• Corpus ID: 166227987

Uniqueness of the phase transition in many-dipole systems

@article{Stokes2019UniquenessOT,
  title={Uniqueness of the phase transition in many-dipole systems},
  author={Adam Oliver Stokes and Ahsan Nazir},
  journal={arXiv: Quantum Physics},
  year={2019}
}

• A. Stokes, A. Nazir
• Published 25 May 2019
• Physics
• arXiv: Quantum Physics

Due to various no-go and counter no-go results, the existence and natures of thermodynamic phases of light-matter systems continue to be disputed. We show using an arbitrary-gauge approach that a unique phase transition does occur in many-dipole cavity QED systems, and manifests unambiguously via a macroscopic gauge-invariant polarisation. Whether the abnormal phase appears superradiant depends on the gauge, because the gauge controls the extent to which the polarisation is included as part of the radiative quantum subsystem. A separate issue is that each gauge provides a different two-level approximation of the material dipoles. Our approach enables characterisation of physical behaviour in terms of any chosen material and radiation subsystems, using any of the non-equivalent approximate models. We provide numerical results for a finite number of dipoles without the two-level approximation, exhibiting clear precursors to the phase transition and demonstrating how accurate approximate predictions can be identified. Arbitrary-gauge QED therefore eliminates any apparent inconsistencies in the description of many-dipole cavity QED systems and their thermodynamic phases.