Turbulence, produced by an impulsive spin down from angular velocity Omega to rest of a cube-shaped container, is investigated in superfluid 4He at temperatures 0.08 K-1.6 K. The density of quantized vortex lines L is measured by scattering negative ions. Homogeneous turbulence develops after time t approximately 20/Omega and decays as L proportional, t-3/2. The corresponding energy flux =nu'(kappaL)2 proportional, t-3 is characteristic of quasiclassical turbulence at high Re with a saturated energy-containing length. The effective kinematic viscosity in T=0 limit is nu'=0.003kappa, where kappa=10(-3) cm2 s(-1) is the circulation quantum.

By injecting negative ions in superfluid 4He in the zero-temperature limit (T0.7 K, a jet of ions generates quasiclassical tangles identical to those produced by mechanical means.

We compare the decay of turbulence in superfluid ^{4}He produced by a moving grid to the decay of turbulence created by either impulsive spin-down to rest or by intense ion injection. In all cases, the vortex line density L decays at late time t as L∝t^{-3/2}. At temperatures above 0.8 K, all methods result in the same rate of decay. Below 0.8 K, the spin-down turbulence maintains initial rotation and decays slower than grid turbulence and ion-jet turbulence. This may be due to a decoupling of the large-scale superfluid flow from the normal component at low temperatures, which changes its effective boundary condition from no-slip to slip.

We have studied the interaction of metastable 4 He à 2 excimer molecules with quantized vortices in superfluid 4 He in the zero temperature limit. The vortices were generated by either rotation or ion injection. The trapping diameter of the molecules on quantized vortices was found to be 96 AE 6 nm at a pressure of 0.1 bar and 27 AE 5 nm at 5.0 bar. We have also demonstrated that a moving tangle of vortices can carry the molecules through the superfluid helium. DOI: 10.1103/PhysRevLett.110.175303 PACS numbers: 67.25.dk, 47.27.Ài, 47.80.Jk Turbulence, the complex dynamics of systems with many degrees of freedom on a broad range of length scales, is common in nature. Its understanding is important for both fundamental science and technology. A special case is the hydrodynamics of superfluid liquids in the limit of zero temperature [1], which, while behaving as an ideal fluid, has a quantum constraint: vorticity is concentrated along the filamentary cores of quantized vortex lines, and the velocity circulation around any such line is equal to ¼ h=m 4 ¼ 1:00  10 À3 cm 2 s À1 (where h is the Planck constant and m 4 is the mass of a 4 He atom). Turbulence in such a system, known as quantum turbulence (QT), is a dynamic tangle of vortex lines.The characterization of classical turbulence is a formidable task: all the velocity field has to be visualized at once, and the most important regions are those of enhanced vorticity. Usually small passive tracers of flow are used [2]. The case for visualization of QT is different. To begin with, velocity tracers cannot be used as they are not entrained by the superfluid. On the other hand, small particles are attracted to the cores of quantized vortices, in which they can be trapped and then traced by optical means. This opens up an entirely new avenue for the visualization of turbulence. Mapping the field of vorticity, not velocity, has advantages for both the classical and quantum ranges of the QT spectrum. Within the former (coarse-grained flow on length scales greater than the mean separation between vortex lines), the regions of enhanced vorticity, i.e., those with an enhanced density of vortex lines, will be most visible. Within the latter (small length scales that resolve discrete vortex lines), one will be able to observe such processes as vortex reconnections, Kelvin waves, and the emission and absorption of small vortex loops-which are believed to be responsible for the quantum cascade of energy and control the dissipation of the vortex tangle [3,4].Micron-sized particles of solid hydrogen have already been used to tag vortex cores at high temperatures, T $ 2 K [5,6]; however, the invasive means of introduction and relatively large particle size preclude implementation of this technique for low temperatures and small length scales. Potentially ideal tracers would be metastable molecules He à 2 in the spin triplet state, which have a relatively long lifetime of ð13 AE 2Þ s [7]. They can be created in situ either by ionization in a strong laser field [8] or after rec...

We report on the extension of the experiments (P. M. Walmsley et al., Phys. Rev. Lett. 99, 265302 (2007)) on the decay of quasiclassical turbulence generated by an impulsive spin-down from angular velocity Ω to rest of superfluid 4 He in a cubic container at temperatures 0.15 K -1.6 K. The density of quantized vortex lines L is measured by scattering negative ions. Following the spin-down, the maximal density of vortices is observed after time t ∼ 10Ω −1 . By observing the propagation of ions along the axis of the initial rotation, the transient dynamics of the turbulence spreading from the perimeter of the container into its central region is investigated. Nearly homogeneous turbulence develops after time t ∼ 100Ω −1 and decays as L ∝ t −3/2 . The effective kinematic viscosity in T = 0 limit is ν = 0.003κ, where κ = 10 −3 cm 2 s −1 is the circulation quantum.