Sharif Digital Repository

Josephson junctions are the basic elements of superconducting technology. They play the same role of p-n junctions in semiconductor technology. Here, we investigated on the optical responses of the fabricated Josephson junctions in order to gain high sensitive optical sensors. The emission has both thermal and non-thermal effect on the current-voltage characteristics of the junctions. While the bolometric effect is the result of slight changes in the bias temperature of device, the non-thermal effect is due to depairing of Cooper pairs and generation of quasi-particles, which is dominant in temperatures far below TC especially in the case the superconducting layer is optically thin. In this... 

During the last decade there have been many attempts to push THz science and technology achievement to the appropriate solid state source for this purpose is a main challenge in this area. One of the best devices which can be used as a source in this gap is the stack of intrinsic Josephson junctions. Josephson junction include a dielectric which is sandwiched between two superconductors and convert the voltage to the electromagnetic wave. After studies in this field for obtaining a suitable source using stack of intrinsic Josephson junctions, an idea which is raised in this area is having a mixer in terahertz gap. The main purpose of this thesis is checking the idea of a structure which can... 

Design of superconducting material based wide band radiation detectors has recently been attractive. Interesting features of detectors, which are based on Josephson Junctions such as high sensitivity in a wide range of frequencies and low power consumption, potentially have many advantages over other semiconductor-based photo-detectors. According to variety of applications of high-Tc superconductors, particularly YBCO, and significant progress in manufacturing of thin films and Josephson junctions, this thesis mainly focuses on investigation of radiation effects on I-V characteristics of high-Tc step-edge Josephson junctions experimentally. The current-voltage characteristics of fabricated... 

Terahertz waves which includes frequencies between 100 GHz to 10 THz of electromagnetic spectrum have found many applications in science, medical treatments and industry. One of the recent methods to produce these waves is using nonlinear properties of superconductors based on Josephson junctions which inherently appear in some superconductors called BSCCO. Stack of intrinsic junctions of these superconducting materials can radiate terahertz waves by only applying a DC voltage across them. This Thesis investigates some of these structures based on Josephson junctions to produce coherent radiation of terahertz waves. For the optimization of the radiation power, this study also investigates... 

High photonic responsivity and excellent quantum efficiency of high-Tc superconductors make them a promising candidate for photonic detectors. Interesting features of detectors which are based on Josephson Junctions such as high sensitivity in a wide range of frequencies, potentially have many advantages over other semiconductor-based photo-detectors. According to variety of applications of high-Tc superconductors, particularly YBCO, and significant progress in manufacturing of thin films and Josephson junctions, this thesis mainly focuses on investigation of light emission effects on high-Tc Josephson Junctions and its theory. In our work, at the beginning, the current-voltage... 

Computational instruments such as personal computers (PC) are among the most important and developed inventions needed for the society. Nowadays, the fastest classical computing machines are based on the conventional semiconductor fabrication technology. But these computers cannot satisfy all of the requirements of today’s ongoing developments. Two important weaknesses of the undergoing technology are the speed of computing which is in the frontend of the semiconductor technology, and solving some complicated problems which may take years and even decades with these computers. This is while, based on quantum theory and related algorithms, solving of these problems would take much less time.... 

Metamaterials are engineered sub-wavelength structures which show electromagnetic properties not found in natural materials. There is a special interest in superconductor metamaterials in microwave engineering. These metamaterials have low loss, are compact and show useful properties like tunability and parametric amplification when Josephson junctions are incorporated in them. When Josephson junctions are used, these metamaterials are called Josephson metamaterials which have attracted a good amount of research interest. Because of nonlinear nature of Josephson junction, Josephson metamaterials show nonlinear properties. One dimensional Josephson metamaterials are called Josephson... 

Quantum bits, also known as Qubits are the smallest building blocks of quantum computers, their correct operation has a great impact on quantum computing fidelity. For this purpose, Qubits need to have the necessary properties. Many properties have been defined for Josephson junction-based Qubits in order to implement better qubits. In this master thesis, the main characteristics of superconducting quantum bits including resonant frequency, anharmonicity factor, output readability signal, and quantum decoherence time including relaxation time and dephasing time have been calculated for cooper pair box topology in different operational regimes from cooper pair box regime to quantronium and...