  Can one certify the preparation of a coherent, many-body quantum state by
measurements with bounded accuracy in the presence of noise and decoherence?
Here, we introduce a criterion to assess the fragility of large-scale quantum
states which is based on the distinguishability of orthogonal states after the
action of very small amounts of noise. States which do not pass this criterion
are called asymptotically incertifiable. We show that, if a coherent quantum
state is asymptotically incertifiable, there exists an incoherent mixture (with
entropy at least log 2) which is experimentally indistinguishable from the
initial state. The Greenberger-Horne-Zeilinger states are examples of such
asymptotically incertifiable states. More generally, we prove that any
so-called macroscopic superposition state is asymptotically incertifiable. We
also provide examples of quantum states that are experimentally
indistinguishable from highly incoherent mixtures, i.e., with an almost-linear
entropy in the number of qubits. Finally we show that all unique ground states
of local gapped Hamiltonians (in any dimension) are certifiable.
