Embedded Spin Disentanglement and Decoherence via Dephasing

It has been demonstrated in various ways, if not rigorously proven, that when a quantum system and an environment interact they become entangled extremely rapidly and are essentially impossible to disentangle. Another interesting matter has received little attention, namely whether non-local entanglement between small systems is more or less susceptible to rapid decay than local measures of system coherence. An instance of potential importance for solid state quantum computing arises if embedded qubit spins are exposed to both global and local noise at the same time. Here we show that phase-noisy channels affect local and non-local measures of system coherence differently. A consequence is that the time for entanglement decay can be significantly shorter than the time for complete local dephasing for two qubits