Spin-squeezed Ground States in the Bilayer Quantum Hall Ferromagnet

TL;DR

This paper demonstrates that the ground state of a bilayer quantum Hall system at specific filling factors can be described as a spin-squeezed state, with the degree of squeezing influenced by layer separation and tunneling parameters.

Contribution

It introduces a novel connection between spin-squeezed states and the ground state of bilayer quantum Hall systems, extending quantum optics concepts to condensed matter physics.

Findings

Ground state is a spin-squeezed state in the boson approximation.

Degree of squeezing depends on layer separation and tunneling gap.

Exciton condensation corresponds to a rotated spin-squeezed state with higher energy.

Abstract

A "squeezed-vacuum" state considered in quantum optics is shown to be realized in the ground-state wavefunction for the bilayer quantum Hall system at the total Landau level filling of $\nu=1/m$ (m: odd integer). This is derived in the boson approximation, where a particle-hole pair creation across the symmetric-antisymmetric gap, $\Delta_{SAS}$, is regarded as a boson. In terms of the pseudospin describing the layers, the state is a spin-squeezed state, where the degree of squeezing is controlled by the layer separation and $\Delta_{SAS}$. An exciton condensation, which amounts to a rotated spin-squeezed state, has a higher energy due to the degraded SU(2) symmetry for $\Delta_{SAS} \neq 0$.