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ARIADNE (Axion Resonant InterAction Detection Experiment) is a table-top experiment that intends to search for QCD axions from exotic spin-dependent interactions mediated by axion between nuclei at sub-mm range. This experiment includes a non-magnetic mass to source the axion field, and a dense ensemble of hyper-polarized 3He nuclei to detect the axion field with nuclear-magnetic-resonance (NMR)-based method. The expected NMR signal from the interaction could be easily buried in the noise spectrum of the magnetometer, especially in a frequency range (~ 100 Hz) where the interaction signal is supposed to exist. In this work, we report optimization of SQUID gradiometer for ARIADNE including noise spectrum measurement. [ABSTRACT FROM AUTHOR]

Recently, Superconducting Quantum Interference Device (SQUID) arrays operating in a coherent voltage-modulation state at 77 K showed a flux-noise 10 times lower than that of single-SQUIDs at similar temperatures. To exploit the flux-noise superiority of SQUID-arrays in applications, however, it is essential to preserve the coherent state, while the magnetic field to be measured, Bz, is highly inhomogeneous along the array as being generated by thin film integrated superconducting input coils or flux-transformers located in close proximity. Indeed, the flux coupled to each individual SQUID may vary significantly along the array, leading to a rapid degradation in the coherency. Here, we present several solutions to avoid that based on a methodology we developed to assess the efficiency of signal coupling to SQUID-arrays while maintaining a highly coherent state. As a proof of concept, we applied it to highly integrated YBa2Cu3O7 800/770 SQUID-arrays inductively coupled to on-chip integrated thin film superconducting input coils. Each SQUID in the array is directly coupled to two individual flux focusers, leading to an increase in the effective area for which we derived an analytical formula. Consequently, we achieved SQUID-like voltage oscillation amplitudes above 10 mV in the temperature range (75–83) K, leading to a magnetic flux noise of 0.2 μΦ0/Hz1/2, consistent with an ultra-enhanced coherent operation reached. For the strongest coupling scheme implemented experimentally, a current white noise of SI1/2 = 32 pA/Hz1/2 was measured. This scheme can be used as the input coil of a flux-transformer, resulting in a SQUID-array-based magnetometer with an estimated field sensitivity of 13 fT/Hz1/2. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the effect of parasitic capacitance and inductance on the dynamics and noise of direct current superconducting quantum interference devices. Experimental procedures; Results and discussion; Conclusion.

We have developed a miniature thin-film SQUID susceptometer for research in magnetic microcalorimetry and miniature magnetic thermometry. We have previously reported measurements at 4 K characterizing performance of the first generation of this device using modulation-based flux-locked feedback electronics and at ∼50 mK using a spherical superconducting test sample. Here we describe the design, fabrication, and new measurements of the second generation of the device using two-stage SQUID amplification to characterize the improved noise, bandwidth, persistence switch and field coil performance. The device now meets or exceeds all requirements for magnetic microcalorimetry sensor testing, achieving noise of ∼0.75 μΦ0/ √Hz and bandwidth ∼1.2 MHz near 50 mK, and trapping and stably holding magnetizing field of at least 5.9 mT. [ABSTRACT FROM AUTHOR]

We have developed a thin-film dc SQUID susceptometer for precision measurements of the magnetization of microscopic samples. The miniature SQUID susceptometer, fabricated using a Nb/Al - A1Ox/Nb Josephson junction process on a 2-mm x 3-mm chip, consists of two 40-μm ID pickup ioops in a series, ‘figure-of-eight’ gradiometric configuration that forms the SQUID inductance and two magnetizing field coils, one centered on each pickup loop. The magnetizing field coils, which apply equal and parallel magnetic fields to each pickup loop, may be operated in persistent current mode using an on-chip thin-film persistence switch. The sample to be measured is placed inside one of the pickup loops, and the SQUID gradiometer is used to sense the change in magnetization of the sample as the temperature is varied. The SQUID susceptometers can be operated using conventional locked-loop feedback electronics over the temperature range from 0 to around 6 K with a typical white flux noise of 3 μΦ0 /Hz1/2 (rms) at 4 K. These susceptometers are currently being used to measure the magnetization of Mn- and Fe-doped Pd samples. [ABSTRACT FROM AUTHOR]

Presents a study in which a low-noise, two-stage dc Superconducting Quantum Interference Device (SQUID) multiplier was described. Design of the SQUID multiplier; Out-put signal of a low-noise SQUID; Operation of the SQUID amplifier.