Northwestern University researchers have successfully achieved quantum state transfer over a 30.2-km fiber carrying 400-Gbps C-band classical traffic. The ability for quantum and conventional networks to operate in the same optical fibers would aid the deployment of quantum network technology on a large scale.
Thomas et al. demonstrated quantum state teleportation over a 30.2-km fiber that is populated with high-power 400-Gbps conventional data traffic; by employing various methods to suppress SpRS noise, teleportation fidelity was well maintained alongside elevated classical powers capable of transmitting many Tbps aggregate data rates. Image credit: Thomas et al., doi: 10.1364/OPTICA.540362.
The optical fiber infrastructure and telecommunications technology that underlie the Internet have been widely adopted by researchers seeking to develop quantum networks capable of applications such as quantum-enhanced cryptography, sensing, and networked quantum computing.
However, since the majority of the existing fiber infrastructure is populated with conventional telecommunications traffic and due to the economic cost of leasing or installing new fiber, whether quantum networking can be realized on a large scale will depend on the ability to propagate quantum signals in the same fiber as high-power classical signals.
“In optical communications, all signals are converted to light,” said Northwestern University’s Professor Prem Kumar.
“While conventional signals for classical communications typically comprise millions of particles of light, quantum information uses single photons.”
Professor Kumar and colleagues found a way to help the delicate photons steer clear of the busy traffic.
“This is incredibly exciting because nobody thought it was possible,” Professor Kumar said.
“Our work shows a path towards next-generation quantum and classical networks sharing a unified fiberoptic infrastructure.”
“Basically, it opens the door to pushing quantum communications to the next level.”
After conducting in-depth studies of how light scatters within fiberoptic cables, the researchers found a less crowded wavelength of light to place their photons.
Then, they added special filters to reduce noise from regular Internet traffic.
“We carefully studied how light is scattered and placed our photons at a judicial point where that scattering mechanism is minimized,” Professor Kumar said.
“We found we could perform quantum communication without interference from the classical channels that are simultaneously present.”
To test the new method, the scientists set up a 30.2-km-long fiberoptic cable with a photon at either end.
Then, they simultaneously sent quantum information and regular Internet traffic through it.
Finally, they measured the quality of the quantum information at the receiving end while executing the teleportation protocol by making quantum measurements at the mid-point.
They found the quantum information was successfully transmitted — even with busy Internet traffic whizzing by.
Next, the authors plan to extend the experiments over longer distances.
They also plan to use two pairs of entangled photons to demonstrate entanglement swapping, another important milestone leading to distributed quantum applications.
Finally, they are exploring the possibility of carrying out experiments over real-world inground optical cables rather than on spools in the lab.
“Quantum teleportation has the ability to provide quantum connectivity securely between geographically distant nodes,” Professor Kumar said.
“But many people have long assumed that nobody would build specialized infrastructure to send particles of light.”
“If we choose the wavelengths properly, we won’t have to build new infrastructure. Classical communications and quantum communications can coexist.”
The team’s paper was published this month in the journal Optica.
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Jordan M. Thomas et al. 2024. Quantum teleportation coexisting with classical communications in optical fiber. Optica 11 (12): 1700-1707; doi: 10.1364/OPTICA.540362
This article was adapted from an original release by Northwestern University.
Source : Breaking Science News