Phase-Locking of a Gunn Oscillator at 3mm Waveband Using High Temperature Superconducting Josephson Junction Harmonic Mixer

A Gunn oscillator at 3mm waveband has been phase-locked to a synthesizer local oscillator using a high T_(c)YBa_(2)Cu_(3)O_(7-δ) Josephson junction operated at 77K as the harmonic mixer,with harmonic numbers up to 52.The observed spectrum of the phase-locked output at the intermediate frequency(IF)shows clearly that the quality of the phase-locking is very good.To drive the analogue phase locking loop successfully,it is essential to have IF output and signal-to-noise ratio both as high as possible.

Experimental demonstrations of high-Q superconducting coplanar waveguide resonators

We successfully designed and fabricated an absorption-type of superconducting coplanar waveguide (CPW) resonators. The resonators are made from a niobium film (about 160 nm thick) on a high-resistance Si substrate, and each resonator is fabricated as a meandered quarter-wavelength transmission line (one end is short to the ground and another end is capacitively coupled to a through feedline). With a vector network analyzer we measured the transmissions of the applied microwave through the resonators at ultra-low temperature. The obtained loaded quality factors are significantly high, i.e. up to ～10 6 . When the temperature increases slowly from the base temperature (20 mK), the resonance frequencies of the resonators are blue shifted and the quality factors are lowered slightly. In principle, this type of device can integrate a series of CPW resonators with a common feedline, making it a promising candidate as the data bus for coupling distant solid-state qubits and the sensitive detector of single photons.

A simple Fourier transform spectrometer for terahertz applications

A simple Fourier transform spectrometer was designed and constructed for the measurement of detectors,sources,passive devices and materials in the terahertz(THz) range.It can be operated at frequencies between 0.3 and 1.5 THz,using a 50-μm-thick Mylar-film beam splitter.The spectral range can be changed by altering the thickness of the beam splitter.The highest frequency resolution is 750 MHz.We studied the properties of heterodyne detectors including superconductor mixers and semiconductor harmonic mixers,direct detectors including an InSb semiconductor bolometer,superconducting tunnel junctions and the Golay cell,and sources including Gunn oscillators and a microwave source with its multipliers,as well as various materials and passive devices including Si wafers and metal mesh filters.

Temperature dependence of the point defect properties of GaN thin films studied by terahertz time-domain spectroscopy

The dielectric functions of GaN for the temperature and frequency ranges of 10–300 K and 0.3–1 THz are obtained using terahertz time-domain spectroscopy.It is found that there are oscillations of the dielectric functions at various temperatures.Physically,the oscillation behavior is attributed to the resonance states of the point defects in the material.Furthermore,the dielectric functions are well fitted by the combination of the simple Drude model together with the classical damped oscillator model.According to the values of the fitting parameters,the concentration and electron lifetime of the point defects for various temperatures are determined,and the temperature dependences of them are in accordance with the previously reported result.Therefore,terahertz time-domain spectroscopy can be considered as a promising technique for investigating the relevant characteristics of the point defects in semiconductor materials.

A single-photon fault-detection method for nanocircuits that use GaN material

As the complexity of nanocircuits continues to increase,developing tests for them becomes more difficult.Failure analysis and the localization of internal test points within nanocircuits are already more difficult than for conventional integrated circuits.In this paper,a new method of testing for faults in nanocircuits is presented that uses single-photon detection to locate failed components(or failed signal lines)by utilizing the infrared photon emission characteristics of circuits.The emitted photons,which can carry information about circuit structure,can aid the understanding of circuit properties and locating faults.In this paper,in order to enhance the strength of emitted photons from circuit components,test vectors are designed for circuits’components or signal lines.These test vectors can cause components to produce signal transitions or switching behaviors according to their positions,thereby increasing the strength of the emitted photons.A multiple-valued decision diagram(MDD),in the form of a directed acrylic graph,is used to produce the test vectors.After an MDD corresponding to a circuit is constructed,the test vectors are generated by searching for specific paths in the MDD of that circuit.Experimental results show that many types of faults such as stuck-at faults,bridging faults,crosstalk faults,and others,can be detected with this method.

Simulation and experiment of vortex transport properties in a Type Ⅱ superconductor with grain boundary

We firstly described a simulation model to investigate the influence of grain boundary(GB)on the vortex transport properties in YBCO film.It is found that the size of inhomogeneous area caused by GB as well as the average velocity in transverse and longitudinal directions shows an angular dependence when the angle between the GB and the sample edge varies.We have also studied the impact of magnetic field intensity on dynamic behavior of vortex lattice and found that a lower vortex density makes it difficult for the vortex lattice to transfer from pinning state to flow state.As the magnetic field is decreased beyond a critical value,sharp jumps and strong fluctuations were observed in the I-V curve.Finally,we conducted measurements on a thin film YBa2Cu3O7 with an individual artificial grain boundary to support the simulation process.