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Physical review. B, Condensed matter

Ground state of a dissipative two-level system: Coupled-cluster approximation

W. H. Wong, Chi‐Fai Lo

Published Nov 1, 1996• 5 citations
Publisher

Abstract

The ground state of a two-level system coupled to a dispersionless phonon bath is studied by the coupled-cluster method. The estimates of both the ground-state energy and the tunneling reduction factor are found to be in good agreement with the exact values. It is also found that within the coupled-cluster approximation there is no indication of the discontinuous localization-delocalization transition. This is consistent with the exact result. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physrevb.54.12859

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The ground state of a two-level system coupled to a dispersionless phonon bath is studied by the coupled-cluster method. The estimates of both the ground-state energy and the tunneling reduction factor are found to be in good agreement with the exact values. It is also found that within the coupled-cluster approximation there is no indication of the discontinuous localization-delocalization transition. This is consistent with the exact result. \textcopyright{} 1996 The American Physical Society.
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The ground states of phonons in a dissipative quantum tunneling system and their influences on the localiza ion-delocalization transtion are investigated by a variational approach. We find that: 1. There are two kind of influences, displacement and deformation, on phonon states due to coupling with a tunneling particle, and displaced -squeezed states are proposed to describe both these influences. 2. The localization-delocahzation transition depends on the choice of phonon ground state. The transition will occur at strong coupling as the energy of the ground state decreases.
We present a systematic analysis of the ground state properties of a tunneling system coupled to an Ohmic bath. The nonadiabatic effects induced by coupling with tunneling particle, on the ground state properties of phonons are taken into account. For this we have considered both displacement and deformation of phonons via a variational treatment. The symmetry breaking transition, or the delocalization-localization transition, of the tunneling particle is presented and is compared with earlier known results. We also show that in the critical regime a gap will be opened near the zero momentum in the spectrum of the phonons. The modified phonon spectrum along with the phonon displacement field correlation functions have been calculated. It is shown that in the critical regime the tunneling system stabilizes the lattice against long wavelength fluctuations.