Using Atoms to Turn Optical Nanofiber Guided Light On and Off

The rubidium atoms are trapped around the optical nanofiber and absorb light of wavelength 780 nm and 776 nm that has leaked out of the nanofiber. This effect can be used to create on/off switches. (Source: OIST)

The rubidium atoms are trapped around the optical nanofiber and absorb light of wavelength 780 nm and 776 nm that has leaked out of the nanofiber. This effect can be used to create on/off switches. (Source: OIST)

Binary code is the classical way of transferring information online. However, OIST researchers are exploring more efficient ways of transferring data, using the quantum properties of light and matter. They have managed to create an on/off switch based on the quantum characteristics of rubidium atoms in the presence of light of different wavelengths. This proof-of-concept system could be used as a building block in a quantum network, the future of our internet.

The OIST team’s experimental setup consists of two lasers that produce light at different wavelengths, an optical nanofiber used to guide light, and rubidium atoms trapped around it. The peculiarity of optical nanofibers is their super-thin diameter. For this study the diameter was 350 nanometers – this is even smaller than the wavelength of the light guided by the fiber. Some of the light, therefore, leaks outside the nanofiber and interacts with the rubidium atoms that are trapped around it. These atoms can function as a quantum node, a redistribution point of a network, the equivalent of today’s servers.

The off switch condition is obtained when only the laser producing 780 nm is on. In this case, at the point where light leaks outside of the optical nanofiber, the rubidium atoms absorb the maximum amount of light and almost no light can continue to pass along the fiber. In contrast, the switch is turned on when both 776 and 780 nm lights are present. In this situation, most of the light is transmitted through the optical nanofiber and the rubidium atoms absorb it only minimally.

Since the optical nanofiber is directly connected to a standard optical fiber, the light can, in principle, be transferred to another quantum system or node some distance away, in the same way you can send a message from your computer to that of your friend’s in another location.

“Using optical nanofibers would allow us to fully integrate our system with existing fiber-based communication networks. While the current work is far from being a practical solution to quantum information, it brings the notion of using atoms and light to develop real devices based on quantum mechanics ever closer to fulfillment”, explains Síle Nic Chormaic, professor at OIST.

While the experiment at OIST currently only generates zeros/off and ones/on consecutively, further exploitation of the quantum behavior of atoms should allow the research team to send light as a combination of “on” and “off” at the same time. In this way, in the future, quantum networks will be able to process more data simultaneously, increase efficiency of information transfer and also provide better cyber security.

“It has been very exciting to work with optical nanofibers which can guide light extremely efficiently even if their diameter is much smaller than the wavelength of light itself. These systems are sure to give us significant progress in quantum networks in the years to come,” enthuses Ravi Kumar, one of the authors of this study and a PhD student at University College Cork in Ireland, doing his research work at OIST. (Source: OIST)

Links: Okinawa Institute of Science and Technology (OIST) Graduate University • University College Cork

Reference: R. Kumar et al.: Multi-level cascaded electromagnetically induced transparency in cold atoms using an optical nanofibre interface, New Journal of Physics, 7 (2015)

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