The Delft researchers managed to teleport quantum information through a rudimentary network in the lab. This first is an important step towards a future quantum internet. The breakthrough was made possible by greatly improved quantum memory and higher quality of quantum links between the three nodes in the network. The researchers, who work at QuTech, a collaboration between TU Delft and TNO, publish their findings 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 bits) between the nodes of the network. This makes possible all kinds of applications, such as the secure exchange of sensitive information, the interconnection of multiple quantum computers to increase their computing power, and the use of highly sensitive and linked quantum applications.
Send quantum information
The nodes of such a quantum network consist of small quantum processors. Sending quantum information between these processors is not that easy. One possibility is to send quantum bits with light particles, but due to the unavoidable losses in fiber optic cables, there is a strong possibility that the light particles will not make it, certainly over great distances. Because simply copying quantum bits is fundamentally impossible, losing a particle of light means that quantum information is irretrievably lost.
A better way to transmit quantum information is teleportation. The quantum teleportation protocol gets its name from the similarities to teleportation in science fiction movies: the quantum bit disappears on the sender’s side and appears on the receiver’s side. Since the quantum bit does not have to travel through the intervening space, there is no longer any chance of it getting lost. This makes quantum teleportation an interesting technique for a future quantum Internet.
Good system control.
Quantum bit teleportation requires a number of ingredients: a quantum entangled link between sender and receiver, a reliable reading method for quantum processors, and the ability to temporarily store quantum bits. Previous QuTech research has shown that it is possible to teleport quantum bits between two neighbour nodes. QuTech researchers now show for the first time that they can meet the requirements and demonstrate teleportation between not neighbor nodes or across a network. They teleport quantum bits from the “Charlie” node to “Alice”, using an intermediate “Bob” node.
Teleport in three steps
Teleportation consists of three steps. First of all, the “teleporter” must be prepared, that is, an entangled state must be created between Alice and Charlie. Alice and Charlie don’t have a direct physical connection to each other, but they both have Bob. First, Alice and Bob create tangles between their processors. Bob then saves the part of him from the tangled state. Then Bob has an affair with Charlie. Now a quantum mechanical trick is being performed: By performing a special measurement on his processor, Bob broadcasts the entanglement, so to speak. Result: Alice and Charlie are entangled 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 sorts of quantum values in between. Charlie prepares this quantum information. To show that teleportation works in a generic way, the researchers repeat the entire experiment for different values of quantum bits.
Step three is the actual teleportation from Charlie to Alice. Charlie performs a joint measurement on her quantum processor with the message and on her half of the entangled state (Alice owns the other half). As a result, something that is only possible in the quantum world happens again: with this measure, the information disappears from Charlie’s side and immediately reappears from Alice’s side.
Then you would think that the stocking is finished, but nothing is further from reality. The quantum bit has been transferred encrypted; the key is determined by the result of Charlie’s measurement. Therefore, Charlie sends the measurement result to Alice, after which Alice performs the corresponding quantum operation to decrypt the quantum bit. For example, by a ‘bit flip’: 0 becomes 1 and 1 becomes 0. If Alice has done the correct operation, the quantum information is suitable for further use. The teleportation was successful!
teleport several times
Follow-up research will focus on reversing steps one and two of the teleportation protocol. That is: first make (or receive) the quantum bit to be teleported, and then prepare the teleporter and perform the teleportation. This sequence is an additional challenge because the quantum information to be teleported must be preserved during entanglement creation. But it brings great advantages, because the teleportation can be performed completely “on demand”, which is relevant, for example, if the quantum information is the result of a difficult calculation or if multiple teleportations have to be performed. In the long term, this teleportation will form the backbone of the quantum Internet.
This post previously appeared on the QuTech news page.
dr Sophie Hermans, first author, SLNHermans@tudelft.nl, +31 6 13 62 13 83
Prof. Dr. Ronald Hanson, Research Leader, R.Hanson@tudelft.nl, +31 6 46 42 84 34
Aldo Brinkman, QuTech Press Officer, +31 6 34 32 12 95