Rotational decoherence of microscale particles may be effectively described by a Markovian quantum master equation of Lindblad form [74, 75]. The ensuing jump operators can be related to the microscopic scattering amplitudes for individual collisions between the particle and environmental agents. The rotational motion of nano- to microscale particles is typically much slower than the collisions, so that the environment mainly gains information about the rotor orientation, rather than its angular momentum. The master equation thus describes predominantly how orientational superpositions decay on a timescale determined by the rotor-environment interaction [76, 77] and bounded by the scattering rate, see below.
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Fundamental tests— The verification of rotational quantum superpositions would also serve to test mod- els of an objective wavefunction collapse. Such theories modify quantum mechanics with the aim of recovering macro-realism without contradicting experimental obser- vations. A prominent example is Continuous Sponta- neous Localization [97], predicting a universal spatial and orientational decoherence and heating mechanism [98]. Observing quantum interference or the lack of collapse- induced heating rules out combinations of the parameters characterising the model [98, 99]. The shape-dependent centre-of-mass and rotational heating rates can be mea- sured with a single trapped particle, facilitating absolute measurements of the collapse parameters.
