Thursday , July 29 2021

Intertwined photons of different colors

Some of the most advanced communications systems currently being developed rely on the properties of quantum science to store and transport information. However, researchers designing quantum communication systems that rely on light rather than electrical current to transmit information are faced with difficulty: Optical components that store and process quantum information typically require photons (visible particles of light) to work. However, only near-infrared photons – about 10 times longer wavelengths – can transport this information over miles of fiber.

Now researchers at the National Institute of Standards and Technology (NIST) have developed a new way to solve this problem. For the first time, the team created quantum-correlated pairs consisting of a visible and near-infrared photon using chip-based optical components that can be produced massively. These photon couples combine the best of both worlds: visible light partners can interact with captured atoms, ions or other systems that serve as quantum versions of computer memory, while the nearby infrared members of each pair are free to propagate to long distances. through the optical fiber.

The achievement promises to increase the ability of light circuits to securely transmit information to distant locations. NIST Xiyuan Lu researchers, Kartik Srinivasan, and colleagues from the University of Maryland NanoCenter at College Park, demonstrated the quantum correlation known as tangling using a specific pair of visible lights and infrared photons. However, researcher design methods can be easily applied to create many other pairs of visible light / near infrared rays adapted to suit specific systems of interest. In addition, the miniature optical components that create the tangles are produced in large quantities.

Lou, Srinivasan and their colleagues recently described their work in Nature Physics.

One of the more opposite properties of quantum mechanics, quantum interlacing occurs when two or more photons or other particles are prepared in a way that makes them so interconnected that they behave as one unit. Measurement that determines the quantum state of one of the entangled particles automatically determines the condition of the other, even if the two particles lie on the opposite sides of the universe. Tangling is the basis of many quantum information schemes, including quantum computing and encryption.

In many situations, the two photons that are entangled have similar wavelengths or colors. But NIST's researchers deliberately tried to create strange pairs – entangling between photons whose colors are very different.

"We wanted to connect visible light photons that are useful for storing information in atomic systems, and telecommunication photons that are in the near infrared field and are good at traveling through fiber optics with low signal loss," Srinivasan said.

To make the photons suitable for interaction with most quantum information storage systems, the team also needed the light to be abruptly reached at a certain wavelength instead of having a wider and more diffuse distribution.

To create tangled pairs, the team developed a specially tailored optical whiskey gallery – a nanosized silicon nitride resonator that drives light around a small runway similar to the way the sound waves move unobstructed around a curved wall such as the dome in the Cathedral of St. . Paul in London. In such curved structures, known as acoustic whispering galleries, a person standing close to one part of the wall easily hears a faint sound coming from any other part of the wall.

When the selected wavelength of laser light was directed toward the resonator, tangled pairs of visible lights and close infrared photons appeared. (The specific type of entanglement used in the experiment, known as time-energetic entanglement, connects the energy of the photon couples with the time they are generated.)

"We understood how to design these whispering galleries of resonators to produce a large number of pairs we wanted with very little background noise and other outside light," said Lou. Researchers have confirmed that entanglement continues even after telecommunication photons pass through several kilometers of optical fiber.

In the future, by combining two of the tangled pairs with two quantum memories, the entanglement inherent in the photon couples can be translated into quantum memories. This technique, known as tangling, allows memories to intertwine with each other at a much greater distance than would normally be possible.

"Our contribution was to figure out how to make a quantum light source with the right properties that could allow such a long distance," said Srinivasan.

Research report: Chip-integrated photon source with visible telecom for quantum communication

Related Links

National Institute of Standards and Technology (NIST)

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Researchers have found anti-laser masking as a perfect absorber

Durham NC (SPX) February 18, 2019

Researchers from Duke University have found that the perfect absorber of electromagnetic waves described in 2017 paper can easily be changed into a "reverse laser" known as a Coherent Perfect Absorber (CPA).

The study appeared online on January 28 in Advanced Optical Materials magazine.

The laser is a device that converts energy into coherent light, which means that the light waves are perfectly aligned with each other. Turning the process, CPA – sometimes called ti … read more

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