German researchers from Leibniz University Hannover have achieved a milestone by sending both quantum and conventional data over a single fiber optic line for the first time. The breakthrough was detailed in Science Advances (SciAdv).
Previously, experts confirmed that quantum information could travel through ordinary fiber optics, but only when the quantum data stood alone. This new work proves that quantum data and classical signals can share the same physical channel without corrupting the fragile quantum information carried by entangled photons.
Quantum data typically exists as entangled qubits, the smallest units of quantum information. Entanglement links two qubits so that their states remain connected even when the particles are separated in time or space. This delicate connection means the two qubits are correlated in ways that classical data cannot reproduce, a feature that underpins many quantum technologies.
Entanglement is highly sensitive and can be disrupted by noise or interference from other signals. When multiple data streams use the same wavelength in a fiber, decoherence can occur, erasing the quantum information. Decoherence is the enemy of reliable quantum communication because it breaks the correlations that make entangled qubits useful.
To counteract these challenges, the Hannover team employed electro-optic phase modulation. This method adjusts the frequency of laser pulses to align with the color, or spectral profile, of the entangled photons. By matching spectral characteristics, the researchers were able to reduce crosstalk and preserve the integrity of the quantum states while conventional data travels on the same fiber.
The result is a single color channel capable of carrying two very different kinds of data without harming the quantum information stored in the entangled photons. In practical terms, this means more capacity can be freed up on existing fiber networks, enabling higher overall data throughput and greater flexibility in network design.
Experts say that sharing channels could be a crucial step toward scalable quantum networks, with applications ranging from ultra-secure communications to advanced quantum cryptography. By integrating quantum channels with classical infrastructure, operators may be able to deploy quantum features without significantly expanding the fiber footprint or laying new cabling. The team notes that the approach opens up new possibilities for combining quantum services with standard telecommunications in a way that can adapt to real-world networks.
The observation aligns with ongoing efforts to embed quantum capabilities into existing communication layers, reducing the cost and complexity of building quantum-ready networks. In addition to enhancing security, the ability to multiplex quantum and classical information could improve reliability and resilience by leveraging mature, established fiber systems that already reach deep into cities and campuses.
While the latest results show promise, researchers emphasize that further work is needed to refine these techniques for long-haul deployment and varied network conditions. The study underscores how careful spectral engineering and precise control of light can bridge quantum and classical information streams, making it easier for industry to adopt quantum-enhanced features on current platforms.
Overall, the research represents a meaningful advance in the broader quest to make quantum technologies practical and scalable. By demonstrating that quantum data can ride alongside traditional signals on a single fiber, the study helps move quantum communication from a laboratory curiosity toward real-world use cases that demand security, efficiency, and compatibility with today’s networks [Science Advances].