Signatures of a quantum dynamical phase transition in a three-spin system in presence of a spin environment

TL;DR

This paper investigates quantum dynamical phase transitions in a three-spin system interacting with a spin environment, revealing a transition from oscillatory to frozen dynamics and the influence of anisotropy on relaxation.

Contribution

It extends previous two-spin models to a three-spin system, analyzing environmental effects and anisotropy on quantum phase transitions using quantum master equations.

Findings

Swapping oscillations are suppressed beyond a critical environment coupling.

A quantum Zeno phase emerges where relaxation decreases with increased environmental interaction.

Anisotropy influences the relaxation dynamics and the nature of the phase transition.

Abstract

We have observed an environmentally induced quantum dynamical phase transition in the dynamics of a two spin experimental swapping gate [J. Chem. Phys. 124, 194507 (2006)]. There, the exchange of the coupled states |+,-> and ,+> gives an oscillation with a Rabi frecuency b/$\hbar$ (the spins coupling). The interaction, $\hbar$/tSE with a spin-bath degrades the oscillation with a characteristic decoherence time. We showed that the swapping regime is restricted only to b\tSE>$hbar$. However, beyond a critical interaction with the environment the swapping freezes and the system enters to a Quantum Zeno dynamical phase where relaxation decreases as coupling with the environment increases. Here, we solve the quantum dynamics of a two spin system coupled to a spin-bath within a Liouville-von Neumann quantum master equation and we compare the results with our previous work within the Keldysh formalism. Then, we extend the model to a three interacting spin system where only one is coupled to the environment. Beyond a critical interaction the two spins not coupled to the environment oscillate with the bare Rabi frequency and relax more slowly. This effect is more pronounced when the anisotropy of the system-environment interaction goes from a purely XY to an Ising interaction form.