Spatio-orientational decoherence of nanoparticles

Abstract

Motivated by trapping and cooling experiments with non-spherical nanoparticles, we discuss how their combined rotational and translational quantum state is affected by the interaction with a gaseous environment. Based on the quantum master equation in terms of orientation-dependent scattering amplitudes, we evaluate the localization rate for gas collisions off an anisotropic van der Waals-type potential and for photon scattering off an anisotropic dielectric. We also show how pure angular momentum diffusion arises from these open quantum dynamics in the limit of weak anisotropies.

Quantum angular momentum diffusion of rigid bodies

“…We remark that a general microscopic theory of environment-induced decoherence between different orientation states was presented in [25,26], and it was also shown in [25], for the special cases of photon and van der Waals scattering off linear molecules, that the limit of small anisotropies gives rise to quantum angular momentum diffusion.…”

“…It is the aim of this section to derive the general form of the quantum angular momentum diffusion equation by using as a starting point the master equation for the orientational decoherence dynamics of an anisotropic nanoparticle in a homogeneous environment. The latter was obtained in [25] from the quantum linear Boltzmann equation [32][33][34][35][36][37][38]. It describes the decay of orientational superposition states due to gas collisions with the nanoparticle surface in terms of the microscopic scattering amplitudes.…”

Probing macroscopic quantum superpositions with nanorotors

“…The proposed interference scheme is based on the fact that an initially tightly oriented quantum rotor rapidly disperses, while at multiples of a much longer quantum revival time the collective interference of all occupied angular momentum states leads to a complete re-appearance of the initial state [21,22]. Surprisingly, we find that such orientational quantum revivals can be probed with modest initial temperatures, involving hundreds of thousands of total angular momentum quanta, and under realistic environmental conditions, taking into account all relevant sources of orientational decoherence [23,24]. The proposed experiment enables the first test of macroscopic angular momentum quantization with massive objects.…”

“…Once the trapping laser is turned off, the orientation state evolves freely while its center-of-mass drops in the gravitational field along the tweezer axis. The ensuing delocalization of the orientation state is counteracted by orientational decoherence processes [23,24] which potentially suppress the revivals. As in other matter-wave experiments [15,17,20,34,35], the dominant sources of environmental decoherence are the scattering of residual gas atoms and the thermal emission of photons.…”

“…As in other matter-wave experiments [15,17,20,34,35], the dominant sources of environmental decoherence are the scattering of residual gas atoms and the thermal emission of photons. Exactly solving the Markovian quantum master equation of orientational decoherence [23,24] is challenging due to the vast number of occupied angular momentum states. As a conservative estimate, we assume that a single decoherence event suffices to completely destroy the alignment signal, by producing a state…”