159 research outputs found
Dispersive Response of a Disordered Superconducting Quantum Metamaterial
We consider a disordered quantum metamaterial formed by an array of
superconducting flux qubits coupled to microwave photons in a cavity. We map
the system on the Tavis-Cummings model accounting for the disorder in
frequencies of the qubits. The complex transmittance is calculated with the
parameters taken from state-of-the-art experiments. We demonstrate that photon
phase shift measurements allow to distinguish individual resonances in the
metamaterial with up to 100 qubits, in spite of the decoherence spectral width
being remarkably larger than the effective coupling constant. Our simulations
are in agreement with the results of the recently reported experiment.Comment: 10 pages, 4 figure
Imaging of Microscopic Sources of Resistive and Reactive Nonlinearities in Superconducting Microwave Devices
The technique of low-temperature Laser Scanning Microscopy (LSM) has been
applied to the investigation of local microwave properties in operating
YBa2Cu3O7/LaAlO3 thin-film resonators patterned into a meandering strip
transmission line. By using a modified newly developed procedure of
spatially-resolved complex impedance partition, the influence of inhomogeneous
current flow on the formation of nonlinear (NL) microwave response in such
planar devices is analyzed in terms of the independent impact from resistive
and inductive components. The modified procedure developed here is dramatically
faster than our previous method. The LSM capability to probe the spatial
variations of two-tone, third-order intermodulation currents on micron length
scales is used to find the 2D distribution of the local sources of microwave
NL. The results show that the dominant sources of microwave NL are strongly
localized in the resistive domains.Comment: 4 pages, 6 figures, 2-column format,submitted for the 2006 Applied
Superconductivity Conferenc
Spatial and frequency dependencies of local photoresponse of HTS strip-line resonator in regime of two-tone microwave intermodulation excitation
A new phenomenological approach to spatially-resolved research of nonlinear
(NL) microwave properties of operating thin-film superconducting resonators is
proposed. The approach is based on frequency and spatial singularity of Laser
Scanning Microscopy (LSM) images that can be extracted from a set of 2-D
patterns representing x-y distribution of the LSM photoresponse, PR(x, y), at
fixed third-order intermodulation (IMD) frequencies 2f1-f2 and 2f2-f1 as a
result of two-tone resonator microwave excitation at equidistant frequencies f1
and f2 relative to the fundamental resonance, f0. It was shown by us earlier
that the total LSM PR(x, y) originates from two independent (resistive, PRR(x,
y), and inductive, PRX(x, y)) contributions which can be extracted directly
from the LSM images acquired at f1 and f2 by using a method of
spatially-resolved complex impedance partition [1]. Here, we show that
practically the same manipulation of LSM images at 2f1-f2 and 2f2-f1 can be
used to present NL components of IMD LSM PR(x, y) in terms of its independent
spatial variations of (i) inductive IMD_IND(x, y) and (ii) resistive IMD_RES(x,
y) contributions reflecting the origin of the local sources of microwave NL.
[1] A.P. Zhuravel, S.M. Anlage, and A.V. Ustinov, Appl. Phys. Lett., vol. 88,
p. 212503, 2006.Comment: 3 pages, 4 figures, submitted to the Seventh International Kharkov
Symposium (MSMW'10) Proceeding
Enhancing the coherence of superconducting quantum bits with electric fields
In the endeavor to make quantum computers a reality, integrated superconducting circuits have become a promising architecture. A major challenge of this approach is decoherence originating from spurious atomic tunneling defects at the interfaces of qubit electrodes, which may resonantly absorb energy from the qubit’s oscillating electric field and reduce the qubit’s energy relaxation time T. Here, we show that qubit coherence can be improved by tuning dominating defects away from the qubit resonance using an applied DC-electric field. We demonstrate a method that optimizes the applied field bias and enhances the average qubit T time by 23%. We also discuss how local gate electrodes can be implemented in superconducting quantum processors to enable simultaneous in situ coherence optimization of individual qubits
Enhancing the Coherence of Superconducting Quantum Bits with Electric Fields
In the endeavour to make quantum computers a reality, integrated
superconducting circuits have become a promising architecture. A major
challenge of this approach is decoherence originating from spurious atomic
tunneling defects at the interfaces of qubit electrodes, which may resonantly
absorb energy from the qubit's oscillating electric field and reduce the
qubit's energy relaxation time . Here, we show that qubit coherence can be
improved by tuning dominating defects away from the qubit resonance using an
applied DC-electric field. We demonstrate a method that optimizes the applied
field bias and enhances the average qubit time by 23%. We also discuss
how local gate electrodes can be implemented in superconducting quantum
processors to enable simultaneous in-situ coherence optimization of individual
qubits.Comment: 5.5 pages and 4 figures (main Text), plus 6 pages with supplementary
figure
Spatial correlation of linear and nonlinear electron transport in superconducting microwave resonator: laser scanning microscopy analysis
Spatially-resolved techniques of laser scanning microscopy (LSM) have been
used to image simultaneously the spatial variations of (i) rf current flow,
J(x,y), of (ii) areas of resistive dissipation and (iii) the sources of
microwave nonlinearity (NL) in an operating superconducting resonator. The RF
power dependent spatial evolution of these linear and NL microwave properties
in the meander strip YBCO/LAO superconducting resonator have been LSM probed at
different temperatures below Tc. The influence of both topologies of the
twin-domain YBCO structure and of J(x,y) peaks at the edges of
superconducting strip line on its NL properties was analyzed in detail with a
micron-scale spatial resolution. Result shows the resistive origin of the
dominant sources of microwave NLsComment: 3 pages, 3 figures, submitted to MSMW-07 Symposium Proceeding
- …