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Abstracts
O4.8
Magnus force on vortex in superfluids without Galilean invariance:
BEC in optical lattice
Sonin, E.B.
Racah Institute of Physics, Hebrew University of Jerusalem, Givat Ram,
Jerusalem 91904, Israel
Broken Galilean invariance suppresses the transverse Magnus force on a vortex as
demonstrated by well-known examples of superfluids without Galilean invariance:
the Josephson-junction array and impure superconductors. Another example of
a superfluid without Galilean invariance is BEC in optical lattices, where up
to now vortex dynamics is in early stages of investigation and usually uses the
Bose-Hubbard model. This report addresses the general case of a superfluid in a
periodic potential based on the Bloch band theory and the momentum balance.
The continuous approximation restores translational invariance broken by the
periodic potential, but the theory is not Galilean invariant. Noether’s theorem
provides the conservation law for quasimomentum, while the balance for true
momentum is derived from the equations of motion. The calculations of the
transverse forces on the vortex, the Magnus and the Lorentz forces, require in
general the analysis of the balance of true momentum. While the developed theory
yields the same Lorentz force, which was known before, a new expression for the
Magnus force was obtained. The theory demonstrates how a small Magnus force
emerges if the particle-hole symmetry is broken. The theory was applied to the
Bose-Hubbard model close to the phase transition “superfluid-Mott insulator”.
There is an area in the phase diagram, where the Magnus force has an inverse
sign with respect to that expected from the sign of velocity circulation. The
present theory predicts the Magnus force much weaker than obtained in previous
estimations, which did not check momentum balance.
O4.9
Vortex reconnections and rebounds in trapped Bose Einstein
condensates
L. Galantucci(1), S. Serafini(2), F. Dalfovo(2), G. Lamporesi(2), G. Ferrari(2), C.
F. Barenghi(1)
(1) Joint Quantum Centre and School of Mathematics and Statistics, Newcastle
University
(2) INO-CNR BEC Center and Dipartimento di Fisica, Universita‘ di Trento
We perform a numerical study of two-vortex interactions in trapped elongated
Bose-Einstein condensates in the T=0 limit. We observe different vortex
interactions regimes depending on the vortex orientations and their relative
velocity: unperturbed orbiting, bounce dynamics, single and double reconnection
events. The key ingredients driving the dynamics are the anti-parallel preferred
alignment of the vortices and the impact of density gradients. The results are
confirmed by ongoing experiments in Trento performed employing a real-time
imaging technique [1].
[1] Serafini et al., Phys. Rev. Lett., 115, 170402 (2015)
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