Viscosity of Helium I and Helium II

Superfluidity: How Quantum Mechanics Became Visible

“…Clark). Burton actually published the results in Nature without the authors of the measurements (Burton 1935 ;Misener et al 1935 ). Anyhow, Wilhelm, Misener and Clark measured the damping of the oscillations of a cylinder immersed in liquid helium and discovered that the viscosity of liquid helium dropped down as the system cooled below T λ .…”

“…The note [1] refers to the article by E.F. Burton (Burton 1935 ) on the work by Wilhelm, Misener and Clark, which I mentioned above. More important for our present purpose is the reference to Kapitsa at the beginning of the article by Allen and Misener.…”

Feedback Cooling of an Atomic Spin Ensemble

“…Initialization procedure -We first generate a fully mixed f = 1 state as described in [12], then optically pump F z ,F y andF x with 5 µs pulses. The mixed state has zero mean and small variance var(F i ) = 1 3 f (f + 1)N A , and serves as a fiducial point. The amplitude and di- showing strong correlations between all three measurements of each spin component Fi (red and orange squares).…”

“…Measurement backaction on the atoms −iτ [F (0) ,F z ]Ŝ (0) z is small provided | F x |, | F y | N A .N (S) arises from the fraction η of atoms that suffer spontaneous emission (see below). During latency, precession by an angle θ = 2πt lat /T L about [1,1,1] causes coherent rotation R B (θ) and dephasing due to field inhomogeneities [27,29]:…”

“…Introduction -Cooling of many-body systems can produce new phases of matter and new collective behaviors, e.g. superfluids [1,2] and the fractional quantum Hall effect [3]. Traditional cooling couples the system to a lowtemperature reservoir, allowing energy to leave the system and thus reducing its entropy (provided the temperature is positive [4,5]).…”