Tag Archives: rubidium

Capturing light in a bottle, a single-atom light switch, and superpositioning

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A Nov. 5, 2013 Vienna University of Technology press release (also available on EurekAlert) describes research that may make quantum optical switches possible,

With just a single atom, light can be switched between two fibre optic cables at the Vienna University of Technology. Such a switch enables quantum phenomena to be used for information and communication technology.

The press release goes on to describe a ‘light in a bottle’ technique which leads, the researchers hope, that they may have discovered how to create a quantum light switch,

Professor Arno Rauschenbeutel and his team at the Vienna University of Technology capture light in so-called “bottle resonators”. At the surface of these bulgy glass objects, light runs in circles. If such a resonator is brought into the vicinity of a glass fibre which is carrying light, the two systems couple and light can cross over from the glass fibre into the bottle resonator.

“When the circumference of the resonator matches the wavelength of the light, we can make one hundred percent of the light from the glass fibre go into the bottle resonator – and from there it can move on into a second glass fibre”, explains Arno Rauschenbeutel.

A Rubidium Atom as a Light Switch
This system, consisting of the incoming fibre, the resonator and the outgoing fibre, is extremely sensitive: “When we take a single Rubidium atom and bring it into contact with the resonator, the behaviour of the system can change dramatically”, says Rauschenbeutel. If the light is in resonance with the atom, it is even possible to keep all the light in the original glass fibre, and none of it transfers to the bottle resonator and the outgoing glass fibre. The atom thus acts as a switch which redirects light one or the other fibre.

Both Settings at Once: The Quantum Switch
In the next step, the scientists plan to make use of the fact that the Rubidium atom can occupy different quantum states, only one of which interacts with the resonator. If the atom occupies the non-interacting quantum state, the light behaves as if the atom was not there. Thus, depending on the quantum state of the atom, light is sent into either of the two glass fibres. This opens up the possibility to exploit some of the most remarkable properties of quantum mechanics: “In quantum physics, objects can occupy different states at the same time”, says Arno Rauschenbeutel. The atom can be prepared in such a way that it occupies both switch states at once. As a consequence, the states “light” and “no light” are simultaneously present in  each of the two glass fibre cables. [emphasis mine]

For the classical light switch at home, this would be plain impossible, but for a “quantum light switch”, occupying both states at once is not a problem. “It will be exciting to test, whether such superpositions are also possible with stronger light pulses. Somewhere we are bound to encounter a crossover between quantum physics and classical physics”, says Rauschenbeutel.

This light switch is a very powerful new tool for quantum information and quantum communication. “We are planning to deterministically create quantum entanglement between light and matter”, says Arno Rauschenbeutel. “For that, we will no longer need any exotic machinery which is only found in laboratories. Instead, we can now do it with conventional glass fibre cables which are available everywhere.”

Darrick Chang offers a good introduction (i.e., it’s challenging but you don’t need a physics degree to read it) and some analysis of this work in his Nov. 4, 2013 article for Physics (6, 121 (2013) DOI: 10.1103/Physics.6.121) titled: Viewpoint: A Single-Atom Optical Switch.

Quantum scientists over the past two decades have dreamt of realizing powerful new information technologies that exploit the laws of quantum mechanics in their operation. While many approaches are being pursued, a prevailing choice consists of using single atoms and particles of light—single photons—as the fundamental building blocks of these technologies [1]. In this paradigm, one envisions that single atoms naturally act as quantum processors that produce and interface with single photons, while the photons naturally act as wires to carry information between processors. Reporting in Physical Review Letters, researchers at the Vienna University of Technology, Austria, have taken an important step forward in this pursuit, by experimentally demonstrating a microphotonic optical switch that is regulated by just a single atom [2].

This article is open access.

For those willing to tackle a more challenging paper, here’s a link to and a citation for the Vienna University of Technology researchers’ paper,

Fiber-Optical Switch Controlled by a Single Atom by Danny O’Shea, Christian Junge, Jürgen Volz, and Arno Rauschenbeute. Phys. Rev. Lett. 111, 193601 (2013) [5 pages]

This work is behind a paywall.

Minutes after publishing: here’s an image that illustrates superpositioning in a quantum switch,

The Quantum Light Switch: It can occupy both possible states at the same time. Courtesy Vienna University of Technology

The Quantum Light Switch: It can occupy both possible states at the same time. Courtesy Vienna University of Technology

With a song in your heart and multiplexed images in an atomic vapor

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A specific piece of research has inspired a song with lyrics based on the text of a research paper and, weirdly, it works. You will have a song in your heart and on your lips and it’s all to do with storing images in an atomic vapor,

Hot, hot, hot, eh?

As for the research paper itself (Temporally multiplexed storage of images in a Gradient Echo Memory), it’s currently availab.e at arXiv.org or in Optics Express, Vol. 20, Issue 11, pp. 12350-12358 (2012) DOI: 10.1364/OE.20.012350(authors: Quentin Glorieux, Jeremy B. Clark, Alberto M. Marino, Zhifan Zhou, Paul D. Lett). The May 29, 2012 news item on Nanowerk offers some tantalizing tidbits about the work,

The storage of light-encoded messages on film and compact disks and as holograms is ubiquitous—grocery scanners, Netflix disks, credit-card images are just a few examples. And now light signals can be stored as patterns in a room-temperature vapor of atoms. Scientists at the Joint Quantum Institute [JQI] have stored not one but two letters of the alphabet in a tiny cell filled with rubidium (Rb) atoms which are tailored to absorb and later re-emit messages on demand. This is the first time two images have simultaneously been reliably stored in a non-solid medium and then played back.

In effect, this is the first stored and replayed atomic movie. Because the JQI researchers are able to store and replay two separate images, or “frames,” a few micro-seconds apart, the whole sequence can qualify as a feat of cinematography.

Here’s a little more detail about how this was done and some information about the implications,

Having stored one image (the letter N), the JQI physicists then stored a second image, the letter T, before reading both letters back in quick succession. The two “frames” of this movie, about a microsecond apart, were played back successfully every time, although typically only about 8 percent of the original light was redeemed, a percentage that will improve with practice. According to Paul Lett, one of the great challenges in storing images this way is to keep the atoms embodying the image from diffusing away. The longer the storage time (measured so far to be about 20 microseconds) the more diffusion occurs. The result is a fuzzy image.

Paul Lett plans to link up these new developments in storing images with his previous work on squeezed light. “Squeezing” light is one way to partially circumvent the Heisenberg uncertainty principle governing the ultimate measurement limitations. By allowing a poorer knowledge of a stream of light—say the timing of the light, its phase—one gain a sharper knowledge of a separate variable—in this case the light’s amplitude. This increased capability, at le ast for the one variable, allows higher precision in certain quantum measurements.

“The big thing here,” said Lett, “is that this allows us to do images and do pulses (instead of individual photons) and it can be matched (hopefully) to our squeezed light source, so that we can soon try to store “quantum images” and make essentially a random access memory for continuous variable quantum information. The thing that really attracted us to this method—aside from its being pretty well-matched to our source of squeezed light—is that the ANU [Australian National University] group was able to get 87% recovery efficiency from it – which is, I think, the best anyone has seen in any optical system, so it holds great promise for a quantum memory.”

I may never totally understand this work but at least I now have a song to sing and for anyone who wants more details, the May 27, 2012 news item on Nanowerk provides details and images, as well as, another opportunity to watch the song.  I did check out the video on YouTube and found that it’s by therockcookiebottom and is part of a project, Song A Day: 1000 Days and Counting that singer-songwriter, Jonathan Mann started in Jan. 2009. I imagine that means he  must be nearing the end. Thank you Jonathan for a very entertaining and educational song. He does offer memberships to support him and his song-a-day project and opportunities to hire him for any songwriting projects you may have.