28 research outputs found
Load flow solution for meshed distribution networks
Power flow is a useful tool in operation, planning and optimisation of a system. Distribution systems, generally, refers to the power system network connected to loads at lower operating voltage. In this thesis an efficient power flow method for solving meshed distribution networks by using current injection method and basic formulations of Kirchhoff's laws has been acknowledged. This method has excellent convergence characteristics and thus is more efficient than Newton-Raphson and Fast Decoupled Method. This method can be applied to the solution of both the three-phase (unbalanced) and single-phase (balanced) representation of the network. The main objective of this thesis is to study the Forward-Backward Sweep and to derive the inference that how much efficient it is in solving the load flow problem of the meshed distribution networks
Exploiting Kerr Cross Non-linearity in Circuit Quantum Electrodynamics for Non-demolition Measurements
We propose a scheme for dispersive readout of stored energy in one mode of a
nonlinear superconducting microwave ring resonator by detection of the
frequency shift of a second mode coupled to the first via a Kerr nonlinearity.
Symmetry is used to enhance the device responsivity while minimizing self
nonlinearity of each mode. Assessment of the signal to noise ratio indicates
that the scheme will function at the single photon level, allowing quantum
non-demolition measurement of the photon number state of one mode. Experimental
data from a simplified version of the device demonstrating the principle of
operation are presented.Comment: 12 pages, 4 figure
Millimeter-Wave Lumped Element Superconducting Bandpass Filters for Multi-Color Imaging
The opacity due to water vapor in the Earth's atmosphere obscures portions of the sub-THz spectrum (mm/sub-mm wavelengths) to ground based astronomical observation. For maximum sensitivity, instruments operating at these wavelengths must be designed to have spectral responses that match the available windows in the atmospheric transmission that occur in between the strong water absorption lines. Traditionally, the spectral response of mm/sub-mm instruments has been set using optical, metal-mesh bandpass filters [1]. An alternative method for defining the passbands, available when using superconducting detectors coupled with planar antennas, is to use on-chip, superconducting filters [2]. This paper presents the design and testing of superconducting, lumped element, on-chip bandpass filters (BPFs), placed inline with the microstrip connecting the antenna and the detector, covering the frequency range from 209–416 GHz. Four filters were designed with pass bands 209–274 GHz, 265–315 GHz, 335–361 GHz and 397–416 GHz corresponding to the atmospheric transmission windows. Fourier transform spectroscopy was used to verify that the spectral response of the BPFs is well predicted by the computer simulations. Two-color operation of the pixels was demonstrated by connecting two detectors to a single broadband antenna through two BPFs. Scalability of the design to multiple (four) colors is discussed
Superconducting resonators as beam splitters for linear-optics quantum computation
A functioning quantum computer will be a machine that builds up, in a
programmable way, nonclassical correlations in a multipartite quantum system.
Linear optics quantum computation (LOQC) is an approach for achieving this
function that requires only simple, reliable linear optical elements, namely
beam splitters and phase shifters. Nonlinear optics is only required in the
form of single-photon sources for state initialization, and detectors. However,
the latter remain difficult to achieve with high fidelity. A new setting for
quantum optics has arisen in circuit quantum electrodynamics (cQED) using
superconducting (SC) quantum devices, and opening up the way to LOQC using
microwave, rather than visible photons. Much progress is being made in SC
qubits and cQED: high-fidelity Fock state generation and qubit measurements
provide single photon sources and detection. Here we show that the LOQC toolkit
in cQED can be completed with high-fidelity (>99.92%) linear optical elements.Comment: 4 pages, 3 figure
Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators
We present measurements of the temperature and power dependence of the resonance frequency and frequency noise of superconducting niobium thin-film coplanar waveguide resonators carried out at temperatures well below the superconducting transition (Tc=9.2 K). The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system (TLS) model for amorphous dielectrics. These results support the hypothesis that TLSs are responsible for the noise in superconducting microresonators and have important implications for resonator applications such as qubits and photon detectors
Experimental evidence for a surface distribution of two-level systems in superconducting lithographed microwave resonators
We present measurements of the temperature-dependent frequency shift of five
niobium superconducting coplanar waveguide microresonators with center strip
widths ranging from 3 m to 50 m, taken at temperatures in the range
100-800 mK, far below the 9.2 K transition temperature of niobium. These data
agree well with the two-level system (TLS) theory. Fits to this theory provide
information on the number of TLS that interact with each resonator geometry.
The geometrical scaling indicates a surface distribution of TLS, and the data
are consistent with a TLS surface layer thickness of order a few nm, as might
be expected for a native oxide layer.Comment: 3 figures, submitted to AP
High coherence hybrid superconducting qubit
We measure the coherence of a new superconducting qubit, the {\em
low-impedance flux qubit}, finding s. It is a
three-junction flux qubit, but the ratio of junction critical currents is
chosen to make the qubit's potential have a single well form. The low impedance
of its large shunting capacitance protects it from decoherence. This qubit has
a moderate anharmonicity, whose sign is reversed compared with all other
popular qubit designs. The qubit is capacitively coupled to a high-Q resonator
in a configuration, which permits the qubit's state to be read out
dispersively
Decoherence of floating qubits due to capacitive coupling
It has often been assumed that electrically floating qubits, such as flux
qubits, are immune to decoherence due to capacitive coupling. We show that
capacitive coupling to bias leads can be a dominant source of dissipation, and
therefore of decoherence, for such floating qubits. Classical electrostatic
arguments are sufficient to get a good estimate of this source of relaxation
for standard superconducting qubit designs. We show that relaxation times can
be improved by designing floating qubits so they couple symmetrically to the
bias leads. Observed coherence times of flux qubits with varying degrees of
symmetry qualitatively support our results.Comment: V1: 4 pages, 3 figures. V2: 5 pages, 3 figures. Published versio