KEYWORDS: Quantum limits, Quantum imaging, Partial coherence, Quantum coherence, Point spread functions, Super resolution, Quantum sources, Quantum Fisher information, Image resolution, Signal to noise ratio
We discuss the quantum-limited resolution of two partially coherent point sources. By establishing the Cramér-Rao bound for measuring the transverse separation of the sources, we show that the precision limit for resolving two points can be greatly improved in the sub-Rayleigh region. Here, we use a Digital Micromirror Devices (DMD) to demonstrate a new measurement scheme called spatial-mode demultiplexing (SPADE), which projects the input light field into different spatial modes. By analyzing the noise model of EMCCD, we measure the intensity of different modes of HG and estimate the separation between two partially coherent sources. Compared with direct imaging, our implementation of SPADE can surpass the Rayleigh limit and approach the quantum limit given by Quantum Fisher Information (QFI) over a range. Our result provides a new vision for super-resolution imaging. It is of great potential in imaging fields such as optical astronomy and fluorescence microscopy.
We report on numerical analysis of the conversion efficiency under different pumping conditions in the nonlinear frequency upconversion system, the influence of initial frequency chirp is also discussed in detail. Our results demonstrate that the wave peak is proportional to the amplitude parameter U. In addition, the positive chirp is conducive to spectrum broadening, while the negative chirp does the opposite. These numerical investigation will be meaningful for further improving the conversion efficiency and provide some reference for quantum communications and quantum manipulation in the single-photon frequency upconversion process.
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