Browsing by Author "Kuniyil, Hashir Puthiyapurayil"
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Conference paperPublication Metadata only Down-conversion emission profile characterisation via camera(Optica Publishing Group, 2020-12-14) Kuniyil, Hashir Puthiyapurayil; Durak, Kadir; Electrical & Electronics Engineering; DURAK, Kadir; Kuniyil, Hashir PuthiyapurayilWe present a method to improve the brightness and collection efficiency of the spontaneous parametric down-conversion source by monitoring the mode shape using camera and correcting it with collection optics.Conference paperPublication Metadata only Effect of phase and spatial distinguishability of photon pairs on the entanglement fidelity(SPIE, 2021) Kuniyil, Hashir Puthiyapurayil; Durak, Kadir; Electrical & Electronics Engineering; DURAK, Kadir; Kuniyil, Hashir PuthiyapurayilPolarization entanglement based cryptography uses the photon pairs generated in a spontaneous parametric down-conversion process and guarantees the security through the violation of Bell's inequality. Certain experimental parameters affects the entanglement fidelity and leads to a possible information leakage. The optical path difference of photons born at different crystals contributes to reduced fidelity, due to the extra birefringence of the nonlinear crystal. Although previous studies suggested methods to erase the distinguishability of photons by introducing compensation crystals, the phase difference, which is due to the lateral ray distribution is not studied. We used two commercially available collection optics; an aspheric and an achromatic lens. With these collection optics, the effect of collection optics on the entanglement fidelity is studied. We developed a simulation of such a system and found that aspheric collection optics is more suitable to achieve high fidelity.ArticlePublication Metadata only Efficient coupling of down-converted photon pairs into single mode fiber(Elsevier, 2021-08-15) Kuniyil, Hashir Puthiyapurayil; Durak, Kadir; Electrical & Electronics Engineering; DURAK, Kadir; Kuniyil, Hashir PuthiyapurayilWe present the analysis of the down-conversion emission profile from a critically phase-matched type-I nonlinear crystal. The emission profile of the down-conversion modes shows asymmetry in cylindrical coordinate system due to the birefringent effects of the nonlinear crystal, i.e. pump walk-off. This effect leads to reduced collection of the pairs from the source to the single mode fiber, which limits the brightness as a function of the crystal length. We propose a method to improve the symmetry of the down-conversion modes by inserting a lens off-centered with respect to the optical axis. Our theoretical and experimental results show that the asymmetry of the system increases with the crystal length by L0.5, and the brightness is proportional to crystal length by L0.72 and L0.91 for uncorrected and corrected down conversion mode profiles, respectively. The proposed method allows more efficient use of photon pair sources in terms of brightness which is to be used in quantum optics applications.ArticlePublication Metadata only Noise-tolerant object detection and ranging using quantum correlations(IOP Publishing, 2022-10) Kuniyil, Hashir Puthiyapurayil; Özel, Helin; Yılmaz, H.; Durak, Kadir; Electrical & Electronics Engineering; DURAK, Kadir; Kuniyil, Hashir Puthiyapurayil; Özel, HelinImaging, detection and ranging of objects in the presence of significant background noise is a fundamental challenge in optical sensing. Overcoming the limitations imposed in conventional methods, quantum light sources show higher resistance against noise in a time-correlation-based quantum illumination. Here, we introduce the advantage of using not only time correlations but also polarization correlations in photon pairs in the detection of an object that is embedded in a noisy background. In this direction, a time- and polarization-correlated photon pair source using the spontaneous parametric down-conversion process is exploited. We found that the joint measurement of correlated pairs allows distinguishing the signal from the noise photons and that leads to an improved signal-to-noise ratio. Our comparative study revealed that using polarization correlations in addition to time correlations provides improved noise rejection. Furthermore, we show that polarization correlation allows undoing the detector limitation where high background often leads to detector saturation.Conference paperPublication Metadata only Object ranging and sensing by temporal cross-correlation measurement(SPIE, 2020) Kuniyil, Hashir Puthiyapurayil; Jam, Naser Chamani; Durak, Kadir; Electrical & Electronics Engineering; Kimata, M.; Shaw, J. A.; Valenta, C. R.; DURAK, Kadir; Kunıyıl, Hashır Puthıyapurayıl; Jam, Naser ChamanıWe present a novel method to measure the range of an object in a lab setting. This is realised by utilizing the phase insensitive cross-correlation analysis of the probe and reference photons generated in a spontaneous parametric down-conversion process. In our technique, the comparative measurement of time-correlated photons after one is transmitted to the target direction and the copy of it retained at the lab allows to single out the signal from the noise lead to sense, range and imaging the sample.PhD DissertationPublication Metadata only Quantum advances in imaging systemsKuniyil, Hashir Puthiyapurayil; Durak, Kadir; Durak, Kadir; Akgiray, Ahmed Halid; Parlak, Mehmet; Müstecaplıoğlu, Ö.; Kiraz, A.; Department of Electrical and Electronics EngineeringQuantum mechanics-based systems are increasingly used for advancing existing technologies. One of the technological frontiers where features of quantum mechanics are shown to have high potential is the imaging industry. Quantum imaging, a quantum version of the conventional imaging system, is becoming increasingly explored for imaging applications. This method of imaging involves taking advantage of unique spatial and temporal quantum correlations to enhance its figure of merit, including modulation transfer function. This thesis discusses the implementation procedure of the photonic quantum imaging scheme with the principal aim of achieving an improved imaging system. In this direction, the efficient generation of quantum sources, as well as their distribution and accurate analysis, are of paramount importance, particularly regarding the practicability of many quantum imaging applications. A quantum source based on the nonlinear process of spontaneous parametric downconversion (SPDC) is well-known and increasingly used for this task. We theoretically study the suitability of the critically phasematched SPDC process and a detailed analysis of it is given in this thesis that will help in engineering a quantum source that is fit for quantum imaging applications. From our theoretical studies and basic experiments, it is well understood that the photon pairs called signal and idler from an SPDC process are capable of showing entanglement time and position correlationsuitable parameters for quantum imaging. These temporal and spatial correlations are used for quantum imaging where spatial correlation supports the extraction of the complete 2D features of the sample under study and the temporal correlation allows us to enhance the SNR of the system, a parameter that affects the modulation transfer function. To learn the temporal correlation’s capability to suppress the noise, hence enhanced SNR, a separate work that is based on the quantum illumination experiment driven by continuous wave laser pumped SPDC is conducted. Our results show that a quantum correlation in the time domain has increased resilience to noise. In a novel method, we demonstrate that with the assistance of polarisation correlation, we can further improve the performance metric of SNR of a quantum illumination system. As we use temporal correlation in the imaging scheme in addition to the spatial correlation, this result has implications for suppressing noise from a quantum imaging system. The advancement of camera technologies offered ample room for experimenting with quantum spatial features, especially in SPDC-based spatial correlation-based imaging. The spatial correlation in SPDC stands out from classical systems- as this showed EPR-type correlations. The task of achieving reconstruction of the spatial feature of an object sample with the assistance of SPDC’s spatial quantum correlation has been shown in this thesis. Our study exploited the transverse spatial correlation in the continuous basis of the SPDC mode to the realization of 2D quantum imaging. Our proof of concept experimental result proves that spatial correlation can be used for reconstructing an image. As this imaging scheme is based on the quantum-correlation behavior of signal and idler photons of the SPDC process, we could suppress the noise in the system by employing the coincidence imaging technique. The demonstrated experimental imaging method is diffraction limited, thus the resolution of the system, at best, is equal to the classical counterparts. Our simulation work shows the performance of the quantum imaging scheme can be affected by input parameters such as the pump beam waist, crystal length, and location of the sample object and the imaging instrument. Therefore, carefully selecting the input parameter values is critical for the system’s performance. The study concludes that quantum-based imaging schemes, like the one presented in this thesis, have high resilience to noise.