Holographic Technique Can Encode Information at Nanoscale

Researchers at École Polytechnique Fédérale de Lausanne (ÉPFL) have developed a method to see how light behaves on the nanoscale, well beyond wavelength limitations. When the method is used with an ultrafast electron microscope, it can encode quantum information in a holographic light pattern trapped in a nanostructure.

The new technique is based on an exotic aspect of electron and light interaction. The researchers used freely propagating electrons as their photographic media. They used the quantum nature of the electron-light interaction to separate the electron-reference and electron-imaging beams in energy instead of space. This made it possible to use light pulses to encrypt information on the electron wave function, which could then be mapped with ultrafast transmission electron microscopy.

According to the researchers, the new method offers two potential benefits: First, it provides additional information on how light behaves, making it a useful tool for imaging electromagnetic fields with attosecond and nanometer precision in time and space. Second, the method can be used in quantum computing applications to manipulate the quantum properties of free electrons.

“Conventional holography can extract 3D information by measuring the difference in distance that light travels from different parts of the object,” professor Fabrizio Carbone said. “But this needs an additional reference beam from a different direction to measure the interference between the two. The concept is the same with electrons, but we can now get higher spatial resolution due to their much shorter wavelength. For example, we were able to record holographic movies of quickly moving objects by using ultrashort electron pulses to form the holograms.”

The research team said its new technique has the highest spatial resolution compared to alternatives. “So far, science and technology have been limited to freely propagating photons, used in macroscopic optical devices,” Carbone said. “Our new technique allows us to see what happens with light at the nanoscale, the first step for miniaturization and integration of light devices onto integrated circuits.”

Recording the phase of light scattered by an object allows retrieval of the object’s full 3D shape. This is the basis of optical holography. However, the spatial resolution of the photo/hologram has, until now, been limited by the wavelength of light, which is around or just below 1 μm. The ÉPFL team showed that holograms of local electromagnetic fields could be obtained with combined attosecond/nanometer resolution in an ultrafast transmission electron microscope. Beyond imaging applications, the ÉPFL approach could allow the implementation of quantum measurements in parallel, providing an efficient tool for electron quantum optics.

The research was published in Science Advances (https://advances.sciencemag.org/content/5/5/eaav8358).

ÉPFL physicists have developed a method based on the principles of holograms to capture 3D images of objects beyond the reach of light. Courtesy of F. Carbone/ÉPFL.