Abstract
Quantum decay in an ac driven biased periodic potential modeling cold atoms in optical lattices is studied for a symmetry-broken driving. For the case of fully chaotic classical dynamics the classical exponential decay is quantum-mechanically suppressed for a driving frequency ω in resonance with the Bloch frequency ωB, qω = rωB with integers q and r. Asymptotically, an algebraic decay ∼ t−γ is observed. For r = 1 the exponent γ agrees with q as predicted by non-Hermitian random matrix theory for q decay channels. The time dependence of the survival probability can be well described by random matrix theory. The frequency dependence of the survival probability shows pronounced resonance peaks with sub-Fourier character.