Observation of Spin Superfluidity in a Bose Gas Mixture

Area of Science:

• Atomic, molecular, and optical physics
• Condensed matter physics
• Quantum gases

Background:

• Bose-Einstein condensates (BECs) are quantum states of matter with unique properties.
• Understanding spin dynamics in multi-component BECs is crucial for quantum technologies.
• Previous studies have explored spin superfluidity in BECs, but experimental evidence at finite temperatures remains key.

Purpose of the Study:

• To experimentally investigate the spin dynamics of a harmonically trapped Bose-Einstein condensed binary mixture of sodium atoms at finite temperature.
• To provide direct evidence for spin superfluidity in a collisional regime.
• To explore spin dynamics in the collisionless regime and measure static polarizability.

Main Methods:

• Experimental investigation of spin dynamics in a Bose-Einstein condensed binary mixture of sodium atoms.
• Utilizing a harmonic trap and operating at finite temperatures.
• Analyzing both collisional and collisionless regimes, including measurements of static polarizability.

Main Results:

• In the collisional regime, thermal component motion is damped by spin drag, while condensates exhibit friction-free counterflow oscillations, demonstrating spin superfluidity.
• In the collisionless regime, both condensate and thermal spin components oscillate without damping, driven by mean-field effects.
• Static polarizability of condensed and thermal parts was measured, showing a significant increase in condensate polarizability at finite temperature compared to T=0.

Conclusions:

• The experiment provides direct evidence for spin superfluidity in Bose-Einstein condensed binary mixtures at finite temperatures.
• Spin drag significantly affects thermal components in the collisional regime.
• Mean-field effects drive spin component oscillations in the collisionless regime, with enhanced condensate polarizability observed.