arXiv subjects

Jun Xin

Publications and source records attributed to Jun Xin.

4 recordsLinked to original sources

arXiv2026

Approaching quantum limits in sub-Rayleigh resolution using phase modulation optimization

Spatial-mode demultiplexing (SPADE) has made significant progress in incoherent optical imaging and has been implemented through various experimental approaches. Holography-based SPADE is widely used in proof-of-principle experiments because of its low cost, stable optical arrangement, and ease of implementation. However, its low photon utilization severely limits its practical applications. Alternating Fourier transforms and phase modulations can implement unitary optical transformations. Building on this idea, we use backpropagation to optimize the phase profiles of spatial light modulators (SLMs) and thereby design quantum measurements that are efficient in both information and energy. We study centroid--separation estimation for two incoherent point sources, using Fisher information or the estimation errors of an auxiliary neural network estimator as optimization objectives. As the number of SLMs increases, the optimized measurements approach the quantum limits characterized by the quantum Cramér-Rao bound and the information-regret tradeoff relation. With a few SLMs, our method can outperform direct imaging, showing its potential for superresolution imaging.

quant-ph↗

arXiv2026

Noise-robust discrimination of incoherent point sources with spatial-mode demultiplexing

We theoretically predict and experimentally demonstrate that a reduced spatial-mode demultiplexing (SPADE) measurement using only the two lowest-order Hermite-Gaussian modes exhibits remarkable robustness against background noise in discriminating between a single source and two incoherent point sources. We establish a theoretical framework incorporating uniform background noise and derive an analytical Chernoff exponent expression, showing that SPADE consistently outperforms direct imaging (DI) across all source separations. Experimental results confirm that SPADE-based hypothesis testing approaches the quantum limit even when the background-to-signal photon ratio per pixel is 0.11. This advantage stems from SPADE's ability to concentrate source information into minimal detection modes, reducing the cumulative background noise impact. Our findings provide a practical detection scheme for applications where background noise is inevitable, such as astronomical observations and quantum sensing.

quant-ph↗

arXiv2025

Measuring the Oscillation Frequency Beyond the Diffraction Limit

High-resolution array detectors are widely used in single-particle tracking, but their performance is limited by excess noise from background light and dark current. As pixel resolution increases, the diminished signal per pixel exacerbates susceptibility to noise, degrading tracking accuracy. To overcome this limitation, we use spatial-mode demultiplexing (SPADE) as a noise-robust approach for estimating the motion characteristics of an optical point-like source. We show that SPADE efficiently concentrate the information into a few key spatial modes, drastically reducing the number of detectors while maintaining high estimation precision. Furthermore, we enhance the robustness of the estimation against excess noise by elaborately designing the modes to be decomposed. We demonstrate, both theoretically and experimentally, that a SPADE with two specific modes outperforms direct imaging in estimating the micro-oscillation frequency of an optical point source in the presence of excess noise.

quant-ph↗

arXiv2023

All-optical correlated noisy channel and its application in recovering quantum coherence

Attenuation and amplification are the most common processes for optical communications. Amplification can be used to compensate the attenuation of the complex amplitude of an optical field, but is unable to recover the coherence lost, provided that the attenuation channel and the amplification channel are independent. In this work, we show that the quantum coherence of an optical filed can be regained if the attenuation channel and the amplification channel share correlated noise. We propose an all-optical correlated noisy channel relying on four-wave mixing process and demonstrate its capability of recovering quantum coherence within continuous-variable systems. We quantitatively investigate the coherence recovery phenomena for coherent states and two-mode squeezed states. Moreover, we analyze the effect of other photon losses that are independent with the recovery channel on the performance of recovering coherence. Different from correlated noisy channels previously proposed based on electro-optic conversions, the correlated noisy channel in our protocol is all-optical and thus owns larger operational bandwidths.

quant-ph↗