Terahertz Radiation Power Characterization and Optimization of Stack of Intrinsic Josephson Junctions

Terahertz radiation of the stack of intrinsic Josephson junctions in the mesa structure of the layered high-Tc superconductors is analyzed and presented in this work. The dependency of the radiated power to the geometrical parameters, cavity-waveguide boundaries, and magnetic and electric bias has been investigated. This has been done by numerical calculation of the previously proposed coupled sine-Gordon equations, which characterize the electromagnetic dynamics of the stack of the intrinsic Josephson junctions. Using the obtained numerical results from these coupled equations, the effect of the design parameters such as dimensions of the mesa structure and the magnitude of the applied magnetic field and the dc current on the enhancement of the radiated power is studied. Thus, the radiated power is optimized with respect to these considered parameters. By variation of the number of layers, we also investigate the effect of the number of intrinsic Josephson junctions on the total radiated power. The results from this part are also compared with the previous analytical models.Comment: 8 pages, 8 figure

Increasing THz Radiation Power and Monochromaticity Using Optically Induced Photonic Crystal in Layered Superconductors

The possibility of enhancing the radiation power and monochromaticity by optically induced photonic crystal in the superconducting cavity is proposed and investigated. In such a structure, by periodically irradiating the stacked Josephson junctions and consequently partially suppression of the superconductivity in the irradiated positions due to depairing, a periodic optical configuration is formed. This leads to photonic band gap opening in the range of the terahertz radiation emitted from the layered superconductor. We show that such a photonic band gap significantly enhances the impedance matching at the boundary of the cavity and the waveguide. Since the weak optical coupling of the outer and inner space of layered superconductor samples is a serious reason of reducing radiated power especially in the experiments, the proposed configuration is capable of extremely enhancement in the emitted power along with attenuation of the undesired harmonics.Comment: 7 Pages, 2 figure

Fate of False Vacuum in Superconducting Flux Qubits

We propose a similarity between the scenario of fate of false vacuum in cosmology at early universe and the situation in where the quantum state decays in superconducting Flux qubit. This is due to the fact that both cases have two homogeneous stable equilibrium states in scalar field, which in quantum theory, could penetrate through the barrier in different possibilities and hence considered unstable decaying in time. In quantum computation, decay rate is among the most important factors in characteristics of the system like coherency, reliability, measurement fidelity, etc. In this considered potential, the decay rate from the penetrating (False vacuum) state to the stable (absolute minimum) state is achieved to leading order in Planck constant by the approach of Instanton model. In case of the superconducting flux qubit having thin barrier potential, the decay rate is calculated and its relations with actual set of parameters in flux qubit design are introduced.Comment: Submitted to IEEE Transactions Applied Superconductivity. arXiv admin note: text overlap with arXiv:1403.576

Precise Time Evolution of Superconductive Phase Qubits

New procedure on precise analysis of superconducting phase qubits using the concept of Feynman path integral in quantum mechanics and quantum field theory has been introduced. The wave function and imaginary part of the energy of the pseudo ground state of the Hamiltonian in phase qubits has been obtained from semi classical approximation and we we estimate decay rate, and thus the life time of meta stable using the approach of Instanton model. We devote the main effort to study the evolution of spectrum of Hamiltonian in time after addition of interaction Hamiltonian, in order to obtain the high fidelity quantum gates.Comment: Submitted to Physical Review B. arXiv admin note: substantial text overlap with arXiv:1403.576

Feynman Path Integral Approach on Superconducting Qubits and Readout Process

In this paper we introduce a new procedure on precise analysis of various physical manifestations in superconducting Qubits using the concept of Feynman path integral in quantum mechanics and quantum field theory. Three specific problem are discussed, we devote the main efforts to studying the wave function and imaginary part of the energy of the pseudo ground state of the Hamiltonian in Phase Qubits and we estimate decay rate, and thus the life time of meta stable states using the approach of 't Hooft's Instantons model. Correction to the Tilted-Washboard potential and current of Phase Qubits by precise analysis of Ginzburg-Landau's free energy equation has been considered. Also we evaluate the most accurate value of energy levels and wave function in Charge and Flux Qubits by Semi classical approximation in path integral formalism by considering limits of experimental errors, comparing them with WKB results and finally, we try to study more specific the evolution of spectrum of Hamiltonian in time after addition of interaction Hamiltonian, in order to obtain the high fidelity quantum gates.Comment: 25 pages, 17 figure

HTS YBCO Resonator Configuration with Coplanar Optimized Flux Concentrator Strongly Coupled to rf SQUID

We developed a novel magnetic coupling module formed of a monolayer superconducting flux concentrator, which is integrated with a coplanar resonator strongly coupled to HTS rf-SQUID. Three types of resonators, including a long stripline resonator between input loop and pick-up loop of the flux concentrator, a complementary split ring resonator (CSRR), and also a spiral shape inside the input loop are explored. The resonance quality factors as well as the coupling to the SQUID of different patterns of these three types of the resonators is evaluated using Finite Element Method (FEM) simulations. Several readout methods to couple the electronic system to the resonators are tested, including inductive (coil) and capacitive (transmission line) couplings, and the optimum readout is reported for each of the resonators. Among the evaluated resonator types, a spiral shape resonator with optimal design showing the highest quality factor (5900) together with the strongest coupling to the SQUID (-0.5 dB) at resonance frequency of 836 MHz, is fabricated using 200 nm thick superconducting YBCO on a 1 mm thick crystalline LaAlO3 substrate. The flux concentrator of the module is optimized by the variation of its linewidths and also its input loop radius to obtain maximum flux transformation efficiency.Comment: 5 page

Effect of Substrate Thickness on Responsivity of Free-Membrane Bolometric Detectors

The effect of substrate thickness and its Debye temperature on the bolometric response of the freestanding-membrane type of superconductor transition-edge detectors is investigated. The investigation is based on the calculation of the variation of the specific heat per unit volume and the heat conductivity using the finite-size scaling method for different Debye temperatures and micron size thickness of substrate. We also calculated the heat capacity and time constant for various materials with Debye temperatures in the range of 600-1400K. The calculated results are compared to previously reported response values obtained theoretically and experimentally for the thermal-based infrared detectors. The IR response versus substrate thickness of these types of devices for different modulation frequencies is also presented. This inspected response at low thicknesses of substrate shows anomalistic behavior with respect to the previously reported results of response analyses. Here, we also obtained the optimized substrate thickness and Debye temperatures for maximum responsivity of these types of devices.Comment: 4 pages, 5 figure

High Power and Wideband Terahertz Modulator Using c-Axis Current Controlled Layered Superconductors

The possibility of applying stacks of capacitive and inductively coupled and synchronized Josephson junctions as either high radiation power or wideband current controlled terahertz modulator is proposed and investigated. The properties of such modulators, which can be fabricated using the mesa structure of the layered high-Tc superconductors, are obtained numerically and analytically in the presence and absence of the external magnetic field with different vortex lattices. Based on these analyses, the peak frequency deviation of modulated signal with respect to input signal is calculated. Typical spectrum of the radiated signal is also obtained in this approach. In addition, the variation of the peak frequency deviation with respect to carrier frequency for different magnetic configurations is obtained analytically. The results for these calculations show carrier frequencies from subtrahertz to multiterahertz.Comment: 8 pages, 5 figure

Tunable Bandgap Opening in the Proposed Structure of Silicon Doped Graphene

A specific structure of doped graphene with substituted silicon impurity is introduced and ab. initio density-functional approach is applied for energy band structure calculation of proposed structure. Using the band structure calculation for different silicon sites in the host graphene, the effect of silicon concentration and unit cell geometry on the bandgap of the proposed structure is also investigated. Chemically silicon doped graphene results in an energy gap as large as 2eV according to DFT calculations. As we will show, in contrast to previous bandgap engineering methods, such structure has significant advantages including wide gap tuning capability and its negligible dependency on lattice geometry.Comment: 4 pages, 4 figure

Blood Glucose Measurement Based on Infra-Red Spectroscopy

An algorithm based on PLS regression has been developed and optimized for measuring blood glucose level using the infra-red transmission spectrum of blood samples. A set of blood samples were tagged with their glucose concentration using an accurate invasive glucometer and analyzed using a standard FTIR spectrometer. Using the developed algorithm, the results of the FTIR spectroscopy of the samples were analyzed to find the glucose concentration in the samples. The obtained glucose concentration by the algorithm were in good agreement with the results obtained by the standard glucometer, and the mean estimation error was 7 mg/dL. This error is in the range of available commercial invasive meters