| We analyze the toric code model in presence of quenched disorder, which is introduced via different types of random magnetic fields. Remarkably, we find that topological order can be robust against arbitrarily strong disorder. In general, close to a quantum phase transition between a spin polarized phase and a topologically ordered one, increasing the amount of disorder favors the topological phase. For some realizations of disorder, a quantum spin glass phase borders the topological phase, thus leading to a peculiar phase transition between two quantum spin liquid phases, which differ purely by nonlocal properties. |
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