Alkali atoms attached to vortex-hosting helium nanodroplets

Area of Science:

• Atomic physics
• Quantum fluids
• Spectroscopy

Background:

• Superfluid helium droplets are quantum systems with unique properties.
• Vortices are topological defects in superfluids, crucial for understanding their behavior.
• Alkali atoms serve as sensitive probes for the local environment in helium droplets.

Purpose of the Study:

• Investigate alkali atom spectroscopy for detecting vortices in helium droplets.
• Analyze spectral shifts and broadening of alkali atoms attached to vortex lines.
• Evaluate the feasibility of this method for vortex detection.

Main Methods:

• Calculated alkali atom equilibrium configurations on a vortex-hosting helium droplet using helium-4 density functional theory.
• Simulated dipole absorption spectra of alkali atoms.
• Compared spectra of atoms on vortex lines versus vortex-free droplets.

Main Results:

• Alkali atom spectra blue-shift and broaden near vortex lines due to deeper dimples.
• These spectral modifications are minor for np ← ns excitations, insufficient for detection.
• Higher energy excitations (n'p ← ns, n's ← ns) show larger shifts, indicating greater sensitivity.
• Lighter alkali atoms and quantum effects reduce spectral shifts.

Conclusions:

• Alkali atom spectroscopy shows potential for vortex detection in helium droplets.
• The current method is insufficient for detecting vortices using simple np ← ns excitations.
• Higher energy transitions offer better prospects for vortex detection due to increased sensitivity to helium density changes.