BREAKDOWN OF VORTEX-FREE STATE IN BEC BY VORTEX-ANTIVORTEX PAIRS W. V. Pogosov and K. Machida Department of Physics, Okayama University, Japan. - презентация
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Презентация на тему: " BREAKDOWN OF VORTEX-FREE STATE IN BEC BY VORTEX-ANTIVORTEX PAIRS W. V. Pogosov and K. Machida Department of Physics, Okayama University, Japan." — Транскрипт:
BREAKDOWN OF VORTEX-FREE STATE IN BEC BY VORTEX-ANTIVORTEX PAIRS W. V. Pogosov and K. Machida Department of Physics, Okayama University, Japan
1. Introduction 2. Stability of the nonvortex state 3. Penetration of topological defects 4. Summary Outlook
Introduction London model in Thomas-Fermi regime Disadvantages: -in reality, there is no TF boundary. How vortices nucleate? -strong gradients of the order parameter Linear analysis; surface modes Disadvantage: -No vortices, only stability of axially-symmetric nonvortex state Numerical simulations Disadvantages: -Transition can be very sharp -Artificial boundary for the system
The aim of the present work: Where and how vortices nucleate? What is the role of surface modes and Landau instability in vortex nucleation?
The energy in dimensionless form: Gas parameter:
Method Nonvortex state: Stability of the nonvortex state
-The same mechanism for vortex penetration is realized for the range of p corresponding to the generation of excitations with l inst = 5
Mechanism of vortex nucleation at even l inst (l inst = 4, 6) -Nonvortex axially-symmetric state becomes unstable with respect to the generation of excitations with l inst -With increasing of the rotation frequency, the number of particles condensed in the state with l inst increases. -Just before the formation of l inst vortices, other harmonics of ψ appear: l = 3 for l inst = 6; l = 2 for l inst = 4 at p > 1.5; l = 1 and 2 for l inst = 4 at p < 1.5; -Final state contains l inst /2 or l inst /4 vortices in the inner part of the cloud
The case of finite-size cloud Boundary condition -When R b > 2-3 R TF, vortex-antivortex pairs nucleate. With increasing of the rotation frequency, antivortices leave the system. -When R b ~ R TF, vortices penetrate from the edge. No antivortices.
3D case -Prediction: vortex loops nucleate instead of vortex-antivortex pairs -Bending of vortices in 3D case was observed in numerical simulations
- Topological defects in BEC nucleate via creation of vortex-antivortex pairs (2D) or vortex loops (3D). Vortices move to the inner part of the cloud and antivortices – in the opposite direction. - Vortices penetrate just above the Landau instability. This supports Anglins scenario (PRL 2001) - Vortex state in infinite BEC always consists of vortices and antivortices. Total topological charge is zero. Summary