Suppression of decoherence and disentanglement by the exchange interaction

Abstract

Entangled qubit pairs can serve as a quantum memory or as a resource for quantum communication. The utility of such pairs is measured by how long they take to disentangle or decohere. To answer the question of whether qubit-qubit interactions can prolong entanglement, we calculate the dissipative dynamics of a pair of qubits coupled via the exchange interaction in the presence of random telegraph noise and $1/f$ noise. We show that for maximally entangled (Bell) states, the exchange interaction generally suppresses decoherence and disentanglement. This suppression is more apparent for random telegraph noise if the noise is non-Markovian, whereas for $1/f$ noise the exchange interaction should be comparable in magnitude to the strongest noise source. The entangled singlet-triplet superposition state of two qubits (${\ensuremath{\psi}}_{\ifmmode\pm\else\textpm\fi{}}$ Bell state) can be protected by the interaction, while for the triplet-triplet state (${\ensuremath{\phi}}_{\ifmmode\pm\else\textpm\fi{}}$ Bell state), it is less effective. Thus the former is more suitable for encoding quantum information.