Tiny optical cavities could make quantum networks possible

Engineers at Caltech have shown that atoms in optical cavities — tiny boxes for light — could lead to the creation of a quantum internet. Their National Science Foundation-funded work was published in the journal Nature Physics.

Quantum networks would connect quantum computers through a system that operates at a quantum, rather than classical, level. In theory, quantum computers will one day be able to perform certain functions faster than classical computers by taking advantage of the special properties of quantum mechanics.

As they can with classical computers, engineers would like to be able to connect multiple quantum computers to share data and work together in a quantum computer network.

“While important in their own right, quantum computer networks also represent an important step toward realizing the goal of a secure quantum internet,” explained Fil Bartoli, director of NSF’s Division of Electrical, Communications and Cyber Systems. Networks would open the door to several applications, including solving computations that are too large to be handled by a single quantum computer and establishing unbreakably secure communications using quantum cryptography.

A quantum network needs to be able to transmit information between two points without altering the quantum properties of the information being transmitted. One current model works like this: A single atom or ion acts as a quantum bit (or “qubit”) storing information via one of its quantum properties, such as spin.

To read that information and transmit it elsewhere, the atom is excited with a pulse of light, causing it to emit a photon whose spin is entangled with the spin of the atom. The photon can then transmit the information entangled with the atom over a long distance via fiber optic cable.

Researchers led by Caltech’s Andrei Faraon, an applied physicist and electrical engineer, constructed a nanophotonic cavity, a beam that is about 10 microns long – a fraction of an inch — with periodic nano-patterning, sculpted from a piece of crystal. In this cavity, scientists can excite an ytterbium ion and efficiently detect the resulting photon it emits, whose spin can be used to read the information stored in the ion’s spin.

“Advances like this fundamental research in quantum information science are important milestones to enable the long-term development of quantum technology,” added Alex Cronin, a program officer in NSF’s Division of Physics.

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