Measuring the Quantum State of Dark Matter

It is shown how the time series obtained from searches for ultralight bosonic dark matter (DM), such as the axion, can be used to determine whether it is in a coherent or incoherent quantum state. The example is essentially trivial, but it is hoped that explicitly addressing it will provoke experimental exploration. In the standard coherent state, O(1) oscillations in the number density occur over the coherence time, tau c=h/mv2, where m is the particle mass and v is the galactic virial velocity, leading to a reduction in the constraining power of experiments operating on timescales T更多