Comment on "Can Two-Photon Correlation of Chaotic Light Be Considered as Correlation of Intensity Fluctuations?"

Illumination Temporal Fluctuation Suppression for Single-Pixel Imaging

Single-pixel cameras offer improved performance in non-visible imaging compared with modern digital cameras which capture images with an array of detector pixels. However, the quality of the images reconstructed by single-pixel imaging technology fails to match traditional cameras. Since it requires a sequence of measurements to retrieve a single image, the temporal fluctuation of illumination intensity during the measuring will cause inconsistence for consecutive measurements and thus noise in reconstructed images. In this paper, a normalization protocol utilizing the differential measurements in single-pixel imaging is proposed to reduce such inconsistence with no additional hardware required. Numerical and practical experiments are performed to investigate the influences of temporal fluctuation of different degrees on image quality and to demonstrate the feasibility of the proposed normalization protocol. Experimental results show that our normalization protocol can match the performance of the system with the reference arm. The proposed normalization protocol is straightforward with the potential to be easily applied in any temporal-sequence imaging strategy.

Quantum discord of thermal two-photon orbital angular momentum state: mimicking teleportation to transmit an image

We formulate a density matrix to fully describe two-photon state within a thermal light source in the photon orbital angular momentum (OAM) Hilbert space. We prove the separability, i.e., zero entanglement of the thermal two-photon state. Still, we reveal the hidden quantum correlations in terms of geometric measures of discord. By mimicking the original protocol of quantum teleportation, we demonstrate that the non-zero quantum discord can be utilized to transmit a high-dimensional OAM state at the single-photon level. It is found that albeit the low fidelity of teleportation due to the inherent component of maximally mixed state, the information of all parameters that characterize the original state can still be extracted from the teleported one. Besides, we demonstrate that the multiple repetitions of the protocol, enable the transmission of a complex-amplitude light field, e.g., an optical image, regardless of being accompanied with a featureless background. We also distinguish our scheme of optical image transmission from that of ghost imaging.

Single-photon-counting polarization ghost imaging

We proposed a method for polarization ghost imaging based on single photon counting. With the time-correlated single-photon-counting technique, we can construct photon time distribution histograms and select a distance gate to accurately estimate the light intensity. Experiments are performed to realize discrimination of the object from the background of different materials in weak illumination. In the situation that ambient noise is significantly stronger than the signal, our method still can retrieve an image as ambient noise is mostly filtered out through distance gate selection. We suppose that our method may facilitate applications in remote target discrimination and biological imaging.

Ultrabroadband ghost imaging exploiting optoelectronic amplified spontaneous emission and two-photon detection

Ghost imaging (GI) is one of the recent fascinating and probably counterintuitive topics of quantum optics. Here, we present an alternative classical GI scheme using spectrally ultrabroadband amplified spontaneous emission from an optoelectronic quantum dot based superluminescent diode source. This light source exhibits highly incoherent properties regarding both first- and second-order correlations with a 70 nm-wide optical spectrum as well as thermal-like photon statistics. Exploiting a two-photon-absorption detection method, we demonstrate for the first time, to the best of our knowledge, a GI experiment handling the corresponding femtosecond correlation timescales. By introducing compact broadband light sources to GI, this work contributes toward practical application of GI.

Evaluation criterion of thermal light ghost imaging based on the receiver operating characteristic analysis

The performances of different thermal ghost imaging (GI) algorithms are compared in an experiment of computational GI using a digital micromirror device. Here we present a rather different evaluation criterion named receiver operating characteristic (ROC) analysis that serves as the performance of merit for the quantitative comparison. A ROC curve is created by plotting the true positive rate against the false positive rate at various threshold settings. Both theoretical analysis and experimental results demonstrate that the ROC curve and the area under the curve are better and more intuitive indicators of the performance of the GI, compared with conventional evaluation methods. Additionally, for examining gray-scale objects, the calculation of the volume under the ROC surface is analyzed and serves as a performance metric. Our scheme should attract general interest and open exciting prospects for ROC analysis in thermal GI.

Differential ghost imaging

We present a new technique, differential ghost imaging (DGI), which dramatically enhances the signal-to-noise ratio (SNR) of imaging methods based on spatially correlated beams. DGI can measure the transmission function of an object in absolute units, with a SNR that can be orders of magnitude higher than the one achievable with the conventional ghost imaging (GI) analysis. This feature allows for the first time, to our knowledge, the imaging of weakly absorbing objects, which represents a breakthrough for GI applications. Theoretical analysis and experimental and numerical data assessing the performances of the technique are presented.

Optimization of thermal ghost imaging: high-order correlations vs. background subtraction

We compare the performance of high-order thermal ghost imaging with that of conventional (that is, lowest-order) thermal ghost imaging for different data processing methods. Particular attention is given to high-order thermal ghost imaging with background normalization and conventional ghost imaging with background subtraction. The contrast-to-noise ratio (CNR) of the ghost image is used as the figure of merit for the comparison.We find analytically that the CNR of the normalized high-order ghost image is inversely proportional to the square root of the number of transmitting pixels of the object. This scaling law is independent of the exponents used in calculating the high-order correlation and is the same as that of conventional ghost imaging with background subtraction. We find that no data processing procedure performs better than lowest-order ghost imaging with background subtraction. Our results are found to be able to explain the observations of a recent experiment [Chen et al., arXiv:0902.3713v3 [quant-ph]].

Interference from a nonlocal double-slit through one-photon process

In this paper, we report an interference experiment in which a spatially incoherent light source illuminates two spatially separated apertures, whose superposition at the same place forms a double-slit. The experimental result exhibits a well-defined interference fringe solely through intensity measurements, in agreement with the theoretical analysis by means of the first-order spatial interference of the incoherent light. Consequently, the nonlocal double-slit interference with thermal light should be attributed to the first-order spatial correlation of incoherent field.

High-order thermal ghost imaging

We show theoretically that high-order thermal ghost imaging has considerably higher visibility and contrast-to-noise ratio than conventional thermal ghost imaging, which utilizes the lowest-order intensity cross correlation of the object and the reference signal. We also deduce the optimal power order of the correlation that gives the best contrast-to-noise ratio.

Holographic ghost imaging and the violation of a Bell inequality

We demonstrate the contrast enhancement of images within a ghost-imaging system by use of nonlocal phase filters. We use parametric down-conversion as the two-photon light source and two separated phase modulators, in the signal and idler arms which represent different phase filters and objects, respectively. We obtain edge enhanced images as a direct consequence of the quantum correlations in the orbital angular momentum (OAM) of the down-converted photon pairs. For phase objects, with differently orientated edges, we show a violation of a Bell-type inequality for an OAM subspace, thereby unambiguously revealing the quantum nature of our ghost-imaging arrangement.

Lensless ghost imaging with true thermal light

We report the first (to our knowledge) experimental demonstration of lensless ghost imaging with true thermal light. Although there is no magnification, the method is suitable for all wavelengths and so may find special applications in cases where it is not possible to use lenses, such as with x rays or gamma rays. We also numerically show that some magnification may be realized away from the focal plane, but the image will always be somewhat blurred.