Hidden nonmacrorealism: Reviving the Leggett-Garg inequality with stochastic operations

The Leggett-Garg inequality (LGI) distinguishes nonmacrorealistic channels from macrorealistic ones by constraining the experimental outcomes of underlying system. In this work, we propose a class which, initially, cannot violate LGI (in form temporal Bell inequality) but can it after application stochastic pre- and post- operations (SPPOs). As proof-of-principle experiment, demonstrate in an amplitude-damping channel with photonic qubits. We denote above phenomenon as hidden channels. also discuss relationship between terms Clauser-Horne-Shimony-Holt (CHSH) strongly nonlocality-breaking channel, which breaks spatial CHSH nonlocality for arbitrary states. general, if satisfies nonmacrorealism, is not channel.