Integrated tuning elements for SIS mixers

The use of inductive elements to tune out the junction capacitance in SIS mixers is examined. Two new integrated tuning structures are introduced which overcome the limitations of earlier designs.The National Radio Astronomy Observatory is operated by the Associated Universities, Inc. under contract with the National Science Foundation.This paper was presented at the 1987 International Superconductivity Electronics Conference, Tokyo, Aug. 1987.     

Low noise submillimeter SIS receiver with niobium nitride quasiparticle tunnel junctions

We have developed and tested a submillimeter waveguide SIS mixer with NbN-MgO-NbN quasiparticle tunnel junctions. The two junction array is integrated in a full NbN printed circuit. The NbN film critical temperature is 15 K and the junction gap voltage is 5 mV. The size of the junctions is 1.4 × 1.4 µm and Josephson critical current density is about 1.5 KA/cm² resulting in junction R_NC product about 40. The inductive tuning circuit in NbN is integrated with each junction in two junction array. A single non contacting backshort was tuned at each frequency in the mixer block.At 306 GHz the minimum DSB receiver noise temperature is as low as 230 K. The sources of the receiver noise and of the limits of the NbN SIS submillimeter mixer improvement are discussed.     

Wide-band low noise MM-wave SIS mixers with a single tuning element

Several SIS quasiparticle mixers have been designed and tested for the frequency range from 80 to 115 GHz. The sliding backshort is the only adjustable RF tuning element. The RF filter reactance is used as a fixed RF matching element. A mixer which uses a single 2×2 m² Pb-alloy junction in a quarter-height waveguide mount has a coupled conversion gain of G_M(DSB)=2.6±0.5 dB with an associated noise temperature of T_M(DSB)=16.4±1.8 K at the best DSB operation point. The receiver noise temperature T_R(DSB) is 27.5±0.8 K for the mixer test apparatus. This mixer provides a SSB receiver noise temperature below 50 K over the frequency range from 91 to 96 GHz, the minimum being T_R(SSB)=44±4 K. Another mixer with an array of five 5×5 m² junctions in series in a full-height wave-guide mount has much lower noise temperature T_M(DSB)=6.6±1.6 K, but less gain G_M(DSB)=–5.1±0.5 dB.Contribution of the U.S. Government, not subject to copyright     

Some recent developments in the design of SIS mixers

SIS mixers in which superconducting tuning elements are integrated with the tunnel junctions have resulted in very low noise heterodyne receivers in the range 68–260 GHz. Above 120 GHz the need for extremely small reduced-height waveguides is avoided by mounting the SIS junctions in a suspended-stripline circuit coupled to a full-height waveguide by a broadband probe. The special characteristics of coplanar transmission line permit the design of SIS mixers with low parasitic reactances. Such a mixer operates over the full WR-10 band (75–110 GHz) without mechanical tuners.An earlier version of this paper was presented at the First International Symposium on Space THz Technology, March, 1990.The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.     

Analytical prediction for the optimum operating conditions of SIS mixers

Using Tucker's quantum theory of mixing and a quasi five-frequency approximation proposed by Kerr et al., this paper explores the optimum operating conditions of SIS mixers in the frequency region of 100 to 650 GHz. Four parameters (i.e., R_nC_j product, normal state resistance R_n, RF source admittance (R_rf ^–+jB), and IF load resistance R_if) affecting the performance of an SIS mixer have been investigated. Our results indicate that, independent of the absolute value of R_n, the SIS mixer performance is dominated by R_rf/R_n and R_if/R_n; and that the mixer performance becomes quite insensitive to the R_nC_j product, as the mixer operating frequency goes up to submillimeter wavelengths. Concerning all properties of an SIS mixer, the optimum R_rf/R_n value seems proportional to f^1/n (n2), and the optimum R_if/R_n and jB/G_n values are relatively independent of frequency, about 0.5 to 1.5 and –j0.5 to –j1.0 respectively.On leave from Purple Mountain Observatory, China     

Scaled model measurements of embedding impedances for SIS waveguide mixers

Several scaled models have been used to determine the contributions of various waveguide mount parameters to the embedding impedance of a mm-wave SIS mixer. Measured effects of waveguide height, substrate orientation and width, junction location, lead inductance and RF-filter impedance are presented and discussed.     

Mixing of 30 THz laser radiation with nanometer thin-film Ni-NiO-Ni diodes and integrated bow-tie antennas

Mixing experiments with 30 THz CO₂-laser radiation as well as the detection of 35 ps 30 THz pulses of an optical-free-induction-decay CO₂-laser system have been performed with the first nanometer thin-film Ni-NiO-Ni diodes with a minimum contact area of 0.012 µm². Difference frequencies up to 85 MHz were detected by mixing two different CO₂-laser beams coupled to the diode with an integrated bow-tie antenna. The dependence of the beat signal on bias voltage, laser power and polarization of the infrared laser radiation was determined.     

Analysis of SIS heterojunctions for use as mm-wave mixers exhibiting coversion gain

We apply the quantum formulation of heterodyne mixer theory to SIS heterojunctions (junctions between dissimilar superconductors). Conversion gain is predicted over a wide range of mm-wave frequencies in the 3-port Y-mixer model by exploiting the naturally occurring region of negative conductance in the DC I-V characteristic. In the signal frequency range 50–250 GHz this region persists in the pumpedjunction I–V characteristic for local oscillator power <1 nW and leads to a negative conductance at the mixer's IF port.     

Production of high quality Nb/Al-oxide/Nb SIS trilayers for submillimeter wave mixers

Owing to a very sharp nonlinearity in the quasiparticle currentvoltage characteristic, which fortuitously occurs on the scale of a few millivolts rather than a few volts as with semiconductor devices, superconductor/insulator/superconductor (SIS) tunnel junctions are the most sensitive detectors for heterodyne mixing at millimeter and submillimeter wavelengths. They can also provide sources of coherent local oscillator power at very high frequencies; more broadly, they have a number of interesting applications as fast, low-power logic elements and as detectors at optical wavelengths. For submillimeterwave mixers, in many ways the most demanding of these applications, the Nb/Al-oxide/Nb material system has emerged as the system of choice to frequencies of ∼ 700 GHz and beyond. Production of SIS devices requires careful attention to a number of critical microfabrication issues, and I describe here some of the insights gained from developing a process for high-quality niobium trilayers that successfully yielded small-area junctions with unusually low sub-gap leakage current.     

Probing non-Abelian statistics with quasiparticle interferometry

We examine interferometric experiments in systems that exhibit non-Abelian braiding statistics, expressing outcomes in terms of the modular S-matrix. In particular, this result applies to fractional quantum Hall interferometry, and we give a detailed treatment of the Read-Rezayi states, providing explicit predictions for the recently observed nu = 12/5 plateau.     

Proton-neutron quasiparticle RPA with separable Gamow-Teller forces

A comprehensive representation is presented of a generalized form of the proton-neutron quasiparticle RPA model, originally introduced by Halbleib and Sorensen almost thirty years ago. The model uses separable Gamow-Teller forces, including, in addition to the particle-hole force of the former model, the particle-particle force, which is of decisive importance for β⁺ decay andββ decay. The above model has further been extended to the treatment of odd-odd nuclei. An extension is also made to transitions from nuclear excited states. This is essential for calculations of nuclear weak transition rates in the high-temperature interior of massive stars. Complementing the discussion of Halbleib and Sorensen on the particle-hole force, the structure of the RPA dispersion relation is discussed with emphasis on effects of the particle-particle force.     

Polarization-maintaining amplifier employing double-clad bow-tie fiber

We report a polarization-maintaining double-clad Yb-doped fiber amplifier employing bow-tie fiber. Borosilicate stress elements were incorporated into the inner cladding of the fiber, yielding a beat length of 5.1 mm at 633 nm. When the fiber was pumped at 975 nm and seeded with linearly polarized light, the polarization extinction ratio was >15 dB , independent of pump power, and the output power was as high as 3.5 W.     

Topological quantum computing with only one mobile quasiparticle

In a topological quantum computer, universal quantum computation is performed by dragging quasiparticle excitations of certain two dimensional systems around each other to form braids of their world lines in 2 + 1 dimensional space-time. In this Letter we show that any such quantum computation that can be done by braiding n identical quasiparticles can also be done by moving a single quasiparticle around n - 1 other identical quasiparticles whose positions remain fixed.     

Study of weakly-bound odd-A nuclei with quasiparticle blocking

The coordinate-space Hartree-Fock-Bogoliubov(HFB) approach with quasiparticle blocking has been applied to study the odd-A weakly bound nuclei ~(17,19)B and ~(37)Mg,in which halo structures have been reported in experiments.The Skyrme nuclear forces SLy4 and UNEDF1 have been adopted in our calculations.The results with and without blocking have been compared to demonstrate the emergence of deformed halo structures due to blocking effects.In our calculations,~(19)B and ~(37)Mg have remarkable features of deformed halos.     

A bow-tie shaped optical fiber loop and ring with double couplers

A theoretical study of a bow-tie shaped optical fiber loop and a ring with double couplers is carried out. The expressions for the circulating (resonant) intensity and the two output (reflected and transmitted) intensities are derived and the computed results are presented as graphs. The special characteristics, advantages, and possible applications of this type of fiber loop and ring, in comparison with other types, are discussed.