Coherent Magnetic Response at Optical Frequencies Using Atomic Transitions

Over the last two decades, there has been a growing interest in a new generation of optical tools using materials that are not available in nature. These materials offer the promise of devices with unique capabilities such as super-resolution lenses and optical cloaks. For these materials to work, they must interact strongly with both the magnetic and the electric field of light. However, the interaction of atoms with the magnetic field is almost always ignored since its strength is many orders of magnitude weaker than the electric field. A paper published in Physical Review X by Nicholas R. Brewer, Zachary N. Buckholtz, Zachary J. Simmons, Eli A. Mueller, and Deniz D. Yavuz shows, for the first time, a strong interaction between the magnetic field of a laser beam and an ensemble of atoms.

The group passed laser light through a special crystal doped with europium atoms, which have a very complex electronic structure. The structure is such that, for a specific wavelength of light (527.5 nm), the electrons prefer to interact with the magnetic field of light instead of the electric field. For this to happen, it is essential that (i) the crystal is cooled to a temperature of 4 K, and (ii) the color of light is very precise (the wavelength should be accurate at the level of one part in ten billion). By measuring how much light is transmitted through the crystal as the laser intensity is varied, they were able to deduce the strength of the magnetic interaction.

The results demonstrate one way to create materials with unusual optical properties. Future work could also use interactions between electrons and the magnetic field of a laser to study quantum interference.