24 May 2022

Nanoantennas target secure long distance quantum data networks

Researchers now have a means of using well-established nano-photonics to advance the prospects of upcoming quantum communication and information networks.

Classical computer information is based on simple on/off readouts – information storage and transfer in the manner of simple ones and zeros. But while it is straightforward to use a repeater to amplify and retransmit this information over long distances. this is insufficient for the quantum technologies under development.

By using abstract physics properties such as entanglement and superposition, quantum technology could provide unprecedented information security and data processing in the coming decades.

Quantum information is based on comparatively more complex and secure readouts, such as photon polarization and electron spin. Semiconductor nanoboxes known as quantum dots are materials that researchers have proposed for storing and transferring quantum information. However, quantum repeater technologies have some limitations, not least that current ways to convert photon-based information to electron-based information are highly inefficient.

Now, researchers from Osaka University in Japan have fabricated a nanoantenna that will help bring quantum information networks closer to practical use.

The transfer efficiency between quantum information carriers is improved, in a manner based on well-established nanoscience and which is compatible with upcoming advanced communication technologies.

The photon-to-electron conversion through a metal nanostructure is substantially enhanced, which is an important step forward in the development of advanced technologies for sharing and processing data.

“The efficiency of converting single photons into single electrons in gallium arsenide quantum dots — common materials in quantum communication research – is currently too low,” explains Rio Fukai. “Accordingly, we designed a nanoantenna – consisting of ultra-small concentric rings of gold — to focus light onto a single quantum dot, resulting in a voltage readout from our device.”

The researchers claim to have enhanced photon absorption by a factor of up to nine, compared with not using the nanoantenna. After illuminating a single quantum dot, most of the photogenerated electrons were not trapped there, and instead accumulated in impurities or other locations in the device. Nevertheless, these excess electrons gave a minimal voltage readout that was readily distinguished from that generated by the quantum dot electrons, and thus didn’t disrupt the device’s intended readout.

“Theoretical simulations indicate that we can improve the photon absorption by up to a factor of 25,” says Akira Oiwa. “Improving the alignment of the light source and more precisely fabricating the nanoantenna are ongoing research directions in our group.”