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Europhysics Letters (EPL)

Decoupling in dissipative two-level systems by a high-frequency driving field

Akira Okada

Published Jul 1, 2000• 1 citation
Publisher

Abstract

The effect of a driving field on the dynamics of a two-level system coupled to a bath is studied. Allowance is made for arbitrary coupling between the two levels, arbitrary coupling of the two levels to the bath, and an arbitrary bath. For a given two-level system, the coupling between the two levels can be made to vanish by applying a high-frequency driving field whose period is much shorter than any characteristic time scale of the driven system, under the condition that the coupling of the driven system to the field is independent of the bath coordinates.

DOI
10.1209/epl/i2000-00104-y

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The effect of a driving field on the dynamics of a two-level system coupled to a bath is studied. Allowance is made for arbitrary coupling between the two levels, arbitrary coupling of the two levels to the bath, and an arbitrary bath. For a given two-level system, the coupling between the two levels can be made to vanish by applying a high-frequency driving field whose period is much shorter than any characteristic time scale of the driven system, under the condition that the coupling of the driven system to the field is independent of the bath coordinates.
The time-dependent average population in a two-level system interacting with an Ohmic boson bath and driven by a dc-ac field is obtained. The study is performed within the noninteracting-blip approximation and for the high-frequency driving case. The integro-differential master equation and the exact formal solution for the average transition probability are obtained. The dissipative quantum decay and the transition temperature from the coherent to the incoherent motion are investigated. The effect of the external electric field on the the dissipative two-level system is found to destroy its coherence.
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When an open quantum system is driven by an external time-dependent force, the coupling of the driving to the central system is usually included, whereas the impact of the driving field on the bath is neglected. We investigate the effect of a quantum bath of linearly driven harmonic oscillators on the relaxation dynamics of a quantum two-level system which is not directly driven. In particular, we calculate the frequency-dependent response of the system when the bath is subject to Dirac and Gaussian driving pulses. We show that a time-retarded effective force on the system is induced by the driven bath which depends on the full history of the perturbation and the spectral characteristics of the underlying bath. In particular, when a structured Ohmic bath with a pronounced Lorentzian peak is considered, the dynamical response of the system to a driven bath is qualitatively different than that of the undriven bath. Specifically, additional resonances appear which can be directly associated with a Jaynes-Cummings-like effective energy spectrum.
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The quantum dynamics of the dissipative two-level system in the Ohmic bath with Rabi driving is studied by means of a modified Bloch-Redfield approach based on a unitary transformation. The main purpose is to understand the effect of counter-rotating terms of the system-environment interaction on the dynamics of the two-level system and, in particular, if it is possible to control the effective system-environment coupling by their effect on the interference between driving and dissipation. By calculating the nonequilibrium correlation P(t)P(t)P(t) for a finite driving it is shown that the counter-rotating terms of the system-environment interaction play an important role in the dynamic evolution with a longer coherent time and a weaker amplitude of the long-time driven oscillation.