Observation of quantum phase transition in spin-orbital-angular-momentum coupled Bose-Einstein condensate

TL;DR

This paper reports the first experimental observation of a quantum phase transition in a spin-orbital-angular-momentum coupled Bose-Einstein condensate, revealing first-order phase transitions through changes in spin polarization and vorticity.

Contribution

It provides the first experimental mapping of the ground-state phase diagram of SOAM coupled BECs, demonstrating control over quantum phases in such systems.

Findings

Discontinuous change in spin polarization at phase boundaries

Observation of vorticity variation indicating phase transitions

Confirmation of first-order quantum phase transitions in SOAM BECs

Abstract

Orbital angular momentum (OAM) of light represents a fundamental optical freedom that can be exploited to manipulate quantum state of atoms. In particular, it can be used to realize spin-orbital-angular-momentum (SOAM) coupling in cold atoms by inducing an atomic Raman transition using two laser beams with differing OAM. Rich quantum phases are predicted to exist in many-body systems with SOAM coupling. Their observations in laboratory, however, are often hampered by the limited control of the system parameters. In this work we report, for the first time, the experimental observation of the ground-state quantum phase diagram of the SOAM coupled Bose-Einstein condensate (BEC). The discontinuous variation of the spin polarization as well as the vorticity of the atomic wave function across the phase boundaries provides clear evidence of first-order phase transitions. Our results open up a new way to the study of phase transitions and exotic quantum phases in quantum gases.