Low-loss deposited dielectrics will benefit superconducting devices such as integrated superconducting spectrometers, superconducting qubits, and kinetic inductance parametric amplifiers. Compared with planar structures, multilayer structures such as microstrips are more compact and eliminate radiation loss at high frequencies. Multilayer structures are most easily fabricated with deposited dielectrics, which typically exhibit higher dielectric loss than crystalline dielectrics. We measure the subkelvin and low-power microwave and millimeter-submillimeter-wave dielectric loss of hydrogenated amorphous silicon carbide (a-SiC:H), using superconducting chips with Nb-Ti-N/a-SiC:H/Nb-Ti-N microstrip resonators. We deposit the a-SiC:H by plasma-enhanced chemical vapor deposition at a substrate temperature of 400°C. The a-SiC:H has a millimeter-submillimeter loss tangent ranging from 0.9×10-4 at 270 GHz to 1.5×10-4 at 385 GHz. The microwave loss tangent is 3.1×10-5. These are the lowest low-power subkelvin loss tangents that have been reported for microstrip resonators at millimeter-submillimeter and microwave frequencies. The a-SiC:H films are free of blisters and have low stress: -20 MPa compressive at 200-nm thickness to 60 MPa tensile at 1000-nm thickness.

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Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here, we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220–440 GHz band in a single shot, corresponding to a redshift range of z = 3.3–7.6 for the ionized carbon emission ([C II] 158 μ m). The first-light experiment of DESHIMA 1.0, using the 332–377 GHz band, has shown an excellent agreement among the on-sky measurements, the laboratory measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign.

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Superconducting integrated circuits (SICs) represent a natural step forward for devices operating at frequencies from microwave up to sub-millimeter wavelengths. They offer massive miniaturization via compact design based on low-loss superconducting transmission lines. At sub-millimeter wavelengths, the development of SICs is driven by astronomical instruments where it could allow the realization of an imaging spectrometer, combining simultaneous imaging and spectroscopy capabilities into a single instrument analogous to integral field units in the infrared and optical regimes. Such an imaging spectrometer can be achieved with SICs by integrating the required elements, such as spectral filters and polarizers, with the detectors onto a single chip. Without this integration, the dispersive system for even a single spatial pixel at these wavelengths would be prohibitively large and could not be realistically scaled up to allow imaging. Astronomical signals are exceedingly weak, typically requiring many nights of exposure to get a good signal to noise ratio. It is therefore imperative that the instrument has minimal losses before its detectors. As a consequence, the losses of each element in the SIC needs to be minimized, which requires careful characterization of the individual elements, including antenna, filters, detectors and connecting transmission lines. The primary focus of this thesis lies on the experimental characterization of the wideband antenna and the low-loss superconducting transmission lines.@en

We present a lab-on-chip experiment to accurately measure losses of superconducting microstrip lines at microwave and submillimeter wavelengths. The microstrips are fabricated from Nb-Ti-N, which is deposited using reactive magnetron sputtering, and amorphous silicon which is deposited using plasma-enhanced chemical vapor deposition (PECVD). Submillimeter wave losses are measured using on-chip Fabry-Perot resonators (FPRs) operating around 350 GHz. Microwave losses are measured using shunted half-wave resonators with an identical geometry and fabricated on the same chip. We measure a loss tangent of the amorphous silicon at single-photon energies of tan⁡δ=3.7±0.5×10-5 at approximately 6GHz and tan⁡δ=2.1±0.1×10-4 at 350 GHz. These results represent very low losses for deposited dielectrics, but the submillimeter wave losses are significantly higher than the microwave losses, which cannot be understood using the standard two-level system loss model.

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We present the design, fabrication, and characterization of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid microwave kinetic inductance detector (MKID) to measure the beam pattern and absolute coupling efficiency at three frequency bands centered around 350, 650, and 850 GHz, covering the full antenna band. We find an aperture efficiency \eta _{ap} \approx 0.4 over the whole frequency band, limited by lens reflections. We find a good match with simulations for both the patterns and efficiency, demonstrating a 1:3 bandwidth in the submillimeter wavelength range for future on-chip spectrometers.

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Superconducting resonators and transmission lines are fundamental building blocks of integrated circuits for millimeter-submillimeter astronomy. Accurate simulation of radiation loss from the circuit is crucial for the design of these circuits because radiation loss increases with frequency, and can thereby deteriorate the system performance. Here we show a stratification for a 2.5-dimensional method-of-moment simulator Sonnet EM that enables accurate simulations of the radiative resonant behavior of submillimeter-wave coplanar resonators and straight coplanar waveguides (CPWs). The Sonnet simulation agrees well with the measurement of the transmission through a coplanar resonant filter at 374.6 GHz. Our Sonnet stratification utilizes artificial lossy layers below the lossless substrate to absorb the radiation, and we use co-calibrated internal ports for de-embedding. With this type of stratification, Sonnet can be used to model superconducting millimeter-submillimeter wave circuits even when radiation loss is a potential concern.@en

We present a lab-on-chip technique to measure the very low losses in superconducting transmission lines at (sub-) mm wavelengths. The chips consist of a 100 nm-thick NbTiN Co-planar Waveguide (CPW) Fabry–Pérot (FP) resonator, coupled, on one side, to an antenna and, on the other side, to a Microwave Kinetic Inductance detector. Using a single frequency radiation source allows us to measure the frequency response of the FP around 350 GHz and deduce its losses. We show that the loss is dominated by radiation loss inside the CPW line that forms the FP and that it decreases with the decreasing linewidth and increasing kinetic inductance as expected. The results can be quantitatively understood using SONNET simulations. The lowest loss is observed for a CPW with a total width of 6 μm and corresponds to a Q-factor of ≈15 000.@en

DESHIMA is a spectrometer for astronomical applications targeting sources at sub-mm wavelengths from 240GHz to 720GHz that will operate in the ASTE telescope in Atacama Desert, Chile. In this work, a quasi-optical system based on a hyper-hemispherical leaky lens antenna and a series of Dragonian reflectors is presented as the coupling chain for the EM radiation captured by the telescope into the detector. The design procedure is based on a field matching technique in reception. The achieved average illumination efficiency over the band is approximately 70%. The directivity patterns in the sky are also estimated. The side lobe, and cross-polarization levels, over the whole frequency band, are below-16dB, and-18dB, respectively. The measurement of the system is on-going, and will be presented at the conference.

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