Nav: Home

Entangling photons of different colors

February 25, 2019

Some of the most advanced communication systems now under development rely on the properties of quantum science to store and transport information. However, researchers designing quantum communication systems that rely on light, rather than electric current, to transmit information face a quandary: The optical components that store and process quantum information typically require visible-light photons (particles of light) to operate. However, only near-infrared photons--with wavelengths about 10 times longer--can transport that information over kilometers of optical fibers.

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

The achievement promises to boost the ability of light-based circuits to securely transmit information to faraway locations. NIST researchers Xiyuan Lu, Kartik Srinivasan and their colleagues at the University of Maryland NanoCenter in College Park, demonstrated the quantum correlation, known as entanglement, using a specific pair of visible-light and near-infrared photons. However, the researchers' design methods can be easily applied to create many other visible-light/near-infrared pairs tailored to match specific systems of interest. Moreover, the miniature optical components that created the entanglements are manufactured in large numbers.

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

One of the more counterintuitive properties of quantum mechanics, quantum entanglement occurs when two or more photons or other particles are prepared in a way that makes them so intrinsically connected that they behave as one unit. A measurement that determines the quantum state of one of the entangled particles automatically determines the state of the other, even if the two particles lie on opposite sides of the universe. Entanglement lies at the heart 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 the NIST researchers deliberately set out to create odd couples--entanglement between photons whose colors are very different.

"We wanted to link together visible-light photons, which are good for storing information in atomic systems, and telecommunication photons, which are in the near-infrared and good at traveling through optical fibers with low signal loss," said Srinivasan.

To make photons suitable for interacting with most quantum information storage systems, the team also needed the light to be sharply peaked at a particular wavelength rather than having a broader, more diffuse distribution.

To create the entangled pairs, the team constructed a specially tailored optical "whispering gallery"--a nano-sized silicon nitride resonator that steers light around a tiny racetrack, similar to the way sound waves travel unimpeded around a curved wall such as the dome in St. Paul's Cathedral in London. In such curved structures, known as acoustic whispering galleries, a person standing near one part of the wall easily hears a faint sound originating at any other part of the wall.

When a selected wavelength of laser light was directed into the resonator, entangled pairs of visible-light and near-infrared photons emerged. (The specific type of entanglement employed in the experiment, known as time-energy entanglement, links the energy of the photon pairs with the time at which they are generated.)

"We figured out how to engineer these whispering gallery resonators to produce large numbers of the pairs we wanted, with very little background noise and other extraneous light," Lu said. The researchers confirmed that entanglement persisted even after the telecommunication photons traveled through several kilometers of optical fiber.

In the future, by combining two of the entangled pairs with two quantum memories, the entanglement inherent in the photon pairs can be transferred to the quantum memories. This technique, known as entanglement swapping, allows the memories to be entangled with each other over a much longer 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 enable such long-distance entanglement," Srinivasan said.
-end-
Paper: X. Lu, Q. Li, D.A. Westly, G. Moille, A. Singh, V. Anant & K. Srinivasan. Chip-integrated visible-telecom entangled photon pair source for quantum communication. Nature Physics. Published online Jan. 21, 2019. DOI: 10.1038/s41567-018-0394-3

National Institute of Standards and Technology (NIST)

Related Memories Articles:

How memories form and fade
Caltech researchers identify the neural processes that make some memories fade rapidly while other memories persist over time.
Firework memories
Recently Weizmann Institute scientists succeeded in recording these rapid bursts of activity -- called 'hippocampal ripples' -- in the human brain, and they were able to demonstrate their importance as a neuronal mechanism underlying the engraving of new memories and their subsequent recall.
Your nose knows when it comes to stronger memories
Memories are stronger when the original experiences are accompanied by unpleasant odors, a team of researchers has found.
Proof it's possible to enhance or suppress memories
Boston University neuroscientist Steve Ramirez and collaborators have published a new paper showing memories are pliable if you know which regions of the brain's hippocampus to stimulate, which could someday enable personalized treatment for people with PTSD, depression and anxiety.
What makes memories stronger?
A team of scientists at NeuroElectronics Research Flanders (NERF- empowered by imec, KU Leuven and VIB) found that highly demanding and rewarding experiences result in stronger memories.
More Memories News and Memories Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...