Browsing by Author "Ismail, Yaseera."

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Characterisation of polarisation-entangled photon source for quantum key distribution.
(2016) Fadol, Samah S. Abu Ali.; Ismail, Yaseera.; Petruccione, Francesco.
Entanglement in real physical systems has been of great interest due to its importance in quantum mechanics. It has applications related to quantum information science speci cally quantum cryptography since it eliminates the possibility of photon number splitting attack during the key distribution process (Quantum Key Distribution). This thesis deals with creation, detection and characterisation of the correlated polarised photon pairs, which were emitted from a nonlinear BBO crystal via Spontaneous Parametric Down Conversion (SPDC) process. The procedure that leads to the construction of a polarisation-based entangled system is discussed by considering some of the measurement techniques, which can be applied to study fundamental quantum mechanics and its applications in quantum communication. This thesis consists of a set of experiments to validate the entanglement of single photon pairs. The rst experiment realised by generating of polarised based entangled photon pairs. The quantum correlation between the entangled photon pairs have been tested by measuring the visibility of the system and by verifying the maximal violation of CHSH (Clauser, Horne, Shimony and Holt) inequality. In the second experiment, the delity of the system has been measured by carrying out the state tomography to reconstruct the two-photon density matrix and consider the interference e ect of two photons. This helps to study the preservation of the quantum state during the propagation.
Development of a post-processing technique for a Quantum Key Distribution system.
(2017) Umuhire, Marie Louise.; Petruccione, Francesco.; Ismail, Yaseera.
Quantum Information, Processing and Communication (QIPC) is a field concerned with technological implementations established on quantum mechanical phenomena. It is established on the concept that the action of manipulating information is controlled by the quantum physical effects. Therefore, quantum information can be characterised, quantified and processed as a physical body applying laws of quantum mechanics. QIPC consists of two major disciplines, quantum computing and quantum communication. Communication is bound by the transfer of information. Quantum communication applies some of the fundamental features of quantum mechanics, such as, the superposition principle and the Heisenberg uncertainty principle to protect the transfer of information. One of the most advanced quantum information related technology at present is Quantum Key Distribution (QKD). It is defined as a process of encoding information into a quantum carrier in the form of single photons and distribute that information amongst legitimate entities.
Development of encoding and entanglement for free space quantum key distribution.
Ismail, Yaseera.; Petruccione, Francesco.
It is established that the manipulation of quantum information is bound only by the laws of physics and thus information can be characterised, quantified and processed as a physical entity using the basic properties of quantum mechanics. The most advanced quantum information related technology at present is Quantum Key Distribution (QKD). QKD encodes information into a quantum data carrier, in particular, a single photon that is transported through a quantum channel to produce secure key. To date QKD has been demonstrated across two types of channels which is generally fibre or free space. Free space QKD is beneficial since it provides various mediums for the encoding. When considering the atmosphere as a medium for free space QKD, one of the challenges is the effects of turbulence. Apart from the turbulence effects, one of the other challenges faced with implementing a QKD system, is the use of an appropriate source of single photons for the encoding. A good implementation of a source of single photons would be to make use of entanglement. This thesis addresses the above two aspects of QKD Entanglement is essentially at the core of quantum mechanics and deals with the ability to couple two or more particles in time and space. It is relevant to all sub-atomic particles which include photons, electrons and ions. One of the techniques to obtaining an entangled photon pair lies in the successful implementation of a second-order nonlinear process which is referred to as Spontaneous Parametric Down Conversion (SPDC). The objective of this study was to build a polarisation encoded entangled single photon source using high powered lasers. The reason for this is that, for the successful implementation of free space QKD using entangled single photons, a bright source with high quality entanglement is required. We reach a power output of 400 mW and a violation of the Clauser, Horne, Shimony and Holt (CHSH) inequality, 0.8 % less than the theoretical limit. Free space QKD is challenged by the effects of atmospheric turbulence due to additional noise introduced to the system. Hence it is of relevance hence to study the effects that turbulence poses on photons. Within this study we simulate atmospheric turbulence which was applied to two well known methods of encoding namely, polarisation and states carrying Orbital Angular Momentum (OAM). Polarisation encoding, when subjected to simulated turbulence, suffered phase dependence on the coincidence. This was due to the inefficient coupling of single mode fibre within the detection scheme. These results suggest that the design of an entangled source is crucial when utilised within non-ideal conditions. An alternative method of encoding is to make use of photons carrying OAM. Here we investigated an alternative approach to encoding of OAM states in the form of higher Development of Encoding and Entanglement for Free Space Quantum Key Distribution order Bessel beams. Although OAM suffers much loss due to the break down of the phase in the presence of atmospheric turbulence, it is promising method of encoding to reach hyper entanglement states. Furthermore this will provide a means to attain dense coding. Encoding and an appropriate single photon source is significant for the implemantation of free space QKD. The aforementioned investgations carried out within this thesis is promising for the further development of free space QKD.
Molecular sensors for evaluating substandard anti-retroviral medication using surface-enhanced raman spectroscopy.
(2023) Thobakgale, Setumo Lebogang.; Mthunzi-Kufa, Patience Thenjiwe.; Ismail, Yaseera.; Ombinda-Lemboumba, Saturnin.
Africa has the highest number of people living with HIV and AIDS, with South Africa housing the largest Anti-retroviral treatment (ART) program in the world. In addition, the continent is troubled by the continuing growth of substandard ART medication which is imported from external continents. The World Health Organization also states that due to the limited information on this issue, adequate remedial measures cannot be put into place. As such, this study proposed the application of surface-enhanced Raman spectroscopy (SERS) as a drug screening method for ART. Sensing platforms were synthesized using a combination of metals, crosslinker organic molecules, deposition, and self-assembly methods. The platforms were used for tailored adsorption of three ART medications in their active pharmaceutical ingredient (API) form: Tenofovir (TDF), Lamivudine (LAM) and Dolutegravir (DLG) prior to evaluation with Raman spectroscopy. Molecular interactions, signal enhancement and statistical methods such as linear regression were carried out on the analytes and data from the SERS analysis showed significant differences in the sensing capabilities of the platforms based on the calibration sensitivity, analytical sensitivity, and limit of detection. The molecular composition and chemical functionality of the sensors allowed specific adsorption and preference to the complementary functional groups of the API samples which led to enhanced Raman signals on each platform. From the results obtained, it was concluded that the synthesis of tailored platforms for molecular sensing of ART medication was successful, providing potential application of these sensors in the quality control of anti-retroviral medication. Future work will entail routine molecular screening of ARVs to monitor changes in ART quality with respect to geographical location, shelf life and formulation methods.
Novel laser beams for optical trapping and tweezing.
(2011) Ismail, Yaseera.; Forbes, Andrew.
Optical trapping and tweezing has been around for the last 30 years and since found its place in the fields of physics and biology. Over the years this technique has advanced exceedingly and is a unique tool to carry out research in the micrometre and nanometre scale regime. The aim of this dissertation was to illustrate that an optical trapping and tweezing system is an effective tool for the manipulation of micron sized particles and that using such a system allows one the ability to accurately and precisely measure optical forces in the piconewton scale. A custom built single gradient optical trapping system was built to illustrate the manipulation of micron sized particles. Here we will highlight some of the key components of such a system and give an explanation of how these components affect the optical trap. To enhance this system, we exploit the ability to shape light and in particular laser light to generate novel laser beams. This was achieved using a diffractive optical element known as a spatial light modulator (SLM). A spatial light modulator is an electronically addressed optical element which when incorporated into an optical system effectively manipulates the phase of light in order to generate various novel laser beams. In particular these novel laser beams include Laguerre-Gaussian, Bessel and recently proposed Bessel-like beams. Each of these beams contains interesting properties which can be beneficially exploited. Laguerre-Gaussian beams are particularly known as ‘donut’ shaped beams since they have a central dark hole. Increasing the order of these Laguerre-Gaussian beams leads to an increase in the central dark region. These beams are of particular interest since they carry orbital angular momentum. This is not easily observed; however, when incorporated into the optical trapping system, leads to the rotation of trapped particles due to the transfer of photons carrying orbital angular momentum. Bessel and Bessel-like beams on the other hand are classes of beam that possess interesting non-diffracting and self-reconstructive properties upon encountering an obstacle. Here the generation and properties of these novel laser beams will be discussed in detail. Furthermore it is well known that these novel laser beams prove highly useful when incorporated into an optical trapping system hence we will illustrate the effects on a trapped particle when incorporating a Laguerre-Gaussian beam carrying a topological charge of one. It is expected that the trapped particle should rotate due to the transfer of orbital angular momentum. The knowledge gained from beam shaping and the means to trap micron sized particles optically allows one the ability to incorporate this technique in a number of fields, including the promising field of microfluidics. This is an emerging field that deals with investigating fluid properties at the nano and microlitre regime. Optical tweezers integrated into a microfluidic device are beneficial since they are an adequate tool for measuring fluid flow using Stokes’ Law.
Quantum key distribution--Undergraduate curriculum.
(2017) Phehlukwayo, Samukelisiwe Purity.; Petruccione, Francesco.; Ismail, Yaseera.
Quantum Key Distribution (QKD) is one of the technological applications of quantum mechanics. The technology allows two users to securely establish an unbreakable key. The key is used to encrypt and decrypt sensitive information such as online banking and emails. This technological application has matured in an industry as it provides real world implementation. It offers a provably secure key based on the principles of quantum mechanics. There are products that are available that can be used to implement this technology. This study demonstrates the implementation of the QKD process for the undergraduate physics curriculum. We outline the procedure of QKD in a convenient way for students to follow and understand. To this end, a comprehensive manual has been developed to enable undergraduate students to learn the foundations of QKD. Students will gain knowledge that using quantum mechanical properties, two remote parties can securely establish a communication by exchanging keys which can then be used as an encryption. We present the QKD system such as the id 3000 as a learning tool in the physics 3rd-year laboratory, to introduce undergraduate students to applications in quantum information science. We demonstrate a typical experiment which undergraduate students can perform using the id 3000 system in the 3rd physics laboratory. Our vision is to see students exploring quantum mechanics in more depth and learning practical work alongside theories taught in the curriculum.