do not have a direct physical connection with each other, but both have Bob. First of all, Alice and Bob create entanglements between their processors. Bob then rescues his part from the tangled state. Then Bob gets tangled up in Charlie. Now a quantum mechanical trick is performed: by performing a special measurement in his processor, Bob passes on the entanglement, so to speak. Result: Alice and Charlie are in a tangled state and the teleporter is ready to go!
The second step is to create the ‘message’ – the quantum bit – which will be teleported. This can be, for example, ‘1’ or ‘0’, but also all kinds of quantum values in between. Charlie prepares this quantum information. To show that the teleportation works generically, the researchers repeat the entire experiment for different quantum bit values.
Step three is the actual teleportation from Charlie to Alice. Charlie performs a joint measurement on his quantum processor with the message and on his half of the entangled state (Alice owns the other half). As a result, something happens that is only possible in the quantum world: Through this measurement, the information on Charlie’s side disappears and immediately reappears on Alice’s side.
Then you would think the stocking is finished, but nothing could be further from the truth. The quantum bit has been transmitted encrypted; the key is determined by Charlie’s measurement result. Charlie therefore sends the measurement result to Alice, after which Alice performs the corresponding quantum operation to decrypt the quantum bit. For example, in a ‘bit flip’: 0 becomes 1 and 1 becomes 0. If Alice has performed the correct operation, the quantum information is suitable for further use. The teleportation succeeded!
Teleport multiple times
Follow-up research will focus on reversing steps one and two of the teleportation protocol. That is: first create (or receive) the quantum bit to be teleported, then prepare the teleporter and perform the teleportation. This sequence is extra challenging because the quantum information to be teleported must be preserved during the creation of entanglements. But it offers great advantages, because the teleportation can then be carried out entirely “on demand”, which is relevant, for example, if the quantum information is the result of a difficult calculation, or if several teleportations are to be made. In the longer term, this teleportation will therefore form the backbone of the quantum internet.
This post previously appeared on the QuTech news site.
Dr. Sophie Hermans, first author, SLNHermans@tudelft.nl, +31 6 13 62 13 83
Prof. Dr. Dr. Ronald Hanson, head of research, R.Hanson@tudelft.nl, +31 6 46 42 84 34
Aldo Brinkman, Press Manager at QuTech, +31 6 34 32 12 95