A team of researchers from the University of Stuttgart and the Julius-Maximilians-Universität Würzburg led by Prof. Stefanie Barz (University of Stuttgart) has demonstrated a source of single photons that combines on-demand operation with record-high photon quality in the telecommunications C-band—a key step toward scalable photonic quantum computation and quantum communication. “The lack of a high-quality on-demand C-band photon source has been a major problem in quantum optics laboratories for over a decade—our new technology now removes this obstacle,” says Prof. Stefanie Barz.

The key: Identical photons on demand In everyday life, distinguishing features may often be desirable. Few want to be exactly like everyone else. When it comes to quantum technologies, however, complete indistinguishability is the name of the game. Quantum particles such as photons that are identical in all their properties can interfere with each other—much as in noise-canceling headphones, where sound waves that are precisely inverted copies of the incoming noise cancel out the background.

When identical photons are made to act in synchrony, then the probability that certain measurement outcomes occur can be either boosted or decreased. Such quantum effects give rise to powerful new phenomena that lie at the heart of emerging technologies such as quantum computing and quantum networking. For these technologies to become feasible, high-quality interference between photons is essential.

Quantum computers are alternative computing devices that process information, leveraging quantum mechanical effects, such as entanglement between different particles. Entanglement establishes a link between particles that allows them to share states in such a way that measuring one particle instantly affects the others, irrespective of the distance between them.

Quantum computers could, in principle, outperform classical computers in some optimization and computational tasks. However, they are also known to be highly sensitive to environmental disturbances (i.e., noise), which can cause quantum errors and adversely affect computations.

Researchers at the International Quantum Academy, Southern University of Science and Technology, and Hefei National Laboratory have developed a new approach to detect these errors in a silicon-based quantum processor. This error detection strategy, presented in a paper published in Nature Electronics, was found to successfully detect quantum errors in silicon qubits, while also preserving entanglement after their detection.