Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Infrared, Millimeter-Wave, and Terahertz Technologies

Microwave SQUID multiplexer for readout of transition-edge sensor array

Zhi-Fa Feng, Xin-Kai Yang, Wen Zhang, Zheng Wang, Qingxiao Ma, Peizhan Li, Jiaqiang Zhong, Wei Miao, Yuan Ren, Qijun Yao, Jing Li, Sheng‐Cai Shi

Published Oct 12, 2023• 0 citations
Publisher

Abstract

Superconducting transition-edge sensors (TESs) are highly sensitive detectors and can detect electromagnetic wave radiations from millimeter/submillimeter, optical to 𝑥/γrays, suitable for cosmology, astrophysics, quantum information, and biosensing. In principle, thousands of TESs even more are required to enhance the detection efficiency for large-scale survey. Among other multiplexing schemes, microwave SQUID multiplexer (μMUX), consisting of resonators and RF SQUIDs, has a bandwidth of several GHz, thus multiplexing factor on the order of thousands, more suitable for readout of large TES arrays. We designed and fabricated superconducting coplanar waveguide (CPW) resonators with a high qualityfactor and second-order gradient RF SQUID with two inductive coupling structures respectively. Then, we optimized the critical current density of the Josephson junction and measured the mutual inductance parameters of the second-order gradient structure SQUID, which are consistent with the simulation results. Finally, we fabricated a cryogenic μMUX chip based on RF SQUID and resonator. We discussed the results of the development of μMUX in more detail.

DOI
10.1117/12.2688546

Related papers

Development of Microwave SQUID Multiplexer for Readout of Transition-Edge Sensor Array

Zhi-Fa Feng, Xianfeng Zhou, Wen Zhang +12 more

Superconducting transition-edge sensors (TESs) with high sensitivity can detect electromagnetic wave radiations from millimeter/submillimeter, optical to x/γ rays, and have been successfully used in many fields. To improve detection efficiency and sensitivity, large-scale TES arrays are required in combination with multiplexing readout electronics. Compared to other multiplexing schemes, microwave SQUID multiplexing (μMUX), consisting of high-quality microwave superconducting resonators and RF SQUIDs, is most suitable since it provides a wider bandwidth (GHz) and consequently higher multiplexing factor. We designed two types of circuits with different mutual inductances (MT) between the resonator and the RF SQUID: 2.3 pH for the weak-coupling channel and 6.5 pH for the strong- coupling channel. The resonator and RF SQUID washers made of 150 nm Nb are first fabricated by magnetron-sputtering and reactive ion etching (RIE), followed by deposition of Nb/Al-AlOx/Nb trilayer and definition of the Josephson junctions of the RF SQUIDs. This work presents a μMUX demonstration chip with five channels with Q1values of 787 and 3626, and the measured frequency shifts (Δfpp) of ∼500 kHz and 4 MHz for the weak- and strong-coupling channels, respectively. The open-loop equivalent noise current, obtained from the measured phase noise and resonator responsivity, is ∼80 pA/ √Hz with the strong-coupling channel.

IEEE Transactions on Applied Superconductivity•Jan 14, 2026•2 citations

Development of a microwave SQUID multiplexer for superconducting transition-edge sensor bolometer arrays

Zhi-Fa Feng, Xian-Feng Zhou, M Y Li +10 more

Abstract A microwave SQUID multiplexer ( μ MUX) with a high multiplexing factor is a promising readout approach for large-scale superconducting transition-edge sensor (TES) bolometer arrays. This paper reports on the characteristics of 16-channel μ MUX prototype chips and a 60-channel readout module developed to read out TES bolometers for the Ali cosmic microwave background polarization telescope (AliCPT). We designed two different coupling structures between the resonator and the radio-frequency superconducting interference device: design A with a mutual inductance ( M T ) of 2.3 pH and design B with an M T of 6.5 pH. For design A, the mean resonator bandwidth ( Δ f BW ) and peak-to-peak frequency shift ( Δ f pp ) are approximately 610 kHz and 290 kHz, respectively. The measured mean open-loop current noise is less than 40 pA / Hz . Preliminary results indicate that crosstalk between adjacent channels is below 1% in our design A μ MUX chip. A measured channel with design B shows a Δ f BW of 586 kHz and a current noise of 33 pA / Hz , similar to the design A channels. In comparison, the Δ f pp of 803 kHz is much larger than the design A channels due to a larger M T . The readout module, consisting of two design A chips and two design B chips, shows 60 resonances, corresponding to a yield of 94%. In the future, we will place 32 design A channels within the same chip dimension to increase the channel density and build a larger readout module suitable for AliCPT TES arrays.

Superconductor Science and Technology•Sep 1, 2026•0 citations

A prototype of 5-channel microwave SQUID multiplexer for primordial gravitational wave detection

Xianfeng Zhou, Zhi-Fa Feng, Min Li +10 more

Abstract Primordial gravitational waves (PGWs) can only be detected by measuring the B-mode polarization of the cosmic microwave background (CMB) and large-scale arrays based on superconducting transition-edge sensors (TES) are the detectors of the choice thanks to the background-limited sensitivity. Different multiplexing readout techniques have been developed to combine the signals from multiple detectors into a reduced number of readout channels. Microwave SQUID multiplexing (μMUX) has the highest multiplexing factor, suitable for large-scale TES array readout. We are developing μMUX chips to read out TES array for the detection of PGWs. We have designed and fabricated a prototype of a 5-channel μMUX chip consisting of distributed quarter-wavelength coplanar waveguide (CPW) resonators and radio-frequency superconducting quantum interference devices (RF SQUIDs). The measured quality factor of the CPW resonators working at 4.7-4.9 GHz is higher than 104. The maximum frequency shift is about 290 kHz on average, compatible with the resonator bandwidth (~380 kHz). The mean value of magnetic flux noise is 1.1 μ$\Phi_0 / \sqrt{\mathrm{Hz}} @ 5$ kHz, corresponding to a current noise of 40 $\mathrm{pA} / \sqrt{\mathrm{Hz}}$.

Chinese Physics B•Feb 12, 2026•1 citation

Prototype of the Room-Temperature Readout System for Microwave Multiplexing Readout of Transition Edge Sensor

Yuanda Wang, Cao Ping, Weigang Yin +8 more

Transition Edge Sensors (TESs) are highly sensitive cryogenic detectors widely used in astronomy, high-energy physics and nuclear radiation detection. As TES is increasingly deployed in large-scale arrays to improve sensitivity and effective collecting area, multiplexed readout becomes essential for reducing system complexity. Microwave SQUID multiplexing (μMUX) technology combining superconducting resonators with radio-frequency superconducting quantum interference devices (RF-SQUIDs), represents a state-of-the-art solution. In this work, a room-temperature readout prototype for TES μMUX readout was designed. The system features a scalable two-stage architecture, including a highly integrated, chassis-independent front-end signal processing module and back-end event-reconstruction module. A high-frequency-resolution frequency-comb signal generation method with real-time, per-tone frequency and phase tunability was developed. In addition, optimization of the firmware implementation effectively overcomes the computational-resource bottleneck of the Field Programmable Gate Array (FPGA). The prototype supports autonomous frequency sweeping, parameter diagnostics, and online event reconstruction. Self-test shows S 21 phase noise better than −110 dBc/Hz at −30 dBm, remaining stable with increasing channel count. Joint tests with a μMUX cryogenic system successfully captured the RF-SQUID response and achieved an equivalent noise current of 44 pA/√Hz referred to the TES, validating the prototype as a practical solution of the room-temperature system for TES μMUX readout.

Nuclear Engineering and Technology•Oct 1, 2026•0 citations

Development of second-order gradient DC SQUIDs for the readout of superconducting TES detectors

Z. F. Feng, Xuefeng Zhou, Q. X. Ma +12 more

Superconducting transition-edge sensors (TESs) are highly sensitive detectors, can detect electromagnetic wave radiations from millimeter/submillimeter, optical to x/γ rays, suitable for astrophysics, quantum information, and biosensing. Direct current superconducting quantum interference devices (DC SQUIDs) are the detector of choice for TES readout, thanks to their low noise, low impedance, and low power dissipation. In this work, we designed the DC SQUID with a second-order gradient structure, which can effectively mitigate the effect of external magnetic flux. We optimized the fabrication process and successfully fabricated the high-performance DC SQUID with Nb/Al-AlOx/Nb Josephson junctions (critical current density: JC~1μA/μm2). The properties of the fabricated DC SQUID were in good agreement with the simulation results. Meanwhile, the measured flux noise was 6 μΦ0/√Hz, corresponding to a current noise of 100 pA/√Hz. Furthermore, we demonstrated the capability of the DC SQUID to read out the TES detector, including I-V curves, photon pulse response, and noise performance.

Infrared, Millimeter-Wave, and Terahertz Technologies•Nov 19, 2025•0 citations

Scalable Microwave SQUID Multiplexer Readout Architecture for TES-Based THz Security Camera

Matthias Schmelz, Erik Heinz, Katja Peiselt +8 more

In this article, we have developed a scalable superconducting quantum interference device (SQUID)-based microwave multiplexer (µMUX) readout architecture adapted for arrays of transition edge sensors (TESs) to be exploited in a terahertz security camera. The camera system combines a scanning optics together with a 128-pixel TES array and aims for security gate operations with a standoff detection distance of up to 25 m. The developed frequency-domain µMUX is used to read out all feed-horn-coupled TESs based on aluminum thermistors, with noise limited by intrinsic TES noise. Both the TESs and µMUXs are operated in a compact cryostat with a base temperature of about 0.9 K. The µMUX has been fabricated in the cross-type$\text{Nb}/ \text{AlO}\_{\rm{x}}/ \text{Nb}$Josephson junction process developed at the Leibniz Institute of Photonic Technology and incorporates high-quality superconducting thin-film resonators with resonant frequencies in the range of 5–6 GHz. An accordingly implemented field-programmable-gate-array-based readout electronics enables the simultaneous and continuous real-time readout of 128 rf-SQUIDs, including a flux ramp modulation scheme. In operation with the aluminum TES, we achieved a dark noise equivalent power of about$2.5\; \text{fW}/ \text{Hz}^{1/ 2}$while providing a TES readout rate of 3.75 kHz, necessary for a video frame rate of 25 Hz of the security camera.

IEEE Transactions on Applied Superconductivity•Feb 25, 2025•0 citations
Superconducting transition-edge sensors (TESs) are highly sensitive detectors and can detect electromagnetic wave radiations from millimeter/submillimeter, optical to 𝑥/γrays, suitable for cosmology, astrophysics, quantum information, and biosensing. In principle, thousands of TESs even more are required to enhance the detection efficiency for large-scale survey. Among other multiplexing schemes, microwave SQUID multiplexer (μMUX), consisting of resonators and RF SQUIDs, has a bandwidth of several GHz, thus multiplexing factor on the order of thousands, more suitable for readout of large TES arrays. We designed and fabricated superconducting coplanar waveguide (CPW) resonators with a high qualityfactor and second-order gradient RF SQUID with two inductive coupling structures respectively. Then, we optimized the critical current density of the Josephson junction and measured the mutual inductance parameters of the second-order gradient structure SQUID, which are consistent with the simulation results. Finally, we fabricated a cryogenic μMUX chip based on RF SQUID and resonator. We discussed the results of the development of μMUX in more detail.
Superconducting transition-edge sensors (TESs) with high sensitivity can detect electromagnetic wave radiations from millimeter/submillimeter, optical to x/γ rays, and have been successfully used in many fields. To improve detection efficiency and sensitivity, large-scale TES arrays are required in combination with multiplexing readout electronics. Compared to other multiplexing schemes, microwave SQUID multiplexing (μMUX), consisting of high-quality microwave superconducting resonators and RF SQUIDs, is most suitable since it provides a wider bandwidth (GHz) and consequently higher multiplexing factor. We designed two types of circuits with different mutual inductances (MT) between the resonator and the RF SQUID: 2.3 pH for the weak-coupling channel and 6.5 pH for the strong- coupling channel. The resonator and RF SQUID washers made of 150 nm Nb are first fabricated by magnetron-sputtering and reactive ion etching (RIE), followed by deposition of Nb/Al-AlOx/Nb trilayer and definition of the Josephson junctions of the RF SQUIDs. This work presents a μMUX demonstration chip with five channels with Q1values of 787 and 3626, and the measured frequency shifts (Δfpp) of ∼500 kHz and 4 MHz for the weak- and strong-coupling channels, respectively. The open-loop equivalent noise current, obtained from the measured phase noise and resonator responsivity, is ∼80 pA/ √Hz with the strong-coupling channel.
Abstract A microwave SQUID multiplexer ( μ MUX) with a high multiplexing factor is a promising readout approach for large-scale superconducting transition-edge sensor (TES) bolometer arrays. This paper reports on the characteristics of 16-channel μ MUX prototype chips and a 60-channel readout module developed to read out TES bolometers for the Ali cosmic microwave background polarization telescope (AliCPT). We designed two different coupling structures between the resonator and the radio-frequency superconducting interference device: design A with a mutual inductance ( M T ) of 2.3 pH and design B with an M T of 6.5 pH. For design A, the mean resonator bandwidth ( Δ f BW ) and peak-to-peak frequency shift ( Δ f pp ) are approximately 610 kHz and 290 kHz, respectively. The measured mean open-loop current noise is less than 40 pA / Hz . Preliminary results indicate that crosstalk between adjacent channels is below 1% in our design A μ MUX chip. A measured channel with design B shows a Δ f BW of 586 kHz and a current noise of 33 pA / Hz , similar to the design A channels. In comparison, the Δ f pp of 803 kHz is much larger than the design A channels due to a larger M T . The readout module, consisting of two design A chips and two design B chips, shows 60 resonances, corresponding to a yield of 94%. In the future, we will place 32 design A channels within the same chip dimension to increase the channel density and build a larger readout module suitable for AliCPT TES arrays.
Abstract Primordial gravitational waves (PGWs) can only be detected by measuring the B-mode polarization of the cosmic microwave background (CMB) and large-scale arrays based on superconducting transition-edge sensors (TES) are the detectors of the choice thanks to the background-limited sensitivity. Different multiplexing readout techniques have been developed to combine the signals from multiple detectors into a reduced number of readout channels. Microwave SQUID multiplexing (μMUX) has the highest multiplexing factor, suitable for large-scale TES array readout. We are developing μMUX chips to read out TES array for the detection of PGWs. We have designed and fabricated a prototype of a 5-channel μMUX chip consisting of distributed quarter-wavelength coplanar waveguide (CPW) resonators and radio-frequency superconducting quantum interference devices (RF SQUIDs). The measured quality factor of the CPW resonators working at 4.7-4.9 GHz is higher than 104. The maximum frequency shift is about 290 kHz on average, compatible with the resonator bandwidth (~380 kHz). The mean value of magnetic flux noise is 1.1 μΦ0/Hz@5\Phi_0 / \sqrt{\mathrm{Hz}} @ 5Φ0​/Hz​@5 kHz, corresponding to a current noise of 40 pA/Hz\mathrm{pA} / \sqrt{\mathrm{Hz}}pA/Hz​.
Transition Edge Sensors (TESs) are highly sensitive cryogenic detectors widely used in astronomy, high-energy physics and nuclear radiation detection. As TES is increasingly deployed in large-scale arrays to improve sensitivity and effective collecting area, multiplexed readout becomes essential for reducing system complexity. Microwave SQUID multiplexing (μMUX) technology combining superconducting resonators with radio-frequency superconducting quantum interference devices (RF-SQUIDs), represents a state-of-the-art solution. In this work, a room-temperature readout prototype for TES μMUX readout was designed. The system features a scalable two-stage architecture, including a highly integrated, chassis-independent front-end signal processing module and back-end event-reconstruction module. A high-frequency-resolution frequency-comb signal generation method with real-time, per-tone frequency and phase tunability was developed. In addition, optimization of the firmware implementation effectively overcomes the computational-resource bottleneck of the Field Programmable Gate Array (FPGA). The prototype supports autonomous frequency sweeping, parameter diagnostics, and online event reconstruction. Self-test shows S 21 phase noise better than −110 dBc/Hz at −30 dBm, remaining stable with increasing channel count. Joint tests with a μMUX cryogenic system successfully captured the RF-SQUID response and achieved an equivalent noise current of 44 pA/√Hz referred to the TES, validating the prototype as a practical solution of the room-temperature system for TES μMUX readout.
Superconducting transition-edge sensors (TESs) are highly sensitive detectors, can detect electromagnetic wave radiations from millimeter/submillimeter, optical to x/γ rays, suitable for astrophysics, quantum information, and biosensing. Direct current superconducting quantum interference devices (DC SQUIDs) are the detector of choice for TES readout, thanks to their low noise, low impedance, and low power dissipation. In this work, we designed the DC SQUID with a second-order gradient structure, which can effectively mitigate the effect of external magnetic flux. We optimized the fabrication process and successfully fabricated the high-performance DC SQUID with Nb/Al-AlOx/Nb Josephson junctions (critical current density: JC~1μA/μm2). The properties of the fabricated DC SQUID were in good agreement with the simulation results. Meanwhile, the measured flux noise was 6 μΦ0/√Hz, corresponding to a current noise of 100 pA/√Hz. Furthermore, we demonstrated the capability of the DC SQUID to read out the TES detector, including I-V curves, photon pulse response, and noise performance.
In this article, we have developed a scalable superconducting quantum interference device (SQUID)-based microwave multiplexer (µMUX) readout architecture adapted for arrays of transition edge sensors (TESs) to be exploited in a terahertz security camera. The camera system combines a scanning optics together with a 128-pixel TES array and aims for security gate operations with a standoff detection distance of up to 25 m. The developed frequency-domain µMUX is used to read out all feed-horn-coupled TESs based on aluminum thermistors, with noise limited by intrinsic TES noise. Both the TESs and µMUXs are operated in a compact cryostat with a base temperature of about 0.9 K. The µMUX has been fabricated in the cross-typeNb/AlO_x/Nb\text{Nb}/ \text{AlO}\_{\rm{x}}/ \text{Nb}Nb/AlO_x/NbJosephson junction process developed at the Leibniz Institute of Photonic Technology and incorporates high-quality superconducting thin-film resonators with resonant frequencies in the range of 5–6 GHz. An accordingly implemented field-programmable-gate-array-based readout electronics enables the simultaneous and continuous real-time readout of 128 rf-SQUIDs, including a flux ramp modulation scheme. In operation with the aluminum TES, we achieved a dark noise equivalent power of about2.5  fW/Hz1/22.5\; \text{fW}/ \text{Hz}^{1/ 2}2.5fW/Hz1/2while providing a TES readout rate of 3.75 kHz, necessary for a video frame rate of 25 Hz of the security camera.