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IEEE Transactions on Applied Superconductivity

Compatibility Study of the LiteBIRD SQUID Controller Unit With a Dual-Stage SQUID Amplification Chain

Mario de Lucia, Paolo Dal Bo, A. Tartari, Jean-François Cliche, Giulia Conenna, Gabriele Coppi, E. Di Giorgi, Matt Dobbs, Tommaso Lari, Maurizio Massa, Andrea Moggi, Joshua Montgomery, Donato Nicolò, Michele Pinchera, Graeme M. Smecher, M. Zannoni, G. Signorelli

Published May 7, 2026• 0 citations
Publisher

Abstract

The LiteBIRD satellite will map the polarisation of the Cosmic Microwave Background (CMB) with unprecedented sensitivity by means of antenna-coupled transition edge sensors (TESs). Its current design features single SQUID-Array Amplifiers (SAA) at a temperature of about 400 mK in order to read out up to 64 TESs in a frequency division multiplexing scheme. The front-end part of the electronics (the SQUID Controller Assembly -SCA) was designed to handle this configuration. Nevertheless, alternative configurations of the experiment are being studied that might require a dual-stage SQUID (DSS) amplification chain in order to meet thermal and noise requirements. In light of this possibility, we have successfully investigated the feasibility of controlling two individual SAAs in a DSS Amplifier (DSSA) configuration with two independent channels of the present SCA. The SQUID directly connected to the sensor, commonly referred to as ‘front-end’, behaves as an emitter-follower, or buffer, circuit and it decouples the impedance of the TES(s) from the rest of the readout chain whilst producing a moderate amplification. The second SQUID, ‘booster’, is responsible for a high-gain amplification of the signal and can be thermally decoupled from the front-end allowing it to dissipate a lot more power and thus exhibiting a higher gain. We characterised a breadboard model in which two SQUID amplifiers are cascaded but hosted on the same circuit board and thus not thermally decoupled. This was intended to perform functional tests and to assess the feasibility of controlling a DSSA without introducing major changes in the already developed LiteBIRD SCA. We present the typical I-V and I-$\Phi$curves of the two SQUIDs along with the characterisation of the DSSA in terms of bandwidth, linearity and total harmonic distortion (THD).

DOI
10.1109/tasc.2026.3690793

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IEEE Transactions on Applied Superconductivity•Nov 10, 2014•14 citations
The LiteBIRD satellite will map the polarisation of the Cosmic Microwave Background (CMB) with unprecedented sensitivity by means of antenna-coupled transition edge sensors (TESs). Its current design features single SQUID-Array Amplifiers (SAA) at a temperature of about 400 mK in order to read out up to 64 TESs in a frequency division multiplexing scheme. The front-end part of the electronics (the SQUID Controller Assembly -SCA) was designed to handle this configuration. Nevertheless, alternative configurations of the experiment are being studied that might require a dual-stage SQUID (DSS) amplification chain in order to meet thermal and noise requirements. In light of this possibility, we have successfully investigated the feasibility of controlling two individual SAAs in a DSS Amplifier (DSSA) configuration with two independent channels of the present SCA. The SQUID directly connected to the sensor, commonly referred to as ‘front-end’, behaves as an emitter-follower, or buffer, circuit and it decouples the impedance of the TES(s) from the rest of the readout chain whilst producing a moderate amplification. The second SQUID, ‘booster’, is responsible for a high-gain amplification of the signal and can be thermally decoupled from the front-end allowing it to dissipate a lot more power and thus exhibiting a higher gain. We characterised a breadboard model in which two SQUID amplifiers are cascaded but hosted on the same circuit board and thus not thermally decoupled. This was intended to perform functional tests and to assess the feasibility of controlling a DSSA without introducing major changes in the already developed LiteBIRD SCA. We present the typical I-V and I-Φ\PhiΦcurves of the two SQUIDs along with the characterisation of the DSSA in terms of bandwidth, linearity and total harmonic distortion (THD).
Abstract LiteBIRD is a satellite mission to be launched by JAXA in the early 2030s. It will measure the Cosmic Microwave Background (CMB) primordial B-modes with an unprecedented sensitivity. Microwave radiation will be detected by Transition Edge Sensors (TESs) arrays multiplexed in frequency domain and read by Superconducting QUantum Interference Devices (SQUIDs). The LiteBIRD SQUID Controller Unit (SCU), based on the heritage of the successful design used for the ground-based SPT3G experiment, presents some novel elements that make it suitable for a space-borne application. We compare our first breadboard model with the ground-based, Off-The-Shelf Components (COTS) version, by driving the same SQUID Array Amplifier (SAA) at 4 K, measuring relevant quantities such as noise, gain and bandwidth. We demonstrate that the noise added by our first prototype (including a switching part for redundancy purposes) never exceeds the noise added by the COTS-based electronics board, representing our benchmark. We also present the first noise estimates with the SAA cooled below 1 K, going closer to the conditions expected for LiteBIRD operation.
LiteBIRD is an upcoming JAXA-led mission that aims to measure primordial gravitational waves in the B-mode polarization of the cosmic microwave background. It is set to launch in 2032. The LiteBIRD detector array consists of around 5000 TES detectors which are read out using digital frequency multiplexing over a bandwidth of 1-6 MHz. The multiplexing factor ranges from 58x to 68x. We are presently developing single-stage SQUID array amplifiers for LiteBIRD readout. Due to the reduced complexity and cost, and greater heritage from ground-based experiments such as the South Pole Telescope and Simons Array, single-stage SQUID array amplification is preferable for the first-stage amplification, as long as it can meet the requirements. The LiteBIRD single-stage SQUID Array is required to have high transimpedance amplification while maintaining a low input inductance and low dynamic resistance. In addition, the input-referred current noise must be very low, and the power dissipation must remain below about 100 nW. These requirements have non-trivial interactions. To maximize performance within these requirements we have performed lumped-element SQUID simulation. We find that by optimizing SQUID internal damping elements and inductive loading, good single-stage SQUID array performance can be obtained for LiteBIRD, including significant engineering margin.
Abstract Direct-current superconducting quantum interference devices (dc-SQUIDs) are one of the most sensitive magnetic detectors. These sensors are extensively used in the readout of superconducting transition edge sensors (TESs), which are used for the detection of weak signals. A cosmic microwave background (CMB) polarization telescope operating in 22–48 GHz is currently under developing. The TESs calorimeter of the telescope will be readout by a time-division multiplexer SQUID readout system. We develop a two-stage dc-SQUID amplifier circuit, comprising an input-stage SQUID with 4 SQUID cells and a series SQUID array with 100 SQUID cells. This configuration has been shown to achieve extremely high signal gain while effectively controlling system noise. We assess the system noise at 300 mK in an adiabatic demagnetization refrigerator. The measured magnetic flux noise of the two-stage SQUID circuit system is approximately 0.3 μ Φ 0 / Hz at 10 kHz. The current noise equivalent to the input coil of input SQUID is about 2.4 pA / Hz . This result meets the low-noise readout requirements of the CMB TES and other applications with TES detectors.
LiteBIRD is a satellite mission designed to map the polarization of the Cosmic Microwave Background (CMB) at degree and larger scales from 40 to 402 GHz. LiteBIRD will use 4,600 Transition-Edge Sensor (TES) bolometers biased and read out using Digital Frequency Domain Multiplexing (DfMux). The DfMux implementation for LiteBIRD uses sub-kelvin Superconducting Quantum Interference Device (SQUID) at the same 0.1 K thermal stage as the detectors, this allows for reduced parasitic impedances within the mK circuit and improved SQUID performance. Additionally it must work in the integrated system with the spacecraft’s wiring harnesses, which will be longer than is typical on similar ground based experiments, and therefore have more significant parasitic impedances which will impact readout performance. The properties of SQUID candidates at millikelvin temperatures and effects of the spacecraft-like meter scale wiring harness are investigated. Additionally, the possibility of inductively rather than resistively biasing our bolometers at the 0.1K stage, to reduce power dissipation in the bias element, is investigated. We will report progress on validating the cryogenic components of this readout system.
Direct-current superconducting quantum interference devices (dc-SQUIDs) are one of the most sensitive magnetic detectors. These sensors are extensively used in the readout of superconducting transition edge sensors (TESs), which are used for the detection of weak signals. A cosmic microwave background (CMB) polarization telescope operating in 22-48 GHz is currently under developing. The TESs calorimeter of the telescope will be readout by a time-division multiplexer (TDM) SQUID readout system. We develop a two-stage dc-SQUID amplifier circuit, comprising an input-stage SQUID with 4 SQUID cells and a series SQUID array (SSA) with 100 SQUID cells. This configuration has been shown to achieve extremely high signal gain while effectively controlling system noise. We assess the system noise at 300300300 mKmKmK in an adiabatic demagnetisation refrigerator (ADR). The the measured magnetic flux noise of the two-stage SQUID circuit system is approximately 0.30.30.3 μΦ0/HzμΦ_{0}/\sqrt{Hz}μΦ0​/Hz​ at 101010 kHzkHzkHz. The current noise equivalent to the input coil of input SQUID is about 2.42.42.4 pA/HzpA/\sqrt{Hz}pA/Hz​. This result meets the low-noise readout requirements of the CMB TES and other applications with TES detectors.
The frequency domain multiplexing (FDM) readout of arrays of transition edges sensors for the X-IFU/Athena and SAFARI/SPICA instruments requires SQUID amplifiers with low input inductance, low flux noise, high-dynamic range and low power consumption. We report the performance of two-stage SQUID amplifiers developed at VTT coupled to multiple high-Q LC resonators of the SRON FDM readout operating in the frequency range from 2 to 5 MHz. The SQUIDs have been tested in the following configurations: 1) the two SQUIDs at base temperature with open input; 2) the amplifier SQUID at 1K temperature and the front-end SQUID at base temperature in the FDM readout of low-G TES bolometers; and 3) and in the FDM readout of X-ray microcalorimeter arrays with both SQUIDS at base temperature. We measured an input flux noise equal to 0.18 μΦ0/Hz1/2at 20 mK, equivalent to an energy resolution of 9 b. The measured current noise at the SQUID input is ~1 pA/Hz1/2at 20 mK, which corresponds to a coupled energy resolution of about 15 b.