Speaker
Description
In the presence of a resonant light field, atoms of a gas spontaneously scatter photons in random directions, leading to a momentum diffusion $D$ that causes the temperature to increase at a rate proportional to the spontaneous emission rate. When light is detuned from the atomic resonance by a frequency $\Delta$, the scattering rate decreases rapidly resulting in $D_A \propto 1/\Delta^2$. In a standing wave configuration, atoms redistribute photons through stimulated emission and experience a dipole force proportional to $1/\Delta$. However, this redistribution process does not lead to momentum diffusion, as photons from a standing wave state $\big[ |+\rangle + |-\rangle \big]/\sqrt 2$ can only be transferred between counterpropagating components of the same quantum state. Since the average momentum of the state is zero, there is no momentum diffusion, indicating that the force is conservative. This property allows for experimental trapping of cold atoms with a very low heating rate.
This work addresses the case where the dipole force is generated by independent travelling waves in the weak field limit, described by a statistical mixture of photons within a reservoir. In this context, photon redistribution between travelling waves causes a momentum kick in a random direction, resulting in a dipole force that is no longer conservative. The irreversible process yields a diffusion coefficient proportional to the stimulated emission rate $D_B \propto 1/\Delta$, which is in general much larger than in the case of a standing wave. This can significantly increase the temperature of atoms interacting with broadband radiation.
We examine the implications of this large heating rate on the temperatures of Earth’s and stellar atmospheres, as well as for general heating processes in astrophysics. Additionally, I propose an experiment using an atom interferometer that could detect momentum diffusion of atoms resulting from the travelling waves of independent counter-propagating beams generated by broadband laser sources.
| Keyword-1 | dipole force |
|---|---|
| Keyword-2 | travelling waves |
| Keyword-3 | atomic heating |