Quantum critical states and phase transitions in the presence of non equilibrium noise
Ultracold atomic, molecular or trapped ion systems, offer unique possibilities to realize interesting quantum phases and phase transitions. On the other hand they are easily driven out of equilibrium by external (classical) noise sources. It is natural to expect that noise will destroy the subtle correlations underlying quantum critical behavior, as does for example thermal noise at equilibrium. Surprisingly we find that the ubiquitous 1/f noise, does in many cases preserve the critical behavior. The emergent states show intriguing interplay of intrinsic quantum-critical and external noise-driven fluctuations. We demonstrate this general phenomenon with several specific examples in solid state and ultracold atomic systems. Our approach shows that genuine quantum phase transitions can be well defined even for systems driven out of equilibrium.