Counting atoms with glass fiber

Dec 07, 2011 By Florian Aigner
The light wave in the glass fiber sticks out and touches the atoms trapped above and below the glass fiber.

(PhysOrg.com) -- Glass fiber cables are indispensable for the internet – now they can also be used as a quantum physics lab. The Vienna University of Technology is the only research facility in the world, where single atoms can be controllably coupled to the light in ultra-thin fiber glass. Specially prepared light waves interact with very small numbers of atoms, which makes it possible to build detectors that are extremely sensitive to tiny trace amounts of a substance.

Professor Arno Rauschenbeutel’s team, one of six research groups at the Vienna Center for Quantum Science and Technology, has presented this new method in the journal Physical Review Letters. The research project was carried out in collaboration with the Johannes Gutenberg University in Mainz, Germany.

Ultra-Thin Glass Fibers

The glass fibers used for the experiment are only five hundred millionths of a millimeter thick (500 nm). In fact,  they are even thinner than the wavelength of visible light. “Actually, the light wave does not really fit into the glass fiber, it sticks out a little”, Arno Rauschenbeutel explains. And this is precisely the big advantage of the new method: the light wave touches which are located outside of, but very close to, the glass fiber.  “First, we trap the atoms, so that they are aligned above and below the glass fiber, like pearls on a string”, says Rauschenbeutel. The light wave sent through the glass fiber is then modified by each individual atom it passes. By measuring changes in the very accurately, the number of atoms trapped near the fiber can be determined. 

Atoms Change the Speed of Light

When scientists study the interaction of atoms and light, they usually look at rather disruptive effects – at least on a microscopic scale: Atoms can, for example, absorb photons and emit them later in a different direction. This way, atoms can be accelerated and hurled away from their original position. In the glass fiber experiments at Vienna UT however, a very soft interaction between light and atoms is sufficient: “The atoms close to the glass fiber decelerate the light very slightly”, Arno Rauschenbeutel explains. When the light wave oscillates precisely upwards and downwards in the direction of the atoms, the wave is shifted by a tiny amount. Another light wave oscillating in a different direction does not hit any atoms and is therefore hardly decelerated at all. Light waves of different polarization directions are sent through the glass fiber – and their relative shift due to their different speed is measured. This shift tells the scientists how many atoms have delayed the light wave. 

Detecting Single Atoms

Hundreds or thousands of atoms can be trapped, less than a thousandth of a millimeter away from the glass fiber. Their number can be determined with an accuracy of several atoms. “In principle, our method is so precise that it can detect as few as ten or twenty atoms”, says Arno Rauschenbeutel. “We are working on a few more technical tricks – such as the reduction of the distance between the atoms and the glass fiber. If we can do this, we should even be able to reliably detect single atoms.”

Non-Destructive Quantum Measurements

The new glass fiber measuring method is not only important for new detectors, but also for basic quantum physical research. “Usually the quantum physical state of a system is destroyed when we measure it”, Rauschenbeutel explains. “Our glass fibers make it possible to control quantum states without destroying them.” The atoms close to the can also be used to tune the plane in which the light wave oscillates. Nobody can tell yet, which new technological possibilities may be opened up by that. “Quantum optics is an incredibly innovative research area today – and the Vienna research groups in this field are competing among the best in the world”, says Arno Rauschenbeutel.

Explore further: Exploring X-ray phase tomography with synchrotron radiation

More information: Original publication: arxiv.org/abs/1108.2469v2

Related Stories

Scientists make quantum breakthrough

Apr 20, 2011

(PhysOrg.com) -- Scientists have demonstrated for the first time that atoms can be guided in a laser beam and possess the same properties as light guided in an optical communications fiber.

Vienna physicists create quantum twin atoms

May 02, 2011

At the Vienna University of Technology, sophisticated atomchips have been used to create pairs of quantum mechanically connected atom-twins. Until now, similar experiments were only possible using photons.

Squeezed light from single atoms

Jun 30, 2011

(PhysOrg.com) -- Max Planck Institute of Quantum Optics scientists generate amplitude-squeezed light fields using single atoms trapped inside optical cavities.

Recommended for you

Backpack physics: Smaller hikers carry heavier loads

1 hour ago

Hikers are generally advised that the weight of the packs they carry should correspond to their own size, with smaller individuals carrying lighter loads. Although petite backpackers might appreciate the ...

Extremely high-resolution magnetic resonance imaging

1 hour ago

For the first time, researchers have succeeded to detect a single hydrogen atom using magnetic resonance imaging, which signifies a huge increase in the technology's spatial resolution. In the future, single-atom ...

'Attosecond' science breakthrough

2 hours ago

Scientists from Queen's University Belfast have been involved in a groundbreaking discovery in the area of experimental physics that has implications for understanding how radiotherapy kills cancer cells, among other things.

User comments : 6

Adjust slider to filter visible comments by rank

Display comments: newest first

antialias_physorg
5 / 5 (1) Dec 07, 2011
Hundreds or thousands of atoms can be trapped, less than a thousandth of a millimeter away from the glass fiber. Their number can be determined with an accuracy of several atoms. In principle, our method is so precise that it can detect as few as ten or twenty atoms

Woha. That is pretty awesome. And with the miniature scale we are dealing here this should be excellent for pollution, drug, explosives detectors - generally with any kind of gas 'spectrometers'.

Especially if they use an array of fibers with light of different wavelengths - which should interact differently with various substances.
Isaacsname
not rated yet Dec 07, 2011
Also maybe a method for " soft " measurements of quantum states, applicable in quantum computing ?
Nanobanano
not rated yet Dec 07, 2011
A_P:

I.e. detecting pollutants or contaminants in the parts per billion or parts per trillion range...or even lower...for quality assurance in nano-devices...

Might have applications in blood tests or cellular biology for better understanding biochemistry at the nano scales.

Wonder if you could use this as some sort of analog logic gate or accumulator?

A type of ultra-low energy, non-volatile memory in which the position and number of atoms is interpreted as data, maybe? Costs energy to move or detect an atom, but unlike electronic memory, it costs nothing to maintain an atom's position, until you need to move it again (i.e. change the data value)...

Maybe I'm stretching too far, just throwing out ideas for possible applications...
MaxwellsDemon
not rated yet Dec 08, 2011
"Bones, are you picking up any life signs with your Tricorder?"
antialias_physorg
not rated yet Dec 08, 2011
A type of ultra-low energy, non-volatile memory in which the position and number of atoms is interpreted as data, maybe? Costs energy to move or detect an atom, but unlike electronic memory, it costs nothing to maintain an atom's position, until you need to move it again (i.e. change the data value)...

It's an interesting thought - but I think the mechanism to write a densely packed ROM array of this type would be extremely complex. Much worse if you actually want to do this rewriteable (RAM).

Then again: 500nm is huge by today's memory standards (and that's only diameter - the length of teh fiber is much longer).
While the polarization angle could be quantized to give you more than zero/one values (i.e. quantization by degree or even fractions of a degree) I think the space requirement is still much too big to compete with current flash/SSD technology.
Skylax123
not rated yet Dec 08, 2011
To the people here already seeing potential applications of this research as gas detectors or something like that, what they do here is laser cooling atoms to uK temperatures in order to trap them with extremely weak optical traps (optical lattice in nanofibre) in a ultrahigh vacuum environment (ca. 10^-10 mbar). Only a select few elements can be cooled this way and there will be no practical (as in everyday live) application of this in the near future or at all. It is a testbed for further understanding of quantum physics and quantum technologies.