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IEEE Transactions on Applied Superconductivity

Study on the Signal Transmission of the RL-Branch in Josephson Junction Switch

Yituo Zhao, Hai Wang, Shijian Wang, Jiajun Chen, Yifan Wu, Zhidan Zhang, Xiangyan Kong

Published Dec 2, 2025• 0 citations

Abstract

Superconducting detectors, with their advantages of low noise and high energy resolution, have become key components for astronomical observation. Time-division multiplexing (TDM) scheme is a widely used technology for the readout of large sensor arrays, owing to its advantages in scalability, ease of integration, and low-noise performance. A primary limitation, however, is the degradation of the signal-to-noise ratio due to noise aliasing, which constrains the scaling of the multiplexing factor. To address this issue, we developed a front-end superconducting switch based on Josephson junction (JJ). Specifically, we fabricated Josephson junction switch (JJ-switch) cells where each junction is shunted by a 4 Ω resistor to ensure its non-hysteretic current-voltage characteristics. Three independent channels are designed on one switch chip, the inductance of Lin and SQUID are fixed values, but the resistance of Rin has three values: 0.1 Ω, 1 Ω and 2.5 Ω. The output of each switch channel is magnetically coupled to a dedicated input superconducting quantum interference device (SQUID) via an independent input coil, with a coefficient of 4.68 μA/Φ0. Finally, the signal transmission ratio, noise, and system sensitivity of the switch were characterized at an operating temperature of 4.2 K. This work verifies the transmission characteristics of the JJ-switch, which will provide a new device foundation for the TDM readout of large-scale superconducting detector arrays

DOI: 10.1109/tasc.2025.3639424

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Superconducting switches are important components in multiplexers based on superconducting quantum interference devices (SQUIDs). In time-division multiplexing (TDM) circuits, the superconducting switches are mainly used to activate and control input SQUIDs. The superconducting switch has the advantages of low power consumption and easy control. Here, a superconducting switch based on weakly damped SQUIDs is proposed. The dynamic resistance of the superconducting switch can be increased by appropriately adjusting the Stewart-McCumber parameter

\beta _{c}

of the Josephson junction. This design is expected to reduce the number of SQUIDs in arrays and simplify the fabrication processes of switches.

We have investigated the transient response of superconducting quantum interference devices (SQUIDs) used in time-division multiplexing schemes for the readout from arrays of superconducting transition-edge sensors (TES). In time-division multiplexing the per channel settling time is an important parameter since it limits the multiplexing frequency as well as the signal-to-noise ratio. Although SQUIDs in general are fast cryoelectronic devices operating at a nanosecond scale, experimental evidence shows that the settling time in bias-switched SQUID multiplexers can, in the case of a low impedance input circuit, reach several microseconds. We have confirmed this behavior through numerical transient analysis using a Josephson circuit simulator. Within the simulation we have found that the transient response can be reduced using an extra inductor in series with the input coil of the dc SQUID. This result in turn has been confirmed experimentally. We furthermore discuss the conflicting constraints that a desired high signal bandwidth places on the parameters of the multiplexer, the readout SQUIDs, and the TES.

Superconducting quantum interference device (SQUID) amplifier is best known for its low input impedance, low noise and low power consumption. Nowadays it is widely used for detecting the weak signals. Compared with other methods, the Nb/Al-AlOx/Nb structure Josephson junction based SQUID has the advantages of high transition temperature, high voltage flux modulation index and good heat recycle ability, wide critical voltage range, so it is a very good option for making SQUID amplifier. In this work, we fabricate the overdamped Josephson junction and washer dc SQUID, and test the I-V characteristics at He3 3 K stage temperature and calculate the current resolution of SQUID. The result of SQUID modulation property is good. The magnification becomes larger after increasing the input line number of loops, and the system noise becomes smaller after the join of the LC filter. This work is very important for designing and manufacturing transition edge sensor readout circuits.

Multiplexed superconducting quantum interference device (SQUID) amplifiers have recently enabled the deployment of kilopixel arrays of superconducting transition-edge sensor (TES) detectors on a variety of receivers for astrophysics. Existing multiplexing techniques for TES arrays, however, have constraints due to aliasing of SQUID noise, the size of the required filtering elements, or the complexity of the room-temperature electronics that make it difficult to scale to much larger arrays. We have developed a Walsh code-division SQUID multiplexer that has the potential to enable the multiplexing of larger arrays or pixels with faster thermal response times. The multiplexer uses superconducting switches to modulate the polarity of coupling between N individual TES detectors and a single output SQUID channel. The polarities of the detector signals are switched in the pattern of an N × N Walsh matrix, so a frame composed of N orthogonal samples can be used to reconstruct the detector signals without degradation. We present an analysis of the circuit architecture and preliminary results.

Dependence of SQUID Intrinsic Flux Noise on Stewart–McCumber Parameter

\beta_{c}

of Josephson Junction

It is known that three superconducting quantum interference device (SQUID) parameters, namely, the intrinsic flux noise δΦs, the flux-to-voltage transfer coefficient ∂V/∂Φ, and the dynamic resistance Rd, increase with increasing the Stewart- McCumber parameter βcof Josephson junction. It is very difficult to obtain the low values of δΦsfor a strongly damped SQUID due to its small ∂V/∂Φ. In this paper, we employ a two-stage scheme (TSS) to measure δΦsdirectly. Here, we use single chip readout electronics and a weakly damped SQUID with a βcof flux noise of the readout-SQUID system is about 4.8 μΦ0/√Hz 1.2, both acting as a readout-SQUID system (a preamplifier). The with a corner frequency of about 10 Hz. The front-end SQUID is coupled to the readout SQUID via the input coil with a mutual inductance of Mi. In our experiment, the flux gain for a readout SQUID, i.e., GΦ= Mi× (∂I/∂Φ)front-endis adjusted to be 20. Using the TSS, we measured δΦswith different βcchanging from 0.3 to 13.5 and found δΦsincreasing from 1.0 to 5.0 μΦ0/√Hz. We also discussed the relations between Ls, βc, and δΦsquantitatively. Finally, we proposed designing a suitable βcto match the preamplifier in a direct readout scheme to simplify a SQUID measurement system.

We report on the development of a microwave superconducting quantum interference device (SQUID) multiplexer to read out arrays of low-temperature detectors. In this frequency-division multiplexer, superconducting resonators with different frequencies couple to a common transmission line and each resonator couples to a different dissipationless SQUID. We demonstrate multiple designs, with high-Q values (4100–18 000), noise as low as 0.17μΦ0∕Hz, and a naturally linear readout scheme based on flux modulation. This multiplexing approach is compatible with superconducting transition-edge sensors and magnetic calorimeters and is capable of multiplexing more than a thousand detectors in a single transmission line.