Numerical variational simulations of quantum phase transitions in the sub-Ohmic spin-boson model with multiple polaron ansatz

TL;DR

This paper uses advanced variational simulations with a multiple polaron ansatz to accurately study quantum phase transitions in the sub-Ohmic spin-boson model, confirming quantum-to-classical correspondence and revealing different critical behaviors.

Contribution

It introduces a generalized trial wave function with coherent-state expansions for precise analysis of quantum phase transitions in the sub-Ohmic spin-boson model.

Findings

Accurate determination of transition points and critical exponents.

Confirmation of quantum-to-classical correspondence across the sub-Ohmic range.

Identification of mean-field and non-mean-field critical behaviors.

Abstract

With extensive variational simulations, dissipative quantum phase transitions in the sub-Ohmic spin-boson model are numerically studied in a dense limit of environmental modes. By employing a generalized trial wave function composed of coherent-state expansions, transition points and critical exponents are accurately determined for various spectral exponents, demonstrating excellent agreement with those obtained by other sophisticated numerical techniques. Besides, the quantum-to-classical correspondence is fully confirmed over the entire sub-Ohmic range, compared with theoretical predictions of the long-range Ising model. Mean-field and non-mean-field critical behaviors are found in the deep and shallow sub-Ohmic regimes, respectively, and distinct physical mechanisms of them are uncovered.