基于质心法的高分辨率高探测效率N光子纠缠N00N态超分辨量子成像
As a breakthrough technology in recent years, super-resolution imaging has become an important research problem in computer vision and image processing and has wide practical applications in medical, biological, security, and other fields. However, classical imaging technology is limited by the diffraction resolution limit, and it is difficult to achieve resolution breakthroughs. Quantum entanglement can transcend diffraction resolution limits by sharpening spatial interference fringes based on quantum technology evolution . The entangled N00N state has been studied because it can exceed the standard quantum limit. The interference visibility of the three-photon N00N state is higher than the limit of classical spatial super-resolution, and the pattern of the N-photon entangled N00N state is N times finer than that of classical light. Thus, the N00N state can improve the resolution of the optical system by N times. However, the probability of all N photons arriving at the same location and the detection efficiency decreases exponentially with increasing N, making the advantages of the N00N state controversial. The optical centroid measurement (OCM) promotes the application of the N00N state in super-resolution imaging. This study further applies the advantages of N-photon entangled N00N state to super-resolution quantum imaging based on existing theories and technologies. This study further proposes a new quantum imaging system to improve the resolution of object imaging.
This study primarily adopts theoretical analysis and simulation methods. A simulation model based on the proposed quantum imaging system is created, and the resolution enhancement of our scheme is quantified by measuring the modulation transfer function (MTF). A photon source model is constructed to generate coherent photons that are irradiated onto the object and transmitted to the receiver. The centroid position of the photons is measured using the OCM method, and the point spread function (PSF) of the imaging system is calculated using the obtained simulation data. Finally, the MTF is obtained using the Fourier transform method. In addition to the theoretical analysis of the detection efficiency enhancement of N00N state by OCM, the advantages of OCM visibility are analyzed through simulation visibility. The data are obtained through model simulation, and the curve is fitted to the data point, following the visibility calculation and analysis using the fitted curve.
The model simulation of the proposed imaging system shows that the MTF curve decreases with the increase of spatial frequency. However, the entangled two-photon curve changes more gently than the spatially uncorrelated two-photon curve, indicating that the resolution of entangled two-photon imaging is better than that of uncorrelated two-photon imaging. Similarly, the presence of more entangled photons changes the curve at a slower pace. The resolution of
The quantum imaging system scheme presented in this study improves the detection efficiency of N00N state by means of optical centroid measurement, and exploits the N-photon entanglement of N00N state to realize super-resolution imaging of objects. OCM does not require all photons to reach the same point in space as compared to the N-photon absorption scheme. The resolution of any number of photons can be improved by photon counting and proper post-processing, which significantly improves the detection efficiency of N00N entangled states. Moreover, the visibility of the OCM signal in N00N state is almost independent of the change in photon number N; therefore, the imaging system is suitable for higher photon numbers. The super-resolution quantum imaging system based on N-photon entanglement overcomes the problem in effectively detecting N-photon states, which improves quantum-enhanced measurement. Moreover, it is significant for Heisenberg finite phase detection and the development of super-resolution quantum imaging. Theoretically, the system can enhance
1 引言
超分辨率成像作为近年来的突破性技术,是计算机视觉和图像处理领域中的重要研究内容,在医疗、生物、安防等领域中有着广泛的应用。但经典成像技术受制于衍射分辨极限,难以实现分辨率突破[1]。随着量子技术的不断发展,研究者利用量子纠缠实现了衍射分辨极限的突破[2]。其中,纠缠N00N态因可以突破标准量子极限而得到了广泛研究,通过模式
本文利用N光子纠缠实现了成像分辨率的增强,基于已有理论与技术进一步将N光子纠缠N00N态的优势应用到超分辨量子成像领域,设计了一种新的量子成像系统,该系统的成像分辨率可超越衍射分辨极限。利用OCM方法提升了N00N态的探测效率,当存在D个像素时,相较于N光子吸收方案[11],理论探测效率增加了
2 原理介绍
待成像物体可以用透射孔径函数
为了使成像系统传输小于PSF尺寸的物体特征,可用量子相关多光子态代替物平面上的经典场分布以构造显式状态。通过引入质心简化该状态的分析,质心位置(
式中:
这里将文献[15]中的理论拓展至N光子,得出N光子质心位置的分辨率损失(r)为
式中:
3 超分辨量子成像系统
本节将介绍所设计的一种量子成像系统,其将N00N态在超分辨量子成像方面的应用具体化。该系统包括激光器、N00N态制备模块、成像系统模块、处理模块和锁定测量模块,排布如
图 1. 量子成像系统示意图。(a)N00N态制备模块和待成像物体;(b)成像系统模块和处理模块;(c)锁定测量模块
Fig. 1. Schematics of quantum imaging system. (a) N00N state preparation module and object to be imaged; (b) imaging system module and processing module; (c) locking measurement module
3.1 N00N态制备
该模块结构如
上述激光透过HWP的角度可以根据实际需求进行设置,满足相位匹配条件即可。若PBS、50∶50分束器的放置角度发生变化,HWP的角度须相应改变。该系统的使用具有较大的灵活性,可选择实际所需波长的激光输入,使用相应的二向色镜、非线性晶体等器件,在满足生成N光子纠缠N00N态的条件下,确保成像分辨率的增加。
3.2 成像部分
完成N00N态的光子制备后,光通过待成像物体进入成像系统模块,依次经过透镜1、可调孔径和透镜2,最终由感光单元接收并检测,如
3.3 锁定测量
为了确保N00N态的形成与稳定,该系统还设置了锁定测量模块。通过状态准备PBS的另一个端口,向该模块发送少量的DC光和激光,产生反馈信号以进行“锁定测量”,结构如
N00N态的产生效率与光子数测量和质心确定相互关联,共同影响着N00N态的性质和应用效果。较高的产生效率可以提高N00N态的制备成功率,而准确地测量光子数并确定质心位置可以提供精确的光子信息。N00N态的产生效率越高,测量的光子数越多,能够提供更多的统计信息和更精确的分布信息,从而获得更多的有效事件以估计质心的位置,减小意外事件引起的不确定性。
4 实验仿真与结果分析
4.1 利用调制传递函数分析分辨率的增加
基于所提出的方案构建模型模拟成像系统,使用倾斜边缘标准测量调制传递函数(MTF),从而量化分辨率增加能力。构建光子源模型生成相干光子,照射物体后传输至接收器,用OCM方法测量光子的质心位置。利用所得模拟数据计算该成像系统的PSF,对其进行傅里叶变换得到MTF。
MTF曲线表示对比度变化程度与空间频率的关系,用于评价成像质量。
图 2. MTF曲线。(a)在非相关态和N00N态双光子的仿真曲线和理论分辨率增加曲线的对比;(b)二、四、八光子纠缠N00N态的分辨率增加对比
Fig. 2. MTF curves. (a) Comparison of simulation curves of two-photon in uncorrelated state and N00N state and theoretical resolution enhancement curve; (b) resolution enhancement comparison of two-, four- and eight-photon entangled N00N states
根据MTF的截止频率计算分辨率,结果如
表 1. 分辨率增加量的对比
Table 1. Comparison of resolution enhancement
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受实验条件、测量误差等的影响,真实实验时的参数无法与仿真所设置的参数完全相同,且受到环境等因素的影响,系统存在不确定性,故无法避免差异。仿真时尽可能采用类似于实验的条件以提高结果的可靠性。
4.2 OCM方法应用于N00N态实现的可见度提升
这里还通过仿真估计了不同光子数下的质心,从而计算可见度。利用多个单光子计数模块进行探测,通过模型仿真得到数据,将曲线拟合到数据点,计算可见度并进行分析。随着光子数的增加,经典光的可见度明显降低,三、四光子的可见度分别为
图 3. 经典光与N00N态纠缠光的质心测量结果。(a)三、(b)四光子经典光质心测量的结果;(c)三、(d)四光子N00N态下质心测量的结果;(e)可见度与光子数的关系
Fig. 3. Centroid measurement results of classical light and entangled light with N00N state. Centroid measurement results of (a) three- and (b) four-photon classical light; centroid measurement results under (c) three- and (d) four-photon N00N states; (e) relationship between visibility and photon number
这里通过测量N00N态的空间干涉模式计算所得的可见度与先前同类研究[4,22]的结果较为接近,该方法具备可靠性。提升可见度并保持其稳定性在成像中起到关键作用。将OCM方法运用于N00N态,可实现成像分辨率和可见度的提升,且随着光子数的增加,分辨率增加量进一步提升,同时能保持可见度相对恒定。由于具有超分辨率和高可见度,N00N态未来可能在成像领域和可视化领域中得到广泛的应用。
5 结论
设计了量子成像系统,通过光学质心测量方法提升了N00N态的探测效率,发挥了N光子纠缠N00N态的优势,实现了物体的超分辨率成像。与N光子吸收方案相比,OCM不需要所有光子到达空间中的同一点,通过光子计数和适当的后处理就可以实现任意数量光子下成像分辨率的提高,大大提升了N00N态的探测效率。N00N态的OCM信号的可见度几乎与光子数N无关,因此该成像系统适用于更高的光子数。基于N光子纠缠的超分辨量子成像系统克服了N00N态的探测效率随着纠缠光子数的增加而呈指数下降的问题,有利于量子增强测量,并对海森堡有限相位检测和超分辨率量子成像的发展具有重要意义。该系统的成像分辨率在理论上能达到(
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Article Outline
张黄杰, 陈晨远, 郝然, 占春连, 金尚忠, 张鹏举, 庄新港, 费丰. 基于质心法的高分辨率高探测效率N光子纠缠N00N态超分辨量子成像[J]. 中国激光, 2024, 51(6): 0612002. Huangjie Zhang, Chenyuan Chen, Ran Hao, Chunlian Zhan, Shangzhong Jin, Pengju Zhang, Xingang Zhuang, Feng Fei. Super‐resolution Quantum Imaging of N‐photon Entangled N00N State with High Resolution and High Detection Efficiency Based on Centroid Method[J]. Chinese Journal of Lasers, 2024, 51(6): 0612002.