Distinguishing decoherence from alternative quantum theories by dynamical decoupling

A long-standing challenge in the foundations of quantum mechanics is the verification of alternative collapse theories despite their mathematical similarity to decoherence. To this end, we suggest a method based on dynamical decoupling. Experimental observation of nonzero saturation of the decoupling error in the limit of fast-decoupling operations can provide evidence for alternative quantum theories. The low decay rates predicted by collapse models are challenging, but high-fidelity measurements as well as recent advances in decoupling schemes for qubits let us explore a similar parameter regime to experiments based on macroscopic superpositions. As part of the analysis we prove that unbounded Hamiltonians can be perfectly decoupled. We demonstrate this on a dilation of a Lindbladian to a fully Hamiltonian model that induces exponential decay.