Quantum Internet May One Day Be Possible Through Optical Cavities, Caltech Scientists Say

A fundamental challenge in the creation of a "quantum internet" is how to securely transmit data between two points. But one team of U.S. scientists may have found the answer.

New research from experts at the California Institute of Technology (Caltech) suggests atoms in small boxes of light — optical cavities — could soon "form the backbone technology" of the futuristic internet that relies on the mysterious properties of quantum mechanics for ultra-fast computing.

Unlike computing devices like phones and laptops which store information as binary bits of zeros and ones, quantum computers use a unit of memory known as a quantum bit or qubit.

Examples of qubits include atoms, ions, photons, or electrons, and quantum systems will, at least in theory, not be limited by the rigid structures of the binary two-state system.

By operating at the atomic and subatomic levels, quantum computers are able to store information as a one and a zero simultaneously — a process called superposition — which gives the machines the ability to become significantly more powerful than any of the top supercomputers of today.

But in the future, much like our current world wide web, scientists will want to connect multiple quantum computers so they can share data. This is known as the "quantum internet."

For this to work, the network needs to be able to transmit information between two points without altering the quantum properties of the information being transmitted. The Caltech team said their new findings, published in journal Nature, could be "foundational" to that creation.

One known transmission model stores information via the spin of an atom.

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

But the Caltech team said it is "challenging" to find atoms that can be controlled and measured. And worse still, rare earth elements — best suited to be qubits — often interact poorly with light.

A team led by Caltech's Andrei Faraon, professor of applied physics and electrical engineering, fixed this by constructing a special type of optical cavity that could be used to bounce light back and forth down a beam multiple times until it is finally absorbed by an ion, which would be the qubit.

The type of ion used, called ytterbium, can store information in its spin for 30 milliseconds. The team said within that time light could transmit information across the continental United States.

"This checks most of the boxes," Faraon said. "It's a rare-earth ion that absorbs and emits photons in exactly the way we'd need to create a quantum network. This could form the backbone technology for the quantum internet." The next step is to connect two quantum bits, the scientist added.

The full academic paper, available online, is titled "Control and single-shot readout of an ion embedded in a nanophotonic cavity" and was funded by the National Science Foundation, the Air Force Office of Scientific Research and the Institute for Quantum Information and Matter (IQIM).

Quantum computing
File photo: Futuristic quantum computing CPU processor concept. iStock