[3] N. Maleeva, M.V. Fistul, A. Karpov, A.P. Zhuravel, A. Averkin, P. Jung, and A.V. Ustinov, J. Appl. Phys., vol. 115, 2014

Recent ten years, a new type of composite with both negative permittivity and permeability, which is called negative index material, double-negative (DNG) material or metamaterial, has received considerable attention among both scientific and engineering communities. Metamaterial based on the composite right/left-handed (CRLH) transmission line, which features a broader bandwidth and lower loss. To design a uniform CRLH transmission line structure with ultra-low loss properties, in this paper, a high-temperature superconducting composite right/left-handed (HTS CRLH) resonator is proposed.
In this paper, the proposed compact high-temperature superconducting (HTS) CRLH resonator with via-free structure and its equivalent circuit model is given and its constitutive parameters are extracted from the dispersion characteristics. By optimizing the physical transmission structure, which has a minimum insertion loss of parameters of the circuit, we obtain a HTS CRLH resonator under balanced condition. In this case, the unbalanced-case gap is close up and a unique LH-RH transition frequency with non-zero group velocity can be produced. The left-handed and right-handed transmission properties of the proposed HTS CRLH resonator are discussed and verified by measurements. Also, the current distribution at stopband, left-handed passband and right-handed passband of the proposed HTS CRLH resonator are investigated. The proposed HTS CRLH resonator was fabricated on 11.25 mm × 16 mm × 0.5 mm double-sided 500-nm-thick YBa₂Cu₃O₇ films deposited on a 0.5-mm-thick MgO substrate with a relative permittivity of εr = 9.78. The measured results exhibit that the proposed HTS CRLH resonator centered at 1.34 GHz with a 3-dB bandwidth of 295 MHz is observed. The measured in-band minimum and maximum insertion losses are 0.02 dB and 0.13 dB, respectively, and the return loss is greater than 16 dB. The out-of–band rejections in the lower and upper stopbands are more than 20 dB and 30 dB, respectively. We also measured the third intermodulation distortion (IMD3) to characterize the nonlinear effect of the proposed HTS CRLH resonator. The proposed HTS CRLH resonator will have great potential applications in planar integrated microwave circuit configurations and give rise to novel applications.

Composite right/left-handed (CRLH) is a new type of composite with both negative permittivity and permeability, and winning a place among the 10 breakthroughs by Science. Due to the unusual specific property of CRLH, the realization and application of the CRLH have received extensive attention. The utilization of structures possessing CRLH characteristics allows realizing concepts for a multitude of applications such as filters, antennas, and stealth material. Such materials are required to be produced artificially since they are not yet found in nature. In addition, it is well-known that high-temperature superconducting (HTS) thin films can be used to produce miniaturized microwave components with very low insertion loss and high out-of-band rejection on account of extremely low microwave surface resistance and high dielectric constant.

A compact, low-loss, and high-selective HTS CRLH with via-free structure and its equivalent circuit model is given in this paper and its constitutive parameters are extracted from the dispersion characteristics. The presented CRLH structure consists of series interdigital capacitors, rectangular patch with meander line, planar ground, and a non-uniform interdigital structure is adopted to increase the design degree of freedom in this letter. The proposed HTS CRLH resonator was fabricated on 16.1 mm × 22 mm × 0.5 mm double-sided 500-nm-thick YBa2Cu3O7 films deposited on a 0.5-mm-thick MgO substrate with a relative permittivity of εr = 9.78. The measured center frequency is 3.5 GHz, the 3-dB bandwidth of response is 3.4-3.6 GHz. The measured in-band minimum insertion loss is 0.13 dB. Furthermore, IMD3 is studied at 77K to characterize the nonlinear effect of the proposed HTS CRLH resonator. In general, the research in this paper lay the foundation for the development of the CRLH.

This paper presents a wideband and low-loss high-temperature superconducting bandpass filter using composite right/left-handed stepped-impedance resonator. The filter works at 2.6 GHz-band for LTE 2600 applications. The structure is designed in an entirely printed circuit board technology based on the composite right/left-handed theory and its equivalent circuit. The equivalent circuit is used to analyze characteristics of the circuit. The filter consists of two isolated conducting strips which are arranged in parallel, and the strip is a stepped impedance microstrip. The ABCD-matrix can be used to analyze circuit properties, such as dispersion characteristics. The dispersion diagram of the filter is available based on dispersion relationship cos(βp). The dispersion diagram shows the filter’s balanced and unbalanced case.For the filter with the same center frequency, fractional bandwidth and stop-band attenuation, the right/left-handed stepped-impedance resonator bandpass filter presented here proves to surpass its conventional counterpart in terms of size without degradation of performance. The right/left-handed stepped-impedance resonator bandpass filter is also significantly easy controllable in its dimensions and response due to the fact that more elementary parameters are available in right/left-handed configuration. The proposed filter is simulated and measured, and measurement result match well with simulation one. The fractional bandwidth of the passband is about 25.7% along with a low in-band insertion loss of 0.14 dB. Good properties of good out-band rejection and compact size have been achieved and verified. Intermodulation distortion and the transmission properties at different temperatures are used to investigate the nonlinearity of the high-temperature superconducting filter.

We present the temperature dependence of the optical response of current biased YBa₂Cu₃O_7-x (YBCO) grain-boundary Josephson junctions and the observed voltage shift with respect to their dynamic resistance. We have successfully deposited high quality c-axis YBCO thin films on the step-edge and bi-crystal substrates using RF sputtering technique. The fabricated junctions with various widths showed mostly non-hysteretic resistively shunted junction behavior.
A visible laser beam with 635nm wavelength was used as a light source for the optical response measurements and the I-V characterizations under irradiation. The light irradiation was observed to change the critical current of the junctions and the I-V characteristics showed clear significant shift in the voltage across the junction, which is interpreted to the lowering of the critical current when compared to the I-V characteristics under no irradiation. The amplitude of the voltage signals versus current are observed to be different of that expected from the dynamic resistance of the junction at a bias temperature particularly in step-edge junctions. This is while the ratio of the peak of the voltage response to the peak of the dynamic resistance was observed to be proportional to the value of the critical current at the bias temperature. Moreover we observed asymmetries in optical response with respect to the current direction. The measured responses and I-V characteristics of the two types of the junctions under irradiation in several temperatures are compared to investigate the above observations and their dependence on the temperature.

Hot-electron bolometer (HEB) mixers are the primary choice for astronomical THz heterodyne receivers. Thin NbN and NbTiN superconducting films have been used for making mixer devices employed in a number of instruments, most noticeably, the HIFI instrument on Herschel Space Observatory. However, the need in a larger intermediate frequency (IF) bandwidth (in NbN HEB, the bandwidth is limited to 3-4 GHz) for high-resolution spectroscopy of molecular lines across the galaxy (e.g., [OI] 4.7 THz line) motivates the search for suitable materials with higher critical temperatures where the electron thermal relaxation may go faster. Also, an HEB mixer with high operating temperature is sought in view of the reduced cryocooling requirement that is very important for applications in space.
At temperatures above 10 K, the electrons in metal are not the only system determining the mixer efficiency and relaxation rate. Interaction of electrons with acoustic phonons plays an increasing role as the operation temperature increases. As a result, a partial loss of the absorbed THz energy to phonons may occur and the overall relaxation may slow down. This loss mechanism is fundamental and careful consideration of material parameters is required in order to achieve a useful HEB mixer in the 10-100 K temperature range.
We will present a comparison of the practically achieved performance figures for HEB mixers made from NbN, MgB₂, and YBCO and will discuss the material parameters leading to the particular dynamics of the mixer response. The novel MgB₂ mixer fabricated using the Hybrid Physical-Chemical Vapor Deposition (HPCVD) process has been promising so far showing a large IF bandwidth of 8-9 GHz in ≈ 10 nm thick film with T_C =36-38 K. In contrast, the THz YBCO mixer was a disappointment in the past with the bandwidth of only ~ 100 MHz mostly limited by the slow phonon escape from the film. We will also introduce a new material system, which may be suitable for the future HEB mixers. This engineered quasi-2D heterostucture consists of a few layers of LaCuO/LaSrCuO (LSCO) grown by atomic-layer-by-layer MBE (ALL-MBE) thus making a superconducting film with a tunable T_C up to 50 K. The extremely small thickness of the LSCO structure makes the phonon escape process very fast thus allowing one to avoid the energy loss associated with the heating of phonons.

We study Nb-Al2O3-Nb (SIS) junctions embedded in a NbTiN radio-frequency (RF) matching circuit having a large superconducting energy gap frequency of 1.1 THz. With this device type we replace earlier technologies where a full Nb RF matching circuit was used, having a smaller superconducting gap, and increase their possible detection frequency. For full Nb devices, used as heterodyne mixers, the lowest noise temperature, which is fundamentally reachable, could only be realized up to a detection frequency of 700 GHz, since signals at higher frequencies are progressively attenuated in Nb. Looking to circumvent this attenuation, it was found that Nb SIS junctions, which are contacted to higher gap superconducting matching circuits made of NbTiN and are biased at voltages comparable to the Nb gap energy, show an elevated effective quasiparticle temperature up to 10% larger than the bath temperature. The cause for this was identified as an Andreev trap that forms at the interface of Nb and NbTiN. State of the art mixers therefore use a normal metal for one of the two layers of the RF matching circuit to avoid the Andreev trap. Using a superconductor for both layers however promises a higher sensitivity compared to these devices if the Andreev trap can be avoided in another way.

We already showed in DC measurements that the non-equilibrium quasiparticles in the Nb junction with two NbTiN contacts can be removed by inserting a small normal metal Au layer of various shapes and thickness and provided a theory to calculate the optimum layer. Quasiparticles diffuse out of the Nb electrodes into the normal metal, where they inelastically scatter with phonons. This provides a very efficient energy relaxation channel, essentially only limited by the scattering time and the Kapitza resistance between the different materials.

In this work we study a practical SIS mixer where in addition to a constant bias voltage, quasiparticles are excited and created by a THz RF local-oscillator (LO) source on a timescale usually larger than the scattering time with phonons in the Au normal-metal. The Au layer was designed and fabricated in such a way to compensate for the energy input of the bias- and LO source and for the steady-state distribution of non-equilibrium quasiparticles. We present transport and heterodyne measurements quantifying our device design.

We propose microwave-driven superconducting resonators, both of lumped-element and coplanar-waveguide types, incorporating short serial arrays of non-hysteretic one-junction SQUIDs and exploiting nonlinear properties of their Josephson inductance L_J(φ). The equilibrium value of the Josephson phase φ_dc is controlled either by external magnetic flux or dc current bias applied to the array and this allows variation of the value 1/L_J (φ_dc) = (2π/Φ₀)I_c cos φ_dc in the full range from -2πI_c/Φ₀ to 2πI_c/Φ₀, where I_c is the critical current. The corresponding variation of shape of the Josephson nonlinearity modifies dramatically the circuit dynamics. Depending on the drive frequency this circuit enables either the Josephson bifurcation amplifier (JBA) regime [1] or the period-doubling-bifurcation (PDB) regime. The later one is characterized by abrupt onset of oscillations at half-frequency of the drive due to parametric excitation caused by odd nonlinearity in L_J(φ) at φ_dc not equal to nπ, where n is integer. Similar to JBA, this effect can also be used for detection of small signals and readout of quantum states of superconducting qubits [2]. To prove the operation principle of such PDB detector we designed the Nb circuits with appropriate electric parameters for resonance frequencies around 3 GHz and performed measurements at the liquid helium temperature of 4.2 K. The dependence of PDB effect on drive power and external flux bias as well as switching characteristics of our circuits had been investigated and will be reported at this conference.

Superconducting nanowire single-photon detectors (SNSPDs) have received considerable attention due to the high detection efficiency, low timing jitter, high count rate, and low dark count rate. Significant improvements have been achieved in optical structures by integrating optical cavity in recent years, thus increasing DE to over 70% and even 90%, and enabling numerous applications in modern physics. In our work, SNSPDs are designed by straightforwardly fabricating nanowire on one-dimensional (1-D) photonic crystal (PC) which effectively acts as an optical cavity to enhance absorption. The calculated absorptance at resonance wavelength is more than 99% for parallel polarization plane waves from visible to near infrared wavelengths. Experimentally, high performance PC based SNSPDs with different sensitive areas aiming at different wavelengths are fabricated and characterized, including 532nm, 850nm, 940nm, 1064nm, 1550nm. The detailed design and experimental results of SNPSDs will be discussed in this presentation.

Superconducting single-photon detectors (SSPDs) are widely applied in quantum optics. These detectors consist of a superconducting nanowire to which bias current is applied. When one or more photons are absorbed in the nanowire, superconductivity is destroyed, leading to a photon detection event.
The present understanding of physics of the microscopic detection mechanism involves vortex-crossing and quasiparticle-diffusion [1,2]. In this description, the absorbed photon excites an electron, which spreads its energy into a cloud of quasiparticles, causing the redistribution of the bias current. The increase of current density on the edges lowers the potential barrier for vortices, which are then able to enter the wire causing dissipation which finally destroys the superconductivity.
Based on this model, the edges of a nanowire, where it is much easier for the absorbed photon to lower the energy barrier for vortex entry, have a much higher efficiency for photon detection than the center of the wire. To directly resolve this edge effect, near-field optical microscopy is required, in which a sharp gold tip with a spatial resolution ~10 nm can be used as a point-like light source to probe the local response of the 150 nm wide nanowire.
We calculate the probability of photon absorption as a function of the tip position using finite-difference-time-domain method. The tip of finite length is excited from the side and concentrates the field at the tip apex, which strongly localizes the excitation of the detector and enhances the absorption. We combine these results with calculations from the vortex based model to do the first ab-initio calculation of the response of a NbN nanowire in a scattering near-field optical microscope. These calculations predict that it is possible to observe a peak with a width of 10-20 nm in the detector response when the tip is above the edge of the wire.
[1] A. Engel et al. IEEE TAS, 25 (2015), 2200407
[2] J.J. Renema et al. PRL, 112 (2014), 117604

Superconducting Single-Photon Detectors (SSPDs) firstly developed and presented in 2001 year [1]. Currently, SSPD have been actively employed in a variety of applications thanks to their low dark count rate and high system detection efficiency (SDE) over a wide range of visible to near-infrared wavelengths. SSPD timing performances such as jitter and recovery time are of particular importance for number of applications and limited by detector kinetic inductance which has direct dependency on its active area size (dimension) [2].Here we present our investigation on characteristic times of voltage response from SSPD having different active area and accordingly kinetic inductance changing over wide range. For this we carried out electrical measurements on fast oscilloscope using wide-band amplification circuit allowing to observe the original voltage pulse without distortion. We observed that falling edges of SSPD voltage pulse change according to value of kinetic inductance. However the rising edge of the pulse remains almost unchanged at reducing the length of the strip more than 10 times. At present this fact of non-scalable time of rising edge with changing kinetic inductance is not discussed and cannot be explained in the framework of the current phenomenological electrical models. In the report we present the results of our measurements and explanation of this unusual behavior. Obtained results allow to create SSPD with better timing performances and give new information for developing the SSPD operation theory which currently is not complete.

Transition-edge sensors (TESs) are single photon detectors attractive for applications and experiments of quantum optics and quantum information for their photon number resolving capability [1, 2]. Nowadays, high energy resolution TESs for telecommunication are based either on tungsten films or on gold and titanium films showing slow recovery time constants.
Since the TES’s response time is related to its transition temperature and faster devices could be obtained at higher temperatures, we started to investigate as sensitive film a bilayer of aluminum and titanium whose critical temperature can be trimmed between the Tc of Ti and the Tc of Al.
TES devices have been fabricated by e-beam deposition, their active areas ranging between 100 µm² and 400 µm². Niobium wiring have been defined by sputtering and lift-off technique.
These devices have been investigated under thermal and optical point of view and show at 200 mK: response time constants of about 2 ms and single photon discrimination at 1550 nm with an intrinsic energy resolution of 0.34 eV. Reducing the device active area at 1 µm² and rising the working temperature up to 700 mK, the response time constant can reduce down to hundreds of ns without worsening of the energy resolution
[1] L. Lolli et al, Appl. Phys. Lett. Vol. 103 (2013) 041107.
[2] D.H.Smith et al, Nature Communications, vol. 3 (2012) 625

We present a new approach for a non-destructive evaluation of metallic objects with defects at different depths in one scan based on multi frequency excitation. In our earlier reports, it is shown that there is an optimum frequency for particular known depth flaws, which helps us to find the depth of the flaws in unknown samples. Though using this approach, successive scans are required for a sample with several cracks at different depths, which would have further complication for defect characterizations in complex structures. We examined the ability of our proposed double frequency excitation to detect deep-lying multi-depth cracks of aluminum plates using our HTS SQUID gradiometer based system. For this purpose, room temperature stationary samples with intentional cracks are tested. The measurements are performed in an ambient noisy environment, and the excitation coil has the form of a double D-shaped printed-circuit-board coil. The system is incorporating an automated two dimensional non-magnetic scanning robot. Using this 2D scanning system, the obtained results from scanning samples with various defects at various depths using double frequency excitation technique are analyzed. Considering the results of the consecutive single frequency excitation measurements, the obtained depths of the flaws using the double frequency excitation method was further confirmed. Using FEM simulation, we have also investigated the above approach and good agreement between the experimental and the theoretical results are obtained in all examined cases.

Here we present a new active shielded based environmental noise cancellation method in a magnetocardiography system without passive magnetic shield. The MCG system is based on two high temperature RF-SQUID sensors used in gradiometer configuration. The implemented active magnetic shield in this work is incorporating two shield frequency ranges. This is due to the fact that the shield design is based on the compensation of the environmental magnetic fields, which ranges from the very low frequencies up to RF high frequencies magnetic fields with wide range of amplitude recognized as noise or unwanted magnetic signals. Therefore, the shield is designed in a multi-shell structure where each shell is a set of magnetic coils designed and optimized by FEM calculations. One set is used for compensating high amplitude and very low frequency magnetic fields, and the second set is used for relatively low amplitude and high frequency magnetic fields.

Because of the nonlinearity of the shielding system, each set of coils needs independent signal noise rejection control system for eliminating the related environmental magnetic field noises. This is while, the same SQUID sensor of the system is used as reference sensor for compensating both field’s components. For designing the controller, methods based on the dynamic model approximation of first and second order were examined, which lead to PI and PID controllers. In addition, the primary SQUID of the system is observed to have a phase shift in comparison to the reference one, which was further considered in designing the control system.

In this paper, investigation of the shielding performance of our bi-layer magnetic shield as the active compensation fed by the optimal feedback control system is reported. The shielding efficiency of the bi-layer active shield system showed an improved effectiveness compared to that of the conventional one layer active shield systems.