Microkelvin thermometry with Bose-Einstein condensates of magnons and applications to studies of the AB interface in superfluid 3^3He

Coherent precession of trapped Bose-Einstein condensates of magnons is a sensitive probe for magnetic relaxation processes in superfluid 3He-B down to the lowest achievable temperatures. We use the dependence of the relaxation rate on the density of thermal quasiparticles to implement thermometry in 3He-B at temperatures below 300 $\mu$K. Unlike popular vibrating wire or quartz tuning fork based thermometers, magnon condensates allow for contactless temperature measurement and make possible an independent in situ determination of the residual zero-temperature relaxation provided by the radiation damping. We use this magnon-condensate-based thermometry to study the thermal impedance of the interface between A and B phases of superfluid 3He. The magnon condensate is also a sensitive probe of the orbital order-parameter texture. This has allowed us to observe for the first time the non-thermal signature of the annihilation of two AB interfaces.Comment: 26 pages, 7 figures, manuscript prepared for EU Microkelvin Collaboration Workshop 2013. Accepted for publication in Journal of Low Temperature Physic

Self-localization of magnon Bose-Einstein condensates in the ground state and on excited levels: from harmonic to box-like trapping potential

Long-lived coherent spin precession of 3He-B at low temperatures around 0.2 Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or magnons in a magnetic trap which is formed by the order-parameter texture and can be manipulated experimentally. When the number of magnons increases, the orbital texture reorients under the influence of the spin-orbit interaction and the profile of the trap gradually changes from harmonic to a square well, with walls almost impenetrable to magnons. This is the first experimental example of Bose condensation in a box. By selective rf pumping the trap can be populated with a ground-state condensate or one at any of the excited energy levels. In the latter case the ground state is simultaneously populated by relaxation from the exited level, forming a system of two coexisting condensates.Comment: 4 pages, 5 figure

Quasiparticle transport in a two-dimensional boundary superfluid

The B phase of superfluid 3He can be cooled into the "pure" superfluid regime, characterised by negligible thermal quasiparticle density. Here, the bulk superfluid is bounded by a two-dimensional quantum well at the boundaries of the container, where creating quasiparticles requires much less energy. In this Article, we carry out experiments where we create a non-equilibrium state within the quantum well and show that the induced quasiparticle currents flow diffusively in the two-dimensional system. We conclude that the bulk of superfluid 3He is wrapped by an independent two-dimensional superfluid that interacts with mechanical probes instead of the bulk superfluid, only providing access to the bulk superfluid if given a sudden burst of energy. That is, superfluid 3He at the lowest temperatures and applied energies is thermo-mechanically two dimensional. Our work opens this two-dimensional quantum condensate and the interface it forms between the observer and the bulk superfluid for exploration, and provides the possibility of creating two-dimensional condensates of arbitrary topology.Comment: 11 pages, 9 figure

Thermal transport in nanoelectronic devices cooled by on-chip magnetic refrigeration

On-chip demagnetization refrigeration has recently emerged as a powerful tool for reaching microkelvin electron temperatures in nanoscale structures. The relative importance of cooling on-chip and off-chip components and the thermal subsystem dynamics are yet to be analyzed. We study a Coulomb blockade thermometer with on-chip copper refrigerant both experimentally and numerically, showing that dynamics in this device are captured by a first-principles model. Our work shows how to simulate thermal dynamics in devices down to microkelvin temperatures, and outlines a recipe for a low-investment platform for quantum technologies and fundamental nanoscience in this novel temperature range.Comment: 11 pages, 10 figure

Thermal Detection of Turbulent and Laminar Dissipation in Vortex Front Motion

We report on direct measurements of the energy dissipated in the spin-up of the superfluid component of 3He-B. A vortex-free sample is prepared in a cylindrical container, where the normal component rotates at constant angular velocity. At a temperature of 0.20Tc, seed vortices are injected into the system using the shear-flow instability at the interface between 3He-B and 3He-A. These vortices interact and create a turbulent burst, which sets a propagating vortex front into motion. In the following process, the free energy stored in the initial vortex-free state is dissipated leading to the emission of thermal excitations, which we observe with a bolometric measurement. We find that the turbulent front contains less than the equilibrium number of vortices and that the superfluid behind the front is partially decoupled from the reference frame of the container. The final equilibrium state is approached in the form of a slow laminar spin-up as demonstrated by the slowly decaying tail of the thermal signal.Comment: 12 pages, 5 figures, to appear in Journal of Low Temperature Physic

A Case Report of Sandhoff Disease

Sandhoff disease is a rare and severe lysosomal storage disorder representing 7% of GM2 gangliosidoses. Bilateral thalamic involvement has been suggested as a diagnostic marker of Sandhoff disease. A case of an 18-month-old infant admitted for psychomotor regression and drug resistant myoclonic epilepsy is presented. Cerebral CT scan showed bilateral and symmetrical thalamic hyperdensity. MRI revealed that the thalamus was hyperintense on T1-weighted images and hypointense on T2-weighted images with a hypersignal T2 of the white matter. Enzymatic assays objectified a deficiency of both hexosaminidases A and B confirming the diagnosis of Sandhoff disease

Proton nuclear magnetic resonance spectroscopic detection of oligomannosidic n glycans in alpha-mannosidosis: a method of monitoring treatment

In Alpha-mannosidosis (MIM 248500) the patients accumulate mainly unbranched oligosaccharide chains in the lysosomes in all body tissues, including the brain. With ensuing therapeutic modalities in man (BMT and ERT) non-invasive methods of monitoring the effect of treatment are needed. Paramount is the possible effect of the treatment on the brain, since this organ is regarded as difficult to reach because of the blood-brain barrier. We therefore performed proton nuclear magnetic resonance spectroscopy (MRS) of the brain in two untreated patients, and a 16-year-old patient treated with BMT at the age of 10 to assess whether this non-invasive method could be applied in the monitoring of the accumulation of abnormal chemicals in the brain of patients. We found an abnormal peak that was not present in the treated patient. A similar pattern was also found in MRS of urine from patients, reflecting the concentration of oligosaccharides in serum and tissues. We therefore conclude that MRS can be a useful method to monitor the effect of treatment for Alpha-Mannosidosis