Researchers led by physicist F.J. “Frank” Duarte — credited with the 1993 invention of the N-slit laser interferometer — have designed practical N-slit quantum interferometers in the nanometer domain. The work, which the researchers said marks the first development of such quantum interferometers for operation at nanometer dimensions, charts a course for the development of quantum interferometers capable of differentiating spatial features down at femtometer-range precision. Beyond signaling forthcoming advancements in practical instrumentation, Duarte said, the physics of the work indicates the theoretical limitlessness in improving the design precision of quantum interferometers, due to the availability of increasingly diminishing wavelengths. According to Duarte, both the design and physics for the developed quantum interferometers are based on the Dirac-Feynman interferometric principle. This principle describes N-slit interferometry using superposition probability amplitudes. The technique of N-slit interferometry builds on the measurement aspect of the classic double-slit experiment. In this experiment, a light beam shone through a pair of slits yields an interference pattern displayed on a screen that is positioned behind the light source and beam. By pairing beam expanders to illuminate a grating (N-slit) and a photodetector, these N-slit interferometers rely on the illumination of the N-slit to deliver a signal that can be optically measured. Additional optical components can be added to the interferometric setup, to support N-slit interferometric microscopy, for example. The system can also be used on its own. N-slit laser interferometers, or N-slit coherent interferometers, were introduced for metrology applications characterizing micro- and nanostructures, particularly of imaging and photographic films. Though they have since been deployed for space-to-space and other communications, practical test and measurement in nanometer dimensions have remained a challenge. “N-slit interferometers in the micrometer domain are within reach of present technology using x-ray laser illumination,” Duarte told Photonics Media. Still, he said, these micro-interferometers, which demonstrate an intra interferometric path of 30 μ, can be used to do metrology in the nanometer domain. “N-slit interferometers in the nanometer domain are somewhat outside the reach of present day technology and utilize gamma-ray illumination,” Duarte said. “These nanometer interferometers have an intra interferometric path of 7.5 nm and can be used to do metrology in the femtometer domain.” “Recently, these N-slit coherent interferometers have been succinctly mentioned in nanometer dimensions whilst considering γ-ray illumination,” the researchers said. Now, they said, the recent work uses probability calculations to show that practical quantum interferometers can be used to determine the diameter of fibers from the nanometer to the femtometer domain. The researchers indicated that currently, the resolution of state-of-the-art commercial optical microscopes is in the tens of nanometers range, whereas commercial electron microscopes extend down to a few nanometers. “Here, we quantify, via interferometric calculations, resolutions down to the 1-nm regime, using x-ray illumination, and down to the 100-fm range under γ-ray illumination,” the researchers said. The research was published in Applied Physics B (www.doi.org/10.1007/s00340-023-08021-y).