Collège Doctoral - Doktorandenkollegien

Statistical Physics of Complex Systems

Coventry - Leipzig - Lviv - Nancy

PhD positions


Title Decoherence of Bell states by local interactions with a suddenly quenched spin environment
Authors Wendenbaum P., Taketani B.G., Karevski D.
Reference Phys. Rev. A 90 (2014) 022125
Abstract We study the dynamics of disentanglement of two qubits initially prepared in a Bell state and coupled at different sites to an Ising transverse field spin chain (ITF) playing the role of a dynamic spin environment. The initial state of the whole system is prepared into a tensor product state ρBell⊗ρchain where the state of the chain is taken to be given by the ground state |G(λi)⟩ of the ITF Hamiltonian HE(λi) with an initial field λi. At time t=0+, the strength of the transverse field is suddenly quenched to a new value λf and the whole system (chain + qubits) undergoes a unitary dynamics generated by the total Hamiltonian HTot=HE(λf)+HI where HI describes a local interaction between the qubits and the spin chain. The resulting dynamics leads to a disentanglement of the qubits, which is described through the Wooter's Concurrence, due to there interaction with the non-equilibrium environment. The concurrence is related to the Loschmidt echo which in turn is expressed in terms of the time-dependent covariance matrix associated to the ITF. This permits a precise numerical and analytical analysis of the disentanglement dynamics of the qubits as a function of their distance, bath properties and quench amplitude. In particular we emphasize the special role played by a critical initial environment.

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