When single- or pair-photon packets are created by spontaneous wave mixing, their properties are determined by the dispersive properties of the devices used. By spatially modulating the refractive index, desirable properties can be achieved.
We show several quantum-sensing experimental realizations dedicated to the qualification of optical-material key-properties, such as chromatic dispersion and refractive index variations. More specifically, the material under test (typically, an optical fibre or a nonlinear crystal) is introduced in one of the two arms or in the loop of interferometric devices, mainly in Mach-Zehnder and Sagnac configurations. Probing such devices using peculiar quantum, or quantum-mimicking, photonic states creates material-under-test-dependent relative-phase differences that are imprinted on the established coherent superposition. Here, the employed photonic states exhibit specific modal structures, in the frequency and/or spatial domains, that exploit or mimic quantum entanglement, providing access to the relative phases and to the optical properties under investigation. Associated measurement results show unprecedented precision and/or accuracy, reduced overhead, and otherwise unreachable stability and repeatability. Such quantum interferometric methods pave the way to redefining the very way optical materials are characterized, finding repercussion in various fields ranging from fundamental optics to industry-grade developments.
We experimentally control the spectral structure of photon pairs created via spontaneous four-wave mixing in microstructured fibers. By fabricating fibers with designed dispersion, one can manipulate the photons' wavelengths, joint spectrum, and, thus, entanglement. As an example, we produce photon pairs with no spectral correlations, allowing direct heralding of single photons in pure-state wave packets without filtering. We achieve an experimental purity of (85.9+/-1.6)%, while theoretical analysis and preliminary tests suggest that 94.5% purity is possible with a much longer fiber.
Atoms excited to Rydberg states can be used to enhance the nonlinearity of medium via electromagnetic induced transparency (EIT) due to their special property. In this letter, focusing on a Rydberg medium with strong nonlinearity, we investigate the space imaging characteristics of generating Rydberg EIT-assisted six-wave mixing in a K-type five-level atomic system. Rydberg spatial image variation regularity modulated by an optical field was obtained. This study on the regulation of image variation was able to establish a relation between the refractive index of the Rydberg medium and optical field, which will not only expand research on Rydberg space optical phenomena but can also provide the basis for advanced designs that are highly dependent on the refractive index materials. More importantly, these results have research value in the field of optical information processing.