Quantum images in double-slit experiments with spontaneous down-conversion light

Quantum ghost imaging of a transparent polarisation sensitive phase pattern

A transparent polarisation sensitive phase pattern exhibits a position and polarisation dependent phase shift of transmitted light and it represents a unitary transformation. A quantum ghost image of this pattern is produced with hyper-entangled photons consisting of Einstein-Podolsky-Rosen (EPR) and polarisation entanglement. In quantum ghost imaging, a single photon interacts with the pattern and is detected by a stationary detector and a non-interacting photon is imaged on a coincidence camera. EPR entanglement manifests spatial correlations between an object plane and a ghost image plane, whereas a polarisation dependent phase shift exhibited by the pattern is detected with polarisation entanglement. In this quantum ghost imaging, the which-position-polarisation information of a photon interacting with the pattern is not present in the experiment. A quantum ghost image is constructed by measuring correlations of the polarisation-momentum of an interacting photon with polarisation-position of a non-interacting photon. The experiment is performed with a coincidence single photon detection camera, where a non-interacting photon travels a long optical path length of 17.83 m from source to camera and a pattern is positioned at an optical distance of 19.16 m from the camera.

Quantum double-double-slit experiment with momentum entangled photons

Double-double-slit thought experiment provides profound insight on interference of quantum entangled particles. This paper presents a detailed experimental realisation of quantum double-double-slit thought experiment with momentum entangled photons and theoretical analysis of the experiment. Experiment is configured in such a way that photons are path entangled and each photon can reveal the which-slit path information of the other photon. As a consequence, single photon interference is suppressed. However, two-photon interference pattern appears if locations of detection of photons are correlated without revealing the which-slit path information. It is also shown experimentally and theoretically that two-photon quantum interference disappears when the which-slit path of a photon in the double-double-slit is detected.

Effect of oceanic turbulence on the visibility of underwater ghost imaging

We carry out a detailed study on underwater ghost imaging (GI) in oceanic turbulence. We set up a physical model of GI through oceanic turbulence, which includes light-field transmission, and interaction between light field and oceanic turbulence without considering the effects of water absorption and scattering of light. We obtain theoretical expressions for the impulse response function and the visibility of GI in oceanic turbulence based on the power spectrum of the turbulence and the extended Huygens-Fresnel integral. The results show that the quality of GI under the effects of oceanic turbulence is related to the intensity of turbulence and the propagation distance of light. The quality of GI could be maintained at a relatively small distance in strong oceanic turbulence, whereas the quality is degraded dramatically at a relatively long distance in strong oceanic turbulence. We further analyze the quality of GI under various turbulence conditions and over different propagation distances by numerical calculation. Our results provide guidance for the realization of adaptive underwater optical GI over different length scales under the effect of oceanic turbulence.

Experimental demonstration of ghost imaging with an electromagnetic Gaussian Schell-model beam

Recently, there has been a controversy about the dependence of the visibility of the ghost image on the degree of polarization (DOP) of a stochastic electromagnetic beam because of different definitions of the visibility. In this paper, we revisit ghost imaging with an electromagnetic Gaussian Schell-model (EGSM) beam. Through numerical examples based on the conventional definition of the visibility, we find that the visibility of the ghost image indeed increases or decreases with the increase of the DOP the beam source under certain conditions. We solve the controversy between literatures and the present paper through analyzing the r.m.s. widths of auto-correlation functions of the x component of the field and of the y component of the field. Furthermore, we carry out experimental demonstration of ghost imaging with an EGSM beam. Our experimental results verify the theoretical predictions.

Reduction or annihilation of aberrations of an optical system by balancing ghost-imaging technique and optimal imaging of a pure weak phase object

It is shown, using ghost-imaging techniques, that it is possible to reduce or even to annihilate the influence of aberrations connected with an arbitrary optical system. To this end, we consider a ghost-imaging setup, which consists of two arms, each containing an optical system. The reduction cancellation of the aberrations of the total imaging system is achieved by manipulating the values of the aberrations in one arm of the optical system. The technique is then applied for the optimal reconstruction of a weak phase object, manipulating the values of the defocusing such that the "Scherzer defocus condition" is obtained.

Interference effects induced by non-local spatial filtering

The spatial correlation between down-converted photons allows for non-local spatial filtering when two-photon coincidences are registered. This allows one to non-locally control the visibility of interference fringes, to observe ghost images and interference patterns, and to "retrieve" a coherent quantum image from an incoherent field distribution. We show theoretically that non-local spatial filtering can lead to counter-intuitive effects when the pump beam is no longer given by a Gaussian profile. Namely, increased non-local filtering can actually decrease the visibility of interference fringes, contrary to what has been observed so far. We explain this behavior through the transverse spatial parity entanglement of the down-converted photons.

Ghost imaging with twisted Gaussian Schell-model beam

Based on the classical optical coherence theory, ghost imaging with twisted Gaussian Schell-model (GSM) beams is analyzed. It is found that the twist phase of the GSM beam has strong influence on ghost imaging. As the absolute value of the twist factor increases, the ghost image disappears gradually, but its visibility increases. This phenomenon is caused by the fact that the twist phase enhances the transverse spatial coherence of the twisted GSM beam on propagation.

Chaotic imaging in frequency downconversion

We analyze and recover, by means of spatial intensity correlations, the image obtained by a seeded frequency-downconversion process in which the seed field is chaotic and an intensity modulation is encoded in the pump field. Although the field generated is as chaotic as the seed field and does not carry any information about the modulation of the pump, one can extract an image of the pump by measuring the spatial intensity correlations between the generated field and one Fourier component of the seed.

Ghost imaging with incoherent and partially coherent light radiation

We theoretically study ghost imaging with incoherent and partially coherent light radiation by using classical optical coherence theory. A Gaussian thin lens equation is derived for the ghost image. The equation depends on both paths. The quality and visibility of the ghost image are influenced by the source's transverse size, coherence width, and object characteristics. The differences between ghost imaging formed with incoherent light radiation and with entangled photon pairs are discussed.

Entangled-photon imaging of a pure phase object

We demonstrate experimentally and theoretically that a coherent image of a pure phase object [implemented by a microelectromechanical system (MEMS) micromirror array] may be obtained by use of a spatially incoherent illumination beam. This is accomplished by employing a two-beam source of entangled photons generated by spontaneous parametric down-conversion. One of the beams probes the phase object while the other is scanned. Though each of the beams is, in and of itself, spatially incoherent, the pair of beams exhibits higher-order interbeam coherence.

Orbital and intrinsic angular momentum of single photons and entangled pairs of photons generated by parametric down-conversion

States of light that are simultaneously eigenstates of orbital, intrinsic, and total angular momentum are found and eigenstates describing pairs of photons from spontaneous parametric down-conversion reveal classes of photon conversion with angular momentum conservation and cases where the initial angular momentum from the pump laser beam is shared between the converted photons and the generating medium. These angular momentum conservation laws open up a wide range of applications to be explored.