Statistical-mechanical formulation of Lyapunov exponents
  We show how the Lyapunov exponents of a dynamic system can in general be expressed in terms of the free energy of a (non-Hermitian) quantum many-body problem. This puts their study as a problem of statistical mechanics, whose intuitive concepts and techniques of approximation can hence be borrowed. 
Sorin Tanase-Nicola and Jorge Kurchan