Lens-less quantum ghost imaging: New two-photon experiments

New types of lens-less two-photon ghost imaging experiments are described that can also be useful for 3D X-ray imaging. In these experimental setups, a CCD array is placed facing a chaotic light source and gated by a photon counting detector that simply counts all randomly reflected photons from an object. A “ghost” image of the object is then observed from the gated CCD. A ghost image of an object can even be observed when the photon path to the photon counting device is obscured. These interesting demonstrations are not only useful for practical applications, such as X-ray lens-less imaging, but are also important from a fundamental point of view. These demonstrations lead to insight regarding the nonclassical two-photon interference nature of thermal light ghost imaging.     

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。     

QUANTUM INFORMATION Quantum imaging,quantum lithography and the uncertainty principle

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. The ‘ghost’ image experiment demonstrated the astonishing nonlocal behaviour of an entangled photon pair. Even though we still have questions with regard to fundamental issues of the entangled quantum systems, quantum entanglement has started to play an important role in practical applications. Quantum lithography is one of the hot topics. We have demonstrated a quantum lithography experiment recently, in which the experimental results have beaten the classical diffraction limit by a factor of two. This is a quantum mechanical two-photon phenomenon but not a violation of the uncertainty principle.     

Evolution process from ghost diffraction to ghost imaging in a lensless imaging system

Ghost diffraction and ghost imaging are investigated in a lensless imaging system. The evolution process from ghost diffraction to ghost imaging is discussed when the object is moved far away from the source in the test arm. The relation of ghost diffraction and imaging is also studied, and it is found that the visibility of ghost imaging is always better than that of ghost diffraction.     

Imaging through an aberrating medium with classical ghost diffraction

We describe a method for image transmission through an aberrating medium by means of a modified configuration for conventional ghost diffraction with classical incoherent beams. On the basis of optical coherence theory, we show that the effects of phase disturbances, be they deterministic or random, can be canceled out in our method and the squared modulus of the Fourier transform of the object is obtained in terms of intensity-correlation measurements. From the measurement data, the object can be reconstructed using standard phase retrieval algorithms.     

Towards time-efficient ghost imaging

Reducing the time necessary to acquire information is highly desirable in almost every context. Ghost imaging is no exception, which is very time consuming due to its scanning nature and low light levels innate to quantum experiments. This work aimed to reduce the time required to reconstruct the image whilst maintaining quality. In doing so, we followed two complementary approaches: one varying the experimental parameters, and another implementing computational processing. We defined a performance measure based on the image reconstruction time and its resemblance to the original object, and determined that the use of image processing and recognition algorithms offers major improvements in temporal efficiency. Importantly, if the main purpose of imaging is solely object recognition, low resolution mask patterns give better results, whereas higher resolution patterns yield better resolved images, at the expense of time. We believe this work will pique interest in the ghost and single-pixel imaging communities.     

Research on the Freezing Phenomenon of Quantum Correlation by Machine Learning

Quantum correlation shows a fascinating nature of quantum mechanics and plays an important role in some physics topics, especially in the field of quantum information. Quantum correlations of the composite system can be quantified by resorting to geometric or entropy methods, and all these quantification methods exhibit the peculiar freezing phenomenon. The challenge is to find the characteristics of the quantum states that generate the freezing phenomenon, rather than only study the conditions which generate this phenomenon under a certain quantum system. In essence, this is a classification problem. Machine learning has become an effective method for researchers to study classification and feature generation. In this work, we prove that the machine learning can solve the problem of X form quantum states, which is a problem of physical significance. Subsequently, we apply the density-based spatial clustering of applications with noise (DBSCAN) algorithm and the decision tree to divide quantum states into two different groups. Our goal is to classify the quantum correlations of quantum states into two classes: one is the quantum correlation with freezing phenomenon for both Rènyi discord (     

Computational ghost imaging for remote sensing

Computational ghost imaging is a structured-illumination active imager coupled with a single-pixel detector that has potential applications in remote sensing. Here we report on an architecture that acquires the two-dimensional spatial Fourier transform of the target object (which can be inverted to obtain a conventional image). We determine its image signature, resolution, and signal-to-noise ratio in the presence of practical constraints such as atmospheric turbulence, background radiation, and photodetector noise. We consider a bistatic imaging geometry and quantify the resolution impact of nonuniform Kolmogorov-spectrum turbulence along the propagation paths. We show that, in some cases, short-exposure intensity averaging can mitigate atmospheric-turbulence-induced resolution loss. Our analysis reveals some key performance differences between computational ghost imaging and conventional active imaging, and identifies scenarios in which theory predicts that the former will perform better than the latter.     

DQE measurement in a scintillating glass optical fiber detector for X-ray imaging

An example of the measurement of detective quantum efficiency is illustrated for a scintillating glass optical fiber detector used in X-ray imaging. We have shown the necessity to filter the input Poisson noise of the incoming beam, by the MTF (Modulation Transfer Function) of the detector, in order to obtain the real DQE (Detective Quantum Efficiency).     

Long-distance teleportation based on a selected receiver in a quantum network

Quantum networks are useful for global communication. A new multi-hop scheme of single unitary transformation method (SUTM) is proposed for long-distance teleportation of an unknown W state in a quantum network. All the measurement outcomes are sent to the selected receiver independently. The initial quantum state can be recovered by a corresponding local operation. The probability of successful teleportation can reach 1 without auxiliary particles. Our scheme is superior to the hop-by-hop method owing to lower delays.     

Perfect Quantum Teleportation via Bell States

Quantum mechanics shows superiority than classical mechanics in many aspects and quantum entanglement plays an essential role in information processing and some computational tasks such as quantum teleportation (QT). QT was proposed to transmit the unknown states, in which EPR pairs, the entangled states, can be used as quantum channels. In this paper, we present two simple schemes for teleporting a product state of two arbitrary single-particle and an arbitrary two-particle pure entangled state respectively. Alice and Bob have shared an entangle state. Two Bell states are used as quantum channels. Then after Alice measuring her qubits and informing Bob her measurement results, Bob can perfectly reconstruct the original state by performing corresponding unitary operators on his qubits. It shown that a product state of two arbitrary single-particle and an arbitrary two-particle pure entangled state can be teleported perfectly, i.e. the success probabilities of our schemes are both 1.     

Semiconductor quantum dots for in vivo imaging

Quantum dots play an important role in the in vitro, ex vivo, and in vivo optical imaging. Dramatic improvements have been achieved in the aspect of surface modification, biocompatibility, and targeting specificity, which had significant impact on the in vivo applications of quantum dots. This review summarizes the recent advances of quantum dots for in vivo imaging using both non-specific and targeted approaches. The toxicity of cadmium chalcogenide materials and alternative approaches such as the use of doped nanocrystal quantum dots were also discussed. The integration of quantum dots with other imaging techniques is also expected to give rise to a new generation of multifunctional probes for biomedical applications.     

Noise reduction from two frame speckle-shifting ghost images with morphology algorithms

Edge detection is the basis of image segmentation and object recognition, as edge generally contains important information of an object. In this paper, we propose a novel speckle-shifting ghost imaging (SSGI) method to extract the edge of an unknown object. In this method, the gradient operation is directly carried out to the illumination patterns rather than the captured object image. The structured patterns for illumination are only divided into two groups, which can extract the edge in all directions. The imaging result is clearer than the conventional SSGI, but the noise is still serious. To solve the problem, we further investigate a denoising method with morphology algorithms, such as frame difference and connected region labelling. Numerical simulations and experiments are carried out to verify the feasibility and effectiveness.     

基于量子关联的显微成像研究进展

简要回顾了量子关联成像的基本原理和发展历程,从量子光源和经典光源的角度详细介绍了量子关联成像在显微成像中的研究进展。做出了基于经典源的量子关联成像因易于实施、成本较低,在显微成像中更具应用前景的判断。     

Simultaneous multicolor imaging of five different lymphatic basins using quantum dots

Quantum dots can be used to perform multicolor images with high fluorescent intensity and are of a nanosize suitable for lymphatic imaging via direct interstitial injection. Here simultaneous multicolor in vivo wavelength-resolved spectral fluorescence lymphangiography is shown using five quantum dots with similar physical sizes but different emission spectra. This allows noninvasive and simultaneous visualization of five separate lymphatic flows draining and may have implications for predicting the route of cancer metastasis into the lymph nodes.     

Quantum state diffusion and time correlation functions

Abstract

In computing the spectra of quantum mechanical systems one encounters the Fourier transforms of time correlation functions, as given by the quantum regression theorem for systems described by master equations. Quantum state diffusion (QSD) gives a useful method of solving these problems by unravelling the master equation into stochastic trajectories; but there is no generally accepted definition of a time correlation function for a single QSD trajectory. In this paper we show how QSD can be used to calculate these spectra directly; by formally solving the equations which arise, we arrive at a natural definition for a two-time correlation function in QSD, which depends explicitly on the stochastic noise of the particular trajectory, and which agrees in the mean with the ensemble average definition of correlation functions.     

量子精密测量参数估计优化研究进展

量子精密测量是利用量子叠加与纠缠、量子相互作用过程与量子测量等方式增强参数估计精度与灵敏度的技术,是在短中期内最具前景的量子技术之一。本文从量子精密测量的最优化研究方案出发,通过对大量的相关文献进行梳理归纳,分析出量子精密测量三大优化方案：量子态制备与测量最优方案、量子演化过程调控方案与经典后处理优化方案,并对三个基本优化方案进行总结分析。同时介绍了国内外量子精密测量技术的最新理论与实验进展。最后,总结了量子精密测量存在的问题与挑战,并对未来工作进行了展望。     

Correlating electronic transport to atomic structures in self-assembled quantum wires

Quantum wires, as a smallest electronic conductor, are expected to be a fundamental component in all quantum architectures. The electronic conductance in quantum wires, however, is often dictated by structural instabilities and electron localization at the atomic scale. Here we report on the evolutions of electronic transport as a function of temperature and interwire coupling as the quantum wires of GdSi(2) are self-assembled on Si(100) wire-by-wire. The correlation between structure, electronic properties, and electronic transport are examined by combining nanotransport measurements, scanning tunneling microscopy, and density functional theory calculations. A metal-insulator transition is revealed in isolated nanowires, while a robust metallic state is obtained in wire bundles at low temperature. The atomic defects lead to electron localizations in isolated nanowire, and interwire coupling stabilizes the structure and promotes the metallic states in wire bundles. This illustrates how the conductance nature of a one-dimensional system can be dramatically modified by the environmental change on the atomic scale.     

Quantum Topological Boundary States in Quasi‐Crystals

Topological phases play a novel and fundamental role in matter and display extraordinary robustness to smooth changes in material parameters or disorder. A crossover between topological material and quantum information may lead to inherent fault‐tolerant quantum simulations and quantum computing. Quantum features may be preserved by being encoded among topological structures of physical evolution systems. This requires stimulation, manipulation, and observation of topological phenomena at the single quantum particle level, which has not, however, yet been realized. It is asked whether the quantum features of single photons can be preserved in topological structures. The boundary states are experimentally observed at the genuine single‐photon level and the performance of the topological phase is demonstrated to protect the quantum features against diffusion‐induced decoherence in coupled waveguides and noise decoherence from the ambient environment. Compatibility between macroscopic topological states and microscopic single photons in the ambient environment is thus confirmed, leading to a new avenue to “quantum topological photonics” and providing more new possibilities for quantum materials and quantum technologies.     

High-dynamic-range magnetometry with a single nuclear spin in diamond

Sensors based on the nitrogen-vacancy defect in diamond are being developed to measure weak magnetic and electric fields at the nanoscale. However, such sensors rely on measurements of a shift in the Lamor frequency of the defect, so an accumulation of quantum phase causes the measurement signal to exhibit a periodic modulation. This means that the measurement time is either restricted to half of one oscillation period, which limits accuracy, or that the magnetic field range must be known in advance. Moreover, the precision increases only slowly (as T(-0.5)) with measurement time T (ref.?3). Here, we implement a quantum phase estimation algorithm on a single nuclear spin in diamond to combine both high sensitivity and high dynamic range. By achieving a scaling of the precision with time to T(-0.85), we improve the sensitivity by a factor of 7.4 for an accessible field range of 16?mT, or, alternatively, we improve the dynamic range by a factor of 130 for a sensitivity of 2.5?μT?Hz(-1/2). Quantum phase estimation algorithms have also recently been implemented using a single electron spin in a nitrogen-vacancy centre. These methods are applicable to a variety of field detection schemes, and do not require quantum entanglement.