New Device Can Entangle Photons Of Different Colors For Quantum Communication

  • Researchers develop a new chip-based optical instrument to securely transfer quantum information over long distances. 
  • It works by creating quantum pairs of one visible-light photon and one near-infrared photon. 

Unlike existing communication systems that use electric current to transfer data, quantum communication systems rely on light. Long-distance quantum communication requires resources for the low-loss storage and transmission of quantum information.

The optical instruments that carry and process quantum information need particles of visible light (called photons) to operate. However, to transport that information over miles via optical fibers, they need near-infrared photons that have 10x longer wavelength than visible light.

Recently, scientists at the National Institute of Standards and Technology came up with a novel technique to solve this issue. They used a chip-based optical instrument to create quantum pairs of one visible-light photon and one near-infrared photon.

The visible photon can effectively interact with trapped ions while the near-infrared photon of each pair can propagate to over long distance via an optical fiber. The discovery can enhance the capability of photon-based circuits to securely transfer data to distant locations.

Entangling Photons Of Different Wavelengths

The quantum entanglement occurs when particles — such as two or more photons — connect intrinsically with each other and together act as one unit. The entangled particles remain connected so that tasks performed on one affect the other, even if it’s separated by great distances.

These entangled particles lie at the core of quantum computing and encryption, and other quantum information schemes. Usually, two entangled photons have similar colors or wavelengths.

Reference: Nature Physics | doi:10.1038/s41567-018-0394-3 | NIST

However, in this study, scientists tried to make odd couples: they wanted to attach visible-light photons (that are perfect for storing data in atomic systems) with near-infrared photons (that can travel through optical fibers without significant signal loss).

To make such pairs, they developed a nanoscale silicon nitride resonator that guides light around a tiny racetrack. They employed a special kind of entanglement, called time-energy entanglement, to link the energy of the photon pair with the time at which it is produced.

Researchers directed a pump laser (purple) into the ring-shaped resonator. It generated a pair of visible-light photon (red patches) and near-infrared photons (blue patches). | Courtesy of researchers 

The team directed a laser light of specific wavelength into the resonator and found that it emerged pairs of near-infrared and visible-light photons. They successfully engineered these resonators to create pairs in large quantities.

Read: Could We Be Performing Quantum Computing In Our Own Brain?

The experiment performed in this study showed that entanglement persisted even after the pair traveled through several miles of optical fiber.

Moreover, the nanophotonic chip source can be manufactured in large numbers, and through further development, this technology can be used to link distant quantum systems via entanglement swapping.

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