Years from now it may be said that the quantum Internet was born today. When the baby system matures, it will be able to process unfathomable amounts of data and never be hacked.
The system only has two nodes, but the Internet's birth started in a similar way back in the late 1960s. The developers — physicists led by Stephan Ritter and Gerhard Rempe of the Max Planck Institute of Quantum Optics in Germany — published their work in this week's issue of the journal "Nature."
The quantum network was built using two atoms of rubidium that exchange photons, or particles of light. Each atom is placed inside a cavity with highly reflecting mirrors on each side, and at a very short distance from each other. The two so-called optical cavities are connected by an optical fiber.
Scientists aim a laser at the first atom, causing the atom to emit a single photon. That photon zooms along the optical fiber to other optical cavity containing the other atom. That's where the mirrors come in — ordinarily it's difficult to get an atom and a photon to interact reliably. But by bouncing the photon off the mirrors in the cavity thousands of times, it's more likley to hit the atom and be absorbed by it. That absorbtion is what transmits the information about the first atom's quantum state to the second atom.
Besides sending information, the two atoms were entangled, meaning that the atoms were linked. If the first node is in quantum state A, for example, the second node will also be in quantum state A. In this experiment, the atoms were entangled for 100 microseconds — a long time in quantum physics.
This entanglement is what makes hacking into a quantum computer and eavesdropping on impossible. As as soon as a hacker tapped into a quantum network, the states of the atoms wouldn't match up — a big red flag that something was awary.
It's a long way yet to a truly large-scale quantum network, but this is a first step.
Image: Andreas Neuzner, Max Planck Institute for Quantum Optics