Observation of Wall-Vortex Composite Defects in a Spinor Bose-Einstein Condensate

Area of Science:

• Condensed matter physics
• Quantum mechanics
• Ultracold atomic gases

Background:

• Spin-1 Bose-Einstein condensates (BECs) exhibit rich spin textures and phase transitions.
• Antiferromagnetic interactions in spinor BECs lead to complex emergent phenomena.
• Phase transitions can drive the spontaneous formation of topological defects.

Purpose of the Study:

• To investigate the formation and dynamics of spin domain walls and their relationship with vortices in a spin-1 BEC.
• To identify the nature of defects created during a quench into the easy-axis polar phase.
• To explore the role of snake instability in defect evolution.

Main Methods:

• Preparation of a spin-1 BEC in the easy-plane polar phase.
• Sudden quench into the easy-axis polar phase, inducing spontaneous symmetry breaking.
• Observation of domain walls and their splitting into composite defects.
• Identification of half-quantum vortices (HQVs) as defect endpoints using Bragg scattering to probe mass supercurrent.

Main Results:

• Spin domain walls bounded by HQVs were observed in the antiferromagnetic spin-1 BEC.
• Domain walls dynamically split into composite defects due to snake instability.
• Bragg scattering confirmed the presence of mass supercurrents near the HQVs.
• In strong quenches, singly charged quantum vortices formed from the relaxation of composite defects.

Conclusions:

• The study demonstrates a novel nucleation mechanism for composite defects driven by phase transition dynamics.
• The findings provide experimental evidence for the formation of HQVs and their connection to domain walls.
• The results offer insights into topological defect formation and dynamics in quantum systems.