Measurements of Angular Momentum in Superfluid Helium

Vortices in Polariton OPO Superfluids

“…Therefore, in general, for polaritonic systems, one has to apply some care when using the appearance of vortices as a diagnostic for the superfluid properties of such a non-equilibrium system. In the case of equilibrium superfluids, the rotation of a condensate is accompanied, above a critical angular velocity [76,75], by the creation of quantised vortices. Here, vortices are stable as far as the system is kept rotating and become unstable when the imposed rotation is halted [77].…”

“…We will see later on that these currents play a crucial role in the occurrence and dynamics of both metastable and spontaneous vortices in OPO. 1 In rotating condensates, a vortex can be created if the angular velocity is higher than a critical value [75,76]. When rotation is halted, then the vortex will spiral out of the condensate [77].…”

Influence of elastic deformations on the supersolid transition

“…The effective potential (red dashed) is given by Eq. (6). The large value of the displacement uo is chosen to vividly illustrate the contraction.…”

“…In the simplest explanation of the experiments 4 a portion of the medium becomes a superfluid at low temperatures that decouples from the measurement apparatus and the moment of inertia associated with the normal part of the system is reduced. Such a "Non Classical Rotational Inertia" (NCRI) effect is known to exist in superfluid liquid helium 5,6 which was probed with similar techniques. 6,7 Experimental results suggest the absence of superfluid features in ideal crystals with no grain boundaries.…”

“…Such a "Non Classical Rotational Inertia" (NCRI) effect is known to exist in superfluid liquid helium 5,6 which was probed with similar techniques. 6,7 Experimental results suggest the absence of superfluid features in ideal crystals with no grain boundaries. 8 Currently, it is not clear if an NCRI lies at the core of the recent experimental findings in solid 4 He.…”