Researchers Successfully Entangle Photons Across a Record 100-Kilometer Distance

Scientists have achieved a massive breakthrough in quantum internet technology by successfully entangling photons across a record 100-kilometer distance. This milestone allows the secure transmission of encrypted data over standard fiber optic cables, bringing us one step closer to a completely unhackable communications network.

The 100-Kilometer Fiber Optic Milestone

For decades, researchers have understood the theory of quantum entanglement. Two particles, like photons of light, can be linked so that the state of one instantly dictates the state of the other. Albert Einstein famously referred to this phenomenon as “spooky action at a distance.” However, moving these fragile entangled photons across physical infrastructure is highly complex.

The recent success in transmitting entangled photons over 100 kilometers of optical fiber marks a major engineering victory. Prior to this, maintaining the delicate quantum state over such a long physical distance resulted in heavy data loss. The glass inside standard telecommunications fiber optic cables naturally absorbs light. Over a stretch of 100 kilometers, only a tiny fraction of the original photons survive the journey. By successfully measuring and verifying the entanglement of these surviving photons at the finish line, scientists have proven that direct quantum communication between distant locations is practically achievable using the fiber optic cables already buried under our cities.

The Hardware Making This Possible

To capture the extremely faint signals at the end of a 100-kilometer fiber line, scientists rely on highly specialized equipment. Standard optical sensors simply cannot detect individual photons reliably enough for quantum encryption. Instead, researchers use Superconducting Nanowire Single-Photon Detectors (SNSPDs).

These advanced sensors are cooled to temperatures near absolute zero. At this extreme cold, the nanowires have zero electrical resistance. When a single entangled photon strikes the nanowire, it briefly breaks the superconductivity and creates a measurable electrical pulse. This incredibly precise detection allows scientists to confirm the photons remained entangled after traveling 100 kilometers. Institutions like the National Institute of Standards and Technology (NIST) actively develop and refine these sensors to improve their efficiency and reduce false readings caused by background heat or ambient light.

Quantum Key Distribution and Unhackable Data

The primary reason governments and corporations are rushing to develop a quantum internet is absolute data security. Today, our current internet relies on mathematical encryption, such as the RSA algorithm. This method protects everything from your online banking portal to classified government communications. Mathematical encryption works because traditional computers take too much time to crack the complex math problems involved.

However, quantum computing technology is advancing rapidly. In the near future, a powerful quantum computer running Shor’s algorithm could break current encryption standards in a matter of minutes. This threat is where the 100-kilometer photon entanglement record becomes critical. It enables a security technology called Quantum Key Distribution (QKD).

Quantum Key Distribution uses the laws of physics, rather than complex math, to secure data. The sender generates a secret encryption key using entangled photons and sends it through the fiber optic cable to the receiver. Under the rules of quantum mechanics, simply observing a quantum system changes its state. If a hacker attempts to intercept or copy the photons while they travel through the 100-kilometer cable, the entanglement is immediately broken. The sender and receiver instantly know the transmission line is compromised, and they can discard the key before any sensitive information is sent.

Eliminating the Trusted Node Vulnerability

Before this 100-kilometer breakthrough, networks covering long distances had to rely on intermediate stops known as trusted nodes. Because photons naturally fade over long fiber optic runs, the signal had to be intercepted, measured, and regenerated at these waypoints.

The major problem with trusted nodes is that the data briefly becomes classical, unencrypted information during the regeneration process. If a bad actor gains physical access to the trusted node, they can steal the encryption keys. Achieving direct entanglement over 100 kilometers removes the need for trusted nodes across regional distances. Two locations separated by 100 kilometers can now establish a direct, end-to-end quantum link. This distance is more than enough to connect financial hubs within a major metropolitan area or secure communications between local government facilities.

Building the Future Quantum Internet

While 100 kilometers is a massive leap forward, building a truly global quantum internet will require connecting endpoints separated by thousands of miles. Scientists are currently developing quantum repeaters to solve this exact problem. Unlike standard signal amplifiers which destroy the quantum state by copying the light, quantum repeaters use a highly advanced process called entanglement swapping. This technique links the entanglement of photons across multiple shorter fiber optic segments, theoretically extending the range indefinitely without compromising security.

Organizations like the Chicago Quantum Exchange and major technology companies including IBM and Toshiba are closely watching and funding these developments. As fiber optic transmission distances increase beyond the 100-kilometer mark, we will begin seeing hybrid networks. These networks will use the traditional internet for everyday tasks like browsing websites and streaming video, while relying on secure quantum channels to transmit highly sensitive encryption keys.

Frequently Asked Questions

What is quantum entanglement? Quantum entanglement is a physical phenomenon where two particles become connected in such a way that the state of one particle instantly influences the state of the other, no matter how far apart they are in space.

Why are fiber optic cables used for quantum transmission? Fiber optic cables transmit data using pulses of light. Since photons (particles of light) are ideal for carrying quantum information, scientists can use the existing global infrastructure of telecommunications fiber to send entangled photons between locations.

Can a quantum internet replace our current internet? No, the quantum internet will not replace the standard internet. Instead, it will run alongside it as a specialized network. Everyday activities will still use classical internet connections, while the quantum internet will be reserved for securing highly sensitive data and linking quantum computers together.