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The contemporary superconductive electronics is widely using planar circuits with micrometer-scale elements for a variety of applications. With the rise of complexity of a circuit and increased number of its components, a simple impedance measurement are often not efficient for diagnostics of problems, nor for clarifying the physics underlying the circuit response. The established Scanning Laser Microscope (LSM) technique generates the micrometer-scale images of the amplitude of the microwave currents in a planar superconductive circuit, but not the phase of the oscillating currents. Here we present a novel, more powerful type of LSM imaging containing the signal phase information. We employ a fast optical modulator in order to synchronize the phase of the laser intensity oscillation with the phase of the probing microwave signal. The loss induced in laser illuminated area strongly depends on the phase difference between the RF probing signal and the laser beam modulation. We explain the detection principle of the phase sensitive LSM and experimentally demonstrate the capability of this method using superconductive microwave resonators. The described technique facilitates understanding of complex RF current distributions in superconductive circuits., Comment: 8 pages, 4 figures

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/cm2. 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.

We will present experimental study of SQUID array based quantum superconductive metamaterials. The cryogenic Laser Scanning Microscope technique gives an insight to confirm a coherent response of the SQUID-based microwave resonator arrays and its tunability.

We present a practical design and implementation of a broadband sample holder suitable for microwave experiments with superconducting integrated circuits at millikelvin temperatures. Proposed design can be easily integrated in standard dilution cryostats, has flat pass band response in a frequency range from 0 to 32 GHz, allowing the RF testing of the samples with substrate size up to 4x4 mm. The parasitic higher modes interference in the holder structure is analyzed and prevented via design considerations. The developed setup can be used for characterization of superconducting parametric amplifiers, bolometers and qubits. We tested the designed sample holder by characterizing of a superconducting flux qubit at 20 mK temperature., 11 pages, 7 figures

An ultra-low noise single sideband SIS receiver has been prepared for radio astronomy at the sub millimeter wavelength /spl lambda//spl ap/0.85 mm. The minimum single sideband receiver noise temperature of 48 K corresponds to 3 h/spl omega//k or equivalent number of 3 photon of noise. The minimum single sideband SIS mixer noise temperature is about 20 K, close to 1.2 h/spl omega//k, or one photon of noise. The Nb/AlOx/Nb junctions with a Josephson critical current density of 9 KA/cm/sup 2/ and with the area of about 0.9 /spl mu/m/sup 2/ were used. The receiver has been tested at the 30 meter IRAM radio telescope in the winter seasons of 1997 and 1998. The observations at the radio telescope are speeded up by a factor of two to three with the new receiver.

We present a method to analyze the electromagnetic behavior of superconducting planar microwave metamaterials. Using a laser scanning microscope (LSM), we image the microwave response of two-dimensional arrays of magnetic meta-atoms. This method allows us to investigate contributions of individual meta-atoms to the macroscopic response and thus provides a useful tool for characterization and optimization. The meta-atoms in the present experiment are frequency tunable superconducting quantum interference devices (SQUIDs).

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 RNωC 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.

An ultra low noise SIS receiver has been prepared for radio astronomy. The minimum double sideband receiver noise temperature is about 30 K which corresponds to 2 /spl planck//spl omega//k or an equivalent number of 4 photons of noise. The minimum measured double sideband mixer noise temperature is about 10 K which corresponds to 0.6 /spl planck//spl omega//k or approximately to 1 photon of noise. The fixed tuned SIS mixer operates in the 290-370 GHz frequency range. The submicron niobium junctions mere fabricated using photoresist lines for junction definition. The receiver has been used at the 30 m IRAM radio telescope in Spain in winter 1994. Telescope system noise temperature of 500 K single sideband has been achieved when the sky opacity was about 0.17. >

A fabrication process for submicron Nb-Al-oxide-Nb tunnel junctions using photoresist lines and optical lithography is described. With 0.6 mu m wide resist lines, junction areas of about 0.4 mu m2 were obtained. At present the maximum current density obtainable is 8500 A cm-2, and for this the best Vm parameters of the submicron junctions are 47 mV at 4.2 K and 150 mV at 2.5 K. Compared with standard photoresist pads for junction definition, photoresist lines are more stable and result in junction areas closer to the areas on the mask. A weak increase of the gap voltage with decreasing junction size is observed. Finally, the performance of a 345 GHz receiver incorporating a two-junction array with integrated filter and tuning circuit is discussed.

International audience; Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

We report the development of a low noise and broadband SIS mixer aimed for 1 THz channel of the Caltech Airborne Submillimeter Interstellar Medium Investigations Receiver (CASIMIR), designed for the Stratospheric Observatory for Infrared Astronomy, (SOFIA). The mixer uses an array of two 0.24 mum^2 Nb/Al-AlN/NbTiN SIS junctions with the critical current density of 30-50 kA/cm^2 . An on-chip double slot planar antenna couples the mixer circuit with the telescope beam. The mixer matching circuit is made with Nb and gold films. The mixer IF circuit is designed to cover 4-8 GHz band. A test receiver with the new mixer has a low noise operation in 0.87-1.12 THz band. The minimum receiver noise measured in our experiment is 353 K (Y = 1.50). The receiver noise corrected for the loss in the LO injection beam splitter is 250 K. The combination of a broad operation band of about 250 GHz with a low receiver noise makes the new mixer a useful element for application at SOFIA.

We have demonstrated the feasibility of a broad band SIS direct detector with a bandwidth up to 70 GHz around 330 GHz. The SIS detector responsivity approaches the quantum limit. The optical noise of 13 mK/spl radic/s measured with the new direct detector receiver is close to the noise of bolometer receiver developed for radioastronomy at the same wavelength. The SIS direct detector works at 4.5 K instead of 0.1-0.3 K required for bolometer receiver.

The objective of the European project EMCOR was the development of a heterodyne receiver for the frequency range of 201 to 210 GHz for the measurement of the amounts of various minor constituents of the stratosphere involved in ozone chemistry. In order to be able to measure even very faint spectral lines a superconducting tunnel junction has been chosen as mixer element. Additionally, special care has been taken in developing the calibration unit of the system. Besides the classical hot-cold calibration three different balancing methods can be employed: a beam-switch technique with an atmospheric reference signal, a beam switch technique with a reference signal from a variable reference load or a frequency switch technique. The system has been integrated and is currently under testing. It will be installed at the International Scientific Station Jungfraujoch in he Swiss Alps and operated within the framework of the European Alpine stations of the Network for the Detection of Stratospheric Change.

A low noise SIS mixer receiver is prepared in IRAM for the operation at 0.8 mm wavelength on the 30 M telescope at Pico Veleta in Spain. For this receiver a new fixed-tuned waveguide SIS mixer is developed. This mixer is able to operate in a wide band being fixed tuned. The present mixer design uses relative large Nb\AIoxide\Nb SIS junctions (1-2 ?2) in which parallel inductive tuning is implemented with quasi-lumped elements. Experimental measurements agree with model predictions of the new SIS mixers performance. At the IRAM 30-m radiotelescope the best receiver DSB noise temperature achieved in the 0.8 mm band is about 70 K It is believed that it is the first wide band receiver with a fixed tuned submillimeter SIS mixer on the radiotelescope with the lowest noise temperature published for the moment.