Super resolution with superposition

Optical imaging and lithography, the processes in which spatial patterns are resolved or transferred onto a detector or substrate via photons, cannot produce spatial features that are much smaller than the wavelength of light. This limitation has its roots in classical diffraction [1], which had been considered as a fundamental limit to all such imaging systems. Most notably, computer chip manufacturers have been moving to evershorter wavelengths and thus need to solve the challenges associated with use of extreme ultraviolet light. These include the lack of cheaply available optical elements that operate at such short wavelengths, and the damaging effects such high-energy photons have on the imaging elements and the photoresist. Nearly ten years ago, a quantum optical approach to imaging—quantum imaging, which uses path-entangled states—was suggested as a solution for this requirement of ever-shorter wavelengths and a way to beat the classical limit [2]. This turned out to be easier said than done. While quantum lithography is viewed as one of the “killer apps” for the nascent field of quantum imaging, the bugaboo in its implementation has been the continued lack of the right kind of multiphoton photoresists that would operate at the low flux levels required for a real proof-of-principle experiment.