Just beyond the horizon of practicality, researchers are trying to develop a new generation of chips that would control photons as reliably as today’s chips control electrons.
But after years of effort they’re still grappling with a crucial step: identifying the best material to trap and tame light.
Jelena Vuckovic has already devoted some 20 years to this pursuit for a simple reason: Photonic chips could become the basis for light-based quantum computers that could, in theory, break codes and solve certain types of problems beyond the capabilities of any electronic computer.
In recent months the Stanford electrical engineer has created a prototype photonic chip made of diamond. Now, however, in experiments described in Nature Photonics, she and her team demonstrate how to make a light-based chip from a material nearly as hard as diamond but far less exotic — silicon carbide.
“These are early stage but promising results with a material that is already familiar to industry,” Vuckovic said.
Commonly used in brake pad linings, silicon carbide is a tough material that has carved out a new niche in electronics, where it is used to make chips for high-voltage, high-heat applications, such as electric car power supplies, that are too extreme for ordinary silicon chips.
Like most chip-making materials, silicon carbide is a crystal — a group of specific atoms arranged in a consistent lattice. In a silicon carbide crystal, every silicon atom is joined to four carbon atoms to form a strong, three-dimensional lattice. The stability of this lattice helps makes silicon carbide useful for high-heat applications, whether that involves dealing with friction in brake pad linings or high currents flowing through chips.
Graduate student researchers Daniil Lukin, Constantin Dory and Melissa Guidry led the effort to make this crystal useful as a photonic chip. They removed silicon atoms at strategic locations throughout the lattice. Each vacancy in the lattice created a subatomic trap that captured a single electron from one of the surrounding carbon atoms. To make the light-based chip work, the researchers sent a stream of photons through the lattice. Whenever a photon struck a trapped electron, the collision between those two particles sent a photon spinning off at a particular energy level, or what scientists call a quantum. Interactions between photons and electrons create what scientists call a qubit, or quantum bit. A qubit is roughly analogous to the transistor in an electronic chip — the fundamental unit that makes the system work.
Many hurdles must still be overcome before photonic chips made of silicon carbide, or diamond for that matter, might become useful as the building blocks for a quantum computing system. “Hype tends to get ahead of science,” Vuckovic says. But within the next five years or so, she envisions using photonic chips to send data via quantum light through fiber optic cables, making such communications more secure by making it possible to detect efforts to tap into the flow of information.
As the director of Q-FARM — short for Quantum Fundamentals, Architecture and Machines — Vuckovic is helping to bring together researchers from Stanford and the SLAC National Accelerator Laboratory to solve the nitty-gritty hardware and software challenges necessary to make quantum technology a reality.
“We’re trying to take small, practical steps,” she says, “while we try to push beyond the limits of our current understanding and discover new platforms for quantum technologies.”