Quantum internet is possible using standard Internet protocol — University engineers send quantum signals over fiber lines without losing entanglement

Engineers at the University of Pennsylvania have successfully sent quantum signals over a standard internet connection with fiber-optic cables in the real world. The researchers have published their work in Science, taking the quantum internet from theory to reality by using existing internet systems.

Quantum signals are famously weak, unable to be measured without losing their quantum entanglement and becoming unreadable with too much noise. But engineers have managed to send the signals over the same busy internet infrastructure that standard IP signals occupy.

This transmission is possible due to the "Q-Chip", the University of Pennsylvania's silicon chip for coordinating traditional and quantum signals over the internet. Short for Quantum-Classical Hybrid Internet by Photonics, the Q-Chip can bundle standard and quantum signals into a package that can be sent successfully across a city's fiber-optic internet lines. The chip can both send and receive these linked signals, automatically correcting for noise without measuring the quantum-linked signals.

Quantum computing is an entirely different realm from traditional computing. Where normal computers use transistors, bits, and electrons to perform computations, represented with 0s and 1s, states of on and off, quantum computing starts from a different point entirely. Using qubits, quantum computers take advantage of quantum entanglement, allowing qubits to represent states of 0, 1, and any other of countless variations of these two states.

But quantum entanglement is tricky to work with, as quantum signals that are measured lose their quantum properties. In Schrödinger's thought experiment, a cat placed in a closed box with a radioactive isotope cannot be confirmed to be alive or dead until the box is opened and the cat is observed. Likewise, quantum particles can exist in the state of superposition (neither 0 nor 1) only until they are observed, at which point they lose their quantum relationship and become effectively 0 or 1. This makes sending these quantum signals over an internet connection highly difficult.

"Normal networks measure data to guide it towards the ultimate destination," said Robert Broberg, a doctoral student on the project who was interviewed by Phys.org. "With purely quantum networks, you can't do that, because measuring the particles destroys the quantum state."

To solve this problem, the Q-Chip pairs the quantum signal with a light-based standard internet signal in a train-like combo. The standard internet signal acts like an engine for routing, with the quantum signal riding alongside it like cargo, never being measured by either end of its internet connection. This relationship also works to correct for noise; as both the sending and receiving Q-Chip know what the standard signal is meant to be, it can error-correct the light-based signal and infer how to correct the quantum signal as well.

"By showing an integrated chip can manage quantum signals on a live commercial network like Verizon's, and do so using the same protocols that run the classical internet, we've taken a key step toward larger-scale experiments and a practical quantum internet," shared Liang Feng, the senior author of the paper.

The Q-Chip system can theoretically work anywhere along the Verizon fiber optic network in Philadelphia, where the university is located, as well as any other metro area's internet infrastructure. Further research will still be needed to successfully repeat quantum signals over long distances, which will be necessary to facilitate quantum internet connections between cities or beyond.

As quantum computing continues to march toward relevance and usefulness in the real world, this research on enabling quantum signals to be sent via existing Internet infrastructure is invaluable. What comes next for quantum is, as always, uncertain, but governments and corporations alike are continually working to be the first to enable its use in real-life applications.

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