Universal Quantum Information Compression
  Suppose that a quantum source is known to have von Neumann entropy less than or equal to S but is otherwise completely unspecified. We describe a method of universal quantum data compression which will faithfully compress the quantum information of any such source to S qubits per signal (in the limit of large block lengths). 
Richard Jozsa, Michal Horodecki, Pawel Horodecki and Ryszard Horodecki