Entangling photons of different colors

February 25, 2019 by Ben P. Stein, National Institute of Standards and Technology
By carefully engineering the geometry of a micrometer-scale, ring-shaped resonator, researchers at NIST produced pairs of entangled photons (particles of light) that have two very different colors or wavelengths. Light from a pump laser (purple regions in the resonator) generates one photon in each pair at a visible-light wavelength (red patches in and around resonator); the other photon has a wavelength in the telecommunications (near-infrared) part of the spectrum (blue patches). From the perspective of quantum communication, these pairings combine the best of both worlds in an optical circuit: The visible-light partner can interact with trapped atoms, ions, or other systems that serve as quantum versions of computer memory, while the telecommunications wavelength member of each couple is free to propagate over long distances through an optical fiber network. Credit: S. Kelley/NIST

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 -correlated pairs made up of one visible and one near-infrared using chip-based 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-. 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 .

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

One of the more counterintuitive properties of quantum mechanics, 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 ," Srinivasan said.

Explore further: Using quantum entanglement to study proteins

More information: Xiyuan Lu et al, Chip-integrated visible–telecom entangled photon pair source for quantum communication, Nature Physics (2019). DOI: 10.1038/s41567-018-0394-3

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Osiris1
1 / 5 (1) Feb 26, 2019
Now about real time instantaneous communication with our satellites millions of miles away from, say, a station in high geosynchronous orbit of earth over the USA. Using quantum entangled matter.
antialias_physorg
4 / 5 (4) Feb 26, 2019
Now about real time instantaneous communication with our satellites millions of miles away

No. Quantum mechanics doesn't allow for that.
The speed of light limit for information transmission is very much intact in quantum mechanics.
Osiris1
1 / 5 (1) Feb 26, 2019
There are reasons that you can not be right, antialias. Many involve quandaries that physics gets into when it relies on foolish quasi-religious fantasies. Our computers came out of transistors which came from reverse engineering of foreign technology from a crashed shuttle from some starship in orbit...shuttle crashed in 1941, not 1947.. in Missouri. We did not have the enabling technology to reverse integrated circuits then.

The announced invention of the transistor by alleged Japanese scientist in 1947 was misinformation. We ran the Japanese government then thru occupation forces. The government certainly knows better than you, but choose to subsidize folks like you in non-monetary buy yet monetized ways in order to better and efficiently maintain classifiability of the truth.

So happy fantasy, maybe even for a decade. Until deniability is gone!

The very existence of star travel belies speedlimits. Don't forget to take your meds!
antialias_physorg
not rated yet Feb 27, 2019
The government certainly knows better than you

Governments can't defy math or the laws of physics. Nowhere in quantum mechanics is faster than light information transmission possible (or even hinted at).
Like so many you confuse information with quantum information. They are two separate concepts. Information can transmit a message. Quantum information cannot.

The very existence of star travel belies speedlimits

What kind of prattle is this? What is 'star travel' supposed to be?

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