Ghost Interference Research Articles

Environment-aware Multi-person Tracking in Indoor Environments with MmWave Radars

Device-free indoor localization and tracking using commercial millimeter wave radars have attracted much interest lately due to their non-intrusive nature and high spatial resolution. However, it is challenging to achieve high tracking accuracy due to rich multipath reflection and occlusion in indoor environments. Static objects with non-negligible reflectance of mmWave signals interact with moving human subjects and generate time-varying multipath ghosts and shadow ghosts, which can be easily confused as real subjects. To characterize the complex interactions, we first develop a geometric model that estimates the location of multipath ghosts given the locations of humans and static reflectors. Based on this model, the locations of static reflectors that form a reflection map are automatically estimated from received radar signals as a single person traverses the environment along arbitrary trajectories. The reflection map allows for the elimination of multipath and shadow ghost interference as well as the augmentation of weakly reflected human subjects in occluded areas. The proposed environment-aware multi-person tracking system can generate reflection maps with a mean error of 15.5cm and a 90-percentile error of 30.3cm, and achieve multi-person tracking accuracy with a mean error of 8.6cm and a 90-percentile error of 17.5cm, in four representative indoor spaces with diverse subjects using a single mmWave radar.

DSPose: Dual-Space-Driven Keypoint Topology Modeling for Human Pose Estimation.

Human pose estimation is the basis of many downstream tasks, such as motor intervention, behavior understanding, and human-computer interaction. The existing human pose estimation methods rely too much on the similarity of keypoints at the image feature level, which is vulnerable to three problems: object occlusion, keypoints ghost, and neighbor pose interference. We propose a dual-space-driven topology model for the human pose estimation task. Firstly, the model extracts relatively accurate keypoints features through a Transformer-based feature extraction method. Then, the correlation of keypoints in the physical space is introduced to alleviate the error localization problem caused by excessive dependence on the feature-level representation of the model. Finally, through the graph convolutional neural network, the spatial correlation of keypoints and the feature correlation are effectively fused to obtain more accurate human pose estimation results. The experimental results on real datasets also further verify the effectiveness of our proposed model.

Frequency Comb-Based Ground-Penetrating Bioradar: System Implementation and Signal Processing.

Radars can be used as sensors to detect the breathing of victims trapped under layers of building materials in catastrophes like earthquakes or gas explosions. In this contribution, we present the implementation of a novel frequency comb continuous wave (FCCW) bioradar module using a commercial software-defined radio (SDR). The FCCW radar transmits multiple equally spaced frequency components simultaneously. The data acquisition of the received combs is frequency domain-based. Hence, it does not require synchronization between the transmit and receive channels, as time domain-based broadband radars, such as ultra wideband (UWB) pulse radar and frequency-modulated CW (FMCW) radar, do. Since a frequency comb has an instantaneous wide bandwidth, the effective scan rate is much higher than that of a step frequency CW (SFCW) radar. This FCCW radar is particularly suitable for small motion detection. Using inverse fast Fourier transform (IFFT), we can decompose the received frequency comb into different ranges and remove ghost signals and interference of further range intervals. The frequency comb we use in this report has a bandwidth of only 60 MHz, resulting in a range resolution of up to 2.5 m, much larger than respiration-induced chest wall motions. However, we demonstrate that in the centimeter range, motions can be detected and evaluated by processing the received comb signals. We want to integrate the bioradar into an unmanned aircraft system for fast and safe search and rescue operations. As a trade-off between ground penetrability and the size and weight of the antenna and the radar module, we use 1.3 GHz as the center frequency. Field measurements show that the proposed FCCW bioradar can detect an alive person through different nonmetallic building materials.

Correction to: Aharonov–Bohm effect in the ghost interference

This article is a corrigendum to the article published in Pramana – J. Phys. 91, 76 (2018)

Spatiotemporal ghost imaging and interference

Ghost imaging retrieves the image of an object by using second-order correlation, and this technique studied so far has been considered in either a spatial or temporal domain, which is hard to apply to the scenario of imaging spatiotemporal dynamic objects (STDOs). Here we propose to demonstrate spatiotemporal ghost imaging and interference (STGII) for STDOs by extending the correlation theory of optical coherence into the spatiotemporal domain. We have derived the generalized analytical formula for such STGII with partially coherent pulsed beams. Through a simple example of spatiotemporal slits at different location and time, the interesting phenomena of STGII are achieved under suitable conditions and it is observed that the image quality and interference visibility are affected by both the spatial and temporal parameters of partially coherent pulsed beams.

Null test of large convex aspheres by subaperture stitching with replaceable holograms

Null test is preferred for measuring surface error of aspheres. However for large convex aspheres, it is challenging to fabricate larger null optics. Subaperture stitching is hence introduced but requires different null optics for subapertures of different off-axis distances. It gets easier by using replaceable computer generated holograms (CGHs). In this paper, a convex high-order even asphere is taken as an example and multiple CGHs are designed for null test of different subapertures. The same transmission flat and tilt carrier are used to facilitate alignment of CGHs. Disturbance orders of diffraction are confirmed to be separated by the tilt carrier without ghost interference. A configuration-based stitching algorithm is applied to successfully retrieve the full aperture surface error. The CGH substrate error is calibrated out before stitching optimization by measuring its transmitted wavefront with a high precision reference flat. Finally, the stitching result is verified by through-the-back null test of the same asphere.

Experimental demonstration of Einstein-Podolsky-Rosen entanglement in rotating coordinate space

Einstein-Podolsky-Rosen (EPR) entanglement involving a pair of particles entangled in their positions and momenta is of special interest in the field of quantum information. Previously, EPR entanglement has been studied in different physical systems but in fixed coordinate spaces. Here, we demonstrate an experiment of ghost imaging and ghost interference in rotated position-momentum spaces by using position-momentum entangled photons generated from a hot atomic ensemble. By using different image objects, the measured position-momentum correlations exhibit intriguing dynamics, including gradual decrease and axis-independent EPR entanglement. The reported results on manipulating the EPR entanglement in rotating coordinate spaces hold promise in quantum communication and distant quantum image processing.

Generation and characterization of position-momentum entangled photon pairs in a hot atomic gas cell.

Continuous-variable position-momentum entanglement (or Einstein-Podolsky-Rosen entanglement) of two particles has played important roles in the fundamental study of quantum physics as well as in the progress of quantum information. In this paper, we propose a scheme to generate Einstein-Podolsky-Rosen (EPR) position-momentum entangled photon pairs efficiently via spontaneous four-wave mixing (SFWM) process in a hot rubidium gas cell. The EPR entanglement between the photon pair is measured and characterized by using the ghost interference and the ghost imaging method. Due to the simplicity of the experimental setup and the high photon pair generation rate, our EPR entangled photon source may has potential applications in quantum imaging, hyperentanglement preparation and atomic ensemble based quantum information processing and quantum communication protocols.

Experimental demonstration of two-color Einstein–Podolsky–Rosen entanglement in a hot vapor cell

Einstein–Podolsky–Rosen (EPR) entanglement, involving pairs of particles that are entangled in position and momenta, is of special importance for quantum information processing. Practical quantum communication requires a two-color entanglement source: visible-band photons used to excite atoms and the communication band used for signal transmission. In this article, we report on the first experimental demonstration of two-color EPR entanglement based on spontaneous Raman scattering thermal Rb atoms using quantum ghost interference and ghost imaging. This work adopts a fundamental experiment that assists in promoting practical quantum communications and in providing a means to perform quantum imaging.

Phase imaging using single-pixel detection in the spatial spectrum plane

We propose a phase imaging method that combines the Fourier ptychography and compressive sensing theories using single-pixel detection in the spatial spectrum plane. Specifically, the spatial Fourier spectrum is shifted based on the Fourier ptychography theory, and the compressive sensing theory is applied to reduce the amount of acquired data. Further, an algorithm has been developed to reconstruct the phase images and an asymmetric mask introduced to eliminate ghost interference. The feasibility of the proposed method was verified through simulation and evaluated in terms of the compressive sensing theory realized. The results show that a two-dimensional image can be restored at a low sampling rate of 5% using the proposed method.

Aharonov–Bohm effect in the ghost interference

In the ghost interference experiment, a pair of entangled particles is sent in the opposite directions; one of the particles passes through a Young double-slit while the other continues its way freely. It turns out that the particles passing through the slits do not show any first-order interference while those propagating freely constitute an interference pattern when they are detected in coincidence with those which pass through the slits and detected at a fixed position. In this work, we consider that the particles are charged and the effect of a confined magnetic field is analysed between the slits in an Aharonov–Bohm configuration.

Vortex-phase-dependent momentum and position entanglement generated from cold atoms

The Einstein Podolsky Rosen (EPR) entangled quantum state is of special importance not only for fundamental research in quantum mechanics, but also for information processing in the field of quantum information. Previous EPR entangled state demonstrations were constructed with photons of equal phase wave fronts. More complex scenarios with structured wave fronts have not been investigated. Here, we report the first experimental demonstration of EPR entanglement for photon pairs carrying orbital angular momentum (OAM) information, resulting in an OAM embedded EPR entangled state. We measured the dynamics of the dependence of the ghost interference on relative phase under projection. In addition, the reconstructed matrix in the OAM and EPR position momentum spaces shows a specific hyper entanglement in high dimension.

25-1 明石海峡大橋によるテレビ電波障害のシミュレーションと検証

25-1 明石海峡大橋によるテレビ電波障害のシミュレーションと検証

基于ViBe的改进运动目标检测算法

ViBe是运动目标检测的常用算法。针对ViBe运动检测算法在实际环境中易出现鬼影、动态背景等干扰的问题，提出结合灰度特征直方图匹配的方法来检测鬼影，并进一步消除鬼影的干扰。针对动态背景错检测为运动前景的问题，为图像中各个像素设置闪烁属性和突变属性来判断各像素是否属于动态背景。实验表明，改进后的算法能有效弥补传统ViBe算法在鬼影消除和动态背景干扰上的不足。 Background subtraction is a common algorithm for moving target detection. Aiming at the prob-lem that the motion detection algorithm of ViBe is prone to ghost and dynamic background in the real environment, it is proposed to detect the ghost by combining the gray feature histogram matching method and further eliminate the ghost interference. Aiming at the problem that motion background is detected as motion foreground, we set the flickering property and mutation property for each pixel in the image to judge whether each pixel belongs to dynamic background. Experiments show that the improved algorithm can effectively compensate for the deficiencies of traditional ViBe algorithm in ghosting and dynamic background jamming.

Einstein-Podolsky-Rosen Entanglement of Narrow-Band Photons from Cold Atoms

Einstein-Podolsky-Rosen (EPR) entanglement introduced in 1935 deals with two particles that are entangled in their positions and momenta. Here we report the first experimental demonstration of EPR position-momentum entanglement of narrow-band photon pairs generated from cold atoms. By using two-photon quantum ghost imaging and ghost interference, we demonstrate explicitly that the narrow-band photon pairs violate the separability criterion, confirming EPR entanglement. We further demonstrate continuous variable EPR steering for positions and momenta of the two photons. Our new source of EPR-entangled narrow-band photons is expected to play an essential role in spatially multiplexed quantum information processing, such as, storage of quantum correlated images, quantum interface involving hyperentangled photons, etc.

Ghost imaging with atoms.

Ghost imaging is a counter-intuitive phenomenon-first realized in quantum optics-that enables the image of a two-dimensional object (mask) to be reconstructed using the spatio-temporal properties of a beam of particles with which it never interacts. Typically, two beams of correlated photons are used: one passes through the mask to a single-pixel (bucket) detector while the spatial profile of the other is measured by a high-resolution (multi-pixel) detector. The second beam never interacts with the mask. Neither detector can reconstruct the mask independently, but temporal cross-correlation between the two beams can be used to recover a 'ghost' image. Here we report the realization of ghost imaging using massive particles instead of photons. In our experiment, the two beams are formed by correlated pairs of ultracold, metastable helium atoms, which originate from s-wave scattering of two colliding Bose-Einstein condensates. We use higher-order Kapitza-Dirac scattering to generate a large number of correlated atom pairs, enabling the creation of a clear ghost image with submillimetre resolution. Future extensions of our technique could lead to the realization of ghost interference, and enable tests of Einstein-Podolsky-Rosen entanglement and Bell's inequalities with atoms.

Understanding ghost interference

The ghost interference observed for entangled photons is theoretically analyzed using wave-packet dynamics. It is shown that ghost interference is a combined effect of virtual double-slit creation due to entanglement, and quantum erasure of which-path information for the interfering photon. For the case where the two photons are of different color, it is shown that fringe width of the interfering photon depends not only on its own wavelength, but also on the wavelength of the other photon which it is entangled with.

Enhanced visibility of ghost imaging and interference using squeezed thermal light

Ghost imaging and interference using squeezed thermal light are investigated. We show that squeezed thermal light can have a very strong photon-bunching effect in the region of very weak squeezing and thermal excitation. As a result, the visibility of the image and interference pattern can be greatly enhanced and raised to be much higher than the limitation $1/3$ to thermal light. In the squeezed vacuum case, especially, the visibility can approach to the level of entangled photon pairs from spontaneous parametric down-conversion. The present investigation may open a new potential application of squeezed light.

Lensless ghost interference with classical incoherent light

As a method to obtain the interference pattern of an object, lensless ghost interference with classical incoherent light source is studied by use of optical coherence theory. It is shown that lensless ghost interference can be regarded as a coherent imaging system. Furthermore, there is a condition to realize lensless ghost interference, and the condition of realizing lensless ghost interference is deduced. Finally, the factors influencing the quality of lensless ghost interference, resolution and contrast, are investigated.

Three-slit ghost interference and non-local duality

A three-slit ghost interference experiment with entangled photons is theoretically analyzed using wave-packet dynamics. A non-local duality relation is derived which connects the path distinguishability of one photon to the interference visibility of the other.