High-resolution ghost image and ghost diffraction are performed by using a single source of pseudo-thermal speckle light divided by a beam splitter. By only operating on the optical setup of the light in the reference arm, that never interacted with the object, we are able to pass from the image to the diffraction pattern. The product of spatial resolutions of the ghost image and ghost diffraction experiments is shown to overcome a limit which was formerly thought to be achievable only with entangled photons. A complementarity between the spatial coherence of the beams and their mutual correlation is demonstrated by showing a complementarity between ghost diffraction and ordinary diffraction patterns.
Temporal ghost imaging is based on the temporal correlations of two optical beams and aims at forming a temporal image of a temporal object with a resolution, fundamentally limited by the photodetector resolution time and reaching 55 ps in a recent experiment. For further improvement of the temporal resolution, it is suggested to form a spatial ghost image of a temporal object relying on strong temporal-spatial correlations of two optical beams. Such correlations are known to exist between two entangled beams generated in type-I parametric downconversion. It is shown that a sub-picosecond-scale temporal resolution is accessible with a realistic source of entangled photons.
In this paper we study the resolution of images illuminated by sources composed of
N+1 photons in which one non-degenerate photon is entangled with
N degenerate photons. The
N degenerate photons illuminate an object and are collected by an
N photon detector. The signal from the
N photon detector is measured in coincidence with the non-degenerate photon giving rise to a ghost image. We discuss the case of three photons in various configurations and generalize to
N+1. Using the Rayleigh criterion, we find that the system may give an improvement in resolution by a factor of
N compared to using a classical source. For the case that the
N-photon number detector is a point detector, a coherent image is obtained. If the
N-photon detector is a bucket detector, the image is incoherent. The visibility of the image in both cases is 1. In the opposite case in which the non-degenerate photon is scattered by the object, then, using an
N-photon point detector may reduce the Airy disk by a factor of
N.
We theoretically discuss the four-photon spatial correlation property under different detection schemes. Compared with the two- and three-photon spatial correlation of thermal light source, we found that the enhancement in the visibility and the contrast when the fourth-order spatial correlation function is measured with quadruple coincidence measurement in the single photon counting regime. The resolution, however, is not changed when we scan three of four detectors with identical speed and direction. But if we scan two of three detectors in opposite directions and same speed, simultaneously, other two in identical direction and speed of one detector is twice of that of the other, we can see that both the contrast and resolution are improved significantly. We also show that the conclusion can be applied to the Nth-order ghost imaging.
Coincidence counters play the role of gating events from the background noise in almost every quantum photonics setup. Precise multi-channel and high count-rate coincidence counting tools have become desirable due to an increase in the complexity of quantum photonics experiments. However, timing analyzers are struggling to meet these needs. We are proposing a Field Programmable Gate Array (FPGA) based coincidence counting system which provides 8 operational channels with 8.9 ps root mean square (RMS) resolution (with a bin width of 7.7 ps) and a count-rate of 320 million counts per second (MCPS) (with 40 MCPS per channel). We have successfully tested our design in different quantum photonics scenarios such as the detection of two-photon interference and pseudo-photon-number resolving detection of a coherent state of light where it has shown its capability of working beyond the saturation of detectors. Also, we have introduced a Dual Data Rate Registration TDC, which improved the linearity of the time tagging operation by using both clock edges without increasing the dead-time or using the space excessively. 1.2 LSB in max DNL error, 1.8 LSB in max INL error, 10 ps in FWHM and 3.2 ps in RMS resolution improvements were achieved.