Synopsis

A “Magic Frequency” for Atomic Spectroscopy

Physics 6, s103
When light is chosen with a special frequency, its absorption by a cloud of atoms is independent of their internal orientation.
M. Givon et al., Phys. Rev. Lett. (2013)

Physicists use lasers to track the quantum evolution of atomic states, but interpreting the measurements can be tricky when the light absorption depends on the orientation of the atom’s internal angular momentum. Menachem Givon at Ben-Gurion University of the Negev, Israel, and his colleagues propose and demonstrate a method to monitor how many atoms are in a particular state, no matter how they are oriented.

Atoms can be in the same electronic state, yet differ in the alignment between the angular momenta of their nucleus and their electrons. And even atoms in the same such “hyperfine” state have different energies depending on how they align with a magnetic field, an effect called Zeeman splitting. In addition to having different peak absorption frequencies, when atoms in different Zeeman levels are illuminated with linearly polarized light at a particular angle, some levels absorb more light and some absorb less light than the average absorption, which is what is measured using unpolarized light. But in a cloud of moving atoms, the absorption peaks are broadened by the Doppler effect. At frequencies between these peaks, light is absorbed both by atoms with a higher transition frequency moving in one direction and by other atoms in the lower-frequency state moving in the opposite direction. If the frequency of light is tuned away from a level that absorbs more than the average absorption and toward one that absorbs less, at some intermediate frequency, the level will absorb just the average amount.

Givon and his colleagues realized that, for any particular motional broadening, this intermediate—or “magic”—frequency is the same for every Zeeman level, so the absorption just measures the total number of atoms in the hyperfine state. The researchers confirmed experimentally that when they illuminated a vapor of rubidium- 87 atoms with light at the magic frequency, a well-known sloshing of atoms between different levels became invisible. – Don Monroe


Subject Areas

Atomic and Molecular Physics

Related Articles

A Synthetic Lattice in a Cold Atomic Cloud
Atomic and Molecular Physics

A Synthetic Lattice in a Cold Atomic Cloud

Defining a fermionic lattice using spin and momentum instead of spatial coordinates opens the door for interacting-fermion simulations with more complex lattice geometries. Read More »

A Liquid Method to Prepare Ion Beams
Atomic and Molecular Physics

A Liquid Method to Prepare Ion Beams

A liquid-metal jet can strip electrons from a high-intensity, accelerator-based ion beam, increasing the beam’s charge and enhancing accelerator performance. Read More »

Controlling Single Photons with Rydberg Superatoms
Atomic and Molecular Physics

Controlling Single Photons with Rydberg Superatoms

New schemes based on Rydberg superatoms placed in optical cavities can be used to manipulate single photons with high efficiency. Read More »

More Articles