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Area of Science:

  • Quantum physics
  • Ultracold atomic gases
  • Condensed matter physics

Background:

  • Understanding the transition between Bose-Einstein condensation (BEC) and Bardeen-Cooper-Schrieffer (BCS) superfluidity is crucial in quantum physics.
  • Ultracold atomic gases provide a tunable platform to study fundamental quantum phenomena.

Purpose of the Study:

  • To map the critical velocity (v_c) in the crossover regime between BEC and BCS superfluidity.
  • To compare measured critical velocities with the speed of sound (v_s) in ultracold 6Li gases.
  • To validate experimental methods through numerical simulations.

Main Methods:

  • Utilizing ultracold 6Li gases.
  • Dragging a small attractive potential through gas samples along lines of constant column density.
  • Measuring induced heating rates to identify critical velocity.
  • Exciting density waves to measure the speed of sound.
  • Performing numerical simulations in the BEC regime.

Main Results:

  • A steep increase in induced heating was observed above a critical velocity (v_c).
  • Measurements of v_c were compared with the speed of sound (v_s).
  • Numerical simulations in the BEC regime showed excellent agreement with experimental data, validating the methodology.

Conclusions:

  • The study successfully mapped the critical velocity in the BEC-BCS crossover using ultracold 6Li.
  • The experimental approach is validated by numerical simulations.
  • Measurements of v_c in the strongly correlated regime serve as a benchmark for theoretical investigations.