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.
Highlights
Maxwell’s hypothetical demon has spurred the imagination of physicists for 150 years[1,2,3]
The energy of an atom in a laser beam will be shifted by an amount U(R) due to the interaction of the dipole moment of the atom with the electric field of the laser, where R is the location of the atom
Schrodinger’s equation is solved numerically, and the results show that quantum mechanics does not predict a velocity-dependent force on an atom along the direction of propagation of a focused laser beam
Summary
The dipole force of interest here is proportional to the gradient in the intensity of the light[13,14], as illustrated in. ∆′ = (ωL + δωD − ωA) instead of 1/Δ (Other authors[19] have considered the opposite limit.) We will assume that the focal length of the laser beam (Rayleigh length) is sufficiently large that the Hamiltonian is slowly varying and the adiabatic theorem applies, in which case there is no dissipation due to a permanent change in the atomic state. Magnetic forces satisfy Liouville’s theorem which precludes the operation of a Maxwell’s demon in thermal equilibrium, whereas the dipole forces of interest here do not
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