arXiv subjects

Shohei Ezaki

Publications and source records attributed to Shohei Ezaki.

5 recordsLinked to original sources

arXiv2026

Demonstration of a Single-chip Dual-polarization Sideband-separation SIS mixer at 2 mm Band

Large-format heterodyne focal plane arrays require highly integrated receiver architectures while maintaining low noise and sufficient sideband rejection, which remains challenging for superconducting SIS mixers at millimeter wavelengths. In this work, we demonstrate, for the first time, a monolithic dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer operating at 2 mm wavelengths (125-163 GHz) on a silicon-on-insulator substrate. The integrated SIS mixer achieves a sideband rejection ratio exceeding 10 dB over the 4-8 GHz intermediate-frequency (IF) band across most of the radio-frequency (RF) range, with a minimum single-sideband (SSB) receiver noise temperature as low as approximately 60 K. As a key building block of the hybrid planar integration (HPI) architecture, this result verifies the feasibility of highly integrated large-format heterodyne focal plane arrays, providing a practical path toward substantially expanding the field of view of millimeter and submillimeter-wave radio telescopes.

astro-ph.IM↗

arXiv2025

Self-heating in SIS Mixers: Experimental Evidence and Theoretical Modeling

This work investigates the relationship between self-heating and the characteristic features observed in the current-voltage characteristics (IVCs) of superconductor-insulator-superconductor (SIS) junctions. Finite-element analysis is employed to evaluate the steady-state temperature distribution around SIS junctions, explicitly accounting for the temperature dependence of the thermal conductivities of the constituent materials. This approach enables flexible estimation of self-heating under various practical conditions, such as different substrate materials, interfacial thermal resistances, and geometric layouts. A heating coefficient is extracted from the simulations and used as an input parameter for IVC modeling. Incorporating self-heating through temperature-dependent gap energy and quasiparticle broadening, the simulated IVCs reproduce bending features near the energy gap that agree with measured characteristics. Furthermore, when a weak link is present near an SIS junction, its critical current can be significantly reduced by junction heating, producing unexpected bends at the linear branch of measured IVCs. Conversely, such bends may serve as indicators that the junction temperature approaches the superconducting transition temperature.

physics.ins-det↗

arXiv2024

Two-level System Loss: significant not only at Millikelvin

Tow-level system (TLS) loss in amorphous dielectric materials has been intensively studied at millikelvin temperatures due to its impact on superconducting qubit devices and incoherent detectors. However, the significance of TLS loss in superconducting transmission lines at liquid helium temperatures remains unclear. This study investigates TLS loss in amorphous $SiO_2$ at liquid helium temperatures (about 4 K) within a frequency range of 130-170 GHz, using niobium microstrip and coplanar waveguide resonators. Our results demonstrate notable power and temperature dependence of dielectric loss, with the dielectric loss and quasiparticle loss exchanging dominance at around 4 K. These findings are consistent with TLS models and provide crucial insights for the design of superconducting devices operating at liquid helium temperatures.

astro-ph.IM↗

arXiv2019

Experimental Study of a Planar-integrated Dual-Polarization Balanced SIS Mixer

A dual-polarization balanced superconductor-insulator-superconductor mixer operating at 2 mm wavelength is realized in form of a monolithic planar integrated circuit. Planar orthomode transducers and LO couplers are enabled by using silicon membranes that are locally formed on the silicon-on-insulator substrate. The performance of the balanced mixer is experimentally investigated. Over the entire RF band (125-163 GHz), the balanced mixer shows an LO noise rejection ratio about 15 dB, an overall receiver noise about 40 K, and a cross-polarization <-20 dB. The demonstrated compactness and the performance of the integrated circuit indicate that this approach is feasible in developing heterodyne focal plane arrays.

astro-ph.IM↗

arXiv2018

Planar Superconductor-Insulator-Superconductor Mixer Array Receivers for Wide Field of View Astronomical Observation

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.

astro-ph.IM↗