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Installation and Characterization of a Superconducting Quantum Interference Device (SQUID) in an Adiabatic Demagnetization Refrigerator (ADR)

Asif Mostafa

Published Jan 1, 2026• 0 citations
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Abstract

Mostafa, Md Asif Installation and Characterization of a Superconducting Quantum Interference Device (SQUID) in an Adiabatic Demagnetization Refrigerator (ADR) Master’s thesis Department of Physics, University of Jyväskylä, 2026. This thesis presents the installation and characterization of a two-stage dc superconducting quantum interference device (SQUID) system in an adiabatic demagnetization refrigerator (ADR). The work combines the physical principles of superconductivity, Josephson junctions, SQUID operation, flux-locked-loop readout, and ADR cooling with practical low-temperature implementation. The SQUID system was integrated into the ADR through a cryogenic signal chain including electrical interface mapping, cryogenic wiring, filtering, thermal anchoring, and room-temperature readout electronics. The experimental characterization included voltage–flux modulation measurements, transfer-function and mutual-inductance calculations, gain calibration, and noise analysis. The measured two-stage combined transfer function was close to the value in the datasheet, confirming that the installed system reached the expected operating regime. The feedback and input-coupling parameters were extracted and compared with datasheet values, while the gain calibration provided the transimpedance needed to convert output-voltage noise into equivalent input- current noise. The initial commissioning-stage measurements showed a white input-current noise level of a few picoamperes per square root hertz and a feedback-resistance- dependent bandwidth. Later optimized measurements demonstrated that the ADR- based SQUID platform could reach a lower noise floor and larger bandwidth after reducing setup-related noise sources. These results show that the installed platform can support low-noise SQUID operation and provides a useful basis for future cryogenic detector and superconducting-device measurements. Keywords: SQUID, Adiabatic Demagnetization Refrigerator (ADR), Josephson junction, flux-locked loop, two-stage SQUID, mutual inductance, cryogenic readout, low-temperature physics.

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Mostafa, Md Asif Installation and Characterization of a Superconducting Quantum Interference Device (SQUID) in an Adiabatic Demagnetization Refrigerator (ADR) Master’s thesis Department of Physics, University of Jyväskylä, 2026. This thesis presents the installation and characterization of a two-stage dc superconducting quantum interference device (SQUID) system in an adiabatic demagnetization refrigerator (ADR). The work combines the physical principles of superconductivity, Josephson junctions, SQUID operation, flux-locked-loop readout, and ADR cooling with practical low-temperature implementation. The SQUID system was integrated into the ADR through a cryogenic signal chain including electrical interface mapping, cryogenic wiring, filtering, thermal anchoring, and room-temperature readout electronics. The experimental characterization included voltage–flux modulation measurements, transfer-function and mutual-inductance calculations, gain calibration, and noise analysis. The measured two-stage combined transfer function was close to the value in the datasheet, confirming that the installed system reached the expected operating regime. The feedback and input-coupling parameters were extracted and compared with datasheet values, while the gain calibration provided the transimpedance needed to convert output-voltage noise into equivalent input- current noise. The initial commissioning-stage measurements showed a white input-current noise level of a few picoamperes per square root hertz and a feedback-resistance- dependent bandwidth. Later optimized measurements demonstrated that the ADR- based SQUID platform could reach a lower noise floor and larger bandwidth after reducing setup-related noise sources. These results show that the installed platform can support low-noise SQUID operation and provides a useful basis for future cryogenic detector and superconducting-device measurements. Keywords: SQUID, Adiabatic Demagnetization Refrigerator (ADR), Josephson junction, flux-locked loop, two-stage SQUID, mutual inductance, cryogenic readout, low-temperature physics.
The goal of my thesis was to construct a general purpose cryostat, capable of measuring multiple devices at 100mK. This included modifying an existing SHASTA model 106 Adiabatic Demagnetization Refrigerator (ADR) by adding a new physical support structure to allow for more weight to be added to the cryostat’s testing stages, as well as custom pieces of electronics, such as a room temperature programmable current source. This allowed for computer programs to be written so we could automate the data acquisition process. \nWe successfully measured multiple superconducting quantum interference devices (SQUIDs), with the goal of proving that our custom electronics were able to control and record the output of the SQUID. This included measuring the biasing conditions of the SQUID with \nthe automated current sources, as well as measuring the noise temperature of a SQUID down to 300mK. Furthermore, we measured the thermal conductivity of our new sup- port structure for the cryostat and were able to prove that the material used was new \nand novel approach for high strength, low thermal conductivity in cryogenic research. We also investigated a new technique in permanently modifying the operational frequency of a SQUID, and were able to show that this new method of laser ablating the input coil could successfully shift the frequency. While the focus of cryogenic testing was on SQUIDs the cryostat itself was designed in such a way such that many types of low temperature devices could be tested within the system.
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.
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 dc Superconducting Quantum Interference Device (dc-SQUID) is one of the most sensitive magnetic field sensors available. In this thesis we concentrate on its application as an amplifier. In this configuration, an input circuit of interest can be connected by means of a coupling coil. The intended application of our developed low-Tc SQUID amplifiers is the readout of the first spherical gravitational wave antenna MiniGRAIL. Using small-signal analysis as well as numerical simulations, we study the achievable signal-to-noise ratio of such sensors in practical measurements. Published theories and studies could be extended. Some interesting points treated are the influence of the often used negative feedback (flux-locked loop), an altered input impedance of the SQUID amplifier and the influence of back-action noise, which directly affects the object of interest. The altered operation of the SQUID due to the presence of the input circuit is studied in numerical experiments. Another important issue, the influence of integrated input coils on the dynamics of SQUIDs, is investigated theoretically and experimentally. The performance of our developed sensors is compared to numerical simulations on detailed models. The results give insights into the behavior, design and usage of dc-SQUIDs with integrated coils. For a SQUID with input inductances of 1.5 μH we reached a good coupled energy sensitivity of about 170 ¯h in a dilution refrigerator. Furthermore, we investigated the hot-electron effect. This effect typically limits the sensitivity of superconducting electronics at sub-Kelvin bath temperatures due to a weakened electron-phonon coupling. We performed heating experiments on thin-film resistors which are similar to the shunt resistors of the Josephson junctions used in our sensors. The suppression of the hot-electron effect via electronic thermal transport to attached cooling fins is investigated both experimentally, theoretically and numerically. The numerical technique turns out to be a useful tool for the thermal design of superconducting electronics.
We have designed and tested a superconducting quantum interference device (SQUID) readout circuit, which can be operated at liquid helium temperatures. Although room-temperature SQUID electronics perform well, it is sometimes desirable to keep the wires between SQUID, readout electronics, and feedback coil as short as possible to minimize phase shifts and time delays. Cooling the readout circuit to low temperatures can also decrease its thermal noise. Our readout circuit uses conventional ac-flux modulation, which significantly reduces low frequency excess noise and drift in the preamplifier. In this case, simple complementary metal–oxide–semiconductor circuits with low power dissipation can be used as amplifier, phase-sensitive detector and integrator. The power dissipation of the complete readout is less than 15mW at 5V supply voltage.
The dynamics and noise of a dc SQUID (the Superconducting Quantum Interference Device), with the McCumber parameter /spl beta//sub c/=2/spl pi/R/sup 2/l/sub c/C//spl Phi//sub 0/ close to the unity (where I/sub c/, R, C is the critical current, the shunt resistance and the capacitance of the Josephson junctions comprising the SQUID, respectively, /spl Phi//sub 0/=2.07 10/sup -15/ Wb is the magnetic flux quantum) integrated with a planar spiral input coil, have been experimentally studied. The length of the spiral input coil was chosen so as to match its /spl lambda//4 microwave resonance frequency to the plasma resonance frequency of the SQUID. The input coil resonance is found to enhance the overall quality factor Q of the Josephson oscillations in the SQUID and, as a result, to increase the dynamic resistance R/sub d/ and the gradient of the flux-to-voltage characteristics, /spl delta/V//spl delta//spl Phi/, without hysteresis. A dc SQUID with a loop inductance L=30.5 pH, /spl beta//sub c/=0.72, and a 6 turn input coil demonstrated a non-distorted quasi-sinusoidal flux-to-voltage transfer function with an exceptionally large modulation depth of 140 /spl mu/V peak-to-peak. The spectral density of the magnetic flux noise was as low as 3.5/spl times/10/sup -7/ /spl Phi//sub 0//Hz/sup 1/2/ in the double stage configuration, measured at a temperature 4.2 K using direct read out electronics. In combination with an intermediary transformer, the current resolution of the SQUID is as low as 1.25 pA/Hz/sup 1/2/ with an input coil inductance of 100 nH.