Nav: Home

Nanoscale one-way-street for light

December 14, 2015

If light is able to propagate from left to right, the opposite direction is usually allowed as well. A beam of light can normally be sent back to its point of origin, just by reflecting it on a mirror. Researchers at TU Wien have developed a new device for breaking this rule. Just like in an electrical diode, which allows current to pass only in one direction, this glass fibre-based device transmits light only in one direction. The one-way-rule holds even if the pulse of light that passes through the fibre consists of only a few photons. Such a one-way-street for light can now be used for optical chips and may thus become important for optical signal processing.

Optical Signal Processing Instead of Electronics

Elements which allow light to pass in only one direction are called "optical isolators". "In principle, such components have been around for a long time", says Arno Rauschenbeutel, from the Vienna Center for Quantum Science and Technology at the Atominstitut at TU Wien. "Most optical isolators, however, are based on the Faraday effect: A strong magnetic field is applied to a transparent material between two crossed polarization filters. The direction of the magnetic field then determines the direction in which light is allowed to pass."

For technical reasons, devices using the Faraday effect cannot be constructed at the nanoscale - an unfortunate fact, because this would have many interesting applications. "Today, researchers seek to build optical integrated circuits, similar to their electronic counterparts", says Rauschenbeutel. Other methods for breaking this symmetry only work at very high intensities. But in nanotechnology, an ultimate goal is to work with extremely faint light signals, which may even consist of individual photons.

Glass Fibres and Atoms

Arno Rauschenbeutel's team chose a completely different approach: Alkali atoms were coupled to the light field of an ultrathin glass fibre. In a glass fibre, the light can propagate forwards or backwards. There is, however, another property of light which has to be taken into account: the direction of oscillation of the light wave, also called the polarization.

The interaction of light and the glass fibre modifies the oscillation state of the light. "The polarization rotates, much like a helicopter's rotor", says Arno Rauschenbeutel. The sense of rotation depends on whether the light travels forwards or backwards. In one case, the light wave oscillates clockwise and in the other, counterclockwise. The direction of propagation and the state of oscillation of the light wave are locked to each other.

If the alkali atoms are prepared in the right quantum state and coupled to the light in the ultrathin glass fibre, it is possible to make them react differently to the two senses of light rotation. "The light in the forward direction is not affected by the atoms. However, light which travels backwards and consequently rotates the other way around, couples to the alkali atoms and is scattered out of the glass fibre", says Arno Rauschenbeutel.

The Atomic State as a Quantum Switch

This effect has been demonstrated in two different ways at TU Wien: In the first approach, about 30 atoms were placed along the glass fibre. Upon sending in light, a high transmission of almost 80% was measured for one propagation direction while it was ten times less in the other direction. In the second approach, only a single rubidium atom was used. In this case, the light was temporarily stored in an optical microresonator, so that it could interact with the atom for a relatively long time. This way, similar control over the transmission could be achieved.

"When we only use one single atom, we have a much more subtle control over the process", says Rauschenbeutel. "One can prepare the atom in a quantum superposition of the two possible states, so that it blocks the light and lets it pass at the same time." According to classical physics, this would be impossible, but quantum physics allows such combinations. This would open the door to new, exciting possibilities for optical processing of quantum information.
-end-
Original paper: http://journals.aps.org/prx/abstract/10.1103/PhysRevX.5.041036

Further information:

Prof. Arno Rauschenbeutel
Institute for Atomic and Subatomic Physics
TU Wien
Stadionallee 2, 1020 Vienna
T: +43-1-58801-141761
arno.rauschenbeutel@tuwien.ac.at

Vienna University of Technology

Related Magnetic Field Articles:

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.
Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.
Adhesive which debonds in magnetic field could reduce landfill waste
Researchers at the University of Sussex have developed a glue which can unstick when placed in a magnetic field, meaning products otherwise destined for landfill, could now be dismantled and recycled at the end of their life.
Earth's last magnetic field reversal took far longer than once thought
Every several hundred thousand years or so, Earth's magnetic field dramatically shifts and reverses its polarity.
A new rare metals alloy can change shape in the magnetic field
Scientists developed multifunctional metal alloys that emit and absorb heat at the same time and change their size and volume under the influence of a magnetic field.
Physicists studied the influence of magnetic field on thin film structures
A team of scientists from Immanuel Kant Baltic Federal University together with their colleagues from Russia, Japan, and Australia studied the influence of inhomogeneity of magnetic field applied during the fabrication process of thin-film structures made from nickel-iron and iridium-manganese alloys, on their properties.
'Magnetic topological insulator' makes its own magnetic field
A team of U.S. and Korean physicists has found the first evidence of a two-dimensional material that can become a magnetic topological insulator even when it is not placed in a magnetic field.
Scientists develop a new way to remotely measure Earth's magnetic field
By zapping a layer of meteor residue in the atmosphere with ground-based lasers, scientists in the US, Canada and Europe get a new view of Earth's magnetic field.
Magnetic field milestone
Physicists from the Institute for Solid State Physics at the University of Tokyo have generated the strongest controllable magnetic field ever produced.
New world record magnetic field
Scientists at the University of Tokyo have recorded the largest magnetic field ever generated indoors -- a whopping 1,200 tesla, as measured in the standard units of magnetic field strength.
More Magnetic Field News and Magnetic Field Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Uncharted
There's so much we've yet to explore–from outer space to the deep ocean to our own brains. This hour, Manoush goes on a journey through those uncharted places, led by TED Science Curator David Biello.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 1: Numbers
In a recent Radiolab group huddle, with coronavirus unraveling around us, the team found themselves grappling with all the numbers connected to COVID-19. Our new found 6 foot bubbles of personal space. Three percent mortality rate (or 1, or 2, or 4). 7,000 cases (now, much much more). So in the wake of that meeting, we reflect on the onslaught of numbers - what they reveal, and what they hide.  Support Radiolab today at Radiolab.org/donate.