The superfluid phases of helium-3 ((3)He) are predicted to be strongly influenced by mesoscopic confinement. However, mapping out the phase diagram in a confined geometry has been experimentally challenging. We confined a sample of (3)He within a nanofluidic cavity of precisely defined geometry, cooled it, and fingerprinted the order parameter using a sensitive nuclear magnetic resonance spectrometer. The measured suppression of the p-wave order parameter arising from surface scattering was consistent with the predictions of quasi-classical theory. Controlled confinement of nanofluidic samples provides a new laboratory for the study of topological superfluids and their surface- and edge-bound excitations.

A dc superconducting quantum interference device (SQUID) magnetometer has been integrated on a 9×9 mm2 chip with eight pick-up loops in parallel to directly form a SQUID inductance of about 0.5 nH. Very simple feedback electronics have been developed which do not require liquid-helium temperature impedance matching circuits or flux modulation techniques. The magnetometer has a typical white noise of 8 fT/(Hz)1/2 and a 1/f  corner frequency below 3.5 Hz. With an additional positive feedback circuit at 4.2 K the white noise level has been further reduced to 4.5 fT/(Hz)1/2. Using a two-pole integrator, a 3 dB bandwidth around 0.5 MHz and a maximum slew rate of 3 mT/s at 1.3 kHz have been attained with a ±0.4 μT feedback range.

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A theoretical analysis of the multiloop dc superconducting quantum interference device (SQUID) magnetometer fabricated from low-Tc (transition temperature) or high-Tc materials is presented. Using simple analytic formulas, the essential parameters of a multiloop magnetometer can be estimated: the effective area A, the effective SQUID inductance L, the transfer function VΦ, and the flux density noise √SB. The theoretical predictions are compared with experimental results of seven different low-Tc versions and good agreement is found. Based on the analytical description, a high-Tc magnetometer design with a 7 mm pickup coil and 16 parallel loops giving a sufficiently small SQUID inductance L≂145 pH is presented. At T=77 K a voltage swing 2δV≂8 μV and a white noise √SB≂8 fT/√Hz are predicted assuming a critical current I0=20 μA and a normal resistance R=2 Ω per junction and a damping resistance Rd=R across the SQUID inductance.

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