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arXiv:2605.24272 · Superconductor Science and Technology

Characterization of aluminum microwave SQUID multiplexers for CE ν NS detection

James Amidei, A. Armatol, C. Augier, L. Bailly-Salins, G. Baulieu, Laurent Bergé, Julien Billard, Juliette Blé, Gaby Brenot, G. Bres, J-.L. Bret, A. Broniatowski, Martino Calvo, A. Cavanna, A. Cazes, E. Celi, D. Chaize, Mohammed Chala, Maurice P. Chapellier, Luke Chaplinsky, Ran Chen, Ion Cojocari, J. Colas, Laurent Couraud, Elspeth Cudmore, M. De Jésus, Pierre de Marcillac, Nicole Dombrowski, L. Dumoulin, Alan Durnez, R. Faure, S Ferriol, Enectali Figueroa-Feliciano, Joseph A. Formaggio, S. Fuard, Jules Gascon, C. Girard-Carillo, Andrea Giuliani, C. Goy, Cyrille Guerin, L. Haegel, P. M. Harrington, S. A. Hertel, Cyrus F. Hirjibehedin, C. Hoarau, Ziqing Hong, Daemon Howard, Jean‐Christophe Ianigro, Yong Jin, A. Juillard, Dimitar Karaivanov, T. Khussainov, Andrew Kubik, J. Lamblin, Tatiana Le Bellec, Laetitia Leroy, M. Li, Alexey Lubashevskiy, S. Marnieros, R Martin, MARTINI Nicolas, J Minet, A. Monfardini, F. Mounier, Bethany M. Niedzielski, V. Novati, William D. Oliver, E. Olivieri, H. D. Pinckney, Denys V. Poda, Dmitrii Ponomarev, J. S. Réal, F. C. Reyes, A Rodriguez, S. Rozov, I. Rozova, Brianna Ryan, D. Sabhari, S. Scorza, Kyle Serniak, Renaud Serra, Yegor Shevchik, T. Söldner, Hannah Stickler, Caitlyn Stone-Whitehead, Christian Ulysse, W. Van De Pontseele, S. Vasilyev, P Vittaz, Steven J. Weber, Evan Wolfe, Wayne H. Woods, E Yakushev, Jinbiao Yang, D. Zinatulina

Published Oct 1, 2026• 0 citations
arXivHTMLPDF

Abstract

Abstract We present the design, fabrication, and characterization of an aluminum-based six-channel microwave SQUID multiplexer ( μ MUX) prototype for transition-edge sensor readout in the Ricochet experiment. The device consists of aluminum coplanar-waveguide resonators and RF superconducting quantum interference devices with Dolan-style Al/AlO x /Al Josephson junctions. By measuring the resonator scattering parameters at a range of probe tone frequencies, powers, and flux bias points, we demonstrate agreement between the device response and existing multiplexer models. We also characterize the noise performance in both open-loop and flux-ramping modes. With a high electron mobility transistor (HEMT) amplifier, open-loop measurements yield a flux sensitivity of 1–1.5 μ Φ 0 / Hz . With flux-ramp modulation, low-frequency 1 / f noise is suppressed, and the flux sensitivity is around 3–4 μ Φ 0 / Hz , corresponding to a current sensitivity of 24–33 pA / Hz at the input coil. We further demonstrate a reduction in readout noise by incorporating a Josephson traveling-wave parametric amplifier between the μ MUX and the HEMT. This achieves an open-loop flux sensitivity of 0.3–0.6 μ Φ 0 / Hz and an effective system noise temperature below 1K. These results establish aluminum μ MUX devices as a viable and extensible readout technology for low-noise cryogenic detector arrays.

DOI
10.1088/1361-6668/aeaa8f

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White noise of dissipationless microwave radio frequency superconducting quantum interference device (RF-SQUID) multiplexers has been experimentally studied to evaluate their readout performance for transition edge sensor (TES) photon counters ranging from near infrared to gamma ray. The characterization has been carried out at 4 K, first to avoid the low-frequency fluctuations present at around 0.1 K, and second, for a feasibility study of readout operation at 4 K for extended applications. To increase the resonant Q at 4 K and maintain low noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1 × 104 ≤ Q ≤ 2 × 104 and the square root of spectral density of current noise referred to the SQUID input √SI = 31 pA/√Hz. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Two-directional readout on the complex plane of the transmission component of scattering matrix S21 enables us to distinguish the flux noise from noise originating from other sources, such as the cryogenic high electron mobility transistor (HEMT) amplifier. Systematic noise measurements with various microwave readout powers PMR make it possible to distinguish the contribution of noise sources within the system as follows: (1) The achieved √SI is dominated by the Nyquist noise from a resistor at 4 K in parallel to the SQUID input coil which is present to prevent microwave leakage to the TES. (2) The next dominant source is either the HEMT-amplifier noise (for small values of PMR) or the quantization noise due to the resolution of 300-K electronics (for large values of PMR). By a decrease of these noise levels to a degree that is achievable by current technology, we predict that the microwave RF-SQUID multiplexer can exhibit √SI ≤ 5 pA/√Hz, i.e., close to √SI of state-of-the-art DC-SQUID-based multiplexers.

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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.

Infrared, Millimeter-Wave, and Terahertz Technologies•Oct 12, 2023•0 citations
Abstract We present the design, fabrication, and characterization of an aluminum-based six-channel microwave SQUID multiplexer ( μ MUX) prototype for transition-edge sensor readout in the Ricochet experiment. The device consists of aluminum coplanar-waveguide resonators and RF superconducting quantum interference devices with Dolan-style Al/AlO x /Al Josephson junctions. By measuring the resonator scattering parameters at a range of probe tone frequencies, powers, and flux bias points, we demonstrate agreement between the device response and existing multiplexer models. We also characterize the noise performance in both open-loop and flux-ramping modes. With a high electron mobility transistor (HEMT) amplifier, open-loop measurements yield a flux sensitivity of 1–1.5 μ Φ 0 / Hz . With flux-ramp modulation, low-frequency 1 / f noise is suppressed, and the flux sensitivity is around 3–4 μ Φ 0 / Hz , corresponding to a current sensitivity of 24–33 pA / Hz at the input coil. We further demonstrate a reduction in readout noise by incorporating a Josephson traveling-wave parametric amplifier between the μ MUX and the HEMT. This achieves an open-loop flux sensitivity of 0.3–0.6 μ Φ 0 / Hz and an effective system noise temperature below 1K. These results establish aluminum μ MUX devices as a viable and extensible readout technology for low-noise cryogenic detector arrays.
White noise of dissipationless microwave radio frequency superconducting quantum interference device (RF-SQUID) multiplexers has been experimentally studied to evaluate their readout performance for transition edge sensor (TES) photon counters ranging from near infrared to gamma ray. The characterization has been carried out at 4 K, first to avoid the low-frequency fluctuations present at around 0.1 K, and second, for a feasibility study of readout operation at 4 K for extended applications. To increase the resonant Q at 4 K and maintain low noise SQUID operation, multiplexer chips consisting of niobium nitride (NbN)-based coplanar-waveguide resonators and niobium (Nb)-based RF-SQUIDs have been developed. This hybrid multiplexer exhibited 1 × 104 ≤ Q ≤ 2 × 104 and the square root of spectral density of current noise referred to the SQUID input √SI = 31 pA/√Hz. The former and the latter are factor-of-five and seven improvements from our previous results on Nb-based resonators, respectively. Two-directional readout on the complex plane of the transmission component of scattering matrix S21 enables us to distinguish the flux noise from noise originating from other sources, such as the cryogenic high electron mobility transistor (HEMT) amplifier. Systematic noise measurements with various microwave readout powers PMR make it possible to distinguish the contribution of noise sources within the system as follows: (1) The achieved √SI is dominated by the Nyquist noise from a resistor at 4 K in parallel to the SQUID input coil which is present to prevent microwave leakage to the TES. (2) The next dominant source is either the HEMT-amplifier noise (for small values of PMR) or the quantization noise due to the resolution of 300-K electronics (for large values of PMR). By a decrease of these noise levels to a degree that is achievable by current technology, we predict that the microwave RF-SQUID multiplexer can exhibit √SI ≤ 5 pA/√Hz, i.e., close to √SI of state-of-the-art DC-SQUID-based multiplexers.
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.
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.
We report on the use of a kinetic-inductance traveling-wave parametric amplifier (KITWPA) as the first amplifier in the readout chain of a microwave superconducting quantum interference device (SQUID) multiplexer (μmux). This μmux is designed to multiplex signals from arrays of low temperature detectors, such as superconducting transition-edge sensor microcalorimeters. When modulated with a periodic flux-ramp to linearize the SQUID response, the flux noise improves, on average, from 1.6 μΦ0/Hz with the KITWPA off to 0.77 μΦ0/Hz with the KITWPA on. When statically biasing the μmux to the maximally flux-sensitive point, the flux noise drops from 0.45 μΦ0/Hz to 0.2 μΦ0/Hz. We validate this new readout scheme by coupling a transition-edge sensor microcalorimeter to the μmux and detecting background radiation. The combination of μmux and KITWPA provides a variety of new capabilities including improved detector sensitivity and more efficient bandwidth utilization.
We report very-low-noise, fast-response, middle-scale multiplexing in a microwave superconducting quantum interference device multiplexer (MW-Mux) as a transition-edge sensor (TES) readout. Our MW-Mux is able to read 40 channels with 500 kHz sampling and has a low readout noise of 0.9 μΦ0/Hz (where Φ0 is the magnetic flux quantum), equivalent to 9 pA/Hz. By contrast, a multiplexer of less than 10 pixels with 500 kHz sampling and ∼2 μΦ0/Hz readout noise has so far been reported in the literature. Owing to the 500 kHz sampling, our MW-Mux exhibits a fast response to detect a TES pulse with a rise time around 12 μs. We demonstrated simultaneous readout of 38 pixels from an array of x-ray TES microcalorimeters. The measured full-width values at half-maximum spectral resolution ranged from 2.79 to 4.56 eV, with a median value of 3.30 eV at 5.9 keV, including a ∼10% contribution of readout noise, i.e., 0.9–1.7 eV.
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.