In this paper, the proposal for a new multichroic pixel camera for the QUBIC instrument is presented, which aims to measure the B-mode polarization of the Cosmic Microwave Background. The camera features antenna-coupled magnetic microbolometers (MMB) read out by a microwave SQUID multiplexer and software-defined radio-based room temperature electronics, which are specifically optimized for MMB readout. The architecture of the detectors and their readout system is introduced, and the main design considerations are also discussed.The initial results of the simulation study suggest that MMBs are capable of achieving background limited detection of the sky when used in an instrument like QUBIC. Additionally, the time response of these detectors appears to be sufficiently fast for the given telescope scan speed and beam size.

Superconducting quantum circuit interfacing frequently entails working with multi-GHz radio frequency signals. The quickly evolving field relies on FPGA-based software-defined radio systems, providing the required flexible low-latency signal synthesis and analysis capabilities. Consequently, there are many custom hardware developments and upcoming commercial systems with proprietary interfaces. In contrast, this contribution presents a compact, platform-agnostic frequency conversion and level matching analogue front-end for 800 MHz vector signal generation, which expands the covered frequency band for any SMA connectorised system from baseband frequencies below 400 MHz to 4–10 GHz. It is in active use for quantum bit characterisation and for quantum sensor readout.

Quantum bit control systems using room temperature electronics provide universities and research institutions a cost-effective entry into quantum computing. Various approaches address the need for straightforward qubit controllers, particularly those based on AMD's next-generation RFSoC FPGA, which integrate adaptive SoCs with internal ADCs and DACs. As superconducting qubit architectures advance to incorporate flux elements for direct Z axis control and the number of qubits grows, the demand for high-quality and numerous control channels increases. This paper explores the requirements for integrating and expanding the QiController electronics from Karlsruhe Institute of Technology. The new system includes up to ten cards capable of driving a total of 240 direct flux lines. Our joint system design leverages the modularity, scalability, and thermal management of the industrial Standard ATCA, ensuring robust performance and ease of maintenance in this multi-FPGA setup. Initial unit tests of the electronics show improvements in noise levels and quality, suggesting that future verification on real qubit devices could establish this approach as a viable solution for scalable room-temperature control hardware.

Several experiments are currently carried out to measure the magnitude of the B mode polarization of the Cosmic Microwave Background (CMB). It is a strong indicator of the presence of gravitational waves from the early universe inflationary epoch. As the average variations of the B mode components of the CMB are expected to be of the order of a few tens of nK or below, the detection of these polarized signals requires an ultra sensitive system. This article is focused on instruments that take advantage of an interferometer stage, followed by a bolometer stage sensitive to frequencies around the 150 GHz band of the EM spectrum, which corresponds to the measured CMB temperature of 2.7 K. The bolometers in the focal plane of these experiments are usually coupled to an array of direct current Superconducting Quatum Interference Devices (SQUIDs), that allow the highly sensitive detection requirements for observing the B modes. We propose a detection system for these kinds of instruments based on a Software Defined Radio (SDR) that uses Frequency Division Multiplexing (FDM), a Goertzel channelizer and a radio frequency SQUID micro multiplexer (uMUX) working at the cryogenic temperatures of 320 mK. These interfaces are used to read an array of 1024 Magnetic Microbolometers (MMBs) as detectors that are photon limited for CMB detection in the band of interest. As part of the requirements for these measurements, we introduce a design of the detection and read out chain, show its expected performance and potential implementation. The proposed system can read the desired number of detectors from an array in a modular way, which allows future expansions, and its frequency division multiplexing (FDM) system improves the cooling capacity of the cryostat by minimizing the amount of active cryogenic electronics.

The Microwave SQUID Multiplexer ( mu MUX) is the device of choice for the readout of a large number of low-temperature detectors in a wide variety of experiments within the fields of astronomy and particle physics. While it offers large multiplexing factors, the system noise performance is highly dependent on the cold- and warm-readout electronic systems used to read it out, as well as the demodulation domain and parameters chosen. In order to understand the impact of the readout systems in the overall detection system noise performance, first, we extended the available mu MUX simulation frameworks, including additive and multiplicative noise sources in the probing tones (i.e., phase and amplitude noise), along with the capability of demodulating the scientific data, either in the resonator's phase or the scattering amplitude. Then, considering the additive noise as a dominant noise source, the optimum readout parameters to achieve minimum system noise were found for both open-loop and flux-ramp demodulation schemes in the aforementioned domains. Later, we evaluated the system noise sensitivity to multiplicative noise sources under the optimum readout parameters. Finally, as a case study, we evaluated the optimal demodulation domain and the expected system noise level for a typical software-defined radio readout system. This work leads to an improved system performance prediction and noise engineering based on the available readout electronics and the selected demodulation domain.

In the realm of quantum computing and low-temperature detectors, precise signal conditioning is crucial for the effective readout and control of superconducting qubits and sensors. As these technologies evolve, the need for increasingly sophisticated and integrated systems becomes more apparent. This contribution presents the design of a mixer-less analog front-end board optimized for superconducting circuit interfacing. It leverages the capabilities of the Radio-Frequency System-on-Chip (RFSoC) from AMD Xilinx and utilizes software-selectable channel filtering stages, ultimately achieving wide-band signals without analog local oscillator leakage.

This work reports the performance evaluation of an SDR readout system based on the latest generation (Gen3) of the AMD's Radio Frequency System-on-Chip (RFSoC) processing platform, which integrates a full-stack processing system and a powerful FPGA with up to 32 high-speed and high-resolution 14-bit Digital-to-Analog Converters (DACs) and Analog-to-Digital Converters (ADCs). The proposed readout system uses a previously developed multi-band, double-conversion IQ RF-mixing board targeting a multiplexing factor of approximately 1,000 bolometers in a bandwidth between 4 and 8 GHz, in line with state-of-the-art microwave SQUID multiplexers ($\mu$MUX). The characterization of the system was performed in two stages, under the conditions typically imposed by the multiplexer and the cold readout circuit. First, in transmission, showing that noise and spurious levels of the generated tones are close to the values imposed by the cold readout. Second, in RF loopback, presenting noise values better than -100 dBc/Hz totally in agreement with the state-of-the-art readout systems. It was demonstrated that the RFSoC Gen3 device is a suitable enabling technology for the next generation of superconducting detector readout systems, reducing system complexity, increasing system integration, and achieving these goals without performance degradation.

Arrays of superconducting sensors enable particle spectrum analysis with superior energy resolution. To efficiently acquire data from frequency multiplexed sensors, the readout electronics operating at room temperature must perform multiple tasks, such as low -noise probe tone generation, frequency demodulation, and data decimation. We designed a Software -Defined Radio (SDR) system composed of an MPSoC board, an analogue -digital conversion stage, and a radio frequency front-end mixing stage to meet the system requirements of 4 GHz instantaneous bandwidth and real-time data analysis. Nevertheless, utilising a Radio Frequency System -on -Chip (RFSoC) could simplify the overall system by integrating the conversion stage. This work investigates the applicability of RFSoCs for the aforementioned use case.

Quantum computing has the potential to revolutionize computation by solving complex problems in a way that classical computers cannot. However, robust and scalable qubit manipulation and control electronics are needed to exploit this potential. Academic efforts in this area are sparse, especially in terms of scalability to hundreds or thousands of qubits. The mod-ular and scalable Quantum Interface Controller (QiController), a room-temperature qubit control architecture, addresses this gap. It is implemented using the Advanced Telecommunications Computing Architecture (ATCA) and its dual-dual star topology. The system has two boards: a “Hub” with an AMD Xilinx RFSoC and a “Node” with peripheral FPGAs and DACs for low-latency flux control. This paper describes the system architecture and firmware developments for multi-board synchronization.

We describe a technique to optimize the dynamic performance of microwave SQUID multiplexer (µMUX)-based systems. These systems proved to be adequate for reading out multiple cryogenic detectors simultaneously. However, the requirement for denser detector arrays to increase the sensitivity of scientific experiments makes its design a challenge. When modifying the readout power, there is a trade-off between decreasing the signal-to-noise ratio (SNR) and boosting the nonlinearities of the active devices. The latter is characterized by the spurious free dynamic range (SFDR) parameter and manifests as an increment in the intermodulation products and harmonics power. We estimate the optimal spectral location of the SQUID signal containing the detector information for different channels. Through the technique, what we refer to as Spectral Engineering, it is possible to minimize the SNR degradation while maximizing the SFDR of the detector signal, thus, overcoming the trade-off.

Recent advances in the development of cryogenic particle detectors such as magnetic microcalorimeters (MMCs) allow the fabrication of sensor arrays with an increasing number of pixels. Since these detectors must be operated at the lowest temperatures, the readout of large detector arrays is still quite challenging. This is especially true for the ECHo experiment, which presently aims to simultaneously run 6,000 two-pixel detectors to investigate the electron neutrino mass. For this reason, we developed a readout system based on a microwave SQUID multiplexer ($\mu$MUX) that is operated by a custom software-defined radio (SDR) at room-temperature. The SDR readout electronics consist of three distinct hardware units: a data processing board with a Xilinx ZynqUS+ MPSoC; a converter board that features DACs, ADCs, and a coherent clock distribution network; and a radio frequency front-end board to translate the signals between the baseband and the microwave domains. Here, we describe the characteristics of the full-scale SDR system. First, the generated frequency comb for driving the $\mu$MUX was evaluated. Subsequently, by operating the SDR in direct loopback, the crosstalk of the individual channels after frequency demultiplexing was investigated. Finally, the system was used with a 16-channel $\mu$MUX to evaluate the linearity of the SDR, and the noise contributed to the overall readout setup.

Neutrino mass estimation experiments and cosmic microwave background (CMB) radiation surveys both employ low-temperature detectors (LTD) known as calorimeters and bolometers, respectively. These detectors operate typically between 10 and 300 mK. LTDs multiplexed by means of a microwave superconducting quantum interference device multiplexer (µMUX) demonstrated to be an excellent device for the readout of several detectors in the microwave region. This entails generating a multi-tonal signal and its subsequent readout. A single-tone detection method based on a Goertzel filter bank (GFB) channelizer was used for the readout of the aforementioned signal, implemented in a software-defined radio readout architecture within a field-programmable gate array. The measurements presented here demonstrate remarkable results in validating the suitability of the GFB channelizer for this system.

The electron capture in $$^{163}$$ Holmium (ECHo) experiment seeks to achieve sub-eV sensitivity of the electron neutrino mass through calorimetric decay spectroscopy of $$^{163}$$ Ho in large arrays of cryogenic magnetic microcalorimeters (MMCs). Microwave SQUID multiplexing serves to efficiently increase the number of readout channels, thus calorimeters per array and ultimately per cryostat. A corresponding frequency multiplexing room temperature software-defined radio (SDR) system is in development to enable the readout of this increased number of MMCs per cable. The SDR consists of a custom FPGA platform that provides signal generation and analysis capabilities, as well as tailored signal conversion and analog conditioning front end electronics that enable the room-temperature-to-cryogenic interface. Ultimately, the system will read out 400 multiplexer channels with double pixel detectors through a bandwidth of 4 GHz (IEEE C band). As high-resolution data converters are limited in sample rate, the C-band is split into five sub-bands using a two-stage mixing method. In this contribution, a prototype of the heterodyne RF design is presented. It comprises one of the five 800 MHz sub-bands for a target frequency range between 4 and 8 GHz. Furthermore, the second version of the A/D converter stage is presented, capable of generating and digitizing up to five complex basebands using 1 GSs $$^{-1}$$ converters, the reference clocks and a flux-ramp signal. We will show first results of their single and combined characterization in the lab. The current state of the prototype hardware enables preliminary measurements, only limited in bandwidth and with slightly higher noise. Potential improvements could be derived and will be implemented in the full bandwidth, 5-sub-band RF PCB design.

Due to their excellent energy resolution, the intrinsically fast signal rise time, the huge energy dynamic range, and the almost ideally linear detector response, metallic magnetic calorimeters (MMC)s are very well suited for a variety of applications in physics. In particular, the ECHo experiment aims to utilize large-scale MMC-based detector arrays to investigate the mass of the electron neutrino. Reading out such arrays is a challenging task which can be tackled using microwave SQUID multiplexing. Here, the detector signals are transduced into frequency shifts of superconducting microwave resonators, which can be deduced using a high-end software-defined radio (SDR) system. The ECHo SDR system is a custom-made modular electronics, which provides 400 channels equally distributed in a 4 to 8 GHz frequency band. The system consists of a superheterodyne RF frequency converter with two successive mixers, a modular conversion, and an FPGA board. For channelization, a novel heterogeneous approach, utilizing the integrated digital down conversion (DDC) of the ADC, a polyphase channelizer, and another DDC for demodulation, is proposed. This approach has excellent channelization properties while being resource-efficient at the same time. After signal demodulation, on-FPGA flux-ramp demodulation processes the signals before streaming it to the data processing and storage backend.