It is demonstrated that time-reversal-symmetry-protected effects are fundamentally unstable against coupling to an environment. When topological bound states protected by anti-unitary symmetries, the decoherence time obeys a power law, ~T;^\gamma while when the protecting symmetry are unitary, the decoherence time is ~ exp(Eg/T), where Eg is the bulk gap.

Reference:

1. Max McGinley and Nigel R. Cooper, "Fragility of time-reversal symmetry protected topological phases", Nature Physics (2020).