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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.

Science and industry demand ever more sensitive measurements on ever smaller systems, as exemplified by spintronics, nanoelectromechanical system, and spin-based quantum information processing, where single electronic spin detection poses a grand challenge.Superconducting quantum interference devices SQUIDs have yet to be effectively applied to nanoscale measurements. Here, we show that a simple bilayer deposition route, combining photolithography with focused ion beam patterning, produces high performance nanoscale SQUIDs. W e present results of noise measurements on these nanoSQUIDs which correspond to a magnetic flux sensitivity of around 0.2 µ0 /Hz1/2. This represents one of the lowest noise values achieved for a SQUID device operating above 1 K.

We investigate the mechanism of spin-lattice relaxation of Er ions encapsulated in polyoxometalate clusters, which below 4 K can only reverse its spin via quantum tunneling processes. The temperature-independent rate −1 is, at zero field, ten orders of magnitude larger than the rates predicted for direct phonon-induced processes. In addition, we observe that −1 is suppressed by external magnetic bias and hyperfine interactions but enhanced by increasing the concentration of Er ions. The observed relaxation agrees with predictions for pure quantum tunneling, showing that this phenomenon drives the thermalization of electronic spins. A possible link between these two phenomena is discussed, involving the collective emission of phonons from particular spin configurations attained via quantum tunneling. The fundamental equations of magnetism, including Curie's law, rely on the ability of magnetic moments to attain thermal equilibrium with the solid lattice. In spite of the progress achieved in studying and manipulating individual spins in solids, 1 the spin-lattice relaxation ͑SLR͒ mechanisms are not well understood yet. An intriguing situation arises, near zero field, for strongly anisotropic spins, e.g., magnetic molecular clusters or rare-earth ions. When thermally activated tunneling processes 2 die out, at sufficiently low temperatures ͑typically T Շ 1 K͒, spins can only flip by pure quantum tunneling ͑QT͒ across the anisotropy energy barrier. Theoretical descriptions 3-5 of QT in the presence of hyperfine couplings and dipolar spin-spin interactions account well for experiments that measure the time-dependent magnetization under such conditions. 6-8 Concerning SLR, a major difficulty arises. It stems from the fact that QT modifies the magnetization but conserves the energy of the ensemble of nuclear and electronic spins. Therefore, equilibrium states might well be reached long after the characteristic time scales of QT. However, a few experiments suggest otherwise. Specificheat studies 10 indicate that Mn 4 and Fe 8 single-molecule magnets ͑SMM͒ attain thermal equilibrium at rates comparable to those found in magnetization relaxation experiments. In addition, NMR experiments on Mn 12 clusters 11 show that the nuclear spin and bath temperatures remain the same down to the neighborhood of absolute zero.In order to elucidate the nature of the SLR mechanism and its relationship with QT, direct measurements of the SLR rates as a function of temperature, magnetic field, concentration of spins, etc., are clearly desirable. Studying the SLR of molecular nanomagnets at very low temperatures and under weak magnetic fields is, however, a demanding experimental task because tunneling time scales are on the order of days even for clusters made of a few atoms. In order to overcome this difficulty, simpler molecules need to be studied. In the present work, we report the SLR rates of polyoxometalate ͑POM͒ clusters containing individual lanthanide ions. The results evidence that the thermalization of electronic spins is dictat...

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W e report the use of an ultralow noise nano-superconducting quantum interference device nanoSQUID_ to measure the hysteretic magnetization behavior of a single FePt nanobead at a temperature of around 7 K in a magnetic field of only 10 mT. W e also show that the nanobead can be accurately positioned with respect to the SQUID loop and then removed without affecting SQUID performance. This system is capable of further development with wide applications in nanomagnetism.

We report on the energy-resolving capability of a superconducting NbN nanowire photon counter, which is read out by a superconducting quantum interference device. For counters operated at 6.5 K, a resolution of 0.55 eV was measured in the wavelength range from 1000 to 1500 nm (photon energies 1.2–0.8 eV) along with a counting rate of 2 MHz. The best energy resolution occurred in the spectral range where the quantum efficiency of the counter began to decrease with the wavelength. The results are explained by the change of the detection scenario from the hot-spot formation to unbinding of vortex–antivortex pairs.

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