Metastable phases in spinor Bose-Einstein condensates in finite temperatures

Spinor Bose-Einstein condensates under external magnetic fields exhibit well-characterized spin domains of its ground state due to spin-dependent interactions. At low temperatures, collision-induced spin-mixing instabilities may promote the condensate to dwell into metastable states occurring near the phase boundaries. In this paper, we study theoretically the metastable spin-phase diagram of a spin-1 antiferromagnetic Bose-Einstein condensate at zero and finite temperatures. The approach makes use of Hartree-Fock theory and exploits the symmetry of the Hamiltonian and of the order parameters yielding a closed system of transcendental equations for the free energy, fully avoiding the use of self-consistency methods. Our results are consistent with recent experiments and allow us to explain qualitatively the different types of observed quench dynamics. In addition, we found that similar phenomena should occur in antiferromagnetic spinor condensates with a sudden change in the temperature. It is shown also that the increase in temperature induces a traceable shift of the ferromagnetic-polar transition boundary, behavior previously not noted by self-consistent mean-field calculations.Spinor Bose-Einstein condensates under external magnetic fields exhibit well-characterized spin domains of its ground state due to spin-dependent interactions. At low temperatures, collision-induced spin-mixing instabilities may promote the condensate to dwell into metastable states occurring near the phase boundaries. In this paper, we study theoretically the metastable spin-phase diagram of a spin-1 antiferromagnetic Bose-Einstein condensate at zero and finite temperatures. The approach makes use of Hartree-Fock theory and exploits the symmetry of the Hamiltonian and of the order parameters yielding a closed system of transcendental equations for the free energy, fully avoiding the use of self-consistency methods. Our results are consistent with recent experiments and allow us to explain qualitatively the different types of observed quench dynamics. In addition, we found that similar phenomena should occur in antiferromagnetic spinor condensates with a sudden change in the temperature. It is shown also that the increase in temperature induces a traceable shift of the ferromagnetic-polar transition boundary, behavior previously not noted by self-consistent mean-field calculations.

arXiv:2109.01986Physical Review ADec 13, 20214 citations

Phase structure and low-energy excitations in spinor Bose-Einstein condensates

瞬内野

Jan 1, 20110 citations

Precise measurement of phase transitions in spinor Bose-Einstein condensates

Anshuman Vinit, Carlo Samson, Chandra Raman

Bulletin of the American Physical SocietyJun 5, 20130 citations

Ferromagnetic phase transition and Bose-Einstein condensation in spinor Bose gases

Qiang Gu, Richard A. Klemm

Phase transitions in spinor Bose gases with ferromagnetic (FM) couplings are studied via mean-field theory. We show that an infinitesimal value of the coupling can induce a FM phase transition at a finite temperature always above the critical temperature of Bose-Einstein condensation. This contrasts sharply with the case of Fermi gases, in which the Stoner coupling ${I}_{s}$ cannot lead to a FM phase transition unless it is larger than a threshold value ${I}_{0}.$ The FM coupling also increases the critical temperatures of both the ferromagnetic transition and the Bose-Einstein condensation.Phase transitions in spinor Bose gases with ferromagnetic (FM) couplings are studied via mean-field theory. We show that an infinitesimal value of the coupling can induce a FM phase transition at a finite temperature always above the critical temperature of Bose-Einstein condensation. This contrasts sharply with the case of Fermi gases, in which the Stoner coupling ${I}_{s}$ cannot lead to a FM phase transition unless it is larger than a threshold value ${I}_{0}.$ The FM coupling also increases the critical temperatures of both the ferromagnetic transition and the Bose-Einstein condensation.

arXiv:cond-mat/0307063Physical Review ASep 25, 200340 citations

Fluctuation-induced and symmetry-prohibited metastabilities in spinor Bose-Einstein condensates

Nguyen Thanh Phuc, Yuki Kawaguchi, Masahito Ueda

Spinor Bose-Einstein condensates provide a unique example in which the Bogoliubov theory fails to describe the metastability associated with first-order quantum phase transitions. This problem is resolved by developing the spinor Beliaev theory which takes account of quantum fluctuations of the condensate. It is these fluctuations that generate terms of higher than the fourth order in the order-parameter field which are needed for the first-order phase transitions. Besides the conventional first-order phase transitions which are accompanied by metastable states, we find a class of first-order phase transitions which are not accompanied by metastable states. The absence of metastability in these phase transitions holds to all orders of approximation since the metastability is prohibited by the symmetry of the Hamiltonian at the phase boundary. Finally, the possibility of macroscopic quantum tunneling from a metastable state to the ground state is discussed.Spinor Bose-Einstein condensates provide a unique example in which the Bogoliubov theory fails to describe the metastability associated with first-order quantum phase transitions. This problem is resolved by developing the spinor Beliaev theory which takes account of quantum fluctuations of the condensate. It is these fluctuations that generate terms of higher than the fourth order in the order-parameter field which are needed for the first-order phase transitions. Besides the conventional first-order phase transitions which are accompanied by metastable states, we find a class of first-order phase transitions which are not accompanied by metastable states. The absence of metastability in these phase transitions holds to all orders of approximation since the metastability is prohibited by the symmetry of the Hamiltonian at the phase boundary. Finally, the possibility of macroscopic quantum tunneling from a metastable state to the ground state is discussed.

arXiv:1301.3642Physical Review AOct 21, 201316 citations

Quantum phase transitions, symmetry breaking, and the Goldstone mode in metastable Bose-Einstein condensates

Lincoln D. Carr, Rina Kanamoto, Masahito Ueda

Bulletin of the American Physical SocietyMar 6, 20070 citations

{I}_{s}

cannot lead to a FM phase transition unless it is larger than a threshold value

{I}_{0}.

The FM coupling also increases the critical temperatures of both the ferromagnetic transition and the Bose-Einstein condensation.