Unveiling environmental entanglement in strongly dissipative qubits

TL;DR

This paper investigates the complex structure of qubit-environment entanglement in strongly dissipative regimes, revealing the formation of Schrödinger cat states and the importance of reservoir mode entanglement for qubit superposition stability.

Contribution

It introduces a detailed analysis of the many-body wavefunction in strong qubit-environment coupling, highlighting the role of non-adiabatic contributions and reservoir mode entanglement.

Findings

Strong-coupling regime leads to Schrödinger cat environmental states.

Reservoir mode entanglement stabilizes qubit superpositions.

Variational coherent states effectively describe the environment's quantum states.

Abstract

The coupling of a qubit to a macroscopic reservoir plays a fundamental role in understanding the complex transition from the quantum to the classical world. Considering a harmonic environment, we use both intuitive arguments and numerical many-body quantum tomography to study the structure of the complete wavefunction arising in the strong-coupling regime, reached for intense qubit-environment interaction. The resulting strongly-correlated many-body ground state is built from quantum superpositions of adiabatic (polaron-like) and non-adiabatic (antipolaron-like) contributions from the bath of quantum oscillators. The emerging Schr\"odinger cat environmental wavefunctions can be described quantitatively via simple variational coherent states. In contrast to qubit-environment entanglement, we show that non-classicality and entanglement among the modes in the reservoir are crucial for the stabilization of qubit superpositions in regimes where standard theories predict an effectively classical spin.