Driven-dissipative quantum matter

4 problems

• Can short-range open quantum systems host stable continuous time crystals

  Open

  Some pumped, leaky systems oscillate forever on their own, breaking time-translation symmetry without a periodic drive. Known examples rely on every atom coupling to every other, and it is unknown whether short-range systems can do this.

• Does KPZ physics destroy order in two-dimensional polariton condensates

  Open

  A two-dimensional light-matter condensate that is constantly pumped and leaking was predicted to lose long-range coherence at very large distances, unlike an equilibrium superfluid. This prediction lacks a decisive experimental test.

• Driven open transitions outside every equilibrium universality class

  Partially resolved

  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.

• Critical exponents of the two-dimensional quantum contact process

  Contested

  In a lattice of Rydberg atoms where an excited atom helps its neighbours become excited and excitations decay, activity either spreads or dies out. Whether quantum coherence changes the universal behaviour of this transition in two dimensions is disputed.