Driven open transitions outside every equilibrium universality class
In plain words
Most transitions in pumped, leaky quantum systems look like ordinary thermal transitions at long distances, because noise acts like a temperature. The question is which open quantum systems have genuinely different critical behaviour.
Precise statement
In Markovian (Lindblad) open systems, low-frequency noise generically produces an effective temperature and classical critical behaviour (Sieberer, Huber, Altman, Diehl 2013). Classify the mechanisms (pure dark steady states, absorbing states with coherent dynamics, symmetry constraints) that yield critical exponents differing from every equilibrium class, and identify at least one experimentally realizable model with computed exponents. Answer: a classification with explicit examples.
What would settle it
Controlled renormalization-group or numerical exponents outside equilibrium classes in a specific model, confirmed in a quantum simulator.
Status in the literature
Unverified note
Several nonequilibrium fixed points are identified theoretically (reviewed in the 2025 RMP); experimental confirmation is lacking.
Related problems
- More general than Universality classes of dissipative phase transitions in atomic gases
- More general than Critical exponents of the two-dimensional quantum contact process