Coherent seeding of the dynamics of a spinor Bose-Einstein condensate: From quantum to classical behavior

We present experiments revealing the competing effect of quantum fluctuations and of a coherent seed in the dynamics of a spin-1 Bose-Einstein condensate and discuss the relevance of a mean-field description of our system. We first explore a near-equilibrium situation, where the mean-field equations can be linearized around a fixed point corresponding to all atoms in the same Zeeman state m = 0. Preparing the system at this classical fixed point, we observe a reversible dynamics triggered by quantum fluctuations, which cannot be understood within a classical framework. We demonstrate that the classical description becomes accurate provided a coherent seed of a few atoms only is present in the other Zeeman states m = +1. In a second regime characterized by a strong nonlinearity of the mean-field equations, we observe a collapse dynamics driven by quantum fluctuations. This behavior cannot be accounted for by a classical description and persists for a large range of initial states. We show that all our experimental results can be explained with a semiclassical description (truncated Wigner approximation), using stochastic classical variables to model the quantum noise.

Automated summary

Experiments show the competition between quantum fluctuations and a coherent seed in the dynamics of a spin-1 Bose-Einstein condensate, with the relevance of a mean-field description discussed. Different behaviors are observed depending on the presence of quantum fluctuations and coherent seed, with classical and semiclassical descriptions used to explain the experimental results.