Sharif Digital Repository

Superconducting SQUID sensors are one of the most sensitive magnetic sensors that have been ever produced. Due to their high sensitivity, these sensors have many applications in different fields. Magnetic Imaging and far away targets detections are of these applications. In this project, a magnetic imaging system based on Superconducting SQUID sensors have been designed and implemented. In SQUID applications one of the most important problems is the cancelation of the unwanted fields including background low frequency and high frequency fields. In residential and urban areas the interference of Electricity network is considered as one of the major noise sources. While the high frequency... 

In this work, we report on a developed single-channel high-Tc SQUID based MCG system for operation in unshielded environment. In brief, our system consists of a liquid Nitrogen Dewar and two high-Tc rf-SQUID capsuled in a holding probe,which is connected via coaxial cables to our multichannel rf-SQUID readout electronics.The rf-SQUIDs were patterned from about 200 nm△10 nm thick YBCO films sputtered on 1 mm thick LaAlO3 substrates. The holding probe integrates rf-SQUIDs, LC resonant circuits, and shielding coils. We have investigated the effects of the lumped element tank circuit resonator parameters on the rf-SQUID signal characteristics and based on the simulation and experimental... 

Superconducting Quantum Interference Devices (SQUIDs) are one of the most sensitive magnetic flux detectors. According to their high sensitivity, these sensors have many applications such as magnetic imaging, magnetocardiography and magnetoencephalography. In this project we have designed and implemented a fluxgate based active shield that would be used in magnetocardiography. One of the main concerns in RF-SQUID applications is suppression of the low and high frequency noises. These noise sources includes earth magnetic force, humming noise and RF noise caused by cell phones. These sources could unlock RF-SQUID sensors and hence needs to be shielded. Low frequency noise suppression could be... 

The aim of this project is design and implementation of the “gradiometer RF SQUID base Vibrating Sample Magnetometer (VSM)”. Different sections of the system have been designed such as pick up coils, vibration system and electronic circuits. The piezoelectric crystal has been concerned for vibration system. At the first step, we have implemented the basic VSM system. In the basic system, voltage induces in two series opposite pick up coils and its output is recognizable via electronic circuits. At the second phase of the project, the electronic circuits of basic VSM system have been replaced with the RF SQUID gradiometer and its electronic circuits. Afterwards, the sensitivity and the gain... 

In this dissertation, we propose and analytically investigate a scheme for effective three-dimensional cooling of a nanoparticle optically trapped in a Fabry-Perot cavity using multiple cavity modes. By employing active feedback cooling using amplitude modulation of cavity modes, our approach allows to access the UHV regime without the need for any additional means like an external tweezer or a radio-frequency trapping approach. For a set of feasible experimental parameters, we demonstrate that the cooling rates achievable are sufficient to overcompensate recoil heating. Therefore the approach is suited to trap a particle for indefinite times at UHV pressures, where air damping cannot... 

Ultra-sensitive magnetometers based on Radio Frequency Superconducting Quantum Interference Device (rf SQUID), have wide applications in Non-destructive Evaluation (NDE), geophysical measurements and biomagnetic measurements, especially in magnetocardiography (MCG) systems. A superconducting module coupled to rf SQUID is designed to provide a resonance frequency in GHz range (according to the electronic system frequency), as well as concentrating the magnetic flux in the effective area of SQUID. The signal can be measured through a port pumping AC power to the module. The resonator has been also implemented by lumped element tank circuits, but the quality factor of these circuits are usually... 

This thesis deals with the theoretical and experimental investigation of quantum interference and coherence, and electromagnetic induced transparency (EIT) in multi-level atomic systems such as hot and cold Rb atoms, semiconductor quantum dots and wells. Optical properties of atomic media in presence of coherent laser fields and incoherent fields are studied.
Theoretical studies verify the crucial role of atomic coherence due to quantum interference in modifying optical properties of atomic media. Suitable and efficient models based on multi-level atomic systems to investigate the optical properties and, optical bistability and multistability are proposed. The most advantages of these... 

Characterization of local magnetic activity of the heart muscles is named magnetocardiography (MCG), which measures magnetic field generated by electrical activity around heart. RF SQUID sensors are appropriate choice for measuring magnetic activity of the heart muscles. Because squid detects weak signals as low as fTesla, while heart magnetic field is near 50 pt which is one millionth of earth magnetic field and thousands of time weaker than the environment noise. One of the problems of mcg system is its urgency to shielding of unwanted magnetic field. In this project design of holders and resonators for well coupled input coil with RF SQUID is improved. As a result, at the first stage... 

Quantum interference and coherence could change the optical response of media and results several effect such as electromagnetically induced transparency (EIT), Lasing Without inversion (LWI) and optical nonlinearityenhancement.In Quantum Computing, by using Quantum coherence, one can producedecoherence free sub-space whichhasoutstandingapplications in this field.
In this work optical bistability behavior studied in two coupled quantum dots which resembles a three-level V type atomic system under influence of squeezed state reservoir. Spontaneously generated coherence (SGC) is responsible for Quantum interference. The squeezed state radiation could break the coherence in media and make... 

The purpose of this thesis is the incorporation of RF SQUID ultra-sensitive magnetic sensors in an implemented SQUID NDE system and also the development of associated inverse solution algorithms for the detection of defects in metallic samples. The system is based on the induction of Eddy currents and the incorporation of SQUIDs for precise detection of the magnetic field anomalies related to the defects in the sample. One of the major parts of the system is the highly stable, multi-channel RF SQUID readout system which has been designed and implemented with novel features for this project. For the magnetic inverse analysis of our SQUID NDE measurements, new models have been presented for... 

Analog SQUIDs have limited slew rate and dynamic range and these problems make it hard to operate SQUID systems in unshielded applications like Bio-magnetic imaging and NDE. Recently by combining analog SQUIDs and RSFQ Logic, new class of magnetic sensors are introduced. These sensors have an acceptable sensitivity and very high dynamic range. On the other hand these sensors, Which are called Digital SQUIDs, can be directly connected to digital signal processing stages. In This work, for first time, a digital SQUID completely based on i-directional RSFQ was designed and optimized. using Bi-directional RSFQ, one can significantly simplify the digital SQUID circuit design and therefore... 

Quantum interference and coherence are responsible for a novel set of physical phenomena, where Electromagnetically Induced Transparency is one of the most important of them. Each of these phenomena can make a new possibility for modifying the optical properties of a coherently prepared medium. Fast controllability of optical properties in one hand and flexibility of this control process in the other hand, are important factors that attract interests into coherent control of light .Coherent control of optical properties of the medium can be used in designing some advanced and challenging devices including All-Optical Switches. In this work , in a consistent picture, using a step by step...