Precision estimation of source dimensions from higher-order intensity correlations

An important topic of interest in imaging is the construction of protocols that are not diffraction limited. This can be achieved in a variety of ways, including classical superresolution techniques or quantum entanglement-based protocols. Here, we consider superresolving imaging in the far field using higher-order intensity correlations. We show that third- and fourth-order correlations can improve upon the first- and second-order correlations that are traditionally used in classical optics and Hanbury Brown–Twiss-type experiments. The improvement is achieved entirely by post-processing of the data. As a demonstrator, we simulate the far field intensity distribution of a circular aperture that emits thermal light and use maximum likelihood estimation to determine the radius of the aperture. We compare the achieved precision to the Cramér-Rao lower bound and find that the variance of measurements for the third- and fourth-order correlation functions are indeed closer to the Cramér-Rao bound than that of the second-order correlation function. The method presented here is general, and can be used for all kinds of incoherent emitters, geometries, and types of noise.