Chaos Enforced Instanton Tunnelling in One-Dimensional Model with   Periodic Potential
  The influence of chaos on properties of dilute instanton gas in quantum mechanics is studied. We demonstrate on the example of one-dimensional periodic potential that small perturbation leading to chaos squeezes instanton gas and increases the rate of instanton tunnelling. 
V.I. Kuvshinov, A.V. Kuzmin and R.G. Shulyakovsky