The future of communications may well rely on quantum technology capable of integrating with our existing infrastructure. Engineers at the University of Pennsylvania have conducted a pioneering experiment by transmitting quantum signals via commercial optical fiber cables, using the same Internet Protocol (IP) that governs the current web.
This breakthrough demonstrates that quantum networks could one day coexist with the classical internet, paving the way for unprecedented applications.
A quantum network node, located about one kilometer (0.6 miles) from the source on a Verizon cable.
Credit: Sylvia Zhang
At the heart of this innovation is a tiny chip called the "Q-chip," which handles both quantum and classical data. It operates with standard IP language, enabling information routing similar to the traditional internet. Quantum signals rely on "entangled" particles—a phenomenon where two particles are linked in such a way that an action on one instantly affects the other, even at a distance. This property could allow quantum computers to connect and share their computing power.
One of the major challenges was preserving the fragile quantum state during transmission, as any direct measurement destroys it. The team circumvented this problem by sending a classical signal just before the quantum signal, acting like a locomotive pulling sealed cars. The classical signal, measurable without damage, guides the entire packet using IP protocols, while the quantum information remains intact and protected.
The real-world conditions of commercial networks, with their temperature variations and vibrations, usually threaten quantum signals. The researchers developed an innovative error-correction method: by analyzing disturbances in the classical signal, they deduce and apply the necessary corrections to the quantum signal without measuring it. This approach maintained a transmission fidelity of over 97% during tests.
Although limited to a connection between two buildings over one kilometer (0.6 miles), this system opens up prospects for expansion. The chip, made of silicon using standard techniques, could be mass-produced and integrated into existing infrastructure. To extend the network beyond metropolitan areas, the current impossibility of amplifying quantum signals without breaking their entanglement must be overcome.
This breakthrough recalls the early days of the classical internet, where connections between universities initiated a global transformation. A quantum internet could one day enable ultra-fast distributed computing, molecular simulations for medicine, or more efficient artificial intelligence. The work, published in
Science, marks a key step toward a future where quantum and classical systems coexist.
Quantum entanglement
Quantum entanglement is a phenomenon where two particles, such as photons, become so closely linked that the state of one instantly influences the other, regardless of the distance separating them. Albert Einstein nicknamed it "spooky action at a distance" due to its counterintuitive nature.
Unlike classical communications, which rely on signals traveling at the speed of light, entanglement appears to operate faster, although this does not allow information to be transmitted faster than light.
In quantum networks, entanglement is used to link distant quantum processors. However, maintaining this delicate state requires controlled environments, as any interaction with the outside world can break it.
Potential applications include quantum cryptography, where encryption keys are generated in an ultra-secure manner, and distributed computing, where multiple quantum computers collaborate to solve problems unsolvable with current technologies.