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Unstable avoided crossing in coupled spinor condensates.

Nathan R Bernier1, Emanuele G Dalla Torre2, Eugene Demler2

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We studied a two-state Bose-Einstein condensate undergoing a quench. The system showed dynamic stability despite negative-frequency modes, illustrating quantum pattern formation.

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Area of Science:

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

Background:

  • Bose-Einstein condensates (BECs) are quantum states of matter with unique properties.
  • Two-component BECs exhibit complex dynamics influenced by inter-state coupling.
  • Nonequilibrium quantum phenomena are crucial for understanding system evolution after perturbations.

Purpose of the Study:

  • To investigate the dynamics of a two-state Bose-Einstein condensate under a specific quench protocol.
  • To analyze the stability of the system after a sudden change in coupling field sign.
  • To explore the emergence of pattern formation in driven quantum systems.

Main Methods:

  • Mean-field theory was employed to model the BEC dynamics.
  • A quench protocol involving a sign change of the coupling field was implemented.
  • Analysis of negative-frequency modes and mode coupling was performed.

Main Results:

  • The system transitioned to a dynamically stable state despite the development of negative-frequency modes.
  • Nonzero detuning induced coupling between 'charge' and 'spin' modes.
  • An unstable avoided crossing was observed, indicative of pattern formation.

Conclusions:

  • The studied quench protocol can lead to stable dynamics in a two-component BEC, even with inherent instabilities.
  • The coupling of charge and spin modes in the presence of detuning is a key mechanism for nonequilibrium pattern formation.
  • This work provides an example of class-I(o) nonequilibrium pattern formation in quantum systems.