Primary current-sensing noise thermometry in the millikelvin regime.

The use of low-temperature platforms with base temperatures below 1 K is rapidly expanding, for fundamental science, sensitive instrumentation and new technologies of potentially significant commercial impact. Precise measurement of the thermodynamic temperature of these low-temperature platforms is crucial for their operation. In this paper, we describe a practical and user-friendly primary current-sensing noise thermometer (CSNT) for reliable and traceable thermometry and the dissemination of the new kelvin in this temperature regime. Design considerations of the thermometer are discussed, including the optimization of a thermometer for the temperature range to be measured, noise sources and thermalization. We show the procedure taken to make the thermometer primary and contributions to the uncertainty budget. With standard laboratory instrumentation, a relative uncertainty of 1.53% is obtainable. Initial comparison measurements between a primary CSNT and a superconducting reference device traceable to the PLTS-2000 (Provisional Low Temperature Scale of 2000) are presented between 66 and 208 mK, showing good agreement within the k=1 calculated uncertainty.

NMR signature of one-dimensional behavior of 3He in nanopores.

We have performed thermodynamic and NMR relaxation time measurements of 3He adsorbed in the pores of the mesoporous molecular sieve MCM-41 at temperatures down to 1.7 K and at a range of frequencies up to 240 kHz. The MCM-41 substrate comprises a uniform array of quasi-1D straight pores with a diameter of 2.3 nm. We preplated the pores with a monolayer of 4He to achieve an effective diameter of 1.6 nm at low temperatures. We made NMR measurements as a function of line density and frequency to investigate the spin dynamics and the effect of dimensionality. We observed T(1) is proportional to ω1/2, which is characteristic of one-dimensional diffusion. At these temperatures this arises from a classical size effect in the narrow pores. Our results demonstrate the possibility to study the spin dynamics of a 1D Tomonaga-Luttinger liquid at lower temperatures, where the 3He liquid will constitute a quantum 1D system.