It’s not news that quantum mechanics can be used to send secret messages without concern of them being intercepted. For years, physicists have been using this technology to do so. However, a true quantum link has only recently been successful. Originally, the messages were sent using quantum mechanics, but then had to be decoded at each node in order to continue the message. Since the nodes weren’t quantum mechanical, this left the information vulnerable to hacking at each node. A quantum link means the message never has to be decoded. By combining many quantum links, a true quantum network could be created. This would mean a completely unhackable telecommunications network.
Stephan Ritter of the Max Planck Institute of Quantum Optics in Garching, Germany and his colleagues built the first quantum link between two atoms in labs on opposite sides of the street. This took many lasers, optical elements, and equipment. Each atom was placed between an “optical cavity” formed by two highly reflective mirrors 0.5 mm apart. Applying an external laser to the first atom caused a photon emitted by that atom to escape from its optical cavity and travel through a 60-meter-long optical fiber to the cavity of the atom across the street. Absorption of this photon by the second atom caused the quantum information to transfer from the first atom to the second. In order to entangle two atoms, the researchers had to start in just the right state with the first atom. It is believed that this could be extended to a third atom, allowing more than two nodes.
What does it mean for atoms to be entangled? Atoms have certain energy states that they belong in based on how their insides are working. An atom can be in two energy states at the same time, but will switch to one or the other when measured. When atoms are entangled, they share the same energy states. That means when researchers in the first lab measure their atom’s energy state, they are essentially measuring the energy state of the atom in the lab across the street. To communicate, the two labs could entangle and measure their atoms repeatedly to create a shared random key through which they could send messages. In theory, they could add a third atom to communicate with.
Couldn’t anyone measure the energy state of the atom and determine the key? Simply put, no. The beauty of measuring energy states is that every time the atom is measured, its energy state is altered. Anyone trying to measure the atom would easily be detected because all three atoms would no longer be in the same energy state.
This experiment gives hope to the formation of a complete quantum network that is totally unhackable. The next step is incorporating a third atom, and then many more. Hackers beware, you’re about to lose your ability to intercept information.