Quantum mechanically entangled light particles break down the boundaries of conventional optics and allow a glimpse into previously invisible wavelength ranges, thus bringing about new possibilities for imaging techniques, microscopy and spectroscopy. Unearthing these possibilities and creating technological solutions was the goal of the Fraunhofer lighthouse project QUILT, the results of which are now available.
Light can do some amazing things. For example, light particles (photons) be entangled upon creation, which connects them inextricably to one another in terms of their properties, not just across great distances, but also across different wavelength ranges. These entangled photons are the tools used by the Fraunhofer researchers in the project "QUILT—Quantum Methods for Advanced Imaging Solutions." They are using the photons to develop quantum optical solutions for wavelength ranges that have thus far proven to be virtually inaccessible. These wavelengths provide us with valuable information beyond the light of the visible spectrum: Short-wave ultraviolet radiation, for example, can be used to make the tiniest structures in cells visible. Infrared radiation provides information about noxious gases in the air or the composition of plastics, and long-wave terahertz radiation can be used to precisely determine the thickness of coating and paint layers. There is thus great potential in the fields of biomedical diagnostics, material testing or process and environmental analytics. The only issue is that creating and detecting these light waves requires significantly more resources than those used in imaging techniques for visible ranges.
For four years, teams of researchers from six Fraunhofer Institutes have been working with external organizations, supported by an advisory board with representatives from industry and science, to find ways of using the entangled photon pairs in different measurement methods in imaging, spectroscopy and metrology—making the invisible visible. The underlying principle is that while one photon has a wavelength that can be captured on camera, the other is designed to interact with the object under examination in the invisible range. The entanglement, dubbed by Einstein as "spooky action at a distance," means that the information gathered by the second photon is transferred to the first, making it visible to the camera.
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