Does noise entail decoherence ?

Every system is in contact with its surroundings and is thus an open system. It is not possible to have exact information about its surroundings, implying a statistical treatment of the interactions between the system and its surrounding. In equilibrium thermodynamics, a statistical weight can be assigned to effect the surrounding. However, in non-equilibrium cases, where dynamics are crucial, noises of certain type are supposed to capture the physics. Usually, white noises, which are the noises from, let's say, a heat bath, cause de-coherence of quantum states. How about 1/f noises ? This kind of noise is pointing and may not be so detrimental. In this piece of work, the authors theoretically examined the fate of a quantum critical state under such 1/f noise. They found that, the criticality can be preserved. To investigate the nature of a system, one may either look at its ground state (by considering static response to certain stimuli) or its excited states (by inspecting its dynamic response to certain stimuli) or both. Basically, these methods should be the same: from G-state one could have some idea (just some idea based on clever guess) what the E-states might be and vice-versa. In many cases, the G-state is preferred, because once the G-state is known, it shows at least how to construct low energy excitations (again, vice versa). In this work, they of course have to study the excitations, since it is a non-equilibrium system. [NATURE PHYSICS, VOL 6, OCTOBER 2010 ,www.nature.com/naturephysics]

Quantum critical points are characterized by scale-invariant correlations and therefore by long-range entanglement. As such, they present fascinating examples of quantum states of matter and their study is an important theme in modern physics.
However, little is known about the fate of quantum criticality under non-equilibrium conditions. Here we investigate the effect of external noise sources on quantum critical points. It is natural to expect that noise will have a similar effect to
finite temperature, that is, destroying the subtle correlations underlying the quantum critical behaviour. Surprisingly, we find that the ubiquitous 1=f noise does preserve the critical correlations. The emergent states show an intriguing interplay of
intrinsic quantum critical and external-noise-driven fluctuations.We illustrate this general phenomenon with specific examples describing solid-state and ultracold-atoms systems. Moreover, our approach shows that genuine quantum phase transitions can exist even under non-equilibrium conditions.