Cloaking and illusion of quantum imaging with entangled photon pairs

Quantum ghost imaging is a nonlocal imaging technique in which the image or diffraction pattern of an object illuminated by photon pairs can be observed through the correlation measurement. This study theoretically demonstrates the cloaking effect of such a quantum imaging. Quantum ghost imaging completely offsets two objects that are placed at proper positions in the interferometer. Furthermore, illusion of quantum imaging, where an object transforms into another object, has also been observed. This phenomenon can be understood by quantum interferences in the correlation measurement.     

太赫兹波计算鬼成像:原理和展望

本文立足于太赫兹波成像领域近年来备受关注的研究热点—太赫兹波计算鬼成像,首先回顾了鬼成像从量子到经典再到计算的历史过程,然后阐述了计算鬼成像的数学原理,随后综述了计算鬼成像在太赫兹波段的发展历程,及其在超衍射分辨成像、石墨烯光电导成像、太赫兹光谱成像等方面的应用,并在最后展望了太赫兹波计算鬼成像的发展前景:计算鬼成像作为一种成像手段,可以绕开在太赫兹频段缺乏经济高效的焦面阵列式探测器的难题,但目前的成像帧率还难以满足快速成像的应用需求,相信在未来随着器件性能的提升和成像算法的优化,其成像帧率可以得到大幅提升。     

Two-wavelength ghost imaging with two-lens system in atmosphere

Based on the extended Huygens–Fresnel principle and the propagation law of a real ABCD optical system in turbulent atmosphere, an expression for two-wavelength ghost imaging with two-lens system is derived and the numerical simulations are made. The results show that the two-lens system can remarkably improve the image for a long propagation distance. The influence of the turbulence strength, the parameters of the radiation source and the focal length of the lenses on the image quality are discussed in detail.     

Multi-receivers and sparse-pixel pseudo-thermal light source for compressive ghost imaging against turbulence

For remote sensing with computational ghost imaging, the atmospheric turbulence will influence much on the performance since the transmitted patterns from the pseudo-thermal source will be distorted. As the distribution of refractive index on the propagation path varies with time, reducing the time consumption of data acquisition will be an effective way for mitigating the influence. We propose using fewer pixels of spatial light modulator to increase the modulation rate of the pseudo-thermal source, with the positions of pixels being randomly distributed. Multi-bucket detectors are employed for further reducing of the data acquisition time. The sparse recovery algorithm from compressed sensing is employed to enhance the quality of image. The performance of this system is demonstrated by comprehensive numerical analyses.     

Engineering the spectral and temporal properties of a GHz-bandwidth heralded single-photon source interfaced with an on-demand,broadband quantum memory

Photonics offers a route to fast and distributed quantum computing in ambient conditions, provided that photon sources and logic gates can be operated deterministically. Quantum memories, capable of storing and re-emitting photons on demand, enable quasi-deterministic operations by synchronizing stochastic events. Interfaced source–memory systems are thus a key building block in photonics-based quantum information processors. We discuss the design of the single-photon source in this type of light–matter interface and present an experimental system based on a Raman-type quantum memory. In addition to the spectral purity of the produced heralded single photons, we find that their temporal distinguishability also becomes important due to the implicit temporal binning derived from photon storage in the memory. When aiming to operate the source–memory system at high repetition rates, a practical compromise between both of these requirements needs to be found. Our implemented photon source system demonstrates such a solution and enables passive stability, high brightness in a single-pass configuration, high purity as well as good mode matching to our Raman memory.     

Optical watermark scheme based on singular value decomposition ghost imaging and particle swarm optimization algorithm

An optical image watermarking algorithm, based on singular value decomposition (SVD) ghost imaging and multiple transforms, is designed. The watermark image is first encrypted by applying an SVD ghost imaging system, then the encrypted watermark is embedded into the cover image with the help of multiple transforms, including lifting wavelet transform (LWT), discrete cosine transform (DCT), discrete fractional angular transform (DFAT) and SVD. Four sub-band images are produced from the host image by LWT and DCT. The improved DFAT, whose scaling factors and parameter are optimized by particle swarm optimization algorithm, is operated in the new matrix. Afterwards, SVD is executed in the two-part image and the encrypted watermark is embedded in the host image by mutual operation of different matrices. Simulation results validate that the proposed watermark scheme is superior in the aspects of security, robustness and imperceptibility.     

Optical asymmetric cryptosystem based on photon counting and phase-truncated Fresnel transforms

We propose a novel optical asymmetric cryptosystem combining the photon counting imaging with phase-truncated Fresnel transform, which can be used for complete information retrieval and authentication verification. The proposed combination overcomes the weakness of photon counting-based double random phase-encoding scheme. For retrieval of original image for authentication, the reverse process of phase truncation approach is followed and a nonlinear correlation filter is used. The complete information retrieval and authentication verification are possible provided sufficient number of photons is available. To check the robustness of the proposed scheme, attack analysis has been carried out. The simulation results are presented to demonstrate the proposed idea.     

随机调相连续信号的模糊函数特性及在医学超声成像上的应用前景探讨

传统的脉冲式医用超声成像系统的模糊函数由于存在周期性的速度模糊和距离模糊，影响了图像的质量和分辨力。本文借鉴噪声雷达理论，证明了随机调相连续波信号具有最优的模糊函数特性，并据此提出了随机调相医用超声成像系统的设计思想。这一思想的提出为克服速度模糊和距离模糊，提高图像质量和分辨力，设计新一代医用超声成像系统提供理论依据。     

A strategy for simultaneously realizing the cubic-to-hexagonal phase transition and controlling the small size of NaYF4:Yb3+,Er3+ nanocrystals for in vitro cell imaging

Hexagonal-phase NaYF(4):Yb(3+),Er(3+) up-conversion nanocrystals (UCNCs) are synthesized by a combination of refluxing and hydrothermal treatment. This strategy leads to only a slight increase in particle size, from 4.5 to ca. 10 nm, during the cubic-to-hexagonal phase transition. The hexagonal UCNCs can be internalized by HeLa cells and exhibit visible emission in the cells under near-infrared excitation.