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

GONZALO A. ÁLVAREZ; PATRICIA R. LEVSTEIN; HORACIO M. PASTAWSKI

PHYSICA B - CONDENSED MATTER

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2007 vol. 398 p. 438 - 441

0921-4526

We have observed an environmentally induced quantum dynamical phase transition in the dynamics of a two-spin experimentalswapping gate [G.A. Alvarez, E.P. Danieli, P.R. Levstein, H.M. Pastawski, J. Chem. Phys. 124 (2006) 194507]. There, the exchange ofthe coupled states |+,-> and |-,+> gives an oscillation with a Rabi frequency b/hbar (the spin-spin coupling). The interaction, hbar/tSE with aspin-bath degrades the oscillation with a characteristic decoherence time. We showed that the swapping regime is restricted only tob*tSE>=hbar. However, beyond a critical interaction with the environment the swapping freezes and the system enters to a Quantum Zenodynamical phase where relaxation decreases as coupling with the environment increases. Here, we solve the quantum dynamics of a two-spinsystem coupled to a spin-bath within a Liouville-von Neumann quantum master equation and we compare the results with ourprevious work within the Keldysh formalism. Then, we extend the model to a three interacting spin system where only one is coupled tothe environment. Beyond a critical interaction the two spins not coupled to the environment oscillate with the bare Rabi frequency andrelax more slowly. This effect is more pronounced when the anisotropy of the system-environment (SE) interaction goes from a purelyXY to an Ising interaction form.