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

TL;DR

This paper develops a new theoretical framework for spinor Bose-Einstein condensates that accurately describes metastability and phase transitions, revealing cases where metastability is symmetry-prohibited and discussing quantum tunneling.

Contribution

The authors introduce the spinor Beliaev theory, accounting for quantum fluctuations, to explain metastability and phase transitions in spinor BECs beyond Bogoliubov theory.

Findings

Quantum fluctuations generate higher-order terms enabling first-order transitions.

Some first-order transitions lack metastability due to symmetry constraints.

Discussion of macroscopic quantum tunneling from metastable states.

Abstract

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.