Production of entanglement with highly-mixed states
  We study production of entanglement with highly-mixed states. We find that entanglement between highly mixed states can be generated via a direct unitary interaction even when both states have purities arbitrarily close to zero. This indicates that purity of a subsystem is not required for entanglement generation. Our result is in contrast to previous studies where the importance of the subsystem purity was emphasized. 
Minsu Kang, M. S. Kim, and Hyunseok Jeong
quant-ph