Abstract
We introduce a Floquet spinor Bose-Einstein condensate induced by a periodically driven quadratic Zeeman coupling whose frequency is larger than any other energy scales. By examining a spin-1 system available in ultracold atomic gases, we demonstrate that such an external driving field has great effect on the condensate through emergence of a unique spin-exchange interaction. We uncover that the ferromagnetic condensate has several unconventional stationary states and thus exhibits rich continuous phase transitions. On the other hand, the antiferromagnetic condensate is found to possess a nontrivial metastable region, which supports unusual elementary excitations and hysteresis phenomena.
Highlights
Quantum degenerate systems with multiple order parameters emerge in diverse fields of physics such as unconventional superconductors [1,2] and superfluid 3He [3,4] in condensed matter, p-wave superfluids in neutron stars [5,6], and color superconductors in quark matter [7,8]
We introduce a Floquet spinor Bose-Einstein condensate induced by a periodically driven quadratic Zeeman coupling whose frequency is larger than any other energy scales
We introduce a Floquet spinor Bose-Einstein condensates (BECs) induced by a high-frequency modulation of an external field and uncover emergence of an unconventional spinexchange interaction
Summary
Quantum degenerate systems with multiple order parameters emerge in diverse fields of physics such as unconventional superconductors [1,2] and superfluid 3He [3,4] in condensed matter, p-wave superfluids in neutron stars [5,6], and color superconductors in quark matter [7,8]. We introduce a Floquet spinor BEC induced by a high-frequency modulation of an external field (see Fig. 1) and uncover emergence of an unconventional spinexchange interaction. By employing high-frequency expansion in the Floquet formalism [46,53,54], we obtain an effective Hamiltonian having the unconventional interaction, which is in sharp contrast to the case of an artificial gauge field In the system with an antiferromagnetic (AFM) interaction, on the other hand, we find a metastable region where two independent nonmagnetic states are stabilized simultaneously This leads to hysteresis phenomena, which do not emerge in conventional spinor systems without the linear Zeeman effect [57]. Some technical details on the Bogoliubov theory and critical behaviors are given in Appendixes
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