Nucleation of vortices in superfluid helium-4

Summary Nucleation of vortices and strings is studied in superfluid helium in the context of phase transitions in this system. It is shown that the formation of these structures depends on the homotopy groups of the manifold of degenerate condensed states. The subsequent evolution of these structures is investigated and then impact on the superfluid nature of this system is analysed. The cross-section for the scattering of quasi-particles is estimated. This is exploited to find the effect of scatterings on the dynamics of shrinking vortex. During the editorial procedure we came to know that this author deceased.     

Cavitation in superfluid helium-4 at low temperature

We have studied the nucleation of bubbles in pure superfluid helium-4 at temperatures down to 65 mK. We have found that the nucleation is a stochastic process, and that at temperatures below 600 mK the nucleation rate is independent of temperature. These results are consistent with the assumption that the nucleation takes place via quantum tunneling. Received: 15 November 1997 / Received in final form: 19 December 1997 / Accepted: 22 January 1998     

Coherent state in the roton region of superfluid helium-4

Summary Coherent states in the roton region of superfluid He⁴ are studied with a view to determine the transition probability from phonon to roton states. These states are formed in such a way that they are found to be identical to those of the angular-momentum states. During the editorial procedure we came to know that this author deceased.     

Mutual-friction induced instability of normal-fluid vortex tubes in superfluid helium-4

It is shown that, as a result of its interactions with superfluid vorticity, a normal-fluid vortex tube in helium-4 becomes unstable and disintegrates. The superfluid vorticity acquires only a small (few percents of normal-fluid tube strength) polarization, whilst expanding in a front-like manner in the intervortex space of the normal-fluid, forming a dense, unstructured tangle in the process. The accompanied energy spectra scalings offer a structural explanation of analogous scalings in fully developed finite-temperature superfluid turbulence. A macroscopic mutual-friction model incorporating these findings is proposed.     

Experimental observation of a superfluid gyroscope in a dilute Bose-Einstein condensate

We have observed a three-dimensional gyroscopic effect associated with a vortex in a dilute Bose-Einstein condensed gas. A condensate with a vortex possesses a single quantum of circulation, and this causes the plane of oscillation of the scissors mode to precess around the vortex line. We have measured the precession rate of the scissors oscillation. From this we deduced the angular momentum associated with the vortex line and found a value close to Planck's over 2pi per particle, as predicted for a superfluid.     

Ground state condensate fraction of liquid 4He

An optimal Jastrow correlation function with intermediate- and long-range structure gives a larger condensate fraction at equilibrium density than a simple short-range correlation function. The condensate fraction is also sensitive to the potentials used in the calculation.     

Atomic quantum dots coupled to a reservoir of a superfluid Bose-Einstein condensate

We study the dynamics of an atomic quantum dot, i.e., a single atom in a tight optical trap which is coupled to a superfluid reservoir via laser transitions. Quantum interference between the collisional interactions and the laser induced coupling results in a tunable dot-bath coupling, allowing an essentially complete decoupling from the environment. Quantum dots embedded in a 1D Luttinger liquid of cold bosonic atoms realize a spin-boson model with Ohmic coupling, which exhibits a dissipative phase transition and allows us to directly measure atomic Luttinger parameters.     

On the experimental value of the intrinsic angular momentum of the A-phase of superfluid helium-3

A simple relation between the equilibrium spin and orbital angular momenta of the superfluid phases of helium-3 close to T_c has been obtained. The intrinsic angular momentum of the A-phase has been found from the existing experimental data using this relation.     

Critical temperature and condensate fraction of a fermion pair condensate

We report on measurements of the critical temperature and the temperature dependence of the condensate fraction for a fermion pair condensate of 6Li atoms. Bragg spectroscopy is employed to determine the critical temperature and the condensate fraction after a fast magnetic field ramp to the molecular side of the Feshbach resonance. Our measurements reveal evidence of level off of the critical temperature and limiting behavior of condensate fraction near the unitarity limit.     

Energy density functional approach to superfluid nuclei

We show that, within the framework of a simple local nuclear energy density functional (EDF), one can describe accurately the one- and two-nucleon separation energies of semimagic nuclei. While for the normal part of the EDF we use previously suggested parametrizations, for the superfluid part of the EDF we use the simplest possible local form compatible with known nuclear symmetries.     

Determination of the helium-4 mass in a Penning trap

The determination of the rotational quadrupole alignment of diatomic molecules via REMPI detection is investigated. In this process a high focal intensity usually increases the detection probability. At high intensities the AC Stark effect may cause a splitting of the normally degenerate m_J sublevels of a rotational state J beyond the spectral width of the exciting radiation. This leads to a selective detection of only certain m_J states with the consequence that deduced alignment factors can be misleading. From the theoretical considerations line profiles are explicitly calculated for dynamic polarizabilities which represent the B ¹Σ⁺ _u←X ¹Σ⁺ _g transition of H₂, in order to fit an experimental (3+1) REMPI spectrum and to predict (1+1') line shapes as a function of laser intensity. It is further shown that the deduced quadrupole alignment factor A ₀ ⁽²⁾ is significantly changed by the second order AC Stark effect when the intensities are chosen high enough to observe asymmetric broadened line profiles. Different combinations of relative linear polarizations of the exciting and ionizing laser beams are discussed. Received 1st August 2000 and Received in final form 2 May 2001