Quantum teleportation win

Quantum teleportation win

News Cryptography Quantum teleportation win QUANTUM teleportation has made a leap in sophistication. Physicists have teleported more information at o...

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News Cryptography

Quantum teleportation win QUANTUM teleportation has made a leap in sophistication. Physicists have teleported more information at once than has ever previously been possible, paving the way for a global quantum internet that would be extremely secure from hacking. This isn’t teleportation as you might imagine it from science fiction. Rather than transporting matter through space, it involves moving information related to the quantum state of a particle. Previously, we have only been able to teleport quantum bits, or qubits, the simplest unit of quantum information in which a particle can be in two states at once. For instance, a photon that is simultaneously vertically and horizontally polarised would be a qubit. Now Jian-Wei Pan at the University of Science and Technology of China and Anton Zeilinger at the University of Vienna in Austria and their colleagues have teleported a more complicated unit of quantum information called a qutrit for the first time. If a qubit can be considered two-dimensional, a qutrit is three‑dimensional: the photon is polarised in three perpendicular directions. “The higher the dimensions of your quantum system, the more secure you can ensure your communication is and the more information you can encode,” says Ciarán Lee at University College London. “But going from a qubit to a qutrit is especially difficult: the tricks you use for qubits have to do with a nice symmetry that qutrits don’t have.” To teleport a qubit, you begin with three particles. One is the qubit whose information you want to teleport. The other two are a pair of particles that have been entangled in such a way 12 | New Scientist | 31 August 2019

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Physicists have used the rules of quantum entanglement to teleport a richer package of information than ever before, reports Leah Crane

that making a measurement on one will affect the result of a measurement made on the other. Now imagine two people, traditionally called Alice and Bob. Alice has the qubit and one of the pair of entangled particles. Bob has the other particle in the pair. If Alice wants to send the qubit’s

“Passing messages through quantum entanglement would be a very secure means of encryption” information to Bob, she performs a special kind of measurement on both her particle and the qubit. Going through this process means that Alice’s particle is now entangled with the qubit, as well as Bob’s particle. Because of all this entanglement, Alice’s measurement forces Bob’s particle into one of four possible states. He can find out which by making a measurement. The results of Alice’s measurement –

which she can send to Bob using non-quantum methods, such as an email – lets him determine how the measured state of his particle is related to that of the original qubit. Once he knows that, he can reconstruct the information from the original qubit. Its information has been teleported. Qutrits are a level up in difficulty because it is much harder for Alice to perform her measurement and entangle her particle with the qutrit. The researchers got around this by adding another particle to the system so Alice is measuring three particles instead of two (Physical Review Letters, doi.org/c9ns). As a result, her measurements contain more information, which she sends to Bob, allowing him to reconstruct the qutrit. The researchers could teleport qutrits with 75 per cent fidelity, meaning Bob’s qutrit was 75 per cent similar to Alice’s original. That may not seem high,

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but the highest fidelity possible if the quantum entanglement had failed is 50 per cent. “Seventy-five per cent is probably not good enough to start communicating in this way with much accuracy, but this is early days,” says Lee. The researchers claim that their method could be used to teleport even larger packets of information with higher fidelity. If that works out, it would be a further step towards quantum communication systems. Passing messages using quantum entanglement would be far more secure than current encryption methods. Quantum teleportation could enable information to be passed over long distances by secure quantum networks, says Lee. “The ability to teleport a high-dimensional system is going to be one of the bedrocks on which a future quantum internet is built.” ❚