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Local oscillator sources have become a major technological deficit approaching the terahertz frequencies. For applications, where a narrow linewidth is necessary, such as coherent remote sensing, the best solution to signal generation is frequency multiplication, where phase locking can be easily achieved using the fundamental source. We present an alternative to existing frequency multiplier technologies for cryogenic applications. The device is a superconducting waveguide that has kinetic inductance dependent on the rf current through the device. The nonlinear kinetic inductance is anomalous to a nonlinear optical medium, where the Kerr effect causes 3- or 4-wave mixing, as demonstrated in microwave parametric amplifiers utilizing the same nonlinear effect. In 4-wave mixing, three photons at the fundamental frequency are mixed to generate a single photon at the third harmonic. Dispersion engineering is used to achieve wideband phase matching and phase out harmonics higher than the third. The device length is designed to be the point where most photons are up-converted to the third harmonic. Simulations of these devices lead to expected efficiencies as high as 90%. We report results from a NbTiN frequency multiplier from 34.2 to 104 GHz with efficiency better than 50%. [ABSTRACT FROM AUTHOR]

Cryogenic detectors are extremely sensitive and have a wide variety of applications (particularly in astronomy), but are difficult to integrate into large arrays like a modern CCD (charge-coupled device) camera. As current detectors of the cosmic microwave background (CMB) already have sensitivities comparable to the noise arising from the random arrival of CMB photons, the further gains in sensitivity needed to probe the very early Universe will have to arise from large arrays. A similar situation is encountered at other wavelengths. Single-pixel X-ray detectors now have a resolving power of ?E < 5?eV for single 6-keV photons, and future X-ray astronomy missions anticipate the need for 1,000-pixel arrays. Here we report the demonstration of a superconducting detector that is easily fabricated and can readily be incorporated into such an array. Its sensitivity is already within an order of magnitude of that needed for CMB observations, and its energy resolution is similarly close to the targets required for future X-ray astronomy missions. [ABSTRACT FROM AUTHOR]

Reports on the development of low-noise quasi-optical SIS mixers for the frequency range 400-850 GHz. Receiver configurations; Receiver layout; Fourier-transform spectroscopy; Mixer design and fabrication; Heterodyne measurements.

Describes the processing method used for the fabrication of a diffusion cooled superconducting hot electron bolometer for THz mixing applications. Development of microbridges; Demonstration of several GHz intermediate frequency (IF) bandwidth; Embedding of the microbridge in a normal metal (Au).

Titanium nitride (TiNx) films are ideal for use in superconducting microresonator detectors for the following reasons: (a) the critical temperature varies with composition (0107) and have noise properties similar to resonators made using other materials, while the quasiparticle lifetimes are reasonably long, 10–200 μs. TiN microresonators should therefore reach sensitivities well below 10-19 W Hz-1/2. [ABSTRACT FROM AUTHOR]

This work culminates in a demonstration of an alternative frequency-domain multiplexing (FDM) scheme for superconducting nanowire single-photon detectors (SNSPDs) using the kinetic inductance parametric up-converter (KPUP) made out of NbTiN. There are multiple multiplexing architectures for SNSPDs that are already in use, but FDM could prove superior in applications where the operational bias currents are very low, especially for mid-infrared and far-infrared SNSPDs. Previous FDM schemes integrated the SNSPD within the resonator, while, in this work, we use an external resonator, which gives more flexibility to optimize the SNSPD architecture. The KPUP is a DC-biased superconducting λ /2 resonator that is sensitive to current perturbations. When coupled to an SNSPD, the KPUP can be used to read out current pulses on a few μA scale. The KPUP is made out of NbTiN, which has a large kinetic inductance and a high operating temperature. Meanwhile, the SNSPD is made from WSi, which is a popular material for broadband SNSPDs. A software-defined radio platform and a graphics processing unit are used to read out the KPUP and SNSPD array. Frequency-domain multiplexed SNSPDs have applications in astronomy, remote sensing, exoplanet science, dark matter detection, and quantum sensing. [ABSTRACT FROM AUTHOR]

An ideal amplifier has very low noise, operates over a broad frequency range, and has large dynamic range. Unfortunately, it is difficult to obtain all of these characteristics simultaneously. For example, modern transistor amplifiers offer multi-octave bandwidths and excellent dynamic range, but their noise remains far above the limit set by the uncertainty principle of quantum mechanics. Parametric amplifiers can reach the quantum-mechanical limit, but generally are narrow band and have very limited dynamic range. Here we describe a parametric amplifier that overcomes these limitations through the use of a travelling-wave geometry and the nonlinear kinetic inductance of a superconducting transmission line. We measure gain extending over 2?GHz on either side of an 11.56?GHz pump tone and place an upper limit on the added noise of 3.4 photons at 9.4?GHz. The dynamic range is very large, and the concept can be applied from gigahertz frequencies to ? 1?THz. [ABSTRACT FROM AUTHOR]

The energy resolution of a single photon counting microwave kinetic inductance detector can be degraded by noise coming from the primary low temperature amplifier in the detector's readout system. Until recently, quantum limited amplifiers have been incompatible with these detectors due to the dynamic range, power, and bandwidth constraints. However, we show that a kinetic inductance based traveling-wave parametric amplifier can be used for this application and reaches the quantum limit. The total system noise for this readout scheme was equal to ∼2.1 in units of quanta. For incident photons in the 800–1300 nm range, the amplifier increased the average resolving power of the detector from ∼6.7 to 9.3 at which point the resolution becomes limited by noise on the pulse height of the signal. Noise measurements suggest that a resolving power of up to 25 is possible if the redesigned detectors can remove this additional noise source. [ABSTRACT FROM AUTHOR]

Large-scale arrays of microwave kinetic inductance detectors (MKIDs) are attractive candidates for use in imaging instruments for next generation submillimeter-wave telescopes such as CCAT. We have designed and fabricated tightly packed \sim250-pixel MKID arrays using lumped-element resonators etched from a thin layer of superconducting TiNx deposited on a silicon substrate. The high pixel packing density in our initial design resulted in large microwave crosstalk due to electromagnetic coupling between the resonators. Our second design eliminates this problem by adding a grounding shield and using a double-wound geometry for the meander inductor to allow conductors with opposite polarity to be in close proximity. In addition, the resonator frequencies are distributed in a checkerboard pattern across the array. We present details for the two resonator and array designs and describe a circuit model for the full array that predicts the distribution of resonator frequencies and the crosstalk level. We also show results from a new experimental technique that conveniently measures crosstalk without the need for an optical setup. Our results reveal an improvement in crosstalk from 57% in the initial design down to \le 2% in the second design. The general procedure and design guidelines in this work are applicable to future large arrays employing microwave resonators. [ABSTRACT FROM PUBLISHER]

We report the development of a low noise SIS mixer aimed for 1 THz channel of the Caltech Airborne Submillimeter Interstellar Medium Investigations Receiver (CASIMIR), designed for the Stratospheric Observatory for Far Infrared Astronomy (SOFIA). The mixer uses Nb/Al-AlN/NbTiN SIS junctions with critical current density of about 45 kA/cm^2. The junctions are shaped in order to optimize the suppression of the Josephson DC currents. We used a double slot planar antenna to couple the mixer chip with the telescope beam. The RF matching microcircuit is made using Nb and gold films. The mixer IF circuit is designed to cover 4–8 GHz band. The test receiver with the new mixer has the low noise operation in a 0.9–1.05 THz band. The minimum DSB receiver noise measured at 1 THz is 260 K (Y=1.64), apparently the lowest reported up to date. [ABSTRACT FROM AUTHOR]

We report on a 275‘425-GHz tunerless wavéguide receiver with a 3.5–8-GHz IF. As the mixing element, we employ a high-current-density Nb-AIN-Nb superconducting-insulating- superconducting (SIS) tunnel junction. Thanks to the combined use of AIN-barrier SIS technology and a broad bandwidth wave-guide to thin-film microstrip transition, we are able to achieve an unprecedented 43% instantaneous bandwidth, limited by the receiver's corrugated feedhorn. The measured double-sideband (DSB) receiver noise temperature, uncorrected for optics loss, ranges from 55 K at 275 GHz, 48 K at 345 GHz, to 72 K at 425 GHz. In this frequency range, the mixer has a DSB conversion loss of 2.3 ± 1 dB. The intrinsic mixer noise is found to vary between 17–19 K, of which 9 K is attributed to shot noise associated with leakage current below the gap. To improve reliability, the IF circuit and bias injection are entirely planar by design. The instrument was successfully installed at the Caltech Submillimeter Observatory (CSO), Mauna Kea, HI, in October 2006. [ABSTRACT FROM AUTHOR]

We have formed AINx tunnel barriers in Nb Josephson junctions using a nitrogen ion beam operated at low energy (<150 eV). Independent control of ion energy and dose allowed for the exploration of a wide parameter space in which devices were fabricated with good quality and reproducibility with Jc < 10 kA/cm2. The junctions were stable up to temperatures of at least 200°C, implying that the nitrogen atoms are strongly bound and do not desorb as gaseous molecular N2. Large-area uniformity was also investigated where the spatial variation in ion current density was correlated with Jc. This technique could be applied to form other metal nitrides at room temperature for device applications where a high degree of control is desired. [ABSTRACT FROM AUTHOR]

A Superconductor-Insulator-Superconductor (SIS) distributed mixer with no integrated tuning circuit has been designed for use in a fixed-tuned waveguide mixer block. This mixer employs two half-wave SIS resonators connected in series across the feed point of the waveguide circuit. By selecting appropriate dimensions for the resonators, we can obtain proper impedance matching over a reasonable input bandwidth. Since there is no lossy thin film microstrip line in front of the SIS junction, efficient power transfer from the waveguide feed to the mixer element can be achieved. A receiver noise temperature of 185 K at 650 GHz has been measured with a dual 0.33 × 16.8 µm SIS resonator. The noise temperature remains below 300 K over an input bandwidth of about 10%. This design can be used at much higher frequency where the loss of tuning circuit becomes significant. [ABSTRACT FROM AUTHOR]

Thin tantalum films were deposited on silicon wafers using a niobium seed layer to promote alpha-phase growth. These films were patterned into submicrometer size diffusion-cooled bolometers with superconducting transition temperatures of up to 2.35 K and a transition width of about 200 mK. The thermal relaxation times of the devices were determined by measuring the device impedance as a function of frequency and by fitting a theoretical model to the data. Measured relaxation times at low bias voltages range from 0.75 GHz for a 400-nm long device to 6 GHz for a 100-nm device, excluding electrothermal feedback. This should allow sufficiently high instantaneous bandwidths for most low-noise mixer applications in astrophysics. [ABSTRACT FROM AUTHOR]

Analyzes the microwave measurements of superconducting aluminum hot-electron bolometer mixers. Local oscillator power requirements; Intermediate frequency bandwidths; Noise temperature; Estimation of bandwidth from the thermal time constant of the device.

Describes aluminum hot-electron bolometer mixers at submillimeter wavelengths. Design and fabrication; Intermediate frequency bandwidths; Coupling efficiency; Operation of the mixers.

The article discusses the results of a 850-GHz superconducting-insulator-superconducting (SIS) heterodyne receiver employing an RF-tuned niobium tunnel junction with a current density of 14 kA/cm2. Fabrication on supporting membrane; Findings of Fourier transform spectrometer (FTS) measurements; Construction of waveguide junctions.

We have demonstrated electrostatic switching in vertically oriented carbon nanofibers synthesized on refractory metallic nitride substrates, where pull-in voltages Vpi ranged from 10 to 40 V. A nanoprobe was used as the actuating electrode inside a scanning-electron microscope and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical Vpi and results were compared to experiment. Nanomanipulation tests also revealed tubes synthesized directly on Si by dc plasma-enhanced chemical-vapor deposition with ammonia and acetylene were electrically unsuitable for dc nanoelectromechanical switching applications. [ABSTRACT FROM AUTHOR]

We present measurements of the low-temperature excess frequency noise of four niobium superconducting coplanar waveguide microresonators, with center strip widths sr ranging from 3 to 20 μm. For a fixed internal power, we find that the frequency noise decreases rapidly with increasing center strip width, scaling as 1/sr1.6. We show that this geometrical scaling is readily explained by a simple semiempirical model which assumes a surface distribution of independent two-level system fluctuators. These results allow the resonator geometry to be optimized for minimum noise. [ABSTRACT FROM AUTHOR]

We present measurements of the temperature-dependent frequency shift of five niobium superconducting coplanar waveguide microresonators with center strip widths ranging from 3 to 50 μm, taken at temperatures in the range of 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 TLSs that interact with each resonator geometry. The geometrical scaling indicates a surface distribution of TLSs and the data are consistent with a TLS surface layer thickness of the order of a few nanometers, as might be expected for a native oxide layer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The authors have measured noise in thin-film superconducting coplanar waveguide resonators. This noise appears entirely as phase noise, equivalent to a jitter of the resonance frequency. In contrast, amplitude fluctuations are not observed at the sensitivity of their measurement. The ratio between the noise power in the phase and amplitude directions is large, in excess of 30 dB. These results have important implications for resonant readouts of various devices such as detectors, amplifiers, and qubits. They suggest that the phase noise is due to two-level systems in dielectric materials. [ABSTRACT FROM AUTHOR]

Develops a low-noise superconductor-insulator-superconductor quasiparticle mixer with niobium titanium nitride (NbTiN) thin-film microstrip tuning circuits and hybrid Nb/AlN/NbTiN tunnel junctions. Use of a quasioptical configuration with a planar twin-slow antenna feeding a two-junction tuning circuit; Uncorrected double-sideband receiver noise temperature.

We have fabricated and tested submillimeter-wave superconductor-insulator-superconductor (SIS) mixers using very high-current-density Nb/AlN/Nb tunnel junctions (J[sub c]approx. 30 kA cm[sup -2]). The junctions have low-resistance-area products (R[sub N]Aapprox. 5.6 Ω μm[sup 2]), good subgap-to-normal resistance ratios R[sub sg]/R[sub N]approx. 10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that ωR[sub N]C=1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlOx/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected double-sideband receiver noise temperature of T[sub RX]=110 K at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing rf loss in the tuning circuits. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]