Quantum Holograms: Metasurfaces intertwin light and information with new research

Quantum entanglement is essentially a fundamental phenomenon and is one of the most interesting aspects of quantum mechanics. Because we explain the correlation between two particles, when we measure one property, no matter how far apart, the other particles are instantly revealed. This unique property is utilized in applications such as quantum computing and quantum communication.

A common method for generating entanglements is to use nonlinear crystals. Nonlinear crystals produce photon pairs with intertwined polarization via spontaneous parametric downconversion (SPDC). It is measured when one photon is polarized horizontally, the other is polarized vertically, and vice versa.

Meanwhile, Metasurfaces (Ultrathin optical devices) are known for their ability to encode vast amounts of information, allowing for the creation of high-resolution holograms. The combination of metasurfaces and nonlinear crystals allows researchers to explore promising approaches to enhance the generation and control of intertwined photon states.

In a recent study published in Advanced Photonics, researchers from Hong Kong and the UK have introduced a new approach to creating quantum holograms using metasurfaces. By carefully designing the orientation of the nanostructures within the metasurface, they have enabled the generation of quantum holograms in which polarized and holographic information are intertwined.

“We have demonstrated that metasurfaces act as a versatile platform for generating quantum holograms. The entanglement properties of these quantum holograms are further clarified by projecting one photon into various polarization states corresponding to interference effects observed elsewhere.”

This approach offers a compact yet flexible method that is difficult to achieve with traditional materials. To demonstrate, the researchers created four holographic characters, “H, “V”, “V”, “D”, “A” holographic characters that were caught in the polarization of the paired photons. By selecting different polarizer orientations for one photon, you can selectively erase specific characters in the hologram, and accurately control the intertwined holographic information.

Beyond basic importance, this study is also promising in practical applications such as quantum communication by encoding information in both letters and polarized states. “Using more complex entanglement patterns may help to increase the information capabilities of quantum key distributions, a secure way to communicate,” said Hong Liang, co-author of the study. “We believe this technology is suitable for everyday use, as metasurfaces can significantly reduce the size of quantum optical systems.”

Furthermore, researchers suggest that metasurfaces can be used in ingestion prevention techniques. Beyond the inherent challenge of replicating the metasurface itself, the complex relationships between letters and polarized states and relative phase profiles between different holograms create unique patterns that are very challenging to reproduce, and enhance security against forgery.

“Our demonstration can also be interpreted as a holographic-level quantum eraser. Compared to traditional double-slit quantum erasers, the setup replaces two slits with two holograms and retrieves “hologram information” from the polarization of intertwined photons. Co-author of the paper.

This study highlights how modern nanofabrication technologies can utilize quantum effects in real-world applications. Despite its ultra-thin nature, metasurfaces allow complex quantum operation that traditionally requires complex optical setups. This achievement not only deepens the collective understanding of quantum mechanics, but also provides further general insight into quantum information processing.