Stability via symmetry breaking in interacting driven systems

Photonic and bosonic systems subject to incoherent, wide-bandwidth driving cannot typically reach stable finite-density phases using only non-dissipative Hamiltonian nonlinearities; one instead needs nonlinear losses, or a finite pump bandwidth. We describe here a very general mechanism for circumventing this common limit, whereby Hamiltonian interactions can cut-off heating from a Markovian pump, by effectively breaking a symmetry of the unstable, linearized dynamics. We analyze two concrete examples of this mechanism. The first is a new kind of $\mathcal{P}\mathcal{T}$ laser, where Hermitian Hamiltonian interactions can move the dynamics between the $\mathcal{P}\mathcal{T}$ broken and unbroken phases and thus induce stability. The second uses onsite Kerr or Hubbard type interactions to break the chiral symmetry in a topological photonic lattice, inducing exotic phenomena from topological lasing to the stabilization of Fock states in a topologically protected edge mode.