A Monte Carlo wavefunction method for semiclassical simulations of spin-position entanglement

TL;DR

This paper introduces a Monte Carlo wavefunction method for semiclassical simulation of spin-1/2 particles in magnetic field gradients, accurately modeling spin-position entanglement and decoherence with efficient computation.

Contribution

It develops a novel approach that modifies the Monte Carlo wavefunction method to handle spin superpositions and classical trajectories simultaneously.

Findings

Method accurately models spin-position entanglement.

Results agree with full quantum simulations.

Efficient and suitable for complex systems.

Abstract

We present a Monte Carlo wavefunction method for semiclassically modeling spin-$\frac12$ systems in a magnetic field gradient in one dimension. Our model resolves the conflict of determining what classical force an atom should be subjected to when it is in an arbitrary superposition of internal states. Spatial degrees of freedom are considered to be an environment, entanglement with which decoheres the internal states. Atoms follow classical trajectories through space, punctuated by probabilistic jumps between spin states. We modify the conventional Monte Carlo wavefunction method to jump between states when population transfer occurs, rather than when population is later discarded via exponential decay. This results in a spinor wavefunction that is continuous in time, and allows us to model the classical particle trajectories (evolution of the environment variables) more accurately. The model is not computationally demanding and it agrees well with simulations of the full spatial wavefunction of an atom.