Qed-Induced Spin Dynamics and Decoherence in the Stern–Gerlach Experiment

César Augusto Dartora

Jonah Maxwell Miller

J. A. Mendoza-Fierro, L. M. Arévalo Aguilar

César Augusto Dartora

Abstract The Stern–Gerlach experiment reveals the quantum mechanical nature of spin through the force experienced by a non-relativistic neutral atom in a static magnetic field gradient. A key open question concerns when, along the atom’s trajectory, the spin state collapses into an eigenstate and by what mechanism. We analyze the influence of quantum electrodynamic (QED) vacuum fluctuations on spin dynamics and show that they induce spin self-interactions, leading to decoherence and memory effects. However, the magnitude of these effects is shown to be too small to account for the deterministic collapse of the spin wavefunction.

J. M. Raimond

Marcel Utz, Malcolm H. Levitt, Nathan Cooper +1 more

The Stern-Gerlach experiment is a seminal experiment in quantum physics, involving the interaction between a particle with spin and an applied magnetic field gradient. A recent article [Wennerström et al., Phys. Chem. Chem. Phys., 2012, 14, 1677-1684] claimed that a full understanding of the Stern-Gerlach experiment can only be attained if transverse spin relaxation is taken into account, generated by fluctuating magnetic fields originating in the magnetic materials which generate the field gradient. This interpretation is contrary to the standard quantum description of the Stern-Gerlach experiment, which requires no dissipative effects. We present simulations of conventional quantum dynamics in the Stern-Gerlach experiment, using extended Wigner functions to describe the propagation of the quantum state in space and time. No relaxation effects are required to reproduce the qualitative experimental behaviour. We also present simulations of quantum dynamics in the Rabi experiment, in which an applied radiofrequency field induces spin transitions in the particle wave.