Spontaneous symmetry breaking in open quantum systems: strong, weak, and strong-to-weak

Understand

Depending on the coupling to the environment, symmetries of open quantum systems manifest in two distinct forms, the strong and the weak.

• We study the spontaneous symmetry breaking among phases with strong symmetry, weak symmetry, and no symmetry.
• Concrete Liouvillian models with strong and weak symmetry are constructed, and different scenarios of symmetry-breaking transitions are investigated from complementary approaches.
• It is demonstrated that strong symmetry always spontaneously breaks, either completely, or into the corresponding weak symmetry.