Experimental multiparticle entanglement dynamics induced by decoherence

A noisy environment is used to study the dynamics of a four-trapped-ion entangled state. The study shows that entanglement properties such as distillability and separability can be altered by controlling the degree of dephasing. The results provide an important insight into the nature of multiparticle entanglement. Multiparticle entanglement leads to richer correlations than two-particle entanglement and gives rise to striking contradictions with local realism 1 , inequivalent classes of entanglement 2 and applications such as one-way or topological quantum computing 3 , 4 . When exposed to decohering or dissipative environments, multiparticle entanglement yields subtle dynamical features and access to new classes of states and applications. Here, using a string of trapped ions, we experimentally characterize the dynamics of entanglement of a multiparticle state under the influence of decoherence. By embedding an entangled state of four qubits in a decohering environment (through spontaneous decay), we observe a rich dynamics crossing distinctive domains: Bell-inequality violation, entanglement superactivation, bound entanglement and full separability. We also develop new theoretical tools for characterizing entanglement in quantum states. Recent quantum-computing, state-engineering and simulation paradigms driven by dissipative or decohering environments 5 , 6 , 7 can benefit from the environment engineering techniques demonstrated here.