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Register a new userPlanar Superconductor-Insulator-Superconductor Mixer Array Receivers for Wide Field of View Astronomical Observation
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We present a conceptual framework of planar SIS mixer array receivers and the studies on the required techniques. This concept features membrane-based on-chip waveguide probes and a quasi-two-dimensional local-oscillator distribution waveguide network. This concept allows sophisticated functions, such as dual-polarization, balanced mixing and sideband separation, easily implemented with the SIS mixer array in the same planar circuit. We have developed a single-pixel prototype receiver by implementing the concept in the design. Initial measurement results show good evidences that support the feasibility of the concept.
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In this study, we designed and experimentally evaluated a series-connected array of superconductor-insulator-superconductor (SIS) junctions in the 100-GHz band mixer for the multi-beam receiver FOREST on the Nobeyama 45-m millimeter-wave telescope. The construction of the junction chip comprised a waveguide probe antenna, impedance matching circuit, SIS array junction, and choke filter, which were made from a superconducting niobium planar circuit on a quartz substrate. The multi-stage impedance matching circuit between the feed point and the SIS junction was designed as a capacitively loaded transmission line, and it comprised two sections with high (~90 Ohm) and low (~10 Ohm) characteristic impedance transmission lines. The structure of this tuning line was simple and easy to fabricate, and the feed impedance matched with the SIS junction in a wide frequency range. The signal coupling efficiency was more than 92% and the expected receiver noise temperature was approximately two times the quantum limit for 75-125 GHz based on quantum theory. The array junction devices with 3-6 connected junctions were fabricated and we measured their performance in terms of the receiver noise temperature and gain compression in the laboratory. We successfully developed an array junction device with a receiver noise temperature of ~15-30 K and confirmed that the improvement in the saturation power corresponded to the number of junctions. The newly developed array junction mixer was installed in the FOREST receiver and it successfully detected the 12CO (J = 1-0) molecular line toward IRC+10216 with the Nobeyama 45-m telescope.
Recent spectroscopic observations by sensitive radio telescopes require accurate molecular spectral line frequencies to identify molecular species in a forest of lines detected. To measure rest frequencies of molecular spectral lines in the laboratory, an emission-type millimeter and submillimeter-wave spectrometer utilizing state-of-the-art radio-astronomical technologies is developed. The spectrometer is equipped with a 200 cm glass cylinder cell, a two sideband (2SB) Superconductor-Insulator-Superconductor (SIS) receiver in the 230 GHz band, and wide-band auto-correlation digital spectrometers. By using the four 2.5 GHz digital spectrometers, a total instantaneous bandwidth of the 2SB SIS receiver of 8 GHz can be covered with a frequency resolution of 88.5 kHz. Spectroscopic measurements of CH$_3$CN and HDO are carried out in the 230 GHz band so as to examine frequency accuracy, stability, sensitivity, as well as intensity calibration accuracy of our system. As for the result of CH$_3$CN, we confirm that the frequency accuracy for lines detected with sufficient signal to noise ratio is better than 1 kHz, when the high resolution spectrometer having a channel resolution of 17.7 kHz is used. In addition, we demonstrate the capability of this system by spectral scan measurement of CH$_3$OH from 216 GHz to 264 GHz. We assign 242 transitions of CH$_3$OH, 51 transitions of $^{13}$CH$_3$OH, and 21 unidentified emission lines for 295 detected lines. Consequently, our spectrometer demonstrates sufficient sensitivity, spectral resolution, and frequency accuracy for in-situ experimental-based rest frequency measurements of spectral lines on various molecular species.
Wide-angle surveys have been an engine for new discoveries throughout the modern history of astronomy, and have been among the most highly cited and scientifically productive observing facilities in recent years. This trend is likely to continue over the next decade, as many of the most important questions in astrophysics are best tackled with massive surveys, often in synergy with each other and in tandem with the more traditional observatories. We argue that these surveys are most productive and have the greatest impact when the data from the surveys are made public in a timely manner. The rise of the survey astronomer is a substantial change in the demographics of our field; one of the most important challenges of the next decade is to find ways to recognize the intellectual contributions of those who work on the infrastructure of surveys (hardware, software, survey planning and operations, and databases/data distribution), and to make career paths to allow them to thrive.
The legacy Ooty Radio Telescope (ORT) is being reconfigured as a 264-element synthesis telescope, called the Ooty Wide Field Array (OWFA). Its antenna elements are the contiguous 1.92 m sections of the parabolic cylinder. It will operate in a 38-MHz frequency band centred at 326.5 MHz and will be equipped with a digital receiver including a 264-element spectral correlator with a spectral resolution of 48 kHz. OWFA is designed to retain the benefits of equatorial mount, continuous 9-hour tracking ability and large collecting area of the legacy telescope and use modern digital techniques to enhance the instantaneous field of view by more than an order of magnitude. OWFA has unique advantages for contemporary investigations related to large scale structure, transient events and space weather watch. In this paper, we describe the RF subsystems, digitizers and fibre optic communication of OWFA and highlight some specific aspects of the system relevant for the observations planned during the initial operation.
How to control collectively ordered electronic states is a core interest of condensed matter physics. We report an electric field controlled reversible transition from superconductor to ferromagnetic insulator in (Li,Fe)OHFeSe thin flake using solid ion conductor as the gate dielectric. By driving Li ions into and out of the (Li,Fe)OHFeSe thin flake with electric field, we obtained a dome-shaped superconducting region with optimal Tc ~ 43 K, which is separated by a quantum critical point from ferromagnetically insulating phase. The ferromagnetism arises from the long range order of the interstitial Fe ions expelled from the (Li,Fe)OH layers by Li injection. The device can reversibly manipulate collectively ordered electronic states and stabilize new metastable structures by electric field.
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