286 research outputs found
Experimental Demonstration of a Structured Material with Extreme Effective Parameters at Microwaves
Following our recent theoretical studies [M. G. Silveirinha, C. A. Fernandes,
Phys. Rev. B, 78, 033108, 2008], it is experimentally verified that an array of
crossed metallic wires may behave as a nonresonant material with extremely
large index of refraction at microwaves, and may enable the realization of
ultra-subwavelength waveguides.Comment: accepted for publication in Applied Physics Letters (in press).
Applied Physics Letters (in press) (2008
Quantum behaviour of a flux qubit coupled to a resonator
We present a detailed theoretical analysis for a system of a superconducting
flux qubit coupled to a transmission line resonator. The master equation,
accounting incoherent processes for a weakly populated resonator, is
analytically solved. An electromagnetic wave transmission coefficient through
the system, which provides a tool for probing dressed states of the qubit, is
derived. We also consider a general case for the resonator with more than one
photon population and compare the results with an experiment on the
qubit-resonator system in the intermediate coupling regime, when the coupling
energy is comparable with the qubit relaxation rate.Comment: 16 pages, 6 figure
In-situ measurement of the permittivity of helium using microwave NbN resonators
By measuring the electrical transport properties of superconducting NbN
quarter-wave resonators in direct contact with a helium bath, we have
demonstrated a high-speed and spatially sensitive sensor for the permittivity
of helium. In our implementation a mm sensing volume is
measured with a bandwidth of 300 kHz in the temperature range 1.8 to 8.8 K. The
minimum detectable change of the permittivity of helium is calculated to be
/Hz with a sensitivity of order
/Hz easily achievable. Potential applications
include operation as a fast, localized helium thermometer and as a transducer
in superfluid hydrodynamic experiments.Comment: 4 pages, 3 figure
Optimization of sample-chip design for stub-matched radio-frequency reflectometry measurements
A radio-frequency (rf) matching circuit with an in situ tunable varactor
diode used for rf reflectometry measurements in semiconductor nanostructures is
investigated and used to optimize the sample-specific chip design. The samples
are integrated in a 2-4 GHz stub-matching circuit consisting of a waveguide
stub shunted to the terminated coplanar waveguide. Several quantum point
contacts fabricated on a GaAs/AlGaAs heterostructure with different chip
designs are compared. We show that the change of the reflection coefficient for
a fixed change in the quantum point contact conductance can be enhanced by a
factor of 3 compared to conventional designs by a suitable electrode geometry
Development and operation of the twin radio frequency single electron transistor for solid state qubit readout
Ultra-sensitive detectors and readout devices based on the radio frequency
single electron transistor (rf-SET) combine near quantum-limited sensitivity
with fast operation. Here we describe a twin rf-SET detector that uses two
superconducting rf-SETs to perform fast, real-time cross-correlated
measurements in order to distinguish sub-electron signals from charge noise on
microsecond time-scales. The twin rf-SET makes use of two tuned resonance
circuits to simultaneously and independently address both rf-SETs using
wavelength division multiplexing (WDM) and a single cryogenic amplifier. We
focus on the operation of the twin rf-SET as a charge detector and evaluate the
cross-talk between the two resonance circuits. Real time suppression of charge
noise is demonstrated by cross correlating the signals from the two rf-SETs.
For the case of simultaneous operation, the rf-SETs had charge sensitivities of
and .Comment: Updated version, including new content. Comments most welcome:
[email protected] or [email protected]
Low-Cost Electronic Microwave Calibration for Rapid On-Line Moisture Sensing of Seedcotton
In order to improve rapid on-line moisture sensing of seedcotton in cotton gins, a means by which to establish a reliable low-cost wide-band electronic calibration is critically needed. This calibration is needed to center the circuit due to changes in the internal signal delays and attenuation drift caused by temperature changes in the various system components and circuit elements. This research examines a hardware technique for use in conjunction with microwave reflective sensing probes having an extended bandwidth from 500 MHz through 2.5 GHz. This new technique was validated experimentally against known electrical propagation delay standards. Results of the measured propagation delay with this type of automatic electronic calibration method was found to agree with results using a vector network analyzer with a traditional S11 single port error correction calibration methodology to within 4% of the measurement, 95% confidence, with a standard error of +/− 18.6 ps for the delay measurements. At this level of performance, the proposed low-cost technique exhibits superior performance, over the typical geosciences time-domain reflectometer “TDR”, instruments in common use in soil moisture testing and is suitable for use in cotton gin moisture sensing
Calculation of electrostatic fields using quasi-Green's functions: application to the hybrid Penning trap.
Penning traps offer unique possibilities for storing, manipulating and investigating charged particles with high sensitivity and accuracy. The widespread applications of Penning traps in physics and chemistry comprise e.g. mass spectrometry, laser spectroscopy, measurements of electronic and nuclear magnetic moments, chemical sample analysis and reaction studies. We have developed a method, based on the Green's function approach, which allows for the analytical calculation of the electrostatic properties of a Penning trap with arbitrary electrodes. The ansatz features an extension of Dirichlet's problem to nontrivial geometries and leads to an analytical solution of the Laplace equation. As an example we discuss the toroidal hybrid Penning trap designed for our planned measurements of the magnetic moment of the (anti)proton. As in the case of cylindrical Penning traps, it is possible to optimize the properties of the electric trapping fields, which is mandatory for high-precision experiments with single charged particles. Of particular interest are the anharmonicity compensation, orthogonality and optimum adjustment of frequency shifts by the continuous SternGerlach effect in a quantum jump spectrometer. The mathematical formalism developed goes beyond the mere design of novel Penning traps and has potential applications in other fields of physics and engineering
Discretely guided electromagnetic effective medium
A material comprised of an array of subwavelength coaxial waveguides
decomposes incident electromagnetic waves into spatially discrete wave
components, propagates these components without frequency cut-off, and
reassembles them on the far side of the material. The propagation of these wave
components is fully controlled by the physical properties of the waveguides and
their geometrical distribution in the array. This allows for an exceptional
degree of control over the electromagnetic response of this effective medium,
with numerous potential applications. With the development of nanoscale
subwavelength coaxial waveguides, these applications (including metamaterial
functionality) can be enabled in the visible frequency range
Scalable synchronization of spin-Hall oscillators in out-of-plane field
A strategy for a scalable synchronization of an array of spin-Hall
oscillators (SHOs) is illustrated. In detail, we present micromagnetic
simulations of two and five SHOs realized by means of couples of triangular
golden contacts on the top of a Pt/CoFeB/Ta trilayer. Results highlight that
the synchronization occurs for the whole current region that gives rise to the
excitation of self-oscillations. This is linked to the role of the
magnetodipolar coupling, which is the phenomenon driving the synchronization
when the distance between oscillators is not too large. Synchronization turns
out to be also robust against geometrical differences of the contacts,
simulated by considering variable distances between the tips ranging from 100nm
to 200nm. Besides, it entails an enlargement of the radiation pattern that can
be useful for the generation of spin-waves in magnonics applications.
Simulations performed to study the effect of the interfacial
Dzyaloshinskii-Moriya interaction show nonreciprocity in spatial propagation of
the synchronized spin-wave. The simplicity of the geometry and the robustness
of the achieved synchronization make this design of array of SHOs scalable for
a larger number of synchronized oscillators
Aberration-free ultra-thin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces
The concept of optical phase discontinuities is applied to the design and
demonstration of aberration-free planar lenses and axicons, comprising a phased
array of ultrathin subwavelength spaced optical antennas. The lenses and
axicons consist of radial distributions of V-shaped nanoantennas that generate
respectively spherical wavefronts and non-diffracting Bessel beams at telecom
wavelengths. Simulations are also presented to show that our aberration-free
designs are applicable to high numerical aperture lenses such as flat
microscope objectives
- …