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First Long-Distance Quantum Link Made

Category: Science & Technology
Posted: 08:31AM

The most powerful encryption system man currently knows of relies on properties of quantum mechanics. According to this area of physics, a particle can exist in multiple states at the same time. When the state of the particle is measured though, only one state can be found, so the multiple states collapse down to one. If a message is sent by a particle in multiple states, the correct sender and receiver will know if it was intercepted, because the particle would not be in multiple states anymore, or will not have the correct multiple states.

While this security system appears to be infallible, it does have some problems. An obvious one has to do with how the information is transmitted. Signals are not just sent along a very long cable from sender to receiver, but instead arrive at nodes along the way. The nodes intercept and retransmit the signal, to prevent degradation. Even a quantum mechanical signal has to use nodes like this, but the nodes are not always quantum mechanical. This means that to retransmit the signal, the multiple states of the particle are destroyed and recreated in another particle at each node. Every node then is a vulnerable spot along the network, as the information can be read before the second particle is created.

Researchers have finally fixed this problem by creating a quantum mechanical node. This is not an easy task as it requires entangling two particles some distance apart. In this case, the particles were in labs across the street from each other. In both labs were atoms held in a cavity. A single photon was shot at one of the atoms, which caused both the atom and the photon to become entangled. The polarization of the photon depends on the state the atom was in, and because the atom was in multiple states, the photon has multiple polarizations. This photon then traveled along a 60 m cable to the second lab where it struck the second atom. This caused the second atom to become entangled with the photon, and the first atom, so the two atoms now have the same states.

It should be possible to repeat this process with a third atom, and then a forth, and so on to create a full quantum network. A full quantum network is still a ways into the future though as the equipment used is not practical for everyday use. This is still a major step toward making that future real.

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