Single-Photon Switches Offer A Path Toward Scalable Quantum Networks

Researchers map steps needed to deliver practical quantum routing

Controlling light at the level of individual photons could one day do for quantum networks what switching and routing have done for classical internet infrastructure. To help realize that vision, researchers at the University of Sheffield are exploring how single-photon switches – devices that can direct individual photons on demand – might underpin the architecture of a future quantum internet.

The findings come from a new review that examines how quantum emitters integrated with photonic structures can route individual photons for future quantum networks.

A single-photon switch uses a quantum emitter, such as a quantum dot or a superconducting qubit, coupled to a nanophotonic structure, like a waveguide or a cavity. When a photon enters, the device steers it to a chosen output port without destroying the information encoded in its quantum state.

“The difference from a classical optical switch is that you need it to preserve the quantum state of the photon,” said lead author and theoretical physics researcher Mateusz Duda.

“We’re interested not just in sending a signal, but in maintaining the delicate quantum properties of the light being controlled.”

Co-author Pieter Kok, a professor of theoretical physics, added that the challenge lies in achieving strong, lossless interaction between light and matter.

“You don’t want to absorb the photon, but you want it to interact just enough that you can control where it goes. We’re right at that difficult edge,” he said.

The team’s review analyzes progress across multiple hardware platforms, including semiconductor quantum dots, color centers, neutral atoms, and superconducting qubits. Each offers trade-offs between efficiency, speed, and fidelity, the metrics that define how well a switch routes quantum information.

According to Duda, fidelity is the toughest barrier.

“In proof-of-principle experiments, people haven’t worried much about what happens to the photon’s state,” he said. “But if you later want those photons to interfere or carry entanglement, they must be identical. Preserving that state is essential.”

For network engineers, the integration question looms large. Kok said practical systems will depend on scalable photonic chips that combine optical and electronic layers while minimizing coupling losses between fiber and chip.

“Integration brings its own challenges, but ultimately it will also be the solution. Miniaturization means you can do things faster and interact less with the noisy outside world,” he added.

The researchers believe these switches could evolve from laboratory curiosities into drop-in components for quantum network testbeds and, later, telecom infrastructure, handling single photons much as routers manage data packets today.

As Duda put it, the need for such building blocks will grow alongside network complexity:

“Quantum networks are still in their early stages, so people haven’t thought much about basic components like single-photon switches,” he said. “But as the number of channels, users, and nodes increases, these devices will be essential for scaling up to complex systems that can operate in the real world.”