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Updated:25/05/2022 19:53h
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The future online will be quantum: apart from greater speed – when true quantum computers become available, which is still a long way off – the main advantage of a quantum internet It will be your security. Because the quantum bits (called qubits), where the information will be stored, for example, of bank transactions, have particular characteristics: they are ‘intertwined’ in such a way that they ‘feel’ instantly what happens to the other; and thanks to this they can teleport information from one to another without needing a direct connection and also faster than the speed of light; but, in addition, the information is destroyed if someone from the outside tries to ‘look’ at the data, which in a world in which the word ‘cyber attack’ is a constant, could be really useful.
Although the quantum internet is a budding field, researchers from Delft University of Technology led by physicist Ronald Hanson, with the Dutch Organization for Applied Scientific Research (TNO) have managed to go a step further, teleporting quantum information through a ‘simple’ network in which there was no direct connection between transmitter and receiver. The results have just been published in the journal ‘Nature’.
‘Ghostly action at a distance’
The power of a future quantum Internet rests on the ability to send quantum information (qubits, or the quantum ‘language’, like bits in classical computing) between network nodes. The nodes of such a quantum network consist of small quantum processors, the ‘interpreters’ of the qubits. “It has been shown that the most efficient way to send information between them is quantum teleportation,” he explains. Juan Jose Garcia-Ripoll, theoretical physicist at the Institute of Fundamental Physics (dependent on the CSIC). The protocol for quantum teleportation owes its name to similarities to teleportation in science fiction movies: the qubit disappears from the sender’s side and appears, so Albert Einstein dubbed as “spooky action at a distance», on the receiver side. The fact that it does not need to physically travel through the intervening space means that information is not lost, and makes quantum teleportation the system of choice to support the foundations of a future quantum Internet.
Several ingredients are required for teleportation: a quantum entangled link between sender and receiver, a reliable method for reading quantum processors, and the ability to temporarily store quantum bits. «In this system you need two components, one quantum memory that saves the states of the qubit and ones repeaters. The special thing about this experiment is that it includes both in the same system”, says García-Ripoll.
The authors were not new to the field. Previous research has already shown that it is possible to teleport qubits between two adjacent and directly connected nodes and called ‘Alice‘ y ‘Bob‘. The challenge was now to introduce a new node, ‘Charlie‘, and connect it to Alice using Bob as an intermediary.
A message in a diamond
The teleportation protocol devised by the Dutch researchers consists of three steps. The first is to prepare the ‘teleporter’, which means that an intertwined state must be created between Alice and Charlie, so that they can communicate. But Alice and Charlie do not have a direct physical connection., but both are directly connected to Bob, who will help them connect. To do this, Alice and Bob first create an entangled state between their processors, and Bob stores Alice’s part of the entangled state. Bob then creates an interlocked state with Charlie and performs the same operation. With both connected to Bob, Bob performs a special measurement on Bob’s processor (a kind of ‘sleight of hand’) and sends out the entangled states, quantumly connecting Alice and Charlie.
The next step was to create the ‘message’, which was ‘written’ (actually embedded) into a type of diamond impurity -which is to quantum computers what silicon is to classical ones- that behaves like a qubit, and that previous experiments by Hanson’s team managed to maintain up to 10 seconds. “Once ’embedded’ in the diamond, the information passes to the nuclei and is stored”, explains García-Ripoll. To check that the system worked correctly, the Dutch team repeated the experiment with different ‘messages’.
The third and final step was the actual teleportation from Charlie to Alice. To do this, Charlie performs a joint measurement with the message in her quantum processor and her half of the entangled state (Alice has the other half). And so, right after the information disappears from Charlie’s side and immediately appears on Alice’s side, that she receives the ‘encrypted’ message, but also the keys to decrypt it. And there we have the data. “This is a very interesting and disruptive experiment in the sense that there are not many tests of its kind, much less a system that includes the combination of memory and quantum repeater,” says García-Ripoll.
The next challenge for the Dutch team will be to reverse steps one and two of the teleportation protocol; that is, first create the quantum qubit and then entangle the nodes (to Charlie and to Alice via Bob). “Reversing the order is particularly challenging as the quantum information to be teleported has to be stored while the entanglement is created. However, it does have a significant advantage in that teleportation can be performed completely ‘on demand,'” explain the authors, who state that “in the long run, this type of teleportation will serve as the backbone of the quantum internet.” “It’s complicated because maintaining the information while the nodes are intertwined, which takes a while or even fails and has to be repeated, is quite a challenge,” says García-Ripoll. Step by step, the qubits begin to circulate (even teleport) beyond theory and science fiction.
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