Multi-parameter Quantum Metrology
  The simultaneous quantum estimation of multiple parameters can provide a better precision than estimating them individually. This is an effect that is impossible classically. We review the rich background of multi-parameter quantum metrology, some of the main results in the field and its recent advances. We close by highlighting future challenges and open questions. 
Magdalena Szczykulska, Tillmann Baumgratz, Animesh Datta
quant-ph