Velocity-dependent optical forces and Maxwell's demon

TL;DR

This paper investigates the velocity-dependent optical forces on atoms in focused laser beams and demonstrates that the expected Maxwell's demon cannot be realized due to a canceling force related to the laser phase gradient.

Contribution

It reveals that the velocity dependence of the dipole force is nullified by a phase-gradient related force, preventing Maxwell's demon implementation in this context.

Findings

Velocity dependence of dipole force is canceled by phase-gradient force.

Photon scattering and dissipation are negligible.

Maxwell's demon cannot be realized via this optical force mechanism.

Abstract

An atom placed in a focused laser beam will experience a dipole force due to the gradient in the interaction energy, which is analogous to the well-known optical tweezers effect. This force will be dependent on the velocity of the atom due to the Doppler effect, which could potentially be used to implement a Maxwell's demon. Photon scattering and other forms of dissipation can be negligibly small, which would seem to contradict quantum information proofs that a Maxwell's demon must dissipate a minimum amount of energy. We show that the velocity dependence of the dipole force is cancelled out by another force that is related to the gradient in the phase of the laser beam. As a result, a Maxwell's demon cannot be implemented in this way.