A novel layered crystal material has been developed by researchers at CDE that could offer a significant step forward in the development of efficient, ultracompact optical microchips.
Such microchips are seen as critical to the future development of advanced, ultra-powerful optical quantum computers that use photons - i.e. particles of light - rather than electrons to carry out computational processes and solve problems many thousands of times faster than is currently possible.
The crystal material, niobium oxide dichloride (NbOCl2), is a so-called two-dimensional material that the researchers say demonstrates the specific light response properties needed to power optical quantum information processing.
Moreover, the researchers say that stacking the thin crystal material in layers significantly enhances its interaction with light - merging two low-energy photons into one high-energy photon or splitting one high-energy photon into two low-energy photons.
In contrast, other layered crystals that have been used previously usually see a reduction in their interaction with light when stacked.
The research was led by Dr. Qiangbing Guo and Associate Professor Cheng-Wei Qiu (Electrical and Computer Engineering); Professor Stephen J. Pennycook (Materials Science and Engineering); with Professor Andrew T. S. Wee (NUS Physics) and collaborators at University of Science and Technology of China.
The team's findings were published recently in the journal Nature.
Optical quantum technologies make use of a strange phenomenon known as entanglement - specifically using pairs of entangled photons to carry out computational processes.
A key step in developing and miniaturising the required optical microchips is to develop an ultra-compact method for generating these entangled photons.
An optical process known as spontaneous parametric down-conversion (SPDC) is used to split a high-energy photon into a pair of low-energy photons that are entangled with each other. The challenge has been finding a material that performs the SPDC process to the necessary specifications at the miniaturised, ultrathin scale that is needed to make optical microchips practical.
Previously, the process has been achieved using so-called bulky nonlinear crystals such as lithium niobate (LiNbO3) and barium borate (BBO). However, these crystals have very low efficiency in the SPDC process (thus a large crystal size is needed), and they can't be easily integrated onto chips, which makes them impractical for use in optical microchips.
The team says the NbOCl2 material, also discovered to be a nonlinear crystal, is different from previously used nonlinear materials because it has significantly higher SPDC efficiency and can be easily integrated onto microchips as it has a layered structure.
"Our experiments have shown that NbOCl2 crystals permit the SPDC process and retain their efficiency at a miniaturised scale - making it, to our knowledge, the world's thinnest nonlinear quantum light source," said Dr. Guo.
Building an efficient, miniaturised optical microchip is a critical step in developing optical quantum computers, which will greatly accelerate the progress of optical quantum information technologies.
Researchers say such computers will be able to run large and complex calculations at ultra-fast speeds, delivering enormous computational power and solving problems that cannot be tackled even by today's most powerful current supercomputers.
"With further refinements of the device structure, we expect to see even better performance for constructing ultracompact on-chip SPDC sources," said Prof. Qiu.
