Developing networks based on quantum physics holds immense potential. Such advancements could enhance communication security, integrate quantum computing capabilities, and facilitate the creation of cutting-edge research tools.
A significant hurdle, however, is the quantum phenomenon known as entanglement—where two objects become intricately linked across any distance. The measurement of one object invariably determines the measurement of the other.
Transmitting entangled particles through our current fiber-optic communication infrastructure presents substantial challenges. Outside controlled laboratory conditions, their quantum states are prone to distortion.
Researchers from the US National Institute of Standards and Technology (NIST) have achieved a breakthrough by successfully transmitting light particles (photons) over 62 kilometers (38.5 miles) of existing network cabling without disrupting their entanglement.
Their findings are detailed in the Journal of Optical Communications and Networking.
Yicheng Shi, a physicist at NIST, describes the effort as “a stress test of quantum networking systems.” He explains, “We put this to an extreme test in an environment that’s really noisy. Amazingly, it turned out it still worked.”
While this transmission doesn’t set a record for distance, the experimental setup is noteworthy. Much of the fiber-optic cabling used was above ground, strung between street-side poles from NIST to the University of Maryland, exposing it to wind, temperature changes, and vibrations from traffic and wildlife.
While classical internet data like streaming movies and video calls remain unaffected by these conditions, quantum data is sensitive. Environmental factors disrupt the polarization of photons, which encodes the entanglement information.
“It’s about as bad a connection as you can possibly have,” remarks Oliver Slattery, a physicist from NIST.
To address these interferences, the researchers used a laser light signal as a reference. By assessing the twisting of this laser light, they could apply corrections to the entangled photons. Alternating between entangled photons and laser light consumed only 7.2 percent of the operation time, leaving 92.8 percent available for transmitting stabilized quantum information.
The researchers state in their paper, “Our results demonstrate the feasibility of distributing polarization-entangled photons over challenging fiber conditions, which is an important step toward the practical deployment of quantum networks.”
Although quantum entanglement has been achieved over 420 kilometers of optical fiber, these recent tests were conducted in a chaotic real-world environment.
The researchers write, “Although aerial-based optical fibers are typically considered unsuitable quantum channels for transmitting polarization-encoded or polarization-entangled photons, we show that a stable distribution of polarization entanglement is achievable if the fiber link is actively stabilized.”
Despite the promising results of this real-world test, there is much room for improvement. The current transmission rate of 200-1,500 entangled photons per second needs enhancement for a viable quantum internet.
Researchers suggest that faster hardware setups and more efficient software algorithms could be potential solutions.
The study reinforces the notion that quantum networks are a promising technology. They could allow telescopes at different locations on Earth to function as one large instrument using entangled photons. Additionally, these systems could offer enhanced quantum security for the internet, allowing network nodes to share a secret code for data verification that cannot be intercepted, as the code remains unset until checked.
Related: The First Room-Temperature Quantum Material of Its Kind Is Spun From Atoms of Gold
Shi concludes, “It’s a demonstration that quantum networking protocols can work in real-world environments.”
The research is documented in the Journal of Optical Communications and Networking.
This article was fact-checked by Clare Watson and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
